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Glossary
: A B C D E F G H I L M P R S T U W Y Z
A
ACCA (Air Conditioning Contractors of America): A leading HVAC/R Association: www.acca.org.
ACH (Air Change Per Hour): The number of times in one hour that air in a house is completely replaced with outdoor air.
AFUE (Annual Fuel Utilization Efficiency): Ratio of annual output of useful energy or heat to the annual energy input to the furnace. A higher AFUE percentage indicates a more efficient unit.
AGITATOR: Device used to cause motion in confined fluid.
AHU (Air Handler Unit): The inside unit of the air conditioning system that contains the blower, evaporator coil, and heater.
AIR CHANGE: The amount of air required to completely replace the air in a room or building.
AIR CLEANER: A device used for removal of airborne impurities.
AIR CONDITIONER: A mechanical refrigeration device used to control temperature, humidity, cleanliness, and movement of air in a confined space.
AIR DIFFUSION: Distribution of the air in a space, called the treated space, by means of devices, called air terminal devices, in a manner so as to meet certain specified conditions, such as air change rate, pressure, cleanliness, temperature, humidity, air velocity and noise level.
AIR HANDLER (AH): Indoor unit of an air conditioning system containing a heat exchange coil, filters, and fan. Provides conditioned air into the space.
AIR INFILTRATION: Leakage of air into rooms through cracks, windows, doors, and other openings.
AIRFLOW: The distribution or movement of air.
AIR CONDITIONING AND REFRIGERATION INSTITUTE (ARI): 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. ARI ensures a level of performance within the industry: www.ari.org.
AMBIENT TEMPERATURE: The temperature, usually of the air, that surrounds operating equipment.
ASHRAE: A leading HVAC/R Association - American Society of Heating, Refrigerating and Air Conditioning Engineers: www.ashrae.org.
ASTM INTERNATIONAL: ASTM International, originally known as the American Society for Testing and Materials (ASTM), was formed over a century ago, when a forward-thinking group of engineers and scientists got together to address frequent rail breaks in the burgeoning railroad industry. ASTM International is one of the largest voluntary standards development organizations in the world-a trusted source for technical standards for materials, products, systems, and services: www.astm.org.
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.
BALANCE POINT: The lowest outdoor temperature at which the refrigeration cycle of a heat pump will supply the heating requirements without the aid of a supplementary heat source.
BALANCING: The process of adjusting the flow of air in duct systems, or water flow in hot-water heating systems. Proper balancing is performed using accurate instrumentation and/or dampers to deliver the right amount of heating or cooling to each area or room of the home
BLOWER OR BLOWER FAN: An air handling device for moving air in a distribution system.
BOILER: A boiler, which uses hot water to heat your home, is also referred to as a hot water system. After the water is heated, it is pumped through baseboards or radiators throughout the home transferring the heat to each room.
BTU: British Thermal Unit. Used to measure cooling or heating capacity.
C
CAPACITY: Refrigerating rating system usually measured in BTU's per hour.
CENTRAL AIR CONDITIONING: A home's "split system" central air conditioning system includes a compressor, a fan, condenser coil, evaporator coil, and refrigerant. It extracts heat from indoor air and transfers it outside, leaving the cooled indoor air to be recirculated. Ducts are used to transfer the cooled air throughout the home. The efficiency of central air conditioning systems is rated using SEER ratios. A central air conditioning system uses electricity as its power source.
The basic components of an air conditioning system are: A condensing unit (the outdoor section) and a matching indoor air handler or furnace with coil (the indoor section).
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.
COMFORT ZONE: The range of temperatures, humidities, and air velocities at which the greatest percentage of people feel comfortable.
COMPRESSOR: A pump found in a refrigerating or air conditioning system which pumps refrigerant through pipes between an outdoor condensing unit and an indoor evaporating unit, using pressure. The compressor maintains adequate pressure within the system to cause refrigerant to flow in sufficient quantities to meet the cooling requirements. There are four types of compressors: reciprocating, rotary, scroll, and centrifugal. Most residential systems have reciprocating or scroll compressors.
