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HVAC Glossary of Terms

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A
 
ACCA: A leading HVAC/R Association - Air Conditioning Contractors of America.
 
Acid Condition In System: Condition in which refrigerant or oil in system is mixed with fluids that are acid in nature.
 
ACR Tubing: Tubing used in air conditioning and refrigeration. Ends are sealed to keep tubing clean and dry.
 
Adjustable Grille: A grille with linear blades which can be adjusted to vary the direction of the discharged air. The linear blades are normally either vertical or horizontal, or both horizontal and vertical.
 
AFUE (Annual Fuel Utilization Efficiency ): This number represents how efficiently a furnace converts fuel to energy. The ratio of annual output of useful energy or heat to the annual energy input to the furnace. The higher the AFUE, the more efficient the furnace -- higher efficiency translates to more savings on fuel bills. This will range from 80% to 95%. Percentage of fuel used for heating. A measure of heating efficiency, in consistent units, determined by applying the federal test method for furnaces. This value is intended to represent the ratio of heat transferred to the conditioned space by the fuel energy supplied over one year.
 
Air Change: The amount of air required to completely replace the air in a room or building; not to be confused with recirculated air.
 
Air Cleaner: Device used for removal of airborne impurities. A device that actively removes impurities from the air, including forced air filtration systems and electronic air cleaners. Air cleaners may be added to HVAC systems or stand-alone room units.
 
Air Conditioning: Control of the temperature, humidity, air movement and cleaning of air in a confined space.
 
Air Diffuser: An air distribution outlet or grille designed to direct airflow into desired patterns. Supply air terminal device, designed to direct airflow into desired patterns, usually placed in the ceiling, generally of circular, square or rectangular shape, and composed of divergent deflecting members.
 
Air Distribution: The transportation of a specified air flow to or from the treated space or spaces, generally by means of ductwork.
 
Air Handler: an-blower, filter and housing parts of a system. Fan-blower, filter, heat transfer coil, and housing parts of a system. Also known as the blower section and part of the split system, this unit is commonly in your home or attic and blows the air through your house. This has to be matched with the condenser properly to assure maximum efficiency. This will contain your heating and evaporator coil.
 
Air Infiltration: Leakage of air into rooms through cracks, windows doors and other openings.
 
Air-Cooled Condenser: Heat of compression, plus the heat of absorption, is transferred from refrigerant within coil to surrounding air, either by convection or fan or blower.
 
Airflow: The distribution or movement of air.
 
Ambient Air Temperature: Surrounding temperature, such as the outdoor air temperature around a building.
 
Appliance Efficiency Standards: California Code of Regulations, Title 20, Chapter 2, Subchapter 4: Energy Conservation, Article 4: Appliance Efficiency Standards. Appliance Efficiency Standards regulate the minimum performance requirements for appliances sold in California and apply to refrigerators, freezers, room air conditioners, central air conditioners, gas space heaters, water heaters, plumbing fittings, fluorescent lamp ballasts and luminaries, and ignition devices for gas cooking appliances and gas pool heaters. New National Appliance Standards are in place for some of these appliances and will become effective for others at a future date.
 
ARI: (Air-Conditioning and Refrigeration Institute) Air-Conditioning and Refrigeration Institute is a nonprofit, voluntary organization comprised of heating, air conditioning and refrigeration manufacturers. ARI publishes standards for testing and rating heat pumps and air conditioners to provide you with a standardized measure of comparison. So, ARI ensures a level of performance within the industry.
 
ASHRAE: A leading HVAC/R Association - American Society of Heating, Refrigerating and Air Conditioning Engineers. The trade association that provides information and sets standards for the industry.
 
ASTM: American Society for Testing and Materials.
 
B
 
Backdrafting: Reverse flow of combustion gases down the chimney of a vented combustion appliance, which is often caused by depressurization of the room where the appliance is located. A condition where the normal movement of combustion products from a combustion appliance up a flue is reversed so that the combustion products can enter the building.
 
Blower door: A large powerful variable-speed fan mounted in a doorway that blows air into (pressurizes) or sucks air out of (depressurizes) a house. It's used to test for air leakage in a house. The size and complexity of the fan varies, but all blower doors have adjustable frames around the fan so that they can fit snugly into most doorways.
 
Boot: A piece of duct used to connect ducts with registers.
 
BTU (British Thermal Unit): The amount of heat that will raise or lower one pound of water 1 degree F. at 39.2 degrees F. One BTU is the equivalent of the heat given off by a single wooden kitchen match. The British Thermal Unit is a standard of measure for cooling and heating capacities. This is how the capacity of air conditioning is measured. A standard measure of heat energy in the U.S., commonly used to measure the energy content of various fuels and steam. It takes one Btu to raise the temperature of one pound of water by one degree Fahrenheit at sea level. For example, it takes about 2,000 Btu's to make a pot of coffee. One Btu is equivalent to 252 calories, 778 foot-pounds, 1055 joules, and 0.293 watt-hours. Note: In the abbreviation, only the B is capitalized. For your home, it represents the measure of heat givens off when fuel is burned for heating or the measure of heat extracted from your home for cooling.
 
BTUH (British Thermal Unit Per Hour): Establishes a time reference to btu input or output rates. A BTUH is how many BTUs are used per hour.
 
Building Energy Efficiency Standards: California Code of Regulations, Title 24, Part 2, Chapter 2-53; regulating the energy efficiency of buildings constructed in California. Building, Envelope the outer walls, windows, doors, roof, and floors of a building; the building shell.
 
