This is an alphabetical list of Energy Efficiency Terms relevant to our product evaluations or our current product offering.

# | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

#

80/20 Make-Up Air
Is a direct fired system, also called recirculation heaters, whose inlet air is composed of 20% fresh outside air and 80% recirculated inside air. These units are a sort of hybrid, intended to combine high BTU/CFM ratio of direct fired heaters with the recirculation benefits of air-rotation. These systems are larger than 100% MUA units, which are usually roof-mounted, and can be vertically wall-mounted to behave more like air-rotation units.

A

The American Council for an Energy-Efficient Economy (ACEEE)
An organization that develops policies and programs to promote technologies and behaviors pertaining to energy efficiency. Its programs are consisted of energy policy, research, and communications. The ACEEE strives to conduct technical and policy analyses, educate businesses and the public through conferences and reports, work with businesses and government officials, and assist the media in publicizing its policies and research on energy efficiency.

AHRI
The American Heating and Refrigeration Institute (AHRI) is an industry trade group composed of 300 manufacturers of HVACR equipment. Research conducted by AHRI supports industry policy in addition to helping develop more advanced energy efficient systems. One of the main functions of AHRI is to act as the industry advocate in Washington. AHRI also certifies equipment and maintains its own set of standards.

Air Change (ACH)
The number of times the air is changed in a room. It is measured as air change per hour. Fresh air is required to maintain a healthy environment so that stale air containing CO2 and CO are not affecting health and moisture issues.
It is measured as:

ACH = 60FV

F = CFM i.e cubic feet per minute
V = volume of space (ft3)
ACH = air change per hour

Common values of air change:
Warehouses = 1-2
Toilets = 10
Malls = 6-10
School classrooms = 4-12

Air Contaminants
The introduction of harmful chemicals, particulate matter and biological waste into the air in such quantity that it causes harm or discomfort to humans and other living beings along with damaging the environment. NAAQS (National Ambient Air Quality Standards) has set the standard on six pollutants: ozone, particulate matter, carbon monoxide, sulphur dioxide, nitrogen oxides and lead. Further information regarding the standards for these air pollutants can be found here.

Air Handling Equipment
Equipment which circulates air throughout a building. The frame is generally a metal box with main components consisting of a blower, heating/cooling coil, dampers, humidifiers and air filters. Most of the time air handling equipment is connected to the ducts where the air conditioned air is distributed to the building. They come  in many sizes and can also be mounted on rooftops, these systems are known as Make-Up Air Units. These units can handle both 100% outside air or the recirculation of a mixture of indoor and outdoor air.

Air-Rotation
These large, stand-alone systems are also indirectly fired. They draw in cold air at ground level and heat it, usually with an internal gas furnace, and then duct the warm air up to the top of the unit where it is “thrown” radially outward. The thrown air hits the walls then it sinks and returns along the floor following the layout of the racks in the warehouse.

Algorithm
Though the exact definition varies somewhat depending on the context, an algorithm is basically a set of instructions on how to carry a certain task or calculation. These instructions may be expressed in natural language, as a flowchart, or in computer code to list some common examples. Devices such as DDCs may contain proprietary algorithms programmed and designed to optimize energy efficiency in HVAC systems.

Anemometer
A device that measures wind velocity and wind pressure. It can be used for weather forecasts, but hand-held anemometers also exist to perform energy audits. After blower door and duct blaster tests are conducted, hand-held anemometers are used to measure the severity of air leaks near windows, doors, and other potential sources of leaks. They are also used to test the efficiency of HVAC systems.

ASHRAE
The American Society of Heating Refrigeration and Air-Conditioning Engineers (ASHRAE) is a professional association of over 50,000 people whose aim is to, “serve humanity and promote a sustainable world through research, standards writing, publishing and continuing education.” ASHRAE is essentially the ruling body of the HVACR community. Although the group is not a governmental body, thus has no formal legal powers, many of the ASHRAE developed standards have been adopted by the government and taken the form of law. For those professionals who wish to take their training to the next level, ASHRAE also provides certification in fields such as energy modeling and healthcare facility design.

Attic Hatch Cover
A cover that acts like a door in the attic to prevent air from leaking out to the attic. Attic hatch openings are one of the major sources of air leaks in the house. A properly insulated and sealed attic hatch cover can help homeowners benefit from reduced energy bills. There are two types of attic hatch covers. One is an attic tent, which is made of cloth and can be opened with a zipper, but some experts say that this type does not provide adequate insulation. The other type is the insulation box, which performs better than the first type and is made up of an energy efficient foam reinforced by a thick foil with a sealant. It is important to note that attic hatch covers must be properly sealed with sealing strips in order for them to stop air leaks. They also contribute to preventing polluted air particles in the attic from entering the house.

B

 

Backdrafting
A process in which combustion gases such as carbon monoxide flow back into the house instead of outward due to a lower air pressure in the house than the air pressure outside. Normally, air should be vented out through a chimney. The cause of this negative pressure is contributed by appliances such as furnaces, fireplaces, water heaters, clothes dryers, and bathroom fans that suck the air outward. Other external factors such as wind and temperature play a role in backdrafting as well. When doors and windows are sealed shut, this prevents air outside from entering the house to neutralize the indoor air pressure. If smoke is seen returning into the house through a chimney, this is a clear sign of backdrafting.

If backdrafting is left unresolved, carbon monoxide and other harmful gases can accumulate in the house, an action that can be fatal to homeowners. The best ways to prevent backdrafting is to limit the use of appliances that contribute to decreasing indoor air pressure. Also, providing air supply for these appliances will help neutralize air pressure. As a precaution, inspections should be regularly conducted to ensure that combustion gas levels are minimal, and that air is properly ventilated.

Ball Bearing
This equipment reduces friction by providing smooth metal balls or rollers and a smooth inner and outer metal surface for the balls to roll against. The balls or rollers "bear" the load, allowing the device to spin smoothly. Ball bearings can handle both radial and thrust loads and are usually found in applications where the load is relatively small, such as blowers and small motors.

Blower Door
A fan system that is attached to the exterior door space to detect air leakage in a building. It is one of the tests performed to conduct an energy audit. When the fan is turned on, air is blown outwards from the inside. Hence, it creates a slightly negative air pressure inside the building relative to the air pressure outside. Meanwhile, assuming that all exterior windows are closed, air then flows back into the building through the air leaks. With a manometer, the CFM50 (cubic feet per minute at -50 Pascals) is measured, and it is compared with the calculated CFM50 based on the total building volume to determine the air tightness of the building. An IR camera and/or a smoke pen can be used to pinpoint the exact location of the leaks.

The use of the blower door is somewhat similar to the use of a standard fan while you ventilate your home. If you open all the windows for ventilation while you turn on the fan that is facing outside through a window, you may begin to feel a small airflow coming inside your home through the other windows. The blower door applies this concept to determine the air tightness of a building.

Boiler
These heating systems burn either oil or gas, though most systems encountered will be oil-fired. The energy generated is used to convert water in liquid form into high pressure water or steam which is then sent to radiators throughout that building. It is the radiators which heat the air. Combustion exhaust gas is vented out via a flue. Despite the fact that even modern boilers are very inefficient at heating large industrial spaces, they still represent a significant percentage of the heating systems encountered in older buildings. This is because they date from an era when fuel costs were of little concern.

BTU/CFM
This is the ratio of total heat capacity per CFM (cubic feet per min). It gives an idea as to how much rise in temperature is possible in an hour for a particular space. It can be used to calculate the ventilation and infiltration loads of a building.

Building Envelope
An area that acts as a border between the interior and exterior space of a building. The major components of the building envelope include doors, windows, roofs, and walls. Please note that building envelope and thermal boundary are different. The interior and exterior spaces of a building are defined based on the physical border between the two, while thermal boundary differentiates the two spaces based on the insulation point-of-view. For instance, an uninsulated attic is considered an interior space based on the definition of the building envelope, but in terms of the thermal boundary, it is considered an exterior space. Please see the definition of thermal boundary for more information.

Butterfly Valves
This equipment is used to regulate flow. Its main advantage is that it can control the flow rate from complete stop, to some throttle, to full throttle. Butterfly valves are manufactured using the strongest and most durable materials, such as stainless steel, steel, PVC, CPVC and aluminum. They are generally lower in cost and weight compared to similar valves.

C

Carbon Fiber Reinforced Polymer (CFRP)
A material that is made up of carbon fibers and a polymer. In many cases, epoxy is used as the polymer. CFRP is particularly known for its high strength to weight ratio; it is relatively light while durable. Studies show that it is 30% lighter than aluminum and 50% lighter than conventional steel. As a result, if a car body frame is made of CFRP, the car would be 10% lighter than a conventional car.

CFRP has many applications. Its use ranges from the body frames of racing cars and bicycles to the ones of helicopters and airplanes, most notably the Boeing 787 Dreamliner. With their lighter weight, vehicles made of CFRP are able to conserve more gasoline than the conventional ones. Recently, for the F35 Lightning II fighter jets, Lockheed Martin began using carbon nanotube reinforced polymer (CNRP), which is several times stronger and 25-30% lighter than CFRP.

Caulking
A method of sealing joints and gaps in structures by using caulk. This activity is important because sealing cracks prevents heat loss and infiltration problems. Application of caulk is best during dry weather when the outdoor temperature is above 45°F (7.2°C). The warmer conditions allow the caulk to set properly and adhere to the surface. Low humidity is also desirable in order to prevent cracks from swelling with moisture. Caulk is typically used for installing sinks, bathtubs, pipes, bathroom wall tiles, roof, door, and windows. It is also used for filling sidewalk cracks and shipbuilding.

Types of caulking material include silicone, polyurethane, expandable spray foam, water-based foam sealant, butyl rubber, latex, oil, and resin-based materials. Out of the listed types, the two major types of caulk are latex and silicone. Latex caulk has the advantages of its ease of use, less odor, and the flexibility for home installers to paint upon it. As a result, it is known as the painter's caulk. On the other hand, silicone caulk has the advantages of longevity and durability in harsh conditions. One of the variants of caulk is made of both latex and silicone to provide the benefits of latex and silicone caulk simultaneously. Other variants include waterproof and fireproof caulk, which is usually red.

CFM
Stands for cubic feet per minute. It is generally used by blower and compressor manufacturers to denote the volumetric capacity of the unit.

Chiller
These are HVAC refrigeration systems used in cooling applications especially for commercial and industrial plants. The system includes a compressor, evaporator, condenser, reservoir, thermal expansion valve and stabilization assembly. HVAC chillers use water, oils and other liquid compounds as refrigerants. It works in the principle of absorption refrigeration cycle. Here a machine removes heat from a liquid which is circulated and used to cool the building via heat exchangers.

Color Rendering Index
This is the measure of the quality of a light source to reproduce the various colors of the light in comparison to the natural light source. A reference source, such as blackbody radiation, is defined as having a CRI of 100 (this is why incandescent lamps have that rating, as they are, in effect, blackbody radiators), and the test source with the same color temperature is compared against this.

Compressor
This is a mechanical device which compresses the gas volume hence its pressure increases. Compressors are an important part of most AC units; they convert low pressure, low temperature refrigerant gas coming from the evaporator into high pressure and high temperature gas for condenser in the refrigeration cycle. It also acts as a pump and transports the refrigerant around the pipes.

Conduction
Is the “net transfer of energy [through a medium] by random molecular motion.” If you place a drop of concentrated dye into a pool of water, the color will gradually diffuse outward from the point of origin. Probability dictates that a drop of dye sitting undispersed is far less likely than a pool filled evenly with a slight tint of color. Dye molecules therefore move from areas of high concentration to low concentration. The same holds true for concentrations of high energy particles (areas of higher temperature). Though the high energy particles may themselves not move very far, or at all in the case of solids. Constant collisions with nearby particles and the subsequent transfer of energy to those particles causes a diffusion of energy. Materials which conduct heat effectively are naturally called thermal conductors and those that conduct very poorly, like air, are termed insulators.

