Carrier 50PQ - Manual (Page 2)

The heat pump reverse cycle
controls the weather all year round
The Carrier single package heat pump — compact,
efficient, reliable. It puts the weather to work for you
and lowers operating costs.
Thermodynamically, there is no difference be­
tween a heat pump and an air conditioning unit or
refrigerator. The heat pump moves heat from a colder
heat source to a warmer heat sink thru the vapor
compression cycle. (The same as a refrigerator or air
conditioner.)
The difference, from a practical standpoint, is in
the heat pump's ability to reverse the roles of the
evaporator and condenser coils.
The heat pump takes advantage of the fact that
even cold winter air contains heat that can be
absorbed for heating a building. During cooling
season operation, the unit can be set to reverse the
evaporator and condenser coils, absorbing heat from
inside the building and discharging it outside — like a
standard air conditioner.
The operating cost advantage of the heat pump
occurs primarily during the heating mode. Depending
on outdoor temperature, the heat pump can actually
produce two to three units of heating energy for
every unit of electrical energy it uses.
The heat pump's cost saving reverse cycle prin­
ciple uses refrigerant circulated within a compact,
closed circuit coil to absorb and transfer heat from
one area to another.
The process begins with the evaporator (cooling)
coil absorbing heat from the air around it. The
compressor then pumps the refrigerant to the con­
denser where this heat is then rejected to the
surrounding air.
As shown in the diagram, the heat pump makes
double use of the two coils by means of a reversing
valve. The two coils alternate as evaporator or
condenser, depending on whether cooling or heating
is required.
Heating Cycle — Refrigerant enters ^ outdoor coil
(evaporator) at a lower temperature than the surrounding
outdoor air and heat is absorbed by refrigerant. The
refrigerant then passes thru tiie reversing valve and into the
compressor v^/here it is brouÿrt to a nigit temperature and
pressure. The hot refrigerant ieaves the compressor, fiows
thru the reversing valve to the indoor coil (condenser). Heat
is ihert rejected to the return air from the hot refrigerant as
the return air passes over the irxioorcoii (condenser).
Cooling Cycle — The two cotis exchange roles as evaporator
and coftdenser tftry tite action of the reversing valve.
Althougii reversed, system operation is exactly the same.
Refrigerant enters the evaporator (indoor coil) at a lower
temperature than the return air, heat is absorbed from
indoors, the cocker air is then distributed throughout the
building. Refrigerant ieaves the evaporator, flows thru the
reversing vaive and into tha compressor where it is brought
to a higher teinperature and pressure. The hot refrigerant
gas flows from the compressor^-ftiru the reversing valve and
into the outdoor coil (condenser). The outdoor coii (con­
denser) rejects the heat from the hot refrigerant to the
cooler outdoor air as it passes over t)te coil The heat
transfer cycle is now ready to be repeated.
JL