Building Envelope: Elements of the building, including all external building materials, windows, and walls, that enclose the internal space.
 
C
 
Capacitor: A device used to start a motor or compressor (or to keep it running after start up.)
 
Capacity: (or System Capacity ) The output or producing ability of a piece of cooling or heating equipment. Cooling and heating capacity are normally referred to in BTUs. The capacity of an air conditioner is measured by the amount of cooling it can do when running continuously. The total capacity is the sum of the latent capacity (ability to remove moisture from the air) and sensible capacity (ability to reduce the dry-bulb temperature). Each of these capacities is rated in Btu's per hour (Btu/h). The capacity depends on the outside and inside conditions. As it gets hotter outside (or cooler inside) the capacity drops. The capacity at a standard set of conditions is often referred to as "tons of cooling."
 
Ceiling Plenum: The space between the suspended and structural ceiling used as part of the air distribution system that accommodates the mechanical and electrical equipment. This space usually accommodates electrical, communications, and mechanical connections as well. The space is kept under negative pressure.
Celsius: A temperature scale based on the freezing (0 degrees) and boiling (100 degrees) points of water. Abbreviated as C in second and subsequent references in text. Formerly known as Centigrade. To convert Celsius to Fahrenheit, multiply the number by 9, divide by 5, and add 32. For example: 10 degrees Celsius x 9 = 90; 90 / 5 = 12; 18 + 32 = 50 degrees Fahrenheit.
 
CFC: (Chlorofluorocarbons or Chlorinated Fluorocarbons) A class of refrigerants. Generally refers to the Chlorofluorocarbon family of refrigerants. Sometimes called Freon A family of artificially produced chemicals receiving much attention for their role in stratospheric ozone depletion. Since they were introduced in the mid-1930s, CFCs have been used as refrigerants, solvents and in the production of foam material. These chemicals and some related chemicals have been used in great quantities in industry, for refrigeration and air conditioning, and in consumer products. CFCs and their relatives, when released into the air, rise into the stratosphere, a layer of the atmosphere high above the Earth. In the stratosphere, CFCs and their relatives take part in chemical reactions which result in reduction of the stratospheric ozone layer, which protects the Earth's surface from harmful effects of radiation from the sun. On a per molecule basis, these chemicals are several thousand times more effective as greenhouse gases than carbon dioxide. The 1987 Montreal protocol on CFCs seeks to reduce their production by one-half by the year 1998. The 1990 CLEAN AIR ACT includes provisions for reducing releases (emissions) and eliminating production and use of these ozone-destroying chemicals.
 
CFM: (Cubic Feet per Minute) A standard measurement of airflow that indicates how many cubic feet of air pass by a stationary point in one minute. The higher the number, the more air is being forced through the system. A typical system produces 400 CFM per ton of air conditioning.
 
Charge: Amount of refrigerant placed in a refrigerating unit.
 
Coil: A cooling or heating element, often including fins, through which treated gas or liquid is passed, exchanging thermal energy with air surrounding it for heating or cooling.
 
Compressor: The heart of an air conditioning or heat pump system. The large (usually black) part in the condenser (outdoor unit) that pumps refrigerant. The pump of a refrigerating mechanism which draws a low pressure on cooling side of refrigerant cycle and squeezes or compresses the gas into the high pressure or condensing side of the cycle. The compressor maintains adequate pressure to cause refrigerant to flow in sufficient quantities to meet the cooling requirements of the system.
 
Condenser: This is the unit that will sit outside and is part of a split system, it contains the compressor which is the heart of your air conditioner or Heat Pump, it pumps the refrigerant through your system. Some people call the condenser the compressor, but the compressor is a component of the condenser along with the fan motor and condenser coil. Coil or outdoor coil dissipates heat from the refrigerant, changing the refrigerant from vapor to liquid.
 
Condenser Coil: [Also see Outdoor Coil] The outdoor portion of a heating or cooling system that either releases or collects heat from the outside air, depending on the time of year. The Condenser Coil is connected directly to the home's Air Handler and is also known as the Outdoor Coil.
 
Condensing Unit: Part of a refrigerating mechanism which pumps vaporized refrigerant from the evaporator, compresses it, liquefies it in the condenser and returns it to the refrigerant control. The outdoor portion of a split system air conditioner contains the compressor and outdoor coil ignoring the reverse cycle operation, also the outdoor in a heat pump system.
 
Conditioned Air: The air that has been heated, cooled, humidified, or dehumidified to maintain an interior space within the "comfort zone."
 
Conductance: The quantity of heat, in Btu's, that will flow through one square foot of material in one hour, when there is a 1 degree F temperature difference between both surfaces. Conductance can be expressed in other units as well. Conductance values are given for a specific thickness of material, not per inch thickness.
 
Conduction: The transfer of heat through a solid material. The transfer of heat energy through a material (solid, liquid or gas) by the motion of adjacent atoms and molecules without gross displacement of the particles.
 
Constant Air Volume Systems: Air handling system that provides a constant air flow while varying the temperature to meet heating and cooling needs.
 
Contactor: In the condenser, the main switch that turns the condenser on.
 
Contaminant: An unwanted constituent that may or may not be associated with adverse health or comfort effects.
 
Convection: The movement of heat by air flow.
 
Cooling Capacity, Latent: Available refrigerating capacity of an air conditioning unit for removing latent heat from the space to be conditioned.
 