Convection
Convection is generally defined as energy transfer due to the bulk motion of fluid particles. The term “bulk motion” is used to differentiate it from the random particle motion that one sees on the molecular level and which is the driving force behind conduction. Convection is actually the sum of two phenomens, advection and eddy diffusion. Advection is the true average (bulk) motion of the fluid and is often used synonymously with convection. In laminar flows, this is reasonable since the heat transfer effects of eddies are relatively weak. However, under turbulent conditions convection calculations must take into account the smaller structures (eddies) which form within the bulk flow and increase the heat and mass transfer coefficients. For fluids such as air, which has an extremely low thermal conductivity, transferring energy via convection is usually much faster than doing so through conduction. This is why most common insulating materials aim to impeed convection and thus reduce the rate of energy transfer to or from the insulated body.

Cool Roof
Roof that reflects sunlight and its heat away from the building to keep it cool and save energy. Some cool roofs have bright colors, which tend to reflect most of the light away, while darker colors tend to absorb light. However, there are special darker-colored pigments that help reflect sunlight, so that homeowners have several options for the color of the cool roofs. Since cool roofs reflect most of the light and heat away from the building, the inside of the building is kept cool, which helps homeowners spend less energy on air conditioning. It is estimated that cool roofs help save energy by 7-15%. At the same time, they provide a higher level of comfort for the building's occupants and increase the lifespan of cool roofs themselves. As a result, building owners benefit from reduced energy bills and maintenance costs. To help homeowners select the best type of cool roof for their homes, cool roofs can be compared by their solar reflectance and thermal emittance.

COP
The Coefficient of Performance is a dimensionless parameter used to rate the effectiveness of a thermodynamic heat pump (opposite of a heat engine). Such heat pumps include air conditioning and refrigeration systems in addition to those systems more traditionally referred to in the HVAC industry as heat pumps. Depending on whether the heat pump is being used for heating or cooling the COP is expressed as:

COPheating = Qadded/Win
COPcooling = Qremoved/Win

In both cases work is added to the system by the compressor. Win actually represents the net amount of work put into a cycle and can theoretically be reduced by adding an energy recovery device such as a turbine between the condenser and the evaporator to make the cycle more efficient. However, in practice, the expense of doing this outweighs any modest efficiency gains that might be realized and therefore a simple expansion valve is nearly always used to create the necessary pressure drop. The highest possible COPs for a heat pump operating between two temperature reservoirs (indoor and outdoor environment) are defined by the Carnot Cycle which is ideal and completely reversible (units are absolute).

COPheating,max = Thot/(Thot-Tcold)
COPcooling,max = Tcold/(Thot-Tcold)

Notice that the COP for a heat pump operating in heating mode is always greater than 1. This shouldn’t be any surprise since all the work being used in the cycle is already being converted into heat and pumped into the space. The least efficient heat pump possible is one which simply acts as an electrical resistance heater. For cooling systems, the COP of performance can take any value, but in general AC units are given an EER or SEER rating and refrigerators are simply labeled with an estimated kWh/yr.

COPheating = Qhot/Win

Qhot is the amount of heat pumped into the space and Win is the amount of work required to do it. The maximum possible COP is given by the Carnot Cycle (see COP). The advantage of heat pumps is two-fold. First, by reversing the vapor-compression cycle used by the heat pump, the unit can be turned from a heating system into an air conditioning system. Second, by taking existing energy from the outside and moving it indoors there is no need to purchase and burn additional fuel, which in theory saves money. However, as the outdoor temperature drops, the heat pump’s COP decreases. In regions such as New England, the winter's are too cold to make a heat pump cost-effective. It is simply cheaper to use a natural gas fired heating system. However, in the south where winters are relatively mild and the heating season is short, heat pumps are economical and widely used.

Corrosion
The deterioration of a material due to its reaction with the environment. It is a diffusion-controlled process, which in HVAC applications usually occurs occurs on surfaces exposed to high humidity. The presence of moisture in the air causes certain metals (Fe, Al) to react with oxygen to form metal oxides which do not adhere to the surface of the metal and flake off. This causes pitting, which weakens the material as the cross sectional area decreases. Even in cases where the oxidized material does not fall off its build may cause equipment to lose its effectiveness. This is especially true of heat exchangers where low conductivity oxides inhibit heat transfer and reduce an exchanger’s efficiency. The problem only intensifies when products of combustion (CO2) combine with water vapor to form acids.
The same phenomenon that causes acid rain can also rust your heating system from the inside if you’re careless.

Cycle
A thermodynamic cycle is when a system goes through a series of state changes (variations in temperature, pressure, entropy, etc.) and arrives back at the same state at which it began. Although the initial and final states may be the same, the work and heat transfer are not properties of an individual state but rather are path dependent. Therefore, depending on which series of intermediate states a system goes through during a cycle, total energy transfer between the system and the surrounding environment may be different. Thermodynamic cycles are commonly plotted on T-s and P-v diagrams such as the one below which shows the Carnot Cycle.

There are two general types of cycles and they are classified based on whether thermal or mechanical energy is transferred at the cycle’s output stage.1 Power cycles produce net power output (mechanical energy) and are the basis of everything, from two-stroke lawn mower engines to massive steam turbine power plants. Refrigeration cycles either add or remove thermal energy as their output. Therefore, in addition to refrigeration and air conditioning, heat pumps also operate on a refrigeration cycle despite the fact that they are not always used for cooling.

1. Although there is technically an element of choice as to which part of the cycle to define as the output, this is generally fairly obvious even if it is not inherent to the physics of the problem.

Cyclical Load
Is when a load is not constant. During the day there is heavy demand for electricity because all of the equipment is running while at night there is less demand. The load profile repeats the next day and the day after, hence load is cyclic in nature.

D

DALI
While a certain level of energy savings can be achieved by swapping out old older, less efficient lighting technologies, such as T12 fluorescent bulbs for more efficient systems such T5s, there is often room further improvement. The saying in lighting is that the most efficient light bulb is the one that is turned off. For this reason, T5 upgrade packages are supposed to include occupancy sensors so that the lights can be automatically turned off when nobody is in the room. But, to achieve maximum savings, lighting operation should be tailored to the specific needs of the customer and the space in which the lights are installed. Even low-rise commercial buildings contain dozens, if not hundreds of light fixtures. To set the operation of all these fixtures manually is an enormous task which is both time consuming and disruptive to building operations. It is much more efficient to set up a network through which a central control panel or computer system can communicate with the lighting ballasts. Digital Addressable Lighting Interface (DALI) does just this by establishing a standard for digital two-way communication between computer controls and 1-10V dimmable ballasts. Adoption of this standard allows lighting designers to mix and match components from different manufacturers and have them communicate with each other. Furthermore, installers do not have to be versed in the communications protocols of many different manufacturers, but rather they only need to be familiar with one DALI. As many as 64 ballasts are wired together in a single DALI network and each ballast is given an identity (address) within that network. Ballasts can then be controlled individually or as a group.

Damper 
This device controls the flow of air in heating or cooling devices. Usually a small synchronous motor is connected to the damper to mechanically control the opening and closing of the damper blades. Usually the damper is in the open position when the blower is operating.

DDC
A DDC controller system works in three stages: sensor stage, control stage and controlled device stage. Sensors are placed in a medium whose properties are measured. Measurements can vary, but often include air temperature, humidity and air pressure inside and outside of the AC system. The sensors then send a signal to the controller which processes the signal digitally in a microchip as opposed to feeding the analog signal into an electric circuit or inducing a mechanical reaction, such as what is found in pneumatic systems. The end result of this process is that a command is sent to either another controller or directly to an HVAC system (direct digital control) such as an AC unit or a boiler. The operation of the HVAC device conditions the space by changing its temperature or reducing humidity and this in turn can be measured by the sensors. This cycle continues until the desired conditions have been met.

Deadband vs. Differential
When speaking of DDCs, the terms deadband and differential are often used synonymously, when in fact they are two distinct concepts. Both deal with the basic algorithm used by the thermostat to decide when to call for heating and cooling. In any space, the air temperature is constantly changing, albeit slowly, and is rarely at the exact set-point temperature specified in the thermostat program. However, were a standard HVAC system to try and maintain air temperatures with a precision equal to that of the thermostat itself (0.1ºF), it would constantly be cycling on and off. Besides being extraordinarily inefficient, a mechanical device, like a compressor, would quickly burn itself out under such conditions. Therefore, the thermostat has a range of temperatures which it considers acceptable. It is only when temperatures stray outside of this range that the thermostat calls for heating or cooling. This range is usually 2º F and the set-point represents the upper-end, lower-end, or midpoint of this range depending on the manufacturer of the HVAC system and the control response being used.

Thermostats typically employ a two-position control. When the room temperature crosses the set-point value, the HVAC system kicks in and the room temperature changes. When the temperature reaches another preset value the signal is given to turn the conditioning unit off. The temperature difference between this value and the set-point is called the differential. Note that such a control system only enforces a temperature maximum or minimum, but not both. Thus a thermostat set to operate an AC unit will do nothing even if the room drops to 20ºF. The thermostat must be manually switched to operate the heating system, assuming it is already wired in.

Now say there is a space with rapidly changing heating and cooling needs and the temperature variation needs to be limited in both directions. In this case, a floating control might be used. When the temperature drops below a certain value the heating system kicks in until the space temperature is returned to that point. Likewise, if the temperature rises above a certain value, the AC will run. Between these two points neither system will run and this region is called the “deadband.” The set-point is the midpoint of the deadband.

Degree Day
Degree days are a measurement of heating and cooling loads used for normalization so that the efficiency of different units operating on different days can be compared. A degree day is the deviation of the outside temperature from a baseline temperature by 1ºF for one day. In the U.S., this baseline temperature is generally chosen as 65ºF. Presumably deviations from this value require conditioning of an indoor space. For example, if the outside temperature is 70ºF for one day, then that represents five cooling degree days. Similarly, temperatures below 65ºF will generate cooling degree days. These values are cumulative so you can look at the total number of degree days for a week, a month, or any other time frame you want. Cooling and heating degree days do not cancel, so a day with dramatic temperature swings, like those experienced in desert climates, may produce both heat and cooling degree days.

Now, say the energy use of air-conditioner A on an 85ºF day is 20 kWh and the energy use of air-conditioner B on a 95ºF day is 25 kWh. Unit B used more energy but does that mean it is less efficient than A? It is difficult to compare the two since one would expect an AC to use more energy on a hotter day. One way to do this is by comparing the units’ respective energy uses per degree day. In other words, the amount of energy used by the systems to produce a given amount of cooling. However, be very careful when using degree days. Their validity is influenced by a number of factors which can lead to wildly inaccurate results. For example, take the baseline temperature whose choice is entirely arbitrary and is in fact different in other countries even though human comfort settings should remain the same everywhere.

Direct Fired vs. Indirect Fired
The difference between these two systems lies in whether or not the combustion process takes place directly in the building's inlet airstream. In a direct fired burner, the fuel is burned in the incoming airstream and the exhaust gas, including the product of combustion, is vented directly into the space. In an indirect fired heater, the building’s air supply and the air supplied for combustion are kept separate with heat transfer taking place between the two via a heat exchanger. However, not all of the available energy is transferred from the exhaust stream in the heat exchanger thus some energy is lost as it leaves the vent. This difference results in the indirect fired systems being 80-85% thermally efficient as opposed to 92% for direct fired heaters. Note that many direct fired systems will say that they are 100% efficient. What this number actually refers to is the combustion efficiency of the burner, which means that all the chemical energy available in the fuel is converted to heat. However, 8% of this energy resides in the latent heat that represents energy difference between liquid water and steam. Therefore, the distinction between combustion and thermal efficiency must be kept in mind to avoid confusion when comparing the stated efficiencies of two systems.

DOE
Stands for the Department of Energy. The mission of this Governmental department is to advance energy technology and promote related innovation in the United States.

Double Pane Window
A window that is made up of two layers of glass as opposed to one to improve thermal insulation. Studies found that a major portion of heat inside homes leak out through conventional single pane windows. To improve thermal insulation of double pane windows, an inert gas such as argon, krypton, or a combination of both is sandwiched and sealed in the space between the two layers of glass, since it is a poor thermal conductor as opposed to air.

