Glossary of Terms
Below are some commonly used terms in the
heating, ventilation and air conditioning industry. These
may be useful when dealing with contractors or assessing a
solution to your problem.
Air Conditioner - Assembly of equipment for the simultaneous
control of air temperature, relative humidity, purity, and
Air Cooled - Uses a fan to discharge heat from the
condenser coil to the outdoors.
AFUE (Annual Fuel Utilization Efficiency) - A rating
that denotes the efficiency of gas heating equipment. It is
the amount of heating your equipment delivers for every dollar
spent on fuel. A higher rating indicates more efficient equipment.
This rating is calculated in accordance with the Department
of Energy test procedures.
Air-Source - Air is being used as the heat source
or heat sink for a heat pump.
Ambient Temperature - The temperature, usually of
the air, that surrounds operating equipment.
BTU (British Thermal Unit) - The standard of measurement
used for measuring the amount of heat required to raise the
temperature of one pound of water by one degree (Fahrenheit).
BTUH - The number of BTUs in an hour.
Central Air Conditioner System -System in which air
is treated at a central location and carried to and from the
rooms by one or more fans and a system of ducts.
Compressor - The pump that moves the refrigerant from
the indoor evaporator to the outdoor condenser and back to
the evaporator again. The compressor is often called "the
heart of the system" because it circulates the refrigerant
through the loop.
Condenser - A device that transfers unwanted heat
out of a refrigeration system to a medium (either air, water,
or a combination of air and water) that absorbs the heat and
transfers it to a disposal point. There are three types of
condensers: air-cooled condensers, water-cooled condensers,
and evaporative condensers. The evaporative condenser uses
a combination of air and water as its condensing medium. Most
residential systems have an air-cooled condenser.
Condenser Coil - A series or network of tubes filled
with refrigerant, normally located outside the home, that
removes heat from the hot, gaseous refrigerant so that the
refrigerant becomes liquid again.
Cooling Capacity - A measure of the ability of a
unit to remove heat from an enclosed space.
COP - Coefficient of Performance of a heat pump means
the ratio of the rate of useful heat output delivered by the
complete heat pump unit (exclusive of supplementary heating)
to the corresponding rate of energy input, in consistent units
and under operating conditions.
DOE -The Department of Energy. A federal agency that
sets industry efficiency standards and monitors the use of
various energy sources.
EER - Energy Efficiency Ratio means the ratio of
the cooling capacity of the air conditioner in British Thermal
Units per hour, to the total electrical input in watts under
ARI-specified test conditions.
Enthalpy - Heat content or total heat, including both
sensible and latent heat. The amount of heat contained in
a refrigerant at any given temperature with reference to -40°F.
Evaporator- Absorbs heat from the surrounding air
or liquid and moves it outside the refrigerated area by means
of a refrigerant. It is also known as a cooling coil, blower
coil, chilling unit or indoor coil.
Evaporator Coil - A series or network of tubes filled
with refrigerant located inside the home that take heat and
moisture out of indoor air as liquid refrigerant evaporates.
Free Delivery - There are no ducts and the unit may
be installed in the field without ducts if needed.
Ground-Source - The ground or soil below the frost
line is being used as the heat source or heat sink for a heat
Ground Water-Source - Water from an underground well
is being used as the heat source or heat sink for a heat pump.
HVAC - Heating, ventilation, and air conditioning.
Heat Pump - An air conditioner capable of heating
by refrigeration. It may or may not include a capability for
cooling. Outside air or water is used as a heat source or
heat sink, depending upon whether the system is heating or
Heating Capacity - A measure of the ability of a unit
to add heat to an enclosed space.
HSPF - Heating Seasonal Performance Factor means the
total heating output of a heat pump in British Thermal Units
during its normal usage period for heating divided by the
total electrical energy input in watt-hours during the same
Insulation - Any material that slows down the transfer
(K) Factor - The insulating value of any material.
Also known as conductivity.
Kilowatt (kW) - Equal to 1,000 watts.
Kilowatt-hour (kWh) - A common unit of electrical
consumption measured by the total energy created by one kilowatt
in one hour.
Latent Heat - The heat energy needed to change the
state of a substance (i.e.: from a liquid to a gas) but not
SEER-(Seasonal Energy Efficiency Ratio) - A rating
that denotes the efficiency of air conditioning equipment.
It is the amount of cooling your equipment delivers for every
dollar spent on electricity. It is the ratio of cooling delivered
by a system, measured in BTUs, to the dollar cost of the electricity
to run the system, as measured in watt-hours. This ratio is
determined using specified federal test procedures. The higher
the SEER, the more efficient the unit. The more efficient
the unit, the lower the operating cost.
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.
Single Package -A central air conditioner which combines
both condenser and air handling capabilities in a single packaged
Split System - A central air conditioner consisting
of two or more major components. The system usually consists
of a compressor-containing unit and condenser, installed outside
the building and a non-compressor -containing air handling
unit installed within the building. This is the most common
type of system installed in a home.
Supercooled Liquid - Liquid refrigerant cooled below
its saturation point.
Subcooling - Creating a drop in temperature by removing
sensible heat from a refrigerant liquid.
Superheated vapor - Refrigerant vapor heated beyond
its saturation point.
Superheating - Creating a rise in temperature by
adding heat energy to a refrigeration vapor.
Ton -The unit of measurement for air conditioning
system capacity. One ton of air conditioning removes 12,000
Btu's of heat energy per hour from a home. Central air conditioners
are sized in tons. Residential units usually range from 1
to 5 tons.
Water-Source -Water is being used as the heat source
or heat sink for a heat pump. Sources of underground water
are wells and sources of surface water are lakes, large ponds,
Watt - A unit of power that equals one joule per
second. Named after James Watt.
Year-Round: Air Conditioner which uses gas or oil
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