Cooling Capacity, Sensible: Available refrigerating capacity of an air conditioning unit for removing sensible heat from the space to be conditioned.
 
Cooling Capacity, Total: Available refrigerating capacity of an air conditioner for removing sensible heat and latent heat from the space to be conditioned.
 
Cooling Load: The rate at which heat must be extracted from a space in order to maintain the desired temperature within the space.
 
Cooling Load Temperature Difference: (CLTD) A value used in cooling load calculations for the effective temperature difference (delta T) across a wall or ceiling, which accounts for the effect of radiant heat as well as the temperature difference.
 
Cooling System: A system of air-to-air, liquid-to-air, liquid-to-liquid, etc., heat exchangers, ducts and/or pipes, etc., for removing head from a system containing heat sources, such as power plants, automobile engines, and homes. Also, an energy Efficiency program promotion aimed at improving the efficiency of the cooling delivery system, including replacement, in the residential, commercial, or industrial sectors.
 
COP: (Coefficient Of Performance) COP compares the heating capacity of a heat pump to the amount of electricity required to operate the heat pump in the heating mode. COP's vary with the outside temperature: as the temperature falls, the COP falls also, since the heat pump is less efficient at lower temperatures. ARI standards compare equipment at two temperatures, 47 F and 17 F, to give you an idea of the COP in both mild and colder temperatures. Geothermal equipment is compared at 32 F enter water temperature. COP & HSPF can not be compared equally. Air Source Equipment is rated by HSPF or COP and Geothermal equipment is rated by COP.
 
D
 
Damper: A device that is located in ductwork to adjust air flow. This movable plate opens and closes to control airflow. Dampers are used effectively in zoning to regulate airflow to certain rooms. There are basically two types of dampers: Manual and motorized. A manual damper generally consists of a sheet metal (or similar material) flap, shaped to fit the inside of a round or rectangular duct. By rotating a handle located outside of the duct a technician can adjust (see Balancing) air flow to match the needs of a particular area or room. A motorized damper is generally used in a zoned system (see Zoning) to automatically deliver conditioned air to specific rooms or zones. In particular, the following types, can be distinguished:
    Multiple leaf dampers, comprising of a number of blades (or shutters) of opposed or parallel leaf type.
    Single leaf dampers (the flap being mounted at one end), commonly called splitter dampers.
    Hit-and-miss dampers, having two or more slotted slide mechanism.
    Butterfly dampers, with two flaps in "V" arrangement.
 
db: (Decibel) A decibel describes the relative loudness of a sound. Some common sounds are fairly close to a typical air conditioner or heat pump's sound level: human voice, 7.0 decibels; blender, 8.8 decibels.
 
Degree Day: A unit, based upon temperature difference and time, used in estimating fuel consumption and specifying nominal annual heating load of a building. When the mean temperature is less than 65 degrees Fahrenheit the heating degree days are equal to the total number of hours that temperature is less than 65 degrees Fahrenheit for an entire year.
 
Dehumidification: The reduction of water vapor in air by cooling the air below the dew point; removal of water vapor from air by chemical means, refrigeration, etc.
 
Delta: (or Delta T) A difference in temperature. Often used in the context of the difference between the design indoor temperature and the outdoor temperature.
 
Design Conditions: Cooling loads vary with inside and outside conditions. A set of conditions specific to the local climate are necessary to calculate the expected cooling load for a home. Inside conditions of 75 degrees Fahrenheit and 50% relative humidity are usually recommended as a guideline. Outside conditions are selected for the 2.5% design point.
 
Dewpoint: Is the temperature at which air becomes saturated with water and begins to condense - forming a dew. Therefore at 100 % RH the ambient or process temperature equals the dewpoint temperature. The more negative the dewpoint temperature is from the ambient temperature the less the risk of condensation and the drier the gas or air stream.
 
Diffusers and Grilles: Components of the ventilation system that distribute and return air to promote air circulation in the occupied space. Generally speaking, supply air enters a space through a diffuser or vent and return air leaves a space through a grille.
 
Direct Expansion: (Refrigeration) Any system that, in operation between an environment where heat is absorbed (heat source), and an environment into which unwanted heat is directed (heat sink) at two different temperatures, is able to absorb heat from the heat source at the lower temperature and reject heat to the heat sink at the higher temperature. The cooling effect is obtained directly from a fluid called a refrigerant that absorbs heat at a low temperature and pressure, and transfers heat at a higher temperature and higher pressure.
 
Direct Gas-Fired Heater: The burner fires directly in the air stream being heated, rather than through a heat exchanger. 100% of available BTUs are delivered to the heated space because no flue or heat exchanger is required. This results in no wasted energy.
 
DOE: (Department of Energy) The Department of Energy is a federal agency in charge of setting industry efficiency standards and monitoring the consumption of energy sources.
 
Downflow: A type of furnace that takes cool air from the top and blows warm air to the bottom - common where your furnace must be located in a second-floor closet or utility area.
 
Drain Trap: A dip in the drain pipe of sinks, toilets, floor drains, etc., which is designed to stay filled with water, thereby preventing sewer gases from escaping into the room.
 
Drier: Sometimes called filter/drier, it removes moisture and keeps the refrigerant clean.
 
Dry Bulb Temperature: (DB) The temperature measured by a standard thermometer. A measure of the sensible temperature of air.
 