With a sealed space filled with inert gas, some double pane windows have a thin, transparent Low-emittance (Low-E) coating that also contributes to the improvement of thermal insulation. It is on the glass surface that faces the space between layers of glass. The coating is composed of metal or metallic oxide that allows heat to enter inside buildings but at the same time prevents heat from escaping. However, in warmer areas, it is on the glass surface that faces outside to reflect heat away. That way, heat cannot enter air-conditioned homes. Depending on the climate, Low-E coating has several variations to optimize its effectiveness from region to region. Other than residential homes, double pane windows are also typically used in skyscrapers and airplanes. In addition, to further improve thermal insulation, some people choose triple pane windows, which have three layers of glass with two spaces of inert gas.

Dry Bulb Temperature
Is the atmospheric temperature of the air measured by a thermometer. It does not take into account humidity. Dry bulb temperature is measured in different temperature scales such as Celsius (°C) or degrees Fahrenheit (°F), however its true SI unit is Kelvin (°K).

E

 

Economizer
As with many words, “economizer” is used as a catch-all term whose precise meaning varies depending on the context. In general, an economizer is a feature or retrofit in an HVAC system which is added to increase energy efficiency. In AC systems, an economizer is a feature which brings in outside air through a bypass to cool the building instead of running the refrigeration cycle to cool the air already within the space. This assumes that the outside air temperature is at or below the desired room temperature and is sufficiently dry. In this case, the building’s heat load would be coming from internal sources such as lighting and occupants. This method saves a great deal of energy since it takes much less electricity to just run fans and blowers than it does to operate the compressor. In heating and power generation systems, economizers are heat exchangers which recover energy from hot exhaust streams and use it to preheat incoming gas or liquid. This reduces the need for heating in the boiler or combustion chamber itself thus saving fuel. Recuperators are a subset of such economizers.

EER/SEER
The EER is similar to the COP, except that is has units of BTUh/W. It is used to rate the performance of air conditioning units. Since indoor and outdoor temperatures and humidity levels all effect the EER, it will constantly change over the course of the year and from region to region. To try and account for this, a seasonal EER (SEER) rating was instituted to more accurately reflect the overall year-round efficiency. In 1987, Congress established a SEER 10 minimum for air conditioners and heat pumps sold in the United States which went into effect in 1992. Under President Clinton, the order was passed down for further efficiency improvements. It was decreed that by 2006, systems sold would have to have a SEER of at least 13. Unfortunately, the Bush administration had other ideas. Thanks to whining by the air conditioning industry and the DOE that meeting such standards would be a serious inconvenience, the decision was made to try and weaken the proposed standard to SEER 12. Thankfully, in 2004 the Second Circuit Court of Appeals ruled that the DOE had overstated the regulatory burdens of enforcing SEER 13 and various industry groups also dropped their challenge to the more stringent standards. As a result SEER 13 went into effect as planned.

Improvements in efficiency standards only apply to new units and many older much less efficient units still exist and will for some time. If buying new AC equipment doesn’t make sense then you want to consider investing in a direct digital controller such as the Pace2. These units can significantly reduce your electric bill without the cost of an entirely new system.

Efficacy
The ratio of an amount of luminous flux produced by a light source to the amount of power that is required to produce it. It is measured in lumen per watt (lm/W).

Energy Audit
Unlike an audit by the IRS, an energy audit is not intended to scare the pants off you or make sure that you’re shelling out enough cash. Actually, the goal of an energy audits, like those performed by Mass Energy Lab, is to save you money, hopefully a great deal. During an energy audit a professional, such as a qualified engineer, comes in and inspects your space in order to figure out how energy flows within the building. Using tools such as mathematical formulas, modeling software, infrared cameras and plain old experience, the auditor will identify sources of energy use and areas of energy input and loss, such walls and windows. The important result of all this will be a series of recommendations on the most effective ways to increase your building’s energy efficiency and in turn your bottom line. One or more energy audits of varying complexities will form the foundation of any efficiency upgrade project since everything from the go-ahead decision to the actual equipment sizing is based upon them.

Energy Management System
A system that helps keep track of energy consumption habits of homeowners on a timely basis. It is made possible by an application software that provides homeowners detailed information regarding their energy consumption habits from utility companies. Such information includes times when homeowners consume a major portion of their daily energy consumption. That way, they would find ways to cut down their energy usage at certain times and benefit from reduced electric bills. One example is a smart thermostat that knows the temperature preferences of a homeowner on a timely basis so that an air conditioner or a heater is automatically turned off when nobody is in the house.

EPAct
As a company CFO or building manager, you’re always looking for ways to cut down on your operating expenses. Energy costs are a sizable fraction of any budget, and in buildings such as warehouses, they usually represent the single largest expense besides payroll. Slashing energy bills by investing in efficiency upgrades is one of the easiest ways to pad your bottom line. Better yet, it does so without the need for pink slips. Replacing old, inefficient equipment with properly chosen modern systems can reap huge financial rewards. The new equipment pays for itself in only a few years and continues to provide those energy savings for years to come. But regardless of those promising ROI numbers, the upgrade projects still require financing, and such costs are nothing to sneeze at. Maybe you’re uneasy about putting up so much money for a project whose benefits you feel are unproven. After all, everybody and their mother is claiming that their product can save you 90% on your energy bill along with washing your car and mowing your lawn. In your eyes the risk just isn’t quite worth it. But what if you didn’t have to finance the entire project yourself? What if somebody else footed part of the bill? Well that’s just what the federal government does with EPAct 2005 in the form of tax credits. The Energy Policy Act, which was signed into law by George Bush in 2006, includes provisions for businesses which decrease their energy use below the standards laid out in ASHRAE 90.1 (2001). A maximum incentive of $1.80/ft2 is given to buildings operating at least 50% below ASHRAE 90.1 levels. Different system types can also be targeted separately for savings even if the overall 50% target is not met. These systems are HVAC and hot water, indoor lighting and building envelope (insulation). For meeting the efficiency targets in each of these categories $0.60/ft2 is awarded. As of March 2008, lighting and HVAC+HW projects must each reduce overall energy consumption by at least 20% below ASHRAE 90.1 levels to receive a deduction. Changes to the building envelope need only result in a 10% energy reduction. Naturally, if all three targets are met then the 50% total automatically met and the full $1.80/ft2 can be claimed. Except for warehouses graded partial deductions are also available for lighting projects. One great thing about EPAct is that the incentives are retroactive. So if a lighting project was completed after the enaction of EPAct but the deduction was never taken it can still be claimed years later and even combined with new projects like heating system upgrades in order to receive even larger tax benefits.

Note: EPAct 2005 (H.R. 6) is a 550 document that touches on all aspects of the country’s energy policy, everything from energy efficient home appliances to oil and gas exploration. Sec. 1331 deals specifically with tax deductions for energy efficient commercial buildings and it is this part that is generally being referenced when EPAct comes up in discussion.

F

 

Faucet Aerator
A grid mesh that is inserted into water faucets to reduce water flow during its use. A faucet aerator has many holes rather than an entirely open space to control the water flow. As a result, water that flows out through the faucet aerator has a foamy texture. Its purpose is to help conserve water. During the use of hot water, it also helps conserve energy that is used to heat water, since more hot water would be conserved. Without the faucet aerator, high quantities of water freely flows out of the faucets wastefully. There are a variety of faucet aerators that are based on the water flow measured in gallons per minute (GPM).

Fibrex
A material that is made up of 40% recycled wood fibers and 60% vinyl. It is used mostly for window frames and is patented by Andersen Corporation. Fibrex visually resembles high quality wood and at the same time does not require frequent maintenance like wood, which absorbs water and rots over time. Not only is Fibrex hassle-free, but it also helps save trees. In fact, it has a high thermal insulating property and is three times stronger than vinyl. Also, unlike vinyl, Fibrex does not crack as a result of contraction and expansion from temperature changes.

Fluorescent
Fluorescent lamps work by passing an electrical current through a tube filled with low-pressure mercury vapor and a low-pressure noble gas. The electric arc excites the mercury vapor which emits radiant energy, primarily in ultraviolet region of the spectrum. This UV radiation in turn excites the phosphor coating on the inside of the tube causing it to fluoresce and emit visible light. Fluorescent lamps are always accompanied by some form of ballast which regulates their operation. The first practical fluorescent bulbs came on the market in 1938 and fairly quickly replaced incandescent bulbs in commercial lighting applications. Unlike the incandescent bulbs, there have been some significant changes in fluorescent lighting technology, namely the introduction of electronic ballasts. Since these ballasts were much smaller than magnetic ballasts, they could be integrated along with specially shaped tubes into compact fluorescent bulbs. These bulbs have roughly the same profile as a standard screw-in incandescent bulb and can easily be substituted and used with existing light sockets.

Fluorescent bulbs are more expensive than their incandescent counterparts, but they last far longer and more than make up for the additional cost on this basis alone. What’s more, they are at least four times more efficient (8%+). A commonly sold 14W compact fluorescent can provide the same light as a 60W incandescent bulb. In commercial and industrial applications where fluorescents have been in use for decades, companies can still save 20% on their lighting bill by replacing older T12 systems with T5 bulbs that have electronic ballasts. The time of the incandescent light bulb has long since passed and the only reason this obsolete technology still exists is due to market inertia created by consumer ignorance.

For those looking to upgrade the lighting in their facility, the experts at Mass Energy Lab can help clients obtain EPAct tax credits for making the switch. Even if a company has completed lighting project in the last few years but  never took advantage of the available incentives, we can help. Professionals here can guide clients through the process of obtaining the incentives retroactively and potentially bundling it with a heating system upgrade to save even more money.

Fuel Cell
This device converts chemical energy from a chemical reaction to produce electricity. Hydrogen, natural gas and methanols have all been used as the fuel source. They are used everywhere from power, cogeneration, car batteries and even smartphones. They are good at handling base load.

G

 

Gas Leak Detector
A device that detects the presence of flue gases. It is used to ensure that gas leaks are not present in residential homes or commercial facilities. Gas leak detectors are equipped with several electrochemical sensors to detect gases such as methane, propane, gasoline, natural gas, and/or other gases, which varies from one device to another. Since electrochemical sensors wear down within a few years of use, other versions of gas leak detectors use infrared, semiconductor, ultrasound, or holographic sensors. If gas concentrations exceed certain thresholds, LED lights and/or an alarm system in gas leak detectors will alert the users regarding such levels.

Greenhouse Effect
A process in which the Sun's thermal energy near Earth's surface is absorbed by greenhouse gases, most notably water vapor and carbon dioxide, that keep Earth warm. When the sunlight reaches Earth, some of it is reflected back into space by Earth's surface and atmosphere, while the rest of it is absorbed by Earth's surface. The absorbed thermal energy is then released back into space, but some of it is reabsorbed by greenhouse gases. With increasing carbon dioxide levels, more heat is reabsorbed, and Earth becomes warmer. This increase of Earth's temperature is known as global warming, which contributes to shrinking ice caps.

The greenhouse effect is analogous to what is happening inside the greenhouse. Some of the sunlight is reflected by the glass ceilings and walls of the greenhouse, while the rest of it enters the greenhouse. At the same time, the glass retains the sunlight's thermal energy inside the greenhouse. This explains why it is usually warmer inside the greenhouse than it is outside.

Greywater System
A system that cleans and recycles water after its use in order to be reused. Its purpose is to save energy and the environment, since water would not have to go through large water treatment facilities and would be less reliant on the use of chemicals to purify water. At the same time, it promotes highly efficient water consumption habits. Greywater systems are particularly very useful in areas where water supply is very limited. Examples of their use include water use in bathrooms and plant irrigation. Note that for safe water consumption, water in greywater systems must be purified. This is achieved through several methods such as sand filtration, UV radiation, or plant soil. Some systems use multiple methods of filtration at the same time to ensure high water quality.

Grid
Generally short form for electrical grid. It consists of three main components: a generator to burn fossil fuel and generate electricity, transmission lines to transfer the electricity to the required location and the transformer to step down the voltage to the required distribution level.