CONDENSER COIL OR OUTDOOR COIL: In an air conditioner, the coil dissipates heat from the refrigerant from vapor to liquid. In a heat pump system, it absorbs heat from the outdoors.
CONDENSING UNIT: The outdoor unit of an air conditioning system that contains the compressor, propeller fan, circuit board, and heat exchange coil. The condensing unit pumps refrigerant to the evaporator.
CONDUCTION: The transfer of heat through a solid material.
CONVECTION: The movement of heat by airflow.
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.
D
DAMPER: A device that is located in ductwork to adjust airflow. 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) airflow 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.
DB: Dry Bulb Temperature.
DB: DECIBEL: A decibel describes the relative loudness of a sound.
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.
DESIGN CONDITIONS: Cooling loads vary with inside and outside conditions. A set of conditions specific to the local climate is 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.
DIRECT GAS-FIRED HEATER: The burner fires directly in the air stream being heated, rather than through a heat exchanger. 100% of available Btu's 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: www.doe.gov.
DOWNFLOW: A type of furnace that takes cool air from the top and blows warm air to the bottom.
DUCTWORK: The delivery system through which air from the furnace or air handler is brought to where it's needed. Ductwork is made of sheet metal, fiberglass, or flexible plastic, and can be round or rectangular in shape.
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 cannot 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: 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. Individual states may require efficiency ratings that are higher than government standards. High efficiency furnaces will be rated 85 to 95% AFUE.
ENERGY RECOVERY VENTILATOR (ERV): 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.
EVAPORATOR COIL: The section of your air conditioning system located inside your home in the indoor unit. The coil absorbs heat from the surrounding air or liquid and moves it outside the refrigerated area by means of a refrigerant. It is also know as a cooling coil, blower coil, chilling unit or indoor coil.
EXHAUST: The airflow leaving the treated space.
F
FILTER: A device for removing dust particles from air or unwanted elements from liquids.
FLOW HOOD: A diagnostic tool used to measure airflow through ducts, supply registers, and return grilles.
FORCED AIR: This describes a type of heating system that uses a blower motor to move air through the furnace and into the ductwork.
FURNACE: With a furnace, air is drawn into and out of the system. That's why it's often called a warm air system. After the air is heated, a blower pushes it through ducts. The warm air is released through vents or registers throughout your house. A furnace's heating ability is gauged with an Annual Fuel Utilization Efficiency (AFUE) percentage. A higher AFUE percentage indicates a more efficient furnace.
G
GEOTHERMAL EQUIPMENT: Heat pumps that use the ground to transfer heat to and from the refrigerant in the unit. The unit circulates water through a heat exchanger in the to a closed loop buried in the ground or by pumping water from a well through the unit.
H
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 airstream. The primary heat exchanger handles the hottest gases.
In high efficiency furnaces, secondary heat exchangers recover heat that formerly was 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.
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.
HEAT PUMP: An outdoor air conditioning unit that is capable of reversing the direction of refrigerant floor to provide either cooling or heating to the indoor space.
HEAT RECOVERY VENTILATOR (HRV): This device brings 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 transfers 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 Season Performance Factor: A rating of the average efficiency of a heat pump unit when operating in the heating mode.
HUMIDIFIER: A device that adds moisture to warm air being circulated or directed into a space.
HUMIDISTAT: A device designed to regulate humidity input by reacting to changes in the moisture content of the air.
HUMIDITY: The amount of moisture in the air. Air conditioners remove moisture for added comfort.
I
IAQ: Indoor Air Quality.
INFILTRATION: Airflow entering into a space through walls, leak around doors and windows, or through the building materials used in the structure.
L
LATENT COOLING LOAD: 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.
LOAD ESTIMATE: A series of studies performed to determine the heating or cooling requirements of your home. An energy load analysis uses information such as the square footage of your home, window and door areas, insulation quality, and local climate to determine the heating and cooling capacity needed by your furnace, heat pump, or air conditioner.
M
MICROPROCESSOR: Electrical component consisting of integrated circuits, which may accept, store, control, and output information.