Duct: A pipe or closed conduit made of sheet metal, fiberglass board, or other suitable material used for conducting air to and from an air handling unit. A passageway made of sheet metal or other suitable material used for conveying air or other gas at relatively low pressures.
 
E
 
EER: (Energy Efficiency Ratio) A ratio calculated by dividing the cooling capacity in Btu's per hour (Btuh) by the power input in watts at any given set of rating conditions, expressed in Btuh per watt (Btuh/watt). EER & SEER can not be compared equally. Air source equipment is rated by SEER and geothermal equipment is rated by EER. EER changes with the inside and outside conditions, falling as the temperature difference between inside and outside gets larger.
 
Efficiency: A rating on comfort equipment is similar to the miles per gallon rating on your car. The higher the rating number, the more efficient the system and the lower your fuel consumption will be. You can save a lot of money with a high efficiency unit. Depending on your local climate, lifestyle and electricity rates, savings will vary. For furnaces. it is the rate at which a furnace maximizes fuel use. This rate is numerically described as a ratio called AFUE (see AFUE). As of January, 1991, no furnaces can be manufactured with efficiencies lower than 78% afue. High efficiency furnaces will be rated 85 to 95% afue.
 
Electric Radiant Heating: A heating system in which electric resistance is used to produce heat which radiates to nearby surfaces. There is no fan component to a radiant heating system.
 
Electric Resistance Heater: A device that produces heat through electric resistance. For example, an electric current is run through a wire coil with a relatively high electric resistance, thereby converting the electric energy into heat which can be transferred to the space by fans.
 
Electrostatic air cleaner: A device that uses an electrical charge to trap particles traveling in the air stream.
 
Emergency Heat: (Supplementary Electric Heat) The back up electric heat built into a heat pump system. The same as an auxiliary heater, except it is used exclusively as the heat source when the heat pump needs repair.
 
ERV: (Energy Recovery Ventilator) This device preheats incoming outside air during the winter and pre-cools incoming air during the summer to reduce the impact of heating and or cooling the indoor air. This means that smaller capacity heating and cooling systems can be used in homes, which results in lower installation costs, lower peak demand for energy, and lower operating costs.
 
Evaporative Cooler: A type of cooling equipment that turns air into moist, cool air by saturating the air with water vapor. It does not cool air by use of a refrigeration unit. This type of equipment is commonly used in warm, dry climates.
 
Evaporative Cooling: Cooling by exchange of latent heat from water sprays, jets of water, or wetted material.
 
Evaporator Coil: [Also see Indoor Coil] The evaporator coil is located inside your house in a split system in the air handler, or above the gas furnace. This will produce cooling in the air conditioning mode and heating in a Heat Pump mode. This coil section in the evaporator is where refrigerant evaporates and absorbs heat from air passed over the coil. This is also very important in removing humidity from your home.
 
Exhaust: Air removed deliberately from a space, by a fan or other means, usually to remove contaminants from a location near their source. The air flow leaving the treated space. Exhaust may be accomplished by one or more of the following methods:
    a. Extraction: exhaust in such a manner that the air is discharged into the atmosphere.
    b. Relief: exhaust in such a manner that the air is allowed to escape from the treated space if the pressure in       that space rises above a specified level.
    c. Recirculation: exhaust in which the air is returned to the air treatment system.
    d. Transfer: exhaust in which air passes from the treated space to another treated space.
 
Exhaust Ventilation: Mechanical removal of air from a portion of a building (e.g., piece of equipment, room, or general area).
 
F
 
Fahrenheit: (F) A temperature scale in which the boiling point of water is 212 degrees and its freezing point is 32 degrees. To convert Fahrenheit to Celsius, subtract 32, multiply by 5, and divide the product by 9. For example: 100 degrees Fahrenheit - 32 = 68; 68 x 5 = 340; 340 / 9 = 37.77 degrees Celsius.
 
Filter: A device for removing dust particles from air or unwanted elements from liquids.
 
Flame roll-out: A dangerous situation that occurs when flame is pushed out of the bottom of a combustion appliance. It can lead to fires.
 
Flex duct: Usually installed in a single, continuous piece between the register and plenum box, a flexible duct usually has an inner lining and an insulated coating on the outside.
 
Flow Hood: A diagnostic tool used to measure air flow through ducts, supply registers, and return grilles. Device that easily measures airflow quantity, typically up to 2,500 cfm.
Furnace: That part of an environmental system which converts gas, oil, electricity or other fuel into heat for distribution within a structure.
 
G
 
Grille: An air terminal device with multiple passages for the air. Grilles Coverings for the ducts where they open to the conditioned space. (Same as Registers)
 
H
 
Heat Capacity: The amount of heat necessary to raise the temperature of a given mass one degree. Heat capacity may be calculated by multiplying the mass by the specific heat.
 
Heat Exchanger: This is a device that enables furnaces to transfer heat from combustion safely into breathable air. The primary heat exchanger transfers heat from combustion gases to the air blowing through the ductwork. It's vital that none of the combustion gas itself gets into the air stream. The primary heat exchanger handles the hottest gases. This device transfers heat from outgoing stale air to incoming cold air. In warm climates, this process can be reversed. In high efficiency furnaces, secondary heat exchangers recover heat that used to be vented up the chimney with the exhaust gases. By recovering this heat, the furnace becomes more efficient. Part of the heat recovered here causes the water and acid to condense out of the exhaust gas. Because this liquid is corrosive, secondary heat exchangers must be designed to prevent deterioration. Usually this means they are made of stainless steel or some derivative of it.
 