H

 

Heat exchanger
A device which exchanges heat from one medium to another by a wall or circular tube hence it is an indirect method of heat transfer. The tubes are very thin in width to allow for sufficient heat transfer. Most older heat exchanger tubes were made out of aluminium whereas newer ones are made from stainless steel due to its higher strength and ability to withstand harsher environments. Heat exchangers are used extensively in air conditioning to make evaporator and condensor coils in refrigeration units.

Heat Load Calculation
The main goal of a heat load calculation would be to determine how much energy is required by the building to keep the building at a certain set temperature, 65°F for most warehouses.

The major parameters required to calculate heat loads are:

1) Determine the set building indoor temperature (Ti) and the outside temperature (To)

Calculate deltaT = To - Ti

2) Building envelope insulation values, R or U values

1. roof insulation
2. wall insulation
3. glazing in windows (neglected in most warehouses due to a lack of windows)
4. door
5. floor

3) Building dimensions (L x B x H) and overall dimensions of all roof, floor, doors etc

Calculation:

1) First calculate the transmission heat load from conduction

For the roof = Net roof area (ft2) x U Value-roof x deltaT
For walls = Net wall area (ft2) x U Value-walls x deltaT
For windows = Net windows area (ft2) x U Value-glazing x deltaT
For the floor = Net floor area (ft2) x U Value-floor x deltaT* (less than deltaT)

*deltaT* is less than deltaT because generally heat is not lost through the ground because hot air rises up

2) Building infiltration load

Calculate the total CFM (cubic foot per minute) volume of air flow required

CFM = (Net Volume of building (ft3) x air-change/hr) / (60 min/hr)
Infiltration Load = CFM x 1.1 x deltaT

3) Operating Heat Load

Open door loss = Quantity of doors x MBH/door x % door-open
Ventilation loss from people = No. of persons x CFM/person x 1.08 x deltaT

Process heat gain (+) or loss (-) from exhaust = CFMe x 1.08 x deltaT

*CFMe is the ventilation loss through process exhaust

Total heat load or the energy required to keep the building at a set temperature would be the addition of the total transmission heat load, building infiltration load and operating heat load.

Heat Transfer
This process occurs when thermal energy transfers between one place and another. Energy transfer may occur in one of three ways: conduction, convection and radiation.

WARNING: The following is to be read only by the thermodynamically inclined, and the semantically obsessive. Reading by the casual browser may result in the following unwanted side-effects: confusion, irritability, headache, nausea, gingivitis, rickets, cranial implosion.

Depending on who you talk to the term “heat” has a couple of meanings, though all agree that the colloquial meaning is incorrect and misleading. Unlike energy, a system cannot contain a specific amount of heat. Inherent in the term is the transfer of energy and therefore heat has no meaning in a completely static system. For most engineers, heat is, "thermal energy in transit due to a spatial temperature difference (1).” Out of respect for a certain graduate professor who shall remain nameless, a narrower definition is also given here. Under such a definition heat cannot even be transferred, but rather it describes a certain type of interaction. In such an interaction, energy is transferred from one thermal reservoir to another thermal reservoir at the same temperature across an infinitesimally small temperature gradient. A heat interaction is completely reversible. (2)

1. Incropera, Dewitt, Bergman, Levine. (2007). Fundemental of Heat and Mass Transfer (6th ed). New Jersey: John Wiley & Sons.

2. Gyftopolous, E.P., Beretta, G. P. (2005). Thermodynamics: Foundations and Applications. New York: Dover Publications Inc.

Heat Trap
A valve that is installed on a water heater tank to prevent hot water from flowing out of the water tank by convection while water is not running. Since hot water is less dense than cold water, this property causes hot water to rise. Heat traps prevent this from happening so that hot water continues to be retained in the water tank to conserve heat. For each water heater tank, two heat traps, which are designed differently, are needed. One is used to allow cold water to flow into the water heater tank when water is running, and the other prevents hot water from flowing out of the tank after water stops running. Each household can save around $15-$30 of annual water heating bills from heat traps. Recent models of the water heater tank either already have heat traps installed or provide homeowners an option to install them.

Heating, Ventilation, and Air Conditioning (HVAC)
A system that circulates air and regulates indoor temperatures with a heater or air conditioner. It is typically present in industrial facilities and office buildings. HVAC's contribute to a major portion of energy consumption in the US. As a result, they are one of the major areas for improvement in energy efficiency. Also, air leakage tests and additional insulation in buildings help further reduce energy consumption by HVAC's.

HID
Like fluorescents, these are a type of gas-discharge lamp. An arc is established within a highly pressurized gas-filled tube known as an arc tube. The pressurization allows the arc to generate temperatures much more than those in fluorescent tubes. These temperatures vaporize a small quantity of materials, such as sodium or metal halide salt. The electric current excites the electrons within the ionized metallic vapor which then emits radiant energy. Because of the high temperatures, a siginificant percentage of the vapor’s radiant energy is emitted in the visible spectrum. Surrounding the arc tube is usually an outer bulb which insulates it thus helping it reach higher temperatures along with providing shielding against UV emissions. HID is the most energy efficient lighting technology currently available with efficiencies of up to 29% for low-pressure sodium lamps. The catch is that these lamps are more complicated and therefore more expensive than other widely available lighting systems. Their adoption has mainly been limited to applications where high intensity lighting is required over a large area such as in headlights, stadiums and warehouses. However, with more compact designs, HID lamps have been making inroads into retail and commercial lighting applications.

HP (horsepower)
Horsepower is one way to measure the power output of a motor though it is defined slightly differently depending the type of motor. For electric motors 1 hp = 746 W exactly. Blowers, fans and compressors may be rated in HP since they all rely on electric motors to operate. The term itself has roots dating back over 300 years to the birth of the steam engine. In order to convey the capabilities of such a device to laymen, and hopefully get them to buy one, it made sense to compare their power to the equipment they were intended to replace, horses. Though all horses are different and some are much lazier than others, 1 HP is actually a reasonable assessment of the power output of a working farm animal.

Hybrid car
A car that is powered by both a conventional gasoline engine and an electric motor. A conventional car has the advantage of traveling more than 300 miles between trips to the gas station, but it significantly contributes to air pollution. Meanwhile, an electric car purely uses electricity instead of gasoline. Its batteries, which are located at the bottom of the car, are recharged as if the battery of a cell phone is charged, but the electric car lasts only 100 miles per trip. Hence, the hybrid car is designed to be a compromise to make up for these downsides. The conventional gasoline engine inside the hybrid car is usually smaller than the one in a conventional car, but electricity from the electric motor provides extra power for the hybrid car. The electric motor provides power through the batteries, but when the hybrid car slows down to a halt, it acts like a generator by temporarily shutting down the gasoline engine and converting kinetic energy into electricity that can recharge the batteries through a process called regenerative brake. This process is much more efficient than the conventional car that converts kinetic energy into dissipated heat after it stops.

There are four different types of hybrid cars. They are the micro hybrid, mild hybrid, parallel hybrid, and series hybrid. The micro hybrid is run only by a gasoline engine while it moves, but when it stops, the electric motor goes through regenerative brake. As soon as the car is ready to go, the electric motor restarts the gasoline engine. The mild hybrid is similar to the micro hybrid, except that it is run by both the gasoline engine and the electric motor. However, the electric motor alone is not enough to power it. On the other hand, the parallel hybrid, or full hybrid, can run solely by either the gasoline engine, the electric motor, or both at the same time. Meanwhile, the series hybrid is like a pure electric car that is supported by a gasoline engine, which is located at the back of the car. The only role of the gasoline engine is to power the electric motor that, in turn, powers the car to move.

I

Ice Dam
Ice that is accumulated on the edge of the roof at freezing temperatures outside and prevents melted snow on the roof from draining properly through the gutter. Snow on the roof is first melted by heat leaking out from underneath the roof. Poorly insulated roofs allow heat to escape, which causes snow above to melt. However, the lost heat cannot reach the outer edge of the roof (where the gutter is). As a result, temperature on the outer edge of the roof is below the freezing point, and the melted snow refreezes there. Eventually, ice accumulates upwards to form an ice dam until it reaches the point where it meets the heat that is leaking from the roof. At that point, the ice stops accumulating, and the concave shape of the ice dam on the roof traps and stores water, which then leaks through the roof. The water then can cause damage to the house by seeping out through walls and ceilings.

The best way to prevent ice dams is to have proper insulation on the roof. Properly insulated roof prevents heat from escaping, which then prevents snow on the roof from melting and forming an ice dam. Signs of ice dams include "missing snow" near the roof ridge (if the roof is slanted) and the formation of icicles along the edges of the roof. If these signs are present, it is recommended to get trained professionals to remove the ice dams.

On a large scale, ice dams can also be formed on rivers. If river water upstream is first melted, and river water downstream is still frozen, the flowing water can be trapped by the ice and as a result forms an ice dam. As river water continues to flow, water is accumulated at the ice dam. Eventually, the accumulated water can overpower the ice dam, causing it to break and create massive floods at areas near the bottom of the river. To prevent those kinds of ice dams, ice blasting using explosives may be needed.

Igniter 
Equipment that is used to start a flame or combustion of gas and air. It is made of silicon carbide material and is very fragile. During ignition, its temperature reaches up to 2400°F. Igniters are usually shock mounted for minimal disturbances.

Implode
Is when an object is caused to blow or collapse inwards. It usually occurs when there is a vacuum created from the pressure difference between areas upstream and downstream in pipes.

Incandescent
These bulbs or lamps operate by passing an electric current through a resistive filament which heats up to very high temperatures, often over 5400ºF. As the temperature increases, a larger portion of the filament’s radiant emissions fall in the spectrum visible to the human eye, thus producing what we think of as light. Since Thomas Edison developed the first commercially successful light bulb in 1879, the device has changed little. Modern bulbs are filled with argon gas instead of the high vacuum he first used and tungsten filaments have replaced the carbon ones but these developments are themselves a century old.

In an age when your top of the line smart phone becomes obsolete in the time between choosing it in the store and sending your first text, the incandescent light bulb represents the gold standard in technological staying power. Unfortunately, it is also the gold standard in energy waste. At roughly 2% efficient a standard 60W bulbs perform far more like electric heaters than light sources. Other than for special applications, incandescents should have died out years ago.

Indoor Air Quality
In addition to thermal comfort, the potential health effects of indoor air quality (IAQ) must be considered when designing an HVAC system. Airborne dust, microorganisms, chemical vapors and other gases can cause illness in sufficiently high concentrations and must be monitored and accounted for in any ventilation scheme. Even excessive humidity levels are cause for concern. Not because of the discomfort they cause, but because such conditions promote the growth of mold whose spores can be very dangerous to humans when inhaled. ASHRAE 62.1 "specif[ies] minimum ventilation rates and other measures intended to provide indoor air quality that is acceptable to human occupants and that minimizes adverse health effects." IAQ is one of the factors in LEED certification and is therefore important to keep in mind even in buildings such as warehouses which traditionally have no mechanical ventilation.

Induction
When a jet of air moves through an environment of still, ambient air it drags some of this air along with it due to viscous effects. This is called induction or more commonly enterainment. Just like thermal energy, momentum diffuses outward from the jet and some of its kinetic energy is transferred to the surrounding air. The higher the initial velocity of the jet, the more energy it has to distribute and the more air it can carry along with it. The Cambridge S-Series Space Heater claims an induction ratio of 10:1. This means that for every ft3 that is ejected from its high speed nozzle an additional nine ft3 are dragged along. Air exiting a roof-mounted unit drags large volumes of air from the ceiling down to the floor. This insures proper mixing of air within the building and minimize stratification.

Infiltration
This is a measure of how fast the air in a building is replaced by air from the outside. Every structure “breathes” to one degree or another, with air constantly flowing in and out through gaps in walls and through open windows, doors and vents. Since it is very difficult, if not impossible, to measure the infiltration rate directly, ANSI standards provide an approximation of the infiltration. For large warehouses, this number is 0.18-0.2 air changes per hour. In other words, approximately 20% of the air volume in the warehouse will leak out every hour and will be replaced by outside air.

