Refrigeration & Air Conditioning Technology, 8e - 42
Section 1 Theory of Heat
Figure 3.7 Power is required to pump water uphill. The same is true for
pumping heat up the temperature scale from a 35°F box temperature to
a 70°F room temperature.
to the outside of the house, just as the household refrigerator
pumps heat from the refrigerator into the kitchen. In addition,
just as heat leaks into the refrigerated compartments in the
refrigerator, heat leaks into the house and must be removed.
The heat is transferred outside by the air-conditioning system.
The cold air in the house is recirculated air. Room air at
approximately 75°F goes into the air-conditioning unit, and
air at approximately 55°F comes out. This is the same air with
some of the heat removed, Figure 3.8.
Figure 3.8 and the following statements illustrate this
concept and are also guidelines to some of the design data
used throughout the air-conditioning field.
1. The outside design temperature is 95°F.
2. The inside design temperature is 75°F.
3. The design cooling coil temperature is 40°F. This coil
transfers heat from the room into the refrigeration system. Notice that with a 75°F room temperature and a
40°F cooling coil temperature, heat will transfer from the
room air into the refrigerant in the coil.
4. The heat transfer makes the air leaving the coil and entering the fan about 55°F. The air exits the fan also at 55°F.
5. The outside coil temperature is 125°F. The coil transfers
heat from the system to the outside air. Notice that when
the outside air temperature is 95°F and the coil temperature is 125°F, heat will be transferred from the system to
the outside air.
Careful examination of Figure 3.8 shows that heat from
the house is transferred into the refrigeration system through
the inside coil and transferred to the outside air from the
Figure 3.8 A window air-conditioning unit.
AT 1258F CAN
GIVE UP HEAT
WALL OF HOUSE
HEAT LEAKS INTO
AIR ENTERS SIDE
OF UNIT AT 958F. 1
COOLING COIL (408F)
ABSORBS HEAT FROM
758F ROOM AIR.
HEAT IS PUMPED TO
THE OUTSIDE COIL.
T AIR IS REJECTED TO THE OUTSIDE.
E OUTDOOR COIL RECEIVES MOST OF
ITS HEAT FROM THE INDOOR COIL
ROUGH THE REFRIGERANT.
HEAT IS TRANSFERRE
TRANSFERRED FROM THE 758F
ROOM AIR INTO THE 4
OVER COIL DROPS
ROOM AIR PASSING O
FROM 758F TO 558F.