Heat Gain: The amount of heat gained, measured in BTU's, from a space to be conditioned, at the local summer outdoor design temperature and a specified indoor design condition. An increase in the amount of heat contained in a space, resulting from direct solar radiation, heat flow through walls, windows, and other building surfaces, and the heat given off by people, lights, equipment, and other sources.
 
Heat Loss: The amount of heat lost, measured in BTU's from a space to be conditioned, at the local winter outdoor design temperature and a specified indoor design condition. A decrease in the amount of heat contained in a space, resulting from heat flow through walls, windows, roof and other building surfaces and from exfiltration of warm air.
 
Heat Pump: A heating and air conditioning unit that heats or cools by moving heat. A Heat Pump is a reverse cycle air conditioner. The Heat Pump uses a compression cycle system to supply heat or remove heat remove a temperature controlled space. An air-conditioning unit which is capable of heating by refrigeration, transferring heat from one (often cooler) medium to another (often warmer) medium, and which may or may not include a capability for cooling. This reverse-cycle air conditioner usually provides cooling in summer and heating in winter. When you run your air conditioner, your outdoor unit will be blowing hot air, (in other words, removing the heat from your home and sending it outside). When you run your heat pump, you reverse the flow of refrigerant and remove the heat from the atmosphere outside and blow it inside. When the temperature dips below 40 degrees outside, the Heat Pump labors in producing heat so they install a back up or auxiliary electric heat strip to supplement the Heat Pump. Electric Heat strips are very expensive to operate. In southern climates where it rarely dips below 40 degrees the heat pump is very efficient. A 3 to 1 savings in heating compared to electric heat strips.
 
Heat Pump Cooling Mode: In the cooling cycle of a Heat Pump , you are removing hot air from inside the house and sending it outside. You can feel the hot air outside, over the condenser fan motor.
 
Heat Pump Heating Mode: In the heating mode of a Heat Pump the refrigerant cycle is reversed and you are now removing the heat from the outside and sending it inside the house. You can feel the cool air outside, over the condenser fan motor. When temperatures go below 40 degrees Heat Pumps labor in producing heat and must use back up electric heat strips. Heat strips cost 3 times as much to operate as a Heat Pump when producing heat.
 
Heat Source: A body of air or liquid from which heat is collected. In an air source heat pump, the air outside the house is used as the heat source during the heating cycle.
 
Heat Transfer: Flow of heat energy induced by a temperature difference. Heat flow through a building envelope typically flows from a heated, or hot area to a cooled, or cold area.
 
Heating Degree Day: A unit that measure the space heating needs during a given period of time.
 
Heating Load: The rate at which heat must be added to a space in order to maintain the desired temperature within the space.
 
Heating System: Energy Efficiency program promotion aimed at improving the efficiency of the heating delivery system, including replacement, in the residential, commercial, or industrial sectors.
 
HFC: (Hydrofluorocarbon) A class of refrigerants. Generally refers to Hydrofluorocarbon family of refrigerants.
 
High-Efficiency Particulate Air (HEPA) Filter: A specialized filter capable of removing 99.97% of particulates 0.3 µ in diameter. High efficiency particulate arrestance (filters).
 
HRV: (Heat Recovery Ventilator) This device bring fresh, outside air into a home while simultaneously exhausting stale indoor air outside. In the process of doing this, an HRV removes heat from the exhaust air and transfer it to the incoming air, pre-heating it. This allows for the reclamation of much of the energy that otherwise would simply be vented outside. The end result: home comfort systems operate more efficiently.
 
HSPF: (Heating Seasonal Performance Factor) Indicates how efficiently a Heat Pump is working. A higher number means the unit works more efficiently. Heating Seasonal Performance Factor is similar to SEER, but it measures the efficiency of the heating portion of your heat pump. Like SEER, industry minimums have been raised recently, and the minimum is now 6.80 HSPF. Most new units have ratings from 7.0 to 9.4. A representation of the total heating output of a central air-conditioning heat pump in Btu's during its normal usage period for heating, divided by the total electrical energy input in watt-hours during the same period, as determined using the specified test procedures. Efficiency is derived according to federal test methods by using the total Btus during its normal usage period for heating divided by the total electrical energy input in watt-hours during the same period. The total heating output of a heat pump during its normal annual usage period for heating divided by the total electric power input in watt-hours during the same period. COP & HSPF can not be compared equally. Air Source equipment is rated by HSPF or COP and Geothermal equipment is rated by COP. ARI standards compares air source equipment at two temperatures, 47 F and 17 F. Geothermal equipment is compared at 32 F enter water temperature.
 
Humidifier: A device that adds moisture to warm air being circulated or directed into a space. This adds necessary moisture to protect your furnishings and reduce static electricity.
 
Humidistat: A device designed to regulate humidity input by reacting to changes in the moisture content of the air. Much like a thermostat but turns the system on & off by sensing the humidity level.
Humidity: The amount of moisture in the air. Air conditioners remove moisture for added comfort.
 
HVAC: (Heating, Ventilating and Air Conditioning) Heating, Ventilating and Air Conditioning
 
HVAC/R: (Heating, Ventilating, Air Conditioning, & Refrigeration) Heating, Ventilating, Air Conditioning, & Refrigeration.
 
Hydronic Heating: A system that heats a space using hot water which may be circulated through a convection or fan coil system or through a radiant baseboard or floor system.
 