Infrared (IR) Camera
A camera that uses infrared light to detect problems such as insufficient insulation, overloaded circuits, and overheating machines to improve energy efficiency. It is used by energy auditors to inspect residential homes and/or commercial facilities. For instance, if they scan outside a residential house and see bright areas in the windows or rooftops through the IR camera screen, this indicates that heat is seeping out in these areas.

The IR camera works when its lens retrieves all the infrared light from everything in their view such as our bodies and electronics. Based on its viewing area, the infrared light detectors create a temperature map called a thermogram. Through signal processing, the IR camera converts the information into electric signals that are used to display thermal images or even videos. That way, energy auditors can estimate the temperature at a particular point in a given area.

Infrared or Radiant Tube Heater
These pieces of equipment are a form of indirect fired heaters which are hung from the ceiling. These gas fired units are passive which means that they bring no outside air into the space. Outside air is heated in a combustion chamber and then passes through a tube at 350ºF-1000ºF. A reflector focuses the tube’s radiant heat down toward the floor warming the occupants and the building’s contents directly instead of first warming ambient air. It is able to do this because the system transfers here via infrared radiation rather than convection as every other heater does. The heated objects, such as the floor, then reradiate some of this energy and warm the ambient air. Electric infrared heaters may be used in areas where it is impractical to run a gas line. However, similar to the powerful electric room heaters you might plug in to warm your feet, these systems are incredibly inefficient and of limited use.

Infrared Sensors
Measures infrared light in the radiation from objects and is invisible to the human eye. These sensors detect movement by the temperature difference of walls/ floors to humans passing infront of the infrared source.

Insulation
Energy costs money. Whether it’s chemical energy for heat or electrical energy to power your woefully inadequate window air conditioner, every kWh you use is more money out of your pocket. Therefore, if you're paying to pump energy into a building to keep it warm, you’d like that energy to stay there instead of leaking out and forcing you to buy even more. In any thermal system, such as the wall of a building, where a temperature gradient exists, energy will naturally move from areas of high temperature to low temperature (to do otherwise would violate the second law of thermodynamics and make a lot of physicists very upset). The goal is to limit the energy transfer through the building envelope and thus minimize heating and cooling costs. Only so much can be done in the way of sealing and draft prevention since the vast majority of a building’s envelope is composed of solid walls and its roof. This is where insulation comes in. Insulation minimizes heat transfer to or from an object such as a building by increasing the R-value of the building envelope. Fiberglass insulation does this by creating a mat within which air finds it difficult to move and establish convection currents. Heat transfer is thus forced to occur by conduction. Since the insulation is mostly air, which has a very low conduction coefficient, this yields a high thermal resistance. In insulation for cryogenic application, layers of similar fiber glass material may be sandwiched between aluminum foil sheets and evacuated. The reflectivity of the foil minimizes radiative heat transfer while creating a vacuum between the sheets eliminates convection and cuts conduction down to nearly zero. A new generation of building insulation may be on the way in the form of aerogels. This novel material has the lowest thermal conductivity of any solid material known, and some variants such as Spaceloft® from Aspen Aerogel are better insulators than air itself. In addition to the energy savings, those seeking to insulate their buildings may be eligible for tax benefits under EPAct. With help from Mass Energy Lab and our consultants you can be sure to obtain the maximum possible deduction.

K

 

Kinetic Energy
Energy possessed by the directed motion of the moving fluid. It is the energy required to move a body from rest to required velocity. If the velocity changes then there is a change in K.E. Hence, the energy of motion, or kinetic energy, for 1 kg of fluid is therefore given
by Ek where:

Ek = v2/2 (J)

v = velocity of fluid in (m/s)

kWh (kilowatt hour)
Unlike in Btuh, the time unit here is multiplicative turning kW which is a unit of power, into a unit of energy. Though there is no qualitative difference between Wh and Btu (1 Wh =  3.41 Btu) a kWh is the standard measurement for electric energy usage. Electricity is priced per kWh and this rate varies from state to state. Due to the nature of their operation, the efficiency of refrigerators and freezers are given kWh/year.

L

 

Leak Barrier
A layer of fiberglass that is installed underneath roof shingles to provide a watertight seal. The problem is that roof shingles alone are not enough to prevent water leaks. Leak barriers are even effective during long periods of heavy rain. During winter, they also prevent the formation of ice dams. As a result, leak barriers prevent damages in walls and ceilings caused by water leaks and help homeowners avoid long-term costs in repairs.

Lean Combustion
Occurs when the ratio of air to fuel is very high, up to 65:1. It is done to have better performance, efficient fuel use and low hydrocarbon exhaust from the combustion process. Although catalytic converters are required to control the NOx emmisons.

LED
Light emitting diodes represent the future of lighting technology. While not yet economically competitive with fluorescent or HID bulbs for most applications, a host of products are already on the market for the more eco-concious early adopters. An LED is essentially a piece of chemically doped semiconductor material (usually silicon) which emits light when a voltage is applied. This material is embedded in plastic which protects it and allows additional modifications to be made to the emission spectrum by impregnating the plastic with certain phospors. Since introduction to the mass market in 1968, LEDs have been used as indicators and have appeared in larger displays of all kinds. However, until recently they have not been powerful enough to act as effective sources of illumination. What is so attractive about LEDs is that they have the potential to be vastly more efficient than any other technology currently on the market. Although the reining L Prize champion currently checks in 13.7% efficient, the potential exists for products to achieve efficiencies greater than 40%. Similarly, many lamps today are expected to last 25,000 hours while the future may see LEDs that can last for over 100,000 hours. In other words, you would only have to replace a bulb every few decades. As if that wasn’t enough, flexible organic LEDs and quantum dots (think spray on LEDs) offer the possibility of light sources in an infinite variety of shapes sizes allowing them to be put to uses one could never imagine for a standard bulb.

LEED
Leadership in Energy and Environmental Design (LEED) is a certification system developed by the U.S. Green Building Council (USGBC) to give building owners and designers a structure to identify and implement green building solutions. Depending on the building type or project, such as new construction, schools and healthcare, there is a LEED system in existance to rate that building's efficiency. These rating systems evaluate buildings based on criteria like water efficiency, indoor environmental quality and recycling of construction materials. Points are awarded in these categories for meeting certain standards then added up to yield a final score. Based on this score, buildings receive different levels of LEED certification ranging from basic to LEED platinum. Having a LEED certified building is one of the best ways for a company to demonstrate its commitment to sustainability and environmental stewardship. As such, certifications are often pursued not just to improve working conditions and save on utility bills, but as a PR marketing tool.

Lighting
Approximately 18% of the electricity produced in the United States is used to illuminate our homes and offices. An additional 4-5% is then needed to remove all of the heat that those lights bring into a building. In commercial buildings, lighting accounts for a third of all electricity use, more than air conditioning and office equipment combined. This energy use represents one of the greatest opportunities for private citizens and businesses to become more energy efficient by reaping the benefits of new lighting technologies such as compact fluorescent light bulbs and new LED fixtures. In addition to the energy savings, tax benefits and utility incentives are often available to help pay for any lighting upgrades you might be considering.

Liquid Air
Air that is converted to liquid. This is made possible by removing any substances that have high boiling points and then rapidly expanding pressurized air. Hence, liquid air is a combined version of liquid nitrogen and liquid oxygen. Since the boiling points of nitrogen and oxygen are -196 and -183 degrees Celsius respectively, oxygen can be isolated and purified by distilling liquid air.

Since the boiling point of nitrogen is lower than the one of oxygen, the boiling point of air is -196 degrees Celsius. To maintain its liquid form, it must be kept in a vacuum. Otherwise, when it is exposed to room temperature, it converts back to gas. To expedite this process, industrial heat waste can be used.

Liquid air can also be potentially used to power wind turbines. During windy days, some of the electricity generated from wind turbines can be used to convert air into liquid, and it can be easily and safely stored. Since there are some days when wind is not available, wind turbines do not generate electricity during these days. At that time, the stored liquid air is then converted back to a gas form, and it expands by over 700 times. This expansion can propel wind turbines to generate electricity during non-windy days.

Load Profile
This is a graph of electricity consumption rate vs. time. The profile may describe anything from a window-mounted AC unit to an entire building. While a meter may tell you how much electricity you have used in total, it will not tell you when that energy was used. By correlating periods of high energy usage to certain events, say the opening of a door, strategies can be devised for minimizing energy use. Perhaps the most important part of any load profile is the peak demand. Many utilities levy a monthly demand charge based on the size of a facility’s peak demand. It is necessary to pinpoint the source of peak need in order to reduce electric bills during that short period of time. For instance, when an AC compressor turns on there is a brief load spike. Alone this phenomenon may not matter, but if 10 AC units in a building all turn on simultaneously then their individual load spikes will overlap and result in one large building-wide spike which can be very expensive.

Low-Emittance (Low-E) Coating
A thin, transparent layer of metal or metallic oxide that is typically used to coat double-paned windows to prevent heat flow through the windows. It is usually placed on the surface of window glass that faces towards the space, which contains argon and/or krypton gas in double-paned or triple-paned windows. The coating and the mixture of the noble gases help prevent heat from seeping out during cold winters and/or from entering during hot summers.

There are many different types of Low-E coatings, but they can divided into three categories, which are high solar gain, moderate solar gain, and low solar gain Low-E coatings. All three categories of Low-E coatings prevent heat loss inside buildings, but they differ from the amount of heat from the Sun that enters buildings. Since high solar gain Low-E glass allows heat to enter buildings, its use is more suitable during winters. On the other hand, low solar gain Low-E glass, which blocks a major portion of the heat from entering buildings, is more suitable during summers. Moderate solar gain Low-E glass tends to be used in areas with moderate climates. The choice of the type of Low-E glass also depends on the house design.

M

 

Manometer
A device that calibrates the blower door or duct blaster to the user's chosen pressure differential to get the measured CFM50 of the building or the building's main duct system respectively. It first allows the user to choose a preferred flow range, which affects the area of the blower door, but an open flow range is usually used in very leaky buildings. Then, the manometer sets a pressure baseline to ensure that the air pressure remains consistent within 1 Pascal over time. Afterwards, the user can enter the pressure differential between outside and inside the building. The pressure differential is usually set to 50 Pascals to obtain the CFM50 value, which then indicates the leakiness of the building. Please see the definition of blower door for more information.

mBtuh (British thermal units per hour)
A measurement of power used to describe how fast a system can add or remove thermal energy from a space. Note that the time unit “h” divides rather than multiplies as it does in kWh. The figure Btuh generally describe the end state of an operation (what you get out) rather than the energy that one puts in. So a 100 mBtuh heater adds that much energy to the space, but if it is 80% efficient it actually consumes 125 mBtuh. Such consumption is generally measured in therms.

mBtu/mBtuh - The m here is the roman numeral for 1000 NOT the shorthand for million like in MW. A million Btu is expressed as mmBtu.

N

 

National Fenestration Rating Council (NFRC)
A non-profit organization that specializes in rating the energy performance of windows, doors, skylights, and other attachment products. It uses its own independent rating system to rate those products based on numerous factors such as their U-factor, solar heat gain coefficient, visible transmittance, air leakage, and condensation resistance. Its rating system helps homeowners, contractors, builders, and architects compare similar products to make the best product selection. It also serves as a guide for building officials and state government officials to enforce the use of certain products that meet the building codes in local areas.

Natural Gas
A fossil fuel that is used as one of the primary energy sources. It is composed primarily of methane. If its composition is nearly 100% pure methane, it is known as "dry" natural gas. Natural gas is normally a colorless, odorless gas in its pure form. However, a colorless gas called methanethiol (methyl mercaptan), which has a smell of rotten eggs, is added to natural gas to detect any leaks for safety reasons. Other forms of natural gas contain small amounts (0-20%) of other hydrocarbons such as ethane, propane, and butane. This version is known as "wet" natural gas.

Natural gas is extracted from underground reservoirs, and impurities are filtered out. Afterwards, the purified natural gas (or "dry" natural gas) is distributed through a network of pipelines. Some of the natural gas also contain small amounts of carbon dioxide. Hence, even though natural gas is a much cleaner energy source than coal, its use still contributes to the release of greenhouse gases. Furthermore, natural gas is used as a fuel for heating and cooling, and sometimes it is burned to power wind turbines when wind is not available to power them.

