49 terms

a/c heat pump principles

heating and cooling
a heat pump is a total electric system capable of providing what?
the fluid which carries the heat in a heat pump is called?
inside, outside
during the cooling season heat is picked up ________ and dumped ________
outside, inside
during the heating season heat is picked up ________ and dumped ________
reverse cycle air conditioners
heat pumps are also known as?
may not
heat pumps ________ be made from regular air conditioner condensing units
four way or reversing valve
the component that changes the direction of refrigerant flow is what?
condenser or evaporator
a heat pump is either a ___________ depending on the direction of refrigerant flow
during the cooling cycle, the indoor coil acts as what?
during the cooling cycle, heat is absorbed by what?
a low side device for holding excess liquid refrigerant is what?
to protect the compressor from liquid flood-back
what is an accumulator used for?
total heat rejected by the condenser equals the heat absorbed by the evaporator plus the heat of what?
absorb heat from the outside air
as the outdoor temperature drops, so does the heat pumps ability to?
the reversing valve is _______ controlled
suction line and the compressor discharge
the reversing valve connections which do not change are the what?
indoor coil and outdoor coil
the connections which do reverse go where?
check valves
a common method of metering the refrigerant to each coil is to use two metering devices along with two what?
check valves permit flow through themselves in how many directions?
unused metering device
the check valves are used to bypass what?
what becomes most important during the heating cycle when the outdoor coil is being used as an evaporator
heating season, when the compressor is coldest
refrigerant migration to the compressor crankcase during its off-cycle is fastest when?
defrost cycle
during the heating cycle, frost build up can create the need for what?
oil foaming, slugging, hard starting, loss of lubrication
migration is a problem because it can cause?
hot discharge gas
defrosting is accomplished by directing ______ to the outdoor coil
during the defrost cycle, the outdoor fan is turned ______
during the defrost cycle, refrigerant flowing to the indoor coil will be?
supplemental heat is added
to prevent circulation of cold air during the defrost cycle _______
coil/air temp differential, air pressure differential, electronic temp sensing
what are 3 methods for sensing fros build-up?
time/temperature, demand
what are two types of defrost control systems?
turn off the outdoor fan motor and put the reversing valve in the cooling mode
the defrost relays 2 main functions are what?
electric heating elements
the defrost relay also energizes one or more banks of what?
defrost over ride control
length of the defros cycle is usually limited to ten minutes by what?
heat pump efficiency is measured in ______
seasonal energy efficiencty ratio ( tells how efficient a heat pump is at providing heating and cooling)
what is seer?
efficiency and performance of the heat pump drops as the outdoor temperature does what?
supplemental heat must be added
because extremely low temperatures reduce capacity, what must be done in these conditions to provide the necessary heat?
emergency heat
local codes may require _______ in case of heat pump failure
2nd stage heat on the thermostat
the supplementary heaters are controlled by ________ set to kick in 2* above the set point
balance point
the point at which unit capacity equals the buildings heat loss is called what?
manual switch on the thermostat
emergency heat is controlled through the use of what?
locks out the compressor, makes second stage heat first stage, allows all heating elements to be used on a call for heat
energizing the emergency heat system does what 3 things?
lower, higher
restriction of air flow over the indoor coil causes ______ discharge temps in the summer and _____ discharge temps in the winter
low outdoor temps during the heating mode of operation
heat pump compressors must be able to operate at higher compression ratios because of?
breakdown the lubricating oil which results in compressor failure
the high compression ratios, pressures and temps found in heat pump systems are dangerous because they?
the most common cause of restricted air flow over the indoor coil is?
slow fan, improper duct size or duct restrictions, blocked diffuser
what are 3 other causes for insufficient air flow?
compressor can overload or the unit will shutdown on high pressure
what problems can occur when the heat pump is operated in the heat cycle at temps above 65*?
free air circulation and out of the prevailing wind, free drainage of defrosted ice, elevation of the unit above the average winter snow fall
installation of the outdoor heat pump unit requires 3 basic considerations, what are they?