Refrigeration & Air Conditioning Technology, 8e - 41

41

Unit 3 Refrigeration and Refrigerants
Figure 3.4 Warm food that is placed in the refrigerator adds heat to the
refrigerator and is also considered heat leakage. This added heat has to be
removed or the temperature inside the refrigerator will rise.

WARM FOOD

The term for this capacity rating is the ton. One ton of
refrigeration is the amount of heat required to melt 1 ton of ice
in a 24-hour period. Previously, we saw that it takes 144 Btu
of heat to melt 1 lb of ice. It would then take 2000 times that
much heat to melt a ton of ice (2000 lb 5 1 ton):
144 Btu/lb 3 2000 lb 5 288,000 Btu
When this is accomplished in a 24-hour period, it is known
as 1 ton of refrigeration. The same rules apply when removing heat from a substance. For example, an air conditioner
that has a 1-ton capacity will remove 288,000 Btu/24 h, or
12,000  Btu/h (288,000 4 24 5 12,000), or 200  Btu/min
(12,000 4 60 5 200), Figure 3.5.
Figure 3.5 Ice requires 144 Btu/lb to melt. Melting 1 ton of ice requires
288,000 Btu (2000 lb 3 144 Btu/lb 5 288,000 Btu).
WARM AIR

3.4 THE REFRIGERATION
PROCESS
The components of the refrigerator have to pump the heat
up the temperature scale from the 35°F or 0°F refrigeration
compartments to the 70°F room, Figure 3.6. Heat leaking into
the refrigerator raises the air temperature inside but does not
normally raise the temperature of the food an appreciable
amount. If it did, the food would spoil. When the temperature
inside the refrigerator rises to a predetermined level, the refrigeration system comes on and pumps the heat out.
The process of pumping heat out of the refrigerator could
be compared to pumping water from a valley to the top of a
hill. It takes just as much energy to pump water up the hill as
it does to carry it. A water pump with a motor accomplishes
the work. If, for instance, a gasoline engine were driving the
pump, the gasoline would be burned and converted to work
energy. An electric motor uses electric power as work energy,
Figure 3.7. Refrigeration is the process of moving heat from
an area of lower temperature into an area or medium of higher
temperature. This takes energy that must be purchased.
The following example uses a residential window airconditioning system to explain the basics of refrigeration.
Residential air-conditioning, whether a window unit or a
central system, is considered to be high-temperature refrigeration and is used for comfort cooling.
The refrigeration concepts utilized in the residential air
conditioner are the same as those in the household refrigerator. The air conditioner pumps the heat from inside the house
Figure 3.6 Heat that leaks into the refrigerator from any source must be
removed by the refrigerator's heat-pumping mechanism. The heat has to