O

 

Occupancy Schedule
An occupancy schedule is just what it sounds like, a regular schedule of when a space will be occupied and by how many people. These schedules are important because they determine operational characteristics of the HVAC system such as heating and cooling schedules, ventilation rates and lighting schedules. Systems can ramp up or down depending on the number of occupants or they can shut off altogether during periods when the building is unoccupied. The occupancy schedule is not an exact count of how many people are in a space at any given time, but rather an estimation based on past data such as head counts and known number of employees.

Ocean Thermal Energy Conversion (OTEC)
A process of creating renewable energy with a fluid that has a low boiling point based on the temperature difference between cold deep ocean water and warm surface ocean water. The boiling point is a threshold, in which a liquid is converted into a gas and vice versa. Hence, for OTEC to work, the boiling point of the fluid must be in between the two ocean temperatures. Using surface ocean water, the fluid is converted into gas that would propel turbines which, in turn, generates electricity. Then, deep ocean water that is pumped upwards to the ocean surface converts the gas back into liquid. The fluid is reused for electricity generation, and the cycle repeats.

OTEC is similar to how steam engines work. Instead of using the fluid with a low boiling point, steam engines use water. In order for steam engines to work, water is boiled and converted into high-pressure steam, which powers the engines. Afterwards, the steam is condensed back into water that is reused to power the steam engines.

Organic Light Emitting Diode (OLED)
LED that contains thin layers of organic compounds. When electricity is applied to these layers, electrons become excited and emit photons, an action that produces light. The organic layers can be made simply by spraying the organic compounds onto the substrates just as the ink printer sprays ink onto a printing paper. When electricity is turned off, OLED's become transparent like a thin sheet of plastic.

OLED's are more energy-efficient, thinner, and brighter than LCD's and standard LED's. Since the substrates can be made of plastic, this advantage provides the property of flexibility in OLED's. With this special trait, they are applied to the screens of cell phones and cameras, so that it is less likely for the screens to break. Most recently, OLED's are applied to television screens. OLED TV screens have shown to be clearer and sharper than the current LCD screens. However, despite the high market potential of OLED's, they are still in the infancy stage due to their high costs.

Organic Rankine Cycle
Most Rankine cycles use water as their working fluid. It has a high specific heat capacity and it’s cheap, what could be better? However, because water doesn’t boil until 212º F, steam-based Rankine cycles requires heat sources above 1000º F for optimal efficiency. There many industrial processes such a metallurgy and glass-making which throw off tremendous amounts of heat. Steam may easily be raised using this energy, but often there is no need for it either within the facility or in the immediate area. Originally, energy was simply wasted because the temperatures involved were too low to make a steam-based power cycle economical and there was no local need for steam itself. In order to operate a reasonably efficient Rankine cycle, a fluid with a lower boiling point is required. Organic fluids are a class of fluids which fit the bill. These include traditional refrigerants such as R-134a, pressurized CO2, and unique blends that individual ORC companies may develop. With such fluids, energy sources of virtually any temperature can be used, though 200ºF-300ºF is generally the minimum. Besides waste heat, ORCs are also key to renewable power sources such as geothermal and solar thermal.

P

 

Parabolic Aluminized Reflector (PAR)
An electric lamp that provides light to a large area. It is typically used in car headlights, landing lights for airplanes, and lighting for residential homes and commercial facilities. PAR's are also commonly used for stage lights. Recently, LED PAR's have replaced the standard PAR's, since they are more energy efficient, and they do not require any color filters. Also, PAR's come with various sizes. To distinguish among them, a number is followed by PAR. For instance, PAR30 and PAR38 lamps have diameters of 3.75 and 4.75 inches respectively.

Pascal (Pa)
A unit of measurement that quantifies pressure. One Pascal, or one Pa, is equivalent to one Newton per square meter (N/m^2), or one kilogram per meter times seconds squared (kg/[m*s^2]). The standard air pressure in Earth is 101.325 kPa (or one atm). Hence, one Pascal is an extremely small amount of pressure. As a result, it is equivalent to 10^-5 bar, 9.87*10^-6 atm, 7.50*10^-3 Torr, and 145.04*10^-6 psi. Also, Pascal is a unit of measurement to quantify stress, Young's modulus, and tensile strength of materials.

Peak Periods
Consist of the demand period when electricity charge is very high. It usually occurs during the middle of the day when most equipment is running. Heat waves cause the electricity demand to rise because most AC units are working at full capacity which could cause load shedding and power outages due to demand exceeding supply.

Perm
A unit that measures the number of water vapor drops that pass through 1 square foot of a material per hour at 23 degrees Celsius and at a differential vapor pressure of 1 inch of mercury. Simply put, it measures the permeability of water vapor through a material. If the perm for one particular material is less than 1.0, it is considered a vapor diffusion retarder (VDR). The purpose of this measurement is to select materials that can help control moisture in areas such as house ceilings, floors, and walls. For instance, an unpainted drywall has a perm of 50, but an aluminum foil that is only 0.35 millimeters thick has a perm of only 0.05. Hence, an aluminum foil is considered as a VDR. It is recommended that in cold areas, the VDR should be installed on the inside walls of the house, while in hot areas, it should be installed on the outside walls. Areas in the middle ground (certain regions of southern states right above the hot areas) may not need any VDR's.

Photovoltaics
A process of converting sunlight into electricity. Solar panels are composed of smaller units called photovoltaic cells, which are made up of semiconductor materials, usually silicon and other impurities. When some of the light, which is made up of photons, is absorbed by the semiconductor materials, the photons displace electrons in the semiconductor materials. This displacement allows electrons to flow freely, which in turn generates electricity. Since silicon is shiny and as a result reflects most of the light, solar panels are covered with an anti-reflective coating to allow the semiconductor materials to absorb light.

Photovoltaics works similarly to photosynthesis. During photosynthesis, plant leaves absorb light to convert carbon dioxide and water into oxygen and sugars. This process powers and nourishes plants to produce oxygen. Similarly, solar panels absorb light to produce electricity that powers all electronics.

Piezoelectricity
Electricity generated as a result of applying pressure. When pressure is applied on a plate, which is usually made of quartz crystals (silicon dioxide - SiO2), protons and electrons in the atoms that make up the crystal plate become displaced. As soon as the plate is returned back to its normal state, electricity is generated.

One simple example is powering a light bulb with a mini pressure plate that is compressed by the kinetic energy of raindrops. Instead of using a socket or battery, each raindrop that falls on the pressure plate would power up a light bulb for one second. Or place a much larger pressure plate underneath a waterfall, which can constantly power up many nearby light bulbs at the same time. To take it to the next level, imagine people walking around in plazas, shopping malls, and dance clubs, where the floors are mostly made up of pressure plates. Each and every person's footstep contributes to powering up the entire city. Piezoelectricity can potentially reduce the use of conventional electricity generated by the combustion of fossil fuels.

If you are a Greek scholar, you might have already guessed what piezoelectricity is. But for those who are not Greek gurus, "piezo" is a Greek word for pressure.

Plant Solar Cell
A plant-based solar cell that generates electricity through photosynthesis. It is composed of zinc oxide nanotubes, which are micro hair-like structures coated with photosystem-I molecules that are derived from plants. These molecules include similar versions of chlorophyll. The nanotubes increase the surface area of the solar cell, which would make the solar cell more efficient.

Plant solar cells are designed to be cheaper compared to the current solar cells. With their proposed lower initial costs, they will eventually be used as a renewable energy source particularly for people from underdeveloped countries. Currently, more research is needed to improve the efficiency of plant solar cells.

Polyvinyl Chloride (PVC)
A synthetic plastic that is commonly used to manufacture consumer goods. They include vinyl sidings, wallpaper, window frames, pipes, bottles, cables, and imitation leather. Its use is very popular due to its durability and affordability. Chemicals such as phthalates are added to PVC to provide its property of flexibility.

However, PVC releases several chemicals, especially when it is burned in a fire. One of the most toxic chemicals it releases is dioxin. Another chemical in PVC is bisphenol A (BPA) that can increase the risk of heart disease, liver failure, and diabetes and can also mimic a female hormone estrogen. Studies have shown that exposure of animals to these chemicals from PVC can increase the risk of cancer and kidney damage. They have also found that PVC from toys can enter children's bodies. As a result, governments and industries have recently been finding ways to eliminate the use of PVC.

Potential Energy
Is the energy of the fluid positioned above some reference level. It is calculated as the potential energy of 1kg of fluid at a height of Z (m) above its reference and is given by Ep, as shown:

Ep = Zg (J)

Z = height difference from datum (m)
g = acceleration due to gravity i.e 9.81m/s2

Pressure Relief Valves
Designed to allow the the (liquid, gas or liquid–gas mixture) to pass through the relief opening which has a predetermined pressure limit. It protects pressure vessels and equipment from over pressurization. In most cases the outlet of these relief valves are in the open air.

Prime Mover
A machine which is designed to convert thermal, electrical or pressure energy into mechanical work. The earliest forms of prime movers were the water wheel. More recent technologies such as heat engines and turbines are also prime movers.

Process Heat 
The heat generated or released from all of the processes, machinery or equipment in an industrial or manufacturing plant. It includes:

1. Heating devices that generate and supply heat
2. Heat transfer devices to move heat from the source to the product
3. Heat containment devices, such as furnaces, heaters, ovens and kilns
4. Heat recovery devices

Reusing this process heat can result in substantial energy savings along with significantly slashing a company's utility costs.

Programmable Thermostat
A thermostat that is pre-programmed to adjust the room temperature based on the times of the day and seasons to reduce energy consumption. It allows its users to choose their temperature preferences at particular times to maintain high levels of comfort while saving energy at the same time. Some programmable thermostats allow users to choose based on the days of the week. Hence, they are called 7-day programmable thermostats. One of the advanced versions of programmable thermostats goes as far as automatically learning the users' temperature preferences and even adjusting room temperatures based on weather forecasts through Wi-Fi connectivity. It also allows users to adjust temperature schedules remotely in real-time with an online account through any computer or a smart-phone.

Studies show that half of the energy bills come from the use of heaters and air conditioners. With conventional thermostats, homeowners are likely to leave their heaters or air conditioners on while they are away at work. However, with a programmable thermostat, if the ideal room temperature during winter is, for example, 70 degrees Fahrenheit, it will set that temperature at the users' predetermined times when they wake up in the morning, and when they come back home from work. Otherwise, the heater is automatically turned off when homeowners are at work or when they are asleep. Hence, the programmable thermostat acts somewhat like a "silent temperature alarm clock". This process of choosing ideal temperatures at appropriate times repeats as seasons change.

R

 

R-Value
This measures the thermal resistance of an insulating product and in the U.S. has units of ft2 Fh/BTU. If we think about a thermal system as an electrical circuit (such models are actually called thermal circuits and are used in simple modeling) the temperature difference across the building wall is equivalent to a voltage (driving force), the energy transfer is the current and the wall is a resistor.

Just as R = V/I for electric circuits so too does Rthermal = T/Qdot"

Since T remains constant, the heat transfer rate Qdot" can be decreased by increasing the thermal resistance Rthermal. The resistive term is composed of the inverse of conductive, convective and radiative terms for all materials making up the building envelope. The goal of insulation is to minimize some or all of these contributing terms thus maximizing the thermal resistance. The R-value depends not only on the material being used, such as fiberglass, but is also proportional to its thickness.

Radiant Barrier
A reflective material that is usually installed inside the attic to reduce heat gain caused by the sunlight's radiant energy on the roof. Normally, when the sunlight heats the roof, heat flows through the roof into the attic by conduction. If a radiant barrier is installed, it reflects the heat away. As a result, during summer, buildings would be kept cool, and building owners would benefit from reduced energy bills. Hence, radiant barriers are more useful in warmer climates. Their performance is based on the angle that the sunlight hits and their properties of heat emittance and reflectivity. There are several different versions of radiant barrier, which include an aluminum reflective foil, a spray version of radiant barriers, and reflective metal roof shingles.

