Useful Definitions of Terms
Heat pump / air conditioning terms (parts)
The refrigerant is the liquid/gaseous substance that circulates
through a refrigeration system, alternately absorbing, transporting and
releasing heat by changing phase.
The reversing valve controls the direction of flow of the
refrigerant in the heat pump and changes the heat pump from heating to
cooling mode or vice versa. The refrigerant flow direction is reversed
in all parts with the exception of the suction line between the
reversing valve and the compressor suction port, and the compressor
discharge line and the reversing valve.
A coil (refrigerant) is a loop, or loops, of tubing made of copper or aluminum
where heat transfer takes place. The tubing may have fins to increase
the surface area available for heat exchange. And as you look at the
fins you will notice in today 13 and above SEER there are more fins and
larger coil area we will talk about this later.
Accumulator as the refrigerant passes from the reversing valve to the compressor, the accumulator
collects any excess liquid that did not vaporize into a gas. Not all
heat pumps, however, have an accumulator. Heat pumps made by GE,
American Standard and Trane use a compressor that has a built in
accumulator.
*move later???
*Basic Heat Pump Cycle The compressor raises the pressure of the
refrigerant on the discharge side and reduces pressure on the suction
side, increasing the temperature of the refrigerant on the discharge
through what is called the Adiabatic process.
The difference between the temperature of the discharge line leaving
the compressor and the discharge saturation temperature is called the
"Discharge Superheat" part of which is the result of the heat of the
compressor motor added to the equation.
The condenser is a coil in which the refrigerant gives off the
discharge Superheat and the Latent Heat to its surroundings and becomes
a liquid.
The "expansion device" or "metering device" meters the refrigerant from
the liquid line to the evaporator by restricting the flow of
refrigerant.
Thermostatic expansion valve. metering device that measures suction temperature and suction pressure to maintain a constant Superheat.
The evaporator is a coil in which the low pressure liquid
refrigerant absorbs heat from its surroundings and boils to become a
low pressure, low-temperature saturated vapor.
The plenum is an air compartment that forms part of the system for
distributing heated or cooled air through the house. It is generally a
large compartment immediately above or around the heat exchanger.
Outdoor Coil for identification purposes we will call the coil located outside,
the Outdoor Coil because it can be either the condenser or the
evaporator depending on where the system is in the heating mode or
cooling mode.
Indoor Coil for identification purposes we will call the coil located inside, the Indoor Coil
because it can be either the condenser or the evaporator depending on
where the system is in the heating mode or cooling mode. If this is a
packaged unit (rooftop unit0 we will call the coil that transfers the
heat to the conditioned space the Indoor Coil.
OTHER TERMS : heat and energy.
Work (quantity) A quantity of energy transfered with no constraint on time.
Power (rate) The rate at which a quantity of energy is transfered in a given time.
Energy 1: The ability (quantity) to do work (potential energy) 2: Work in motion (kinetic energy)
Sensible Heat is heat energy added to or removed from a substance that does not change the phase of the material.
Latent Heat "hidden heat" is heat energy added to or removed from a substance that
changes the phase but does not raise or lower the temperature of the
material.
Btu or British Thermal Unit is a unit used to measure
heat quantity, it is the amount of heat required to change the temperature of one pound (one pint liquid) water one degree Fahrenheit, without changing its phase.
A Btu/h, or British thermal unit per hour is a unit used to measure heat transfer rate. One Btu is the amount of heat energy given off by a
typical birthday candle. If this heat energy were released over the
course of one hour, it would be the equivalent of one Btu per hour.
Therm A real world measure of heat quantity. 1 Therm = 100,000
Btus . A heat pump that puts out 33,000 Btus per hour that runs for 3
hours will supply 1 Therm. A gas furnace that supplies 100,000 Btus per hour that runs for 1 hour will supply 1 Therm of heat.
MBtu M is the Roman numeral for 1000, 1 MBtu = 1 Therm.
MMBtu = 1000 Therms or 1 million Btus
Watt (power) the rate of heat (rate not quantity) that is
dissipated when one ampere of electrical current is flowed through one
ohm of resistance.
Horsepower (electrical) is 746 watts.
