a/c heat pump principles

Created by nirishd 

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49 terms

heating and cooling

a heat pump is a total electric system capable of providing what?

refrigerant

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

evaporator

during the cooling cycle, the indoor coil acts as what?

evaporator

during the cooling cycle, heat is absorbed by what?

accumulator

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?

compression

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?

solenoid

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?

one

check valves permit flow through themselves in how many directions?

unused metering device

the check valves are used to bypass what?

accumulator

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

off

during the defrost cycle, the outdoor fan is turned ______

cold

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?

seer

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?

drops

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?

dirt

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?

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