Radiant Floor Heating (RFH)
A heating system that is installed underneath floors of residential homes. Heat flows upwards through the floor to provide warmth to the entire house. RFH provides comfort to homeowners by warming the floors while they are walking barefoot. Hence, RFH acts like sunlight in terms of floor heating. Also, its use can reduce heating costs by 25-50% compared to the use of a standard furnace.

There are two different kinds of RFH, which are hydronic RFH and electric RFH. Hydronic RFH is made up of hot water tubes that emit heat through floors. It is usually installed for the entire house. The source of heat to supply the hot water depends on the climate. In colder areas, a boiler system is needed to supply hot water for hydronic RFH, but in warmer areas, a standard water heater is enough.

Meanwhile, electric RFH is made up of a plastic mat that contain coils of wires. These wires generate heat through electrical resistance. Electric RFH is best used for floors made up of ceramic tiles. Hardwood floors also work well, but thick carpets reduce its effectiveness. Its temperature can be controlled through a switch or a thermostat. However, it is much more expensive than hydronic RFH. Hence, it is usually installed for only one room in the house such as a bathroom or kitchen. For both kinds of RFH, they are best installed for newly constructed homes. They can be installed in older homes, but floors must be torn up in order for the installation to be possible.

Radiation
When people think of radiation, the first things that generally come to mind are nuclear reactor meltdowns and super-power inducing cosmic rays. While the former generally involves particle emissions, the latter is actually a small part of the larger electromagnetic spectrum. Any body above absolute zero emits energy in the form of thermal radiation. The energy takes the form of waves whose frequency fall somewhere along the EM spectrum. Depending on the temperature of the body, these emissions may be anything from radio waves to gamma rays, with the wavelength decreasing with increasing temperature. Visible light is part of this same spectrum which is why lighting often has a temperature designation. 2700K is not supposed to indicate the temperature of the bulb, but rather that the color it gives off is the same as a black body of the given temperature. At the terrestrial temperatures which humans experience energy is emitted in the infrared region of the spectrum. Therefore, we tend to associate thermal radiation specifically with infrared radiation although this is only a small part of the spectrum. Unlike conduction and convection, radiation does not require a transfer medium and therefore energy can be transferred between two bodies (not only solid, but gas as well) that are not in contact. Energy transfer rates between two objects at different temperatures depend not only on their respective temperatures but also on their shapes and emissivities.

Did You Know: What we call the visible spectrum is only visible to us because our eyes have evolved to detect that part of the spectrum at which our sun emits the most energy/light (390-750 nm).

Rankine Cycle
Power cycles are divided into gas power cycles and vapor cycles. Vapor cycles take advantage of the gas-liquid phase change of a working fluid in order to more closely approximate the Carnot Cycle. The Rankine cycle is an idealization of the vapor power cycle, without any irreversibilities. It consists of four stages:1

1. Isentropic compression in a pump
2. Constant pressure heat addition in a boiler
3. Isentropic expansion in a turbine
4. Constant pressure heat rejection in a condenser

The thermal energy source for the boiler may be just about anything. In power plants, energy may be generated through the burning a fossil fuels or the fission of uranium atoms. On the more sustainable side, liquid sodium may deliver energy to the boiler in solar applications or waste heat from industrial processes may be used. The work output of the system is delivered via the turbine shaft and this will generally be connected to an electric generator. The condenser is a heat exchanger whose job it is to get rid of low-quality thermal energy from which no further useful work can be efficiently extracted. The most common approach to making Rankine cycle devices more efficient is to make use of the low-quality energy rejected in the cycle. In cogeneration plants, this waste heat is used to raise steam which then can be used for building or process heating. In others, the condenser forms the heating element for another boiler in a second Rankine cycle (bottoming cycle) using a different working fluid which can efficiently extract further work.

1. Cengel, Y.A., Boles, M.A. (2002). Thermodynamics an Engineering Approach (4th ed). Boston: McGraw Hill.

Refrigeration Cycle
There are several types of refrigeration cycles, most are more or less the reverse of various power cycles. Gas refrigeration cycles are used in aircraft cooling and for cryogenic applications. Absorption refrigeration is useful when there is a waste heat source that can be used instead of purchasing electrical power. When most people refer to a refrigeration cycle they are thinking about the cycle which governs the operation of their household Frigidaire® or AC system. This is a vapor-compression refrigeration cycle, which is essentially the reverse of a Rankine cycle. Here a refrigerant such a R-134a is used as the working fluid. The four steps of a typical vapor compression cycle are as follows:

1. Isentropic compression of the refrigerant vapor in a compressor - The compressors used in smaller refrigeration applications are generally reciprocal compressors, while larger systems may use scroll or screw compressors among others.

2. Constant pressure heat rejection in a condenser - The heat rejection is most often done through a heat exchanger actively or passively cooled by the ambient air. As an example, the coil assembly on the back of your refrigerator is the condenser. It is warm because it needs to be able to shed its thermal energy load into room temperature air.

3. Throttling through an expansion valve - This is where most refrigeration cycles deviate from being a strict reverse of the Rankine cycle. The natural question to ask is, "why not put in a turbine and recover some of the energy which is otherwise just being wasted?" In larger super-efficient systems this is in fact what they do. However, in the vast majority of cases, the additional cost and complexity associated with having a turbine instead of an expansion valve is not justified by the small increase in energy efficiency.

4. Constant pressure heat addition in an evaporator - The evaporator is another heat exchanger which operates below the temperature of the refrigerated or air conditioned space.

Repository
Is the location where energy is deposited and stored. It can be large ice boxes to heavily insulated thermal storage devices.

Ridge Vent
A ventilation system that is installed directly underneath the roof ridge. It helps get rid of excess heat and moisture. Since heat flows upwards by convection, the installation of the ridge vent in the middle of a slanted roof is a great choice to control the amount of heat in the attic. Too much heat and moisture can contribute to the deterioration of wooden structures, roof shingles, and paint. Also, excess moisture can decrease the effectiveness of insulation and can promote mold growth.

High quality ridge vents contain an external wind baffle and an internal weather filter. The external wind baffle prevents wind from flowing into the attic. This prevention helps create a low pressure in the attic, which further helps air flow out through the ridge vents. It also helps prevent rain or snow from entering inside. Meanwhile, the major contribution of the internal weather filter is to provide a stronger weather barrier. Besides rain and snow, it even prevents insects from entering. Since roof shingles can cover over the ridge vents, ridge vents are more aesthetically pleasing than other types of roof vents.

Roof Deck Protection
A protective layer that covers the roof deck. It lies underneath roof shingles and leak barriers. In addition to preventing water leaks, roof deck protection also allows excess moisture in the attic to escape. That way, it prevents mold from growing and as a result helps improve the air quality in the attic. In addition, on the aesthetics aspect, roof deck protection helps roof shingles lie flat and well-organized.

S

 

Set-Point
When most refer to the set-point of a thermostat, they are referring to a desired room temperature which is programmed in by the user and which the heating or cooling system tries to maintain. However, in controls lingo the meaning of set-point may be slightly different than the definition just given (see Deadband vs. Differential).

Setback
With programmable thermostats, temperature schedules can be set up such that the target room temperature changes depending on the time of day or the day of week. These temperature changes are meant to reflect the occupancy schedule of the space. The goal of a setback is to save energy by maintaining a less demanding set point during periods when a space is unoccupied and human comfort is not as much of a concern. In the winter, this means lowering the temperature (from 65ºF to 55ºF), while in the summer it is raised or the AC may be turned off all together. During the winter, the heating system cannot be turned off altogether, regardless of occupancy, because a minimum temperature is required to keep water pipes from freezing.

Smoke Pen
A pen-shaped device that holds a wick, which is burned with a lighter to generate smoke. Also called a smoke pencil, having the shape of a fountain pen or a mechanical pencil, its main purpose is to pinpoint the location of air leaks. For instance, if air leaks are present in windows, a smoke pen is used so that energy auditors can track down the direction that the smoke moves. In this case, the smoke that is created near the windows would be blown away by air leaks from the windows. Another variant of the smoke pen is a smoke puffer that generates steam from a water solution like a mini fog machine.

Solar Power Tower
A tower that receives concentrated amounts of sunlight from many mirrors called heliostats to generate clean electricity. Since the Sun constantly moves, the heliostats gradually move to continuously reflect sunlight directly at the solar power tower. The collector that receives all the sunlight in the solar power tower uses thermal energy from the sunlight to heat liquid sodium or other kinds of liquid salt that can go as high as 1,000 degrees Celsius. Liquid salt is kept in an insulated storage tank that stores heat in case of non-sunny days. Afterwards, the heat exchanger transfers the stored heat from liquid salt to water. As the water begins to boil, its steam powers the turbines, which then generate electricity.

Solar Shingle
A solar cell that mimics and is used as a roof shingle. Also called a photovoltaic shingle, its process of generating electricity works very similarly to a typical solar panel, but it is much smaller. As a result, unlike solar panels, solar shingles used as roof shingles are more aesthetically pleasing. Needless to say, many solar shingles are needed to cover the rooftops of residential houses or commercial facilities.

Not surprisingly, the areas that benefit the most from the installation of solar shingles are the ones that receive significant amounts of sunlight. Solar shingles can be initially expensive, but energy savings in a long-term can pay off through reduced electric bills. In fact, if the influx of solar energy is higher than the energy consumption, depending on the location of the building with solar shingles, the excess electricity can be sent to the nearest electric company, which then pays the building owner for the electricity.

Solid-State Lighting
Refers to the group of lighting that uses semi-conductor light emitting diodes (SLED), organic LEDs and polymer LEDs. It is light emitted by solid state electroluminescence and not by thermal radiation and gas discharge. It generates less heat and is more efficient than any other types of lighting available today. It also has greater resistance to shock.

Stack Effect
Drives natural ventilation and occurs due to the density difference between the outside and inside air. The larger the difference, the greater the stack effect. It drives the movement of hot air up and cold air seeps in from the bottom during the heating season vise versa in the cooling season.

Steam Trap
A valve which functions by removing condensate steam and air. It retains steam so that it can be used for further processes such as heating. After steam does its work it condenses and this condensate builds up; it is necessary to use steam traps to allow the clow of consate and not the steam out of the system. Steam traps work on differences in temperature, specific gravities, and pressure. Each has its own advantages and applications.

Stratification
This term refers to the vertical temperature difference that may develop between the floor and the ceiling of an indoor space. Warm air, being less dense, naturally rises while cooler air sinks. In a space where air does not mix properly, warm air exiting from a heater will retain its thermal energy and therefore remain at a higher temperature than the ambient air. This means that it will keep its buoyant property and rise, or stratify. In small spaces with 8-10 foot ceilings this is not noticeable (though it may be detected between floors). In warehouses, where roofs are regularly 30’+ the effects of stratification can be pronounced, often to the tune of 10ºF or more. This creates two problems. The first is that if all of the warm air is stuck at ceiling level it is not doing its job of keeping occupants and goods at ground level warm. The second problem is that by creating a greater temperature difference across the roof, the rate of energy loss through the roof increases proportionally.

T

 

Terra Watts
Is a unit of power equivalent to 1 trillion watts.

Therm
A therm is a unit used to measure the heating potential stored in a fuel. Just as Btuh deals with the thermal energy output of a heating system, therms (or therms/hr) are used to describe that system’s consumption. One therm is roughly equivalent 100,000 Btu. In Europe, the definition is slightly different and naturally more convenient (1 therm = 100,000 Btu exactly). Just remember that an 80% efficient heater that consumes 1 therm/hr delivers only 80,000 Btuh to the space being heated. It is often convenient to discuss the purchase of fuel in terms of the chemical energy being purchased rather than the commodity itself. Comparing the price of a gallon of heating oil #2 to a cubic foot of natural gas makes little sense because the two have very different thermal energies. By normalizing the price of these fuels in terms of a unit of energy like a therm, their prices can be directly compared. The therm is a more convenient unit for pricing and therefore is used instead of the Btu. Nobody wants to discuss paying $0.00013/Btu.

