HVAC Glossary

Alternative HVAC Solutions would like to offer the following HVAC Glossary as a helpful tool for you, our customer, to help with the various terms and technical definitions for the heating, cooling and indoor air quality industry.

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Half-Life -  The amount of time it takes for half of the existing amount of a radioactive element to decay to non-radioactive products.
HCFC -  (Hydrochlorofluorocarbon) A class of refrigerants. Generally refers to Halogenated Chlorofluorocarbon family of refrigerants.
Heat Balance -  The outdoor temperature at which a building's internal heat gain (from people, lights and machines) is equal to the heat loss through windows, roof and walls.
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 Engine -  An engine that converts heat to mechanical energy.
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. 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 Rate -  A number that tells how efficient a fuel-burning power plant is. The heat rate equals the Btu content of the fuel input divided by the kilowatt-hours of power output.
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.
Hertz -  A unit of electromagnetic wave frequency that is equal to one cycle per second. -- It is named after Henrich R. Hertz.
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).
Home Energy Assistance Program -  (HEAP) A centrally operated direct payment program that assists eligible households in offsetting the cost of heating and cooling their homes. Payments are generally made in the form of dual party warrants (checks) made payable to the applicant and their designated utility company. For example, the program is administered in California by the California Department of Economic Opportunity using federal and state funds.
Horsepower -  HP) A unit for measuring the rate of doing work. One horsepower equals about three-fourths of a kilowatt (745.7 watts).
House Dust Mite -  A common microscopic household arachnid, which feeds on shed skin scales, and so tends to concentrate around mattresses and furniture. Antigens present in the mite's excreta are implicated in cases of allergic asthma and allergic rhinitis.
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 Btus during its normal usage period for heating, divided byu the total electrical energy input in watt-hours during the same period, as 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.