P
PLENUM: Airflow passage made of duct board, metal, drywall, or wood. Joins supply and return ducts with HVAC equipment.
R
RADIANT HEAT: By circulating warm water - from 80ºF to 140ºF - through flexible, durable PEX tubing that has been installed in the floor. The floor, in effect, becomes a large "radiator". Radiant waves of energy move off the floor and travel out in all directions to warm the walls, ceiling, and furniture. As these objects become warm, you experience less heat loss because you are standing next to warm things.
RADIATION: The transfer of heat directly from one surface to another (without heating the intermediate air acting as a transfer mechanism).
RECIPROCATING COMPRESSOR: A type of compressor used in air conditioners that compresses refrigerant by using a type of "piston" action.
REFRIGERANT: Substance used in refrigerating mechanism. It absorbs heat in evaporator by change of state from a liquid to a gas, and releases its heat in a condenser as the substance returns from the gaseous state back to a liquid state.
REFRIGERANT LINES: Insulated copper tubing through which refrigerant flows between condensing and evaporator units.
REGISTER: Combination grille and damper assembly covering an air opening or end of an air duct.
RETURN AIR: Air drawn into a heating unit after having been circulated from the heater's output supply to a room.
RH: Relative Humidity.
RSES: A leading HVAC/R Association - Refrigeration Service Engineers Society: www.rses.org.
S
SEER: Seasonal Energy Efficiency Ratio. The rating of the average efficiency of an air conditioning unit.
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 energy that causes a rise or fall in the temperature of a gas, liquid, or solid when added or removed from that material. Sensible heat changes the temperature by changing the speed at which the molecules move.
SETPOINT: The temperature to which a thermostat is set to result in a desired heated space temperature.
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.
SOUND ATTENUATORS: Components that are inserted into the air distribution system and designed to reduce airborne noise, which is propagated along the ducts.
SPLIT-DUCTLESS SYSTEM: Comprised of a remote outdoor condensing unit connected by refrigerant pipes to a matching, non-ducted indoor air handler. Special cases for introducing fresh air may call for limited ducting to air handler from outside.
SPLIT SYSTEM AIR CONDITIONER: A traditional home comfort system has two parts: an indoor unit, such as a furnace or air handler, and an outdoor unit. An air conditioner is the outdoor unit that cools air and sends it to the indoor unit to be circulated through your home. The indoor and outdoor units are designed to work together, and when the air conditioner is properly matched with a furnace or air handler, the result is maximum efficiency and extended system life. Air conditioning and cooling efficiency is measured using a Seasonal Energy Efficiency Ratio (SEER). A higher SEER signifies higher energy efficiency.
SUPPLY: The ductwork that carries air from the air handler to the rooms in the house.
T
THERM: Another measurement of heat. One therm equals 100,000 BTUH.
THERMOSTAT: A temperature sensitive switch consisting of a series of sensors and relays that monitor and control the operation and function of a heating and/or cooling system.
TIME DELAY: Usually refers to a device that will not allow the condenser to restart for an average of 5 minutes.
TON: A sizing measure for the capacity of air conditioners and heat pumps. A ton is the total BTU capacity of a system. One ton is equal to the BTU's required to melt one ton of ice in a 24-hour period. There are 12,000 BTU's in a ton, a 2 ton air conditioner will produce 24,000 BTU's, a 3 ton will produce 36,000 BTU's and so on... The size of the area to be cooled will determine the correct size of the system in tons. Published capacity ratings are based on ARI standard temperatures of 95°F, outside and 80°F inside, but the actual capacity of a system changes with outdoor and indoor temperatures.
U
UPFLOW: A type of furnace that draws cool air from the bottom and blows the warmed air out the top into the ductwork. This type of furnace is usually installed in a basement or an out-of-the-way closet.
W
WB: Wet Bulb.
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.
Z
ZONE: 1) Conditioned space in a house under the control of a thermostat. 2) A space within a house with a distinct pressure compared to other pressure zones.
ZONING: A system in which living areas 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).
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