Thermal Boundary
An area that acts as an insulation border between the interior and exterior space of a building. A space is considered interior if it is directly heated or air conditioned. Otherwise, unheated spaces such as the garage or attic is considered exterior. Hence, the wall that lies between a living room and a garage is part of the thermal boundary. The purpose of the thermal boundary is to help maintain a reasonable level of air quality, moisture, and comfort from outside factors. Through the use of an IR camera, energy auditors can ensure that the thermal boundary is functioning effectively as an insulator to save energy.

Thermal Efficiency
The thermal efficiency is a dimensionless parameter (0<th<1) which measures the efficacy of process in which thermal energy is used. Energy may leave the system either in the form of thermal energy (hot exhaust gas) or as usable work such as the spinning of a turbine shaft. In heating systems such as boilers and direct fired heaters, the thermal efficiency is simply given by the ratio:

th = Qout/Qin

Qoutis is the heat delivered to the space (BTUs) and Qinis thermal (fuel) energy supplied to the heater. For calculation purposes this latter value would be expressed in BTUs but is generally discussed in terms of therms. The maximum efficiency for any system such as this operating between two temperature reservoirs Thot and Tcold is given by the Carnot efficiency.

Carnot = (Thot-Tcold)/Thot

The units of temperature are Rankine or Kelvin (absolute). If the device is a heat engine and does work on its environs than the Carnot efficiency is expressed as:

Carnot = Wout/Qin

Qin represents the energy input into the system in the form of heat. The effectiveness for heat pumps, which from a thermodynamic perspective include AC as well as refrigeration systems, are also given by similar equations (see COP, EER) though these values will be greater than 1 and thus are not generally called “efficiencies.”

Thermocouple
Is a temperature measuring device. It has two dissimilar metals joined at one end and when it is heated or cooled, produce a voltage that corresponds to a temperature difference. They are usually selected based on the temperature range, sensitivity, inertness and magnetism.

Ton of Cooling
One ton of cooling/refrigeration is equal to 12,000 Btuh (for comparison this is the cooling capacity of a large window-mounted air conditioner). This is purely an industry term and has its roots in the early days of air conditioning. Back then, air conditioning and refrigeration were accomplished with ice, of which buildings would receive huge daily shipments. Air would be passed over these blocks of ice and circulated throughout the building thus providing cooling. In trying to market air conditioning in the early 20th century, men such as Willis Carrier wanted to compare their systems to existing cooling methods. Therefore, the cooling capacity of a mechanical AC unit would be described in terms of how many tons of daily ice shipments it could replace. In other words, the energy required to melt one ton of ice (heat of fusion) is roughly the same as the energy removed from a space over a 24 hour period by a one ton AC unit.

U

 

U-Value
Is the overall heat transfer coefficient. It measures how much heat is conducted by a building element over a given area under standard conditions. It is the inverse of R-value (U = 1/R). As the value of U decreases, the quality of insulation material increases.

US units = BTU/(h°F ft²)
SI units = W/(m²K).

Ultrasonic Sensors
Are devices which emit high frequency sound in the range of 18 khz. The principle is that the sound wave is reflected when it encounters a stiffer medium. So an ultrasonic wave travelling in air will bounce off from the stiffer and tougher medium such as humans. This helps in detecting moving objects. Sensors calculate the time interval between sending the signal and receiving the echo to determine the distance to an object. It can be used to trigger lighting and HVAC.

Unit Heater
Is a form of an indirect fired heater which is comparatively small and ceiling-mounted. unit heaters represent roughly 60% of the space heating market, probably because they are the cheapest to install based on first cost. However, besides boilers and furnaces they are the most inefficient and therefore the most costly to operate.

Units and Metrics
HVACR is all about the flow of mass and energy. Therefore, the metrics given here are used to describe the performance of different pieces of space conditioning HVACR equipment.

Urban Heat Island (UHI)
A metropolitan area that is warmer than its surrounding areas. The effect of UHI is stronger during non-windy evenings. Naturally, land is moist, but the accumulation of roads and buildings cause these areas to be dryer and thus warmer, which contributes to the formation of UHI. As cities become more populated, heat and greenhouse gases dissipated from vehicles and appliances in buildings further contributes to the UHI. According to the Environmental Protection Agency (EPA), the average temperature difference caused by UHI in cities with at least one million people is 1.8 - 5.4 F, but on a calm evening, the difference can be as high as 22 F.

To reduce the effect of UHI, the best solution for this problem is to replace dark, heat absorbing roofs with cool roofs or green roofs, which have vegetation planted on top of roofs. Plants help cool the nearby areas and convert excess carbon dioxide to oxygen. Studies show that areas with high amounts of vegetation are less affected by UHI. Reducing UHI helps reduce energy consumption of refrigerators and air conditioners especially during summers. Also, UHI can intensify the effect of heat waves, which are responsible for several deaths from the extreme heat in urban areas that experience dramatic climate changes over the year.

U.S. Green Building Council (USGBC)
A private, non-profit organization that promotes energy efficiency in the design, construction, and operations of buildings. Its primary goal is to educate the public, industry professionals, and government sectors on the green building industry. To achieve this, the USGBC provides memberships to companies that are interested in the green building industry. It also created and adopted the use of the Leadership in Energy and Environmental Design (LEED) accreditation to certify buildings that meet the energy efficiency requirements and to provide credibility for green building experts.

V

Vapor Barrier
A material that is used to slow down the movement of water vapor through the material. Its more accurate term is vapor diffusion retarder (VDR). Vapor barrier materials include aluminum foil and polyethylene plastic, which are typically installed in the building envelope of houses to prevent moisture from entering. The unit of measurement for vapor barriers is perm. Please see the definition of perm for more information.

Volatile Organic Compound (VOC)
An organic compound that has a low boiling point, which causes it to evaporate quickly at room temperatures. Studies have shown that it is detrimental to a person's health. Its health effects include eye and nose irritation, headaches, and nausea. Long-term exposure to VOC can cause respiratory problems, allergic reactions, and even cancer. One notable example is formaldehyde. It is typically present in building materials such as paint and wall boards, from where it slowly seeps out throughout the buildings. As a result, the use of VOC's is limited by state government regulations.

W

 

W (watt)
Wattage is the way we measure electric power in the U.S. despite the fact that it is metric (at least we got something right). In addition to HP, it is how the power of an electric motor is measured. Components incorporating motors such as compressors and fans may be rated in kW.

Waste Heat
Is the heat that is produced from machine processes such as heat engines and turbines. It includes the by-product heat that is produced from the combustion process. The burning of transport fuels is a major endorser of waste heat. Reusing waste heat for pre-heating or even direct heating application such as CHP makes use of more efficient energy saving technologies.

Wave Power
A process of converting wave energy from the ocean into another form of energy that is used to generate electricity. Unlike the sun and wind, ocean waves are continuously present to provide renewable energy throughout the day. To take advantage of this property, buoys or long rubber tubes have been set up on the ocean surface, since the energy density is much higher in the ocean surface than the one deep in the ocean. They are connected to the pistons, which are installed at the bottom of the ocean. As the buoys are oscillating from the waves, this movement causes the pistons to move, which in turn generates electricity. Wave farms, which are sets of buoys or tubes, have recently been installed, and they are currently in the early stages.

Weatherstripping
A process of sealing openings to prevent water and air leaks. Its primary purpose is to prevent rain water from entering inside and retain heat from seeping out, which in turn helps reduce heating bills. Weatherstrips are installed on window and exterior door frames in buildings. They are also used to seal car doors, windows, and sunroofs. Since windows and doors are opened and closed on a regular basis, weatherstrips will eventually wear down and will need to be replaced.

Weatherstrips can be made of either vinyl or metal (aluminum, copper, or stainless steel). Metal weatherstrips are typically used for older homes for aesthetic reasons, but vinyl ones are commonly used. Since vinyl weatherstrips are soft and flexible, manufacturers are designing them to be durable and withstand extreme temperatures, sunlight, and gasoline (for cars only). Some weatherstrips can even be magnetic, which is usually used for refrigerator doors.

Wet Bulb Temperature
Measures the amount of moisture in the air. It is the the lowest temperature that can be reached by the evaporation of water only. If the moisture content is high in air then the evaporation is reduced. It can be measured by using a thermometer with the bulb wrapped in wet muslin, and when there is evaporation of the liquid then there is temperature drop in the thermometer which is measured as wet bulb temperature. It is always lower than dry bulb temperature.

Wind Power
A process of converting wind energy into another form of energy that is used to generate electricity through wind turbines. There are two different kinds of wind turbines, which are vertical-axis wind turbines (VAWT's) and horizontal-axis wind turbines (HAWT's). VAWT's, which are shaped like egg beaters, can be pushed by wind from any direction. However, wind alone is not enough; their electrical systems are also needed to start moving. VAWT's are easy to build, but with their low height, their effectiveness is limited by slower wind speeds caused by ground interference. As a result, few of them are currently used.

Meanwhile, HAWT's, which are much more popular than the VAWT counterparts, are powered by the movement of three rotor blades through wind. The rotor blades are similarly shaped like airplane wings, so that the forces of lift and drag cause them to move after the wind is blown directly towards them. In response to changing wind directions, rotor blades themselves rotate around to maximize the performance of HAWT's. As winds push the rotor blades, their movement causes the shaft to move, which in turn causes the generator to produce electricity. Then, electricity flows down through the transformer, which increases its voltage, towards the center point, where electricity from multiple HAWT's in a wind farm meet. Afterwards, electricity continues to flow until it reaches its destinations.

Also, a larger diameter of wind turbines (twice the length of a rotor blade) outputs higher amounts of electricity. As a general rule of thumb, twice the diameter generates four times more electricity. At the same time, since the height of wind turbines affects their effectiveness, and wind speeds become higher at higher elevation, HAWT's are usually tall. Hence, it is possible that a low HAWT with shorter rotor blades are more efficient than a low HAWT with longer rotor blades, because shorter rotor blades, which are lighter than longer rotor blades, require lower wind speeds for movement. However, if wind speeds reach levels beyond the safe zone, HAWT's have a safety mechanism that automatically shuts them down to slow down the movement of their rotor blades.

Wind Washing
A movement of air caused by winds that enter through building insulation and strip heat away inside buildings. Through this process, the R-value of the insulation decreases. As a result, more heat is lost, and homeowners would suffer from increasing heating bills.

Wind washing usually occurs either in building corners or attics. To detect this problem, blower door tests are recommended to check for any air leaks. Also, the use of high density insulation such as cellulose is resistant to wind washing. On the other hand, less dense, porous insulation such as fiberglass is prone to wind washing. Other methods to counter wind washing include caulking, weatherstripping, and installing attic vents with a wind barrier.

Z

 

Zero Energy Building
A building that spends as much energy as it produces. Currently, most conventional buildings only spend energy for electricity, but they do not produce any energy. They would be considered as negative energy buildings. However, if buildings, for instance, are installed with solar panels and at the same time equipped with high-efficiency lighting, heating/air conditioner system, and insulation, energy produced from solar panels would be enough to meed the demands of the reduced energy consumption resulting from high energy efficiency. That way, they would not need to rely on coal as the source of electricity.

Energy consumption of a building can be compared to money in business. The use of energy is similar to cost, while energy production is similar to revenue. Zero energy buildings can be viewed as a company with a net profit of zero. On the other hand, if a building's energy production is higher than its energy consumption, it would be considered as a positive energy building, which would be even better just as a company is benefiting from its positive net profit.

Zigbee
Although Zigbee sounds like the name of a comic book character, it is actually a standard for wireless communication between electronic devices just like Wi-Fi and Bluetooth. However, the latter two are designed for high data transfer rates which increase power requirements as well as transmission lag time. Zigbee was designed for the operation of wireless sensor networks where data rates are low but rapid communication and fast response times are required. Zigbee capability requires little power and therefore is ideal for battery powered wireless devices. It also supports wireless mesh networks, which have the ability to auto-adapt to changes in network membership and device failure making them much more flexible. Another bonus of Zigbee is that signals tend to transmit more reliably. In environments such as underground parking garages, whose thick concrete walls and floors might otherwise interfere with wireless signals, Zigbee devices can communicate over multiple levels allowing the entire garage to operate as a single network.

 

 

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