A KW, or Kilowatt, is equal to 1000 watts or 3,400 Btu s
per hour. This is the amount of power (rate of energy) required by ten
100-watt light bulbs.
A kWh, or Kilowatt Hour is the amount or quantity of
energy that a 1000 watt electrical load consumes in one hour, any
electrical device converts that electrical energy will result in
to 3,400 Btus per hour of heat.
A Ton is a measure of heat transfer rate. It is equal to 3.5 kW
or 12,000 Btu/h. A Ton is the amount of heat required to melt one ton
of ice in 24 hours. It takes 144 Btu of latent heat to change one pound (one
pint) of water from solid to liquid or vice versa. 1 ton (weight)
is 2,000 pounds of ice = 288,000 Btus to melt, divided by 24 hours =
12,000 Btus per hour.
Note: heat transfer rate can be expressed in Horsepower, Btus/hour, Watts (Kw s) or Tons.
Heat pump and efficiency measurements and terms
Degree-days are a measure of the difference in temperature between the
indoor temperature and the outdoor temperature averaged over a 24 hour
period. If the indoor temperature is 70 degrees F and the outdoor
temperature is 60 degrees F then in a 24 hour period 10 Degree-Days of
heating load has occurred. The reverse is true for cooling load. A
building that experiences 20 degree days will pass twice as much energy
to the outside (to the inside in cooling) as a building that experiences 10 degree days in the
same time period.
The coefficient of performance (COP) is a measure of a heat
pump’s efficiency. It is determined by dividing the energy output
(cooling will be evaporator input) of the heat pump by the electrical
energy (using the same units for both) needed to run the heat pump
(including the compressor and fan motors), at a specific temperature.
The higher the COP, the more efficient the heat pump. This number is
comparable to the steady-state efficiency of oil and gas furnaces.
The heating seasonal performance factor (HSPF) is a measure (benchmark) of
the total heat output in Btu s of a heat pump over the entire heating
season divided by the total energy in watt hours it uses during that
time. This number is similar to the seasonal efficiency of a fuel-fired
heating system and includes energy for, including all electrical
components such as fan motors and electric supplementary heating.
Weather
data characteristic of long-term climatic conditions are used to
represent the heating season in calculating the HSPF.
The energy efficiency ratio (EER) measures (benchmarks) the
steady state cooling efficiency of a heat pump. It is determined by
dividing the cooling capacity of the heat pump in Btu/h by the
electrical energy input in watts at a specific temperature. The higher
the EER, the more efficient the unit. Note: while EER only measures cooling efficiency it directly relates heating efficiency. See HSPF
The seasonal energy efficiency ratio (SEER) measures
(benchmarks) the cooling efficiency of the heat pump over the entire
cooling season. It is determined by dividing the total Btu s removed
from the conditioned space over the cooling season in by the total
energy used by the heat pump during that time in watt hours. The SEER
is based on a climate with an average summer temperature of 82F. Note:
while SEER only measures cooling efficiency it directly relates heating
efficiency. See HSPF
The thermal balance point is the (outside) temperature at which
the amount of heating provided by the heat pump equals the amount of
heat lost from the house at setpoint. At this point, the heat pump
capacity matches the full heating needs of the house. Below this
temperature (outside), supplementary heat is required from another
source to maintain setpoint.
The economic balance point is the (outside) temperature at which
the cost of heat energy supplied by the heat pump equals the cost of
heat supplied by a supplementary heating system. Below this point, it
is not economical to run the heat pump compared to another heat source.
In most cases the thermal balance point will be reached long before the
economic balance point on a properly working heat pump.
Setpoint The temperature that the indoor thermostat is set to at the time.
Emergency heat Electric or other heat source that is intended to
replace the heat output from a heat pump usually in case of a
malfunction. The emergency heat setting on a thermostat has 2 functions
1: to provide enough heat to bring the building to setpoint. 2: To
prevent further damage to equipment by disabling the compressor.
Auxiliary heat Electric or other heat source that is
intended to supplement the heat output from a heat pump, usually in
case of the outside temperature going below the thermal balance point or to help bring the indoor space to setpoint from a recovery. In order for auxiliary heat to supplement the heat pump it must be managed so as to not use all the available capacity (emergency heat).
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