I
 
IAQ: (Indoor Air Quality) Indoor Air Quality - characteristics of the indoor climate of a building, including the gaseous composition, temperature, relative humidity, and airborne contaminant levels.
 
Infiltration: Air movement into an enclosed space through cracks and openings. Unintentional movement of outdoor air into a house. Air flow inward into a space through walls, leaks around doors and windows or through the building materials used in the structure. It results from the forces of wind, temperature difference, and HVAC operation.
 
IWC: (Inches of water column) Commonly used in the USA.
 
J
 
K
 
L
 
Latent Cooling Load: (or Latent Load) The cooling load caused by moisture in the air. The net amount of moisture added to the inside air by plants, people, cooking, infiltration, and any other moisture source. The amount of moisture in the air can be calculated from a combination of dry-bulb and wet-bulb temperature measurements.
 
Latent Heat: Heat, that when added or removed, causes a change in state - but no change in temperature. A change in the heat content that occurs without a corresponding change in temperature, usually accompanied by a change of state (as from liquid to vapor during evaporation).
 
Life-Cycle Cost: Amount of money necessary to own, operate and maintain a building, system, plant, piece of equipment, etc., over its useful life.
 
M
 
Make-Up Air: See "Outdoor Air Supply."
 
Manometer: An instrument that measures air pressure differences between locations. Tubes are usually attached to a manometer and run to the spaces where pressures are measured.
 
Manual D: Manual D is the ACCA method for designing duct systems. Contractors often find it a laborious process and most duct systems are just installed, not designed. The amount of time necessary to design a duct system is certainly warranted in tract construction where the design is used repeatedly and for custom homes where the total cost of the home warrants a proper design. In short, designing a duct system is essential for proper equipment performance and customer comfort.
 
Manual J: Manual J is a widely accepted method of calculating the sensible and latent cooling (and heating) loads under design conditions. It was jointly developed by the Air Conditioning Contractors of America (ACCA) and the Air-Conditioning and Refrigeration Institute (ARI).
 
Manual S: Manual S is the ACCA method of selecting air conditioning equipment to meet the design loads. It ensures that both the sensible capacity and the latent capacity of the selected equipment will be adequate to meet the cooling load.
 
Matched System: A heating and cooling system comprised of products that have been certified to perform at promised comfort and efficiency levels when used together, and used according to design and engineering specifications.
 
Mold: A fungal infestation that causes disintegration of a substance. Molds are a group of organisms that belong to the kingdom Fungi. In this document, the terms fungi and mold are used interchangeably. There are over 20,000 species of mold.
 
N
 
Natural Ventilation: The supply of outdoor air through passive flow from windows, chimneys, doors, and other infiltration.
 
Negative Pressure: Condition that exists when less air is supplied to a space than is exhausted from the space, so the air pressure within that space is less than that in surrounding areas. Under this condition, if an opening exists, air will flow from surrounding areas into the negatively pressurized space.
 
O
 
Outdoor Air Supply: Air brought into a building from the outdoors (often through the ventilation system) that has not been previously circulated through the system. Also known as "Make-Up Air."
 
Outside Air: Air taken from outdoors and not previously circulated through the HVAC system.
 
P
 
Package Unit or Package System: A self-contained unit or system that has the Air Handler & Condenser in same unit. Normally placed outside the home and connected to a duct system by a penetration through the homes foundation. Except for geothermal which is a self-contained indoor unit that is place in a closet, attached garage, basement, or mechanical room.
 
Pascals: (Pa) A small unit of air pressure. One pound per square inch equals 6,895 pascals.
 
Plenum: Air compartment connected to a duct or ducts. Air flow passage made of duct board, metal, drywall, or wood. Joins supply and return ducts with HVAC equipment. The portions of the air distribution system that makes use of the building structure, and the sheet meal that connects distribution ductwork to an air handling unit. Many buildings use the space above a dropped ceiling as a plenum.
 
Positive Pressure: Condition that exists when more air is supplied to a space than is exhausted, so the air pressure within that space is greater than that in surrounding areas. Under this condition, if an opening exists, air will flow from the positively pressurized space, outward to surrounding areas.
 
Pressure balancing: The process of neutralizing pressure differences within a home.
 
Preventive Maintenance: (PM) A program of building maintenance implemented to reduce the possibility of problems, usually through periodic inspection, cleaning, adjustment. calibration. and replacement of functioning, parts of the HVAC system, as well as housekeeping practices to reduce the buildup of potential contaminants. Primarily done on a building's mechanical systems, this involves a regular and systematic inspection, cleaning, and replacement of worn parts, materials, and systems. Preventive maintenance helps to prevent parts, material, and systems failure by ensuring that parts, materials and systems are in good working order.
 
Price of Quality, The: There is more to buying a heat pump or air conditioner than ratings. The quality of construction and materials used as well as the reliability of the manufacturer and installing contractor can all affect your long-term satisfaction and comfort. Top quality, high efficiency equipment will cost more initially, but it will save you money on utility bills and service calls for years to come. Be sure to weigh all the factors before choosing your new system.
 
Q
 
R
 
R-Value: A measure, in Btu/(ft2 F), of the resistance to transmission of heat by an insulating material. The higher the R-value of a material, the greater is its insulating properties and the slower the heat flow through it. The specific value needed to insulate a home depends on climate, type of heating system and other factors.
 
Radiant: System that uses hot surfaces to radiate or convect heat into the environment. Without the use of fans or blowers.
 
Radiant Barrier: A device designed to reduce or stop the flow of radiant energy.
 
Reclaiming: Processing or returning used refrigerant to the manufacturer or processor for disposal or reuse.
 
Refrigerant Charge: The amount of refrigerant contained within the air conditioning equipment and required for proper operation.
 
Refrigerant Lines: Two copper lines that connect the Condenser (Outdoor) Coil to the Evaporator (Indoor) Coil.
 
Registers: Combination grille and damper assembly covering an air opening or end of an air duct. Coverings for the ducts where they open to the conditioned space. (Same as Grilles)
 
Relative Humidity: (RH) Relative humidity is defined as the ratio of the water vapor pressure to the saturation vapor pressure (over water) at the temperature of the gas. RH = Pw/Pws * 100
 
Return: The ductwork that carries air from the house to the air handler.
 
Return Air: Air drawn into a heating unit after having been circulated from the heater's output supply to a room. The air removed from an occupied space and returned to the air handler to be exhausted or recirculated.
 
RSES: A leading HVAC/R Association - Refrigeration Service Engineers Society.
 
S
 
Saturation Temperature: Also referred to as the boiling point or the condensing temperature. This is the temperature at which a refrigerant will change state from a liquid to a vapor or visa versa.
 
SEER: (Seasonal Energy Efficiency Ratio) An efficiency measurement that is similar to Miles Per Gallon for cars. The higher this number, the more energy efficient they system is. The amount of cooling your equipment delivers per every dollar spent on electricity. The higher the number the lower the operating cost (not more cooling.) SEER applies to air conditioners and heat pumps. In the past, a unit with a SEER of 8.00 was considered standard efficiency, and a unit with a 10.00 SEER was considered high efficiency. After January 1, 1992, the minimum SEER required by the DOE is 10.00 and 15.00+ SEER is considered high efficiency. EER & SEER can not be compared equally. Air source equipment is rated by SEER and geothermal equipment is rated by EER. New units have SEER ratings from 10 to 17 BTUs per watt. The total cooling of a central unitary air conditioner or unitary heat pump in Btu's during its normal annual usage period for cooling divided by the total electric energy input in watt-hours during the same period. The Seasonal Energy Efficiency Ratio is a standard method of rating air conditioners based on three tests. All three tests are run at 80 degrees Fahrenheit inside and 82 degrees Fahrenheit outside. The first test is run with humid indoor conditions, the second with dry indoor conditions, and the third with dry conditions cycling the air conditioner on for 6 minutes and off for 24 minutes. The published SEER may not represent the actual seasonal energy efficiency of an air conditioner in your climate. The total cooling output of a central air conditioning unit in Btus during its normal usage period for cooling divided by the total electrical energy input in watt-hours during the same period, as determined using specified federal test procedures. [Title 20, Section 2-1602(c)(11)].
 
Sensible Cooling Load: The heat gain of the home due to conduction, solar radiation, infiltration, appliances, people, and pets. Burning a light bulb, for example, adds only sensible load to the house. This sensible load raises the dry-bulb temperature.
 
Sensible Heat: Heat, that when added or removed, causes a change in temperature but not in state. Heat that results in a temperature change.
 
Setback: A reduction of climate control energy demand in HVAC controls when a building is unoccupied.
 
Setpoint: The temperature to which a thermostat is set to result in a desired heated space temperature.
 
Short-Circuiting: Situation that occurs when the supply air flows to return or exhaust grilles before entering the breathing zone (area of a room where people are). To avoid short-circuiting, the supply air must be delivered at a temperature and velocity that results in mixing throughout the space.
Single Package: A year 'round heating and air conditioning system that has all the components completely encased in one unit outside the home.
 
Sizing: Refers to the procedure a heating contractor goes through to determine how large a furnace (measured in Btuh) is needed to heat a house efficiently. Too small a furnace won't deliver enough heating; too large a furnace increases energy costs and can have an adverse effect on comfort. Sizing depends on the square-footage of the home, the amount of ceiling and wall insulation, the window area, use of storm doors, storm windows, and more.
 
Smoke stick: A diagnostic tool used to observe air flow. Usually it consists of a chemical in a squeezable container. When squeezed it emits smoke which visibly follows air flow currents.
 
Sound Attenuators: Components which are inserted into the air distribution system and designed to reduce airborne noise which is propagated along the ducts.
 
Sound Rating Number: (SRN) Sound is measured in bels (a bel equals 10 decibels). The SRN of a unit is based on ARI test, performed at ARI standard rating conditions. Average sound rating range from 7.0 to 8.0 decibels. The lower the SRN rating, the quieter the unit.
 
Specific Heat: In English units, the quantity of heat, in Btu, needed to raise the temperature of one pound of material one degree Fahrenheit.
 
Split System: Refrigeration or air conditioning installation, which places condensing unit outside or away from evaporator. These unit are connected together by a supply and return refrigerant lines. Also applicable to heat pump installations. A combination heat pump or air conditioner with indoor components such as a furnace or blower coil. To maximize effectiveness, Split Systems should be matched.
 
Spore: Molds reproduce by means of spores. Spores are microscopic; they vary in shape and size (2-100 micrometers). Spores may travel in several ways--they may be passively moved (by a breeze or waterdrop), mechanically disturbed (by a person or animal passing by), or actively discharged by the mold (usually under moist conditions or high humidity).
 
SRN: (Sound Rating Number ) Sound is measured in bels (a bel equals 10 decibels). The SRN of a unit is based on ARI test, performed at ARI standard rating conditions. Average sound rating range from 7.0 to 8.0 decibels. The lower the SRN rating, the quieter the unit.
 
Static Pressure: Condition that exists when an equal amount of air is supplied to and exhausted from a space. At static pressure, equilibrium has been reached.
 
Subcooled Liquid: Liquid refrigerant which is cooled below its saturation temperature.
 
Superheated Vapor: Refrigerant vapor which is heated above its saturation temperature. If a refrigerant is superheated, there is no liquid present.
 
Supplementary Heat: (Emergency Heat) The auxiliary or emergency heat provided at temperatures below a heat pump's balance point. It is usually electrical resistance heat.
 
Supply: The ductwork that carries air from the air handler to the rooms in the house.
 
Supply Air: The air flow entering the treated space.
 
Switchover Valve: A device in a heat pump that reverses the flow of refrigerant as the system is switched from cooling to heating. Also called a reversing valve or four-way valve.
 
System: A combination of equipment and/or controls, accessories, interconnecting means and terminal elements by which energy is transformed to perform a specific function, such as climate control, service water heating, or lighting.
 
T
 
Temperature: Degree of hotness or coldness measured on one of several arbitrary scales based on some observable phenomenon (such as the expansion).
 
Testing, Adjusting, And Balancing: (TAB) The diagnostic and corrective procedures for HVAC controls and operating components to ensure provision of specified airflow rates and environmental conditions.
 
Therm: Another measurement of heat. One therm equals One hundred thousand (100,000) British thermal units (1 therm = 100,000 Btu).
 
Thermal Mass: A material used to store heat, thereby slowing the temperature variation within a space. Typical thermal mass materials include concrete, brick, masonry, tile and mortar, water, and rock or other materials with high heat capacity.
 
Thermostat: A temperature sensitive switch for controlling the operation of a heater or furnace. Typically found on a wall inside the home, that consists of a series of sensors and relays that monitor and control the functions of a heating and cooling system. A device that allows you to control the temperature inside your home by telling the heating or cooling system how much air to produce. An automatic control device designed to be responsive to temperature and typically used to maintain set temperatures by cycling the HVAC system.
Thermostat, Setback: (Programmable Thermostat) A state-of-the-art electronic thermostat with a built-in memory that can be programmed for different temperature settings at different times of the day. A device, containing a clock mechanism, which can automatically change the inside temperature maintained by the HVAC system according to a preset schedule. The heating or cooling requirements can be reduced when a building is unoccupied or when occupants are asleep.
 
Time Delay: Usually refers to a device that will not allow the condenser to restart for an average of 5 minutes.
 
Ton or "Ton of Cooling": A cooling unit of measure. Each ton equals the cooling effect of 12,000 Btuh. Heat pumps and air conditioners are generally sized in tons. Typical sizes for single family residences are between two and five tons. It is important to note that actual capacity is not constant and will change based on outdoor or indoor temperatures. The published capacity rating of air conditioners and heat pumps is based on performance at the ARI standard temperature levels of 95 F outside, 80 F inside, and 50% relative humidity. The number of tons a system has is the total BTU capacity of the system. The size of the area to be cooled will determine the correct size of the system in tons. While an air conditioner may be called a three ton unit, it may not produce 36,000 Btu/h in cooling. There is a wide variety of actual capacities that are called "three tons."
 
Transformer: A device, which through electromagnetic induction but without the use of moving parts, transforms alternating or intermittent electric energy in one circuit into energy of similar type in another circuit, commonly with altered values of voltage and current.
 
U
 
Upflow Furnace: A furnace that pulls cool return air in from the bottom and blows/expels warm air out the top into the duct work. This type of furnace is usually installed in a basement or an out-of-the-way closet.
 
V
 
Ventilation: The process of supplying or removing air by natural or mechanical means to or from any space. Such air may or may not have been conditioned or treated.
 
Ventilation Rate: The rate at which indoor air enters and leaves a building. Expressed in one of two ways: the number of changes of outdoor air per unit of time (air changes per hour, or "ach") or the rate at which a volume of outdoor air enters per unit of time (cubic feet per minute, or "cfm").
 
W
 
WB: Wet Bulb
 
WC: (Water Column) Common measure of air pressure used in HVAC systems.
 
Wet-bulb Temperature: When a wet wick is placed over a standard thermometer and air is blown across the surface, the water evaporates and cools the thermometer below the dry-bulb temperature. This cooler temperature (called the wet-bulb temperature) depends on how much moisture is in the air.
 
Whole House Fan: A system capable of cooling a house by exhausting a large volume of warm air when the outside air is cool.
 
X
 
Y
 
Z
 
Zonal Control: A method of designing and controlling the HVAC system of a residence so that living areas can be maintained at a different temperature than sleeping areas using independent setback thermostats. If specific requirements are met, zonal control may earn a credit towards compliance with whatever building energy efficiency standards are applicable.
 
Zoning: A system in which living areas or groups of rooms are divided into separate spaces and each space's heating/air conditioning is controlled independently. This can be accomplished by using either multiple independent systems, or a single system using electronic controls and motorized dampers (see Damper). For example, you might prefer to have the kitchen area of your home be slightly cool, while at the same time keeping the temperature in the bedrooms warmer.
 
 

 
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Last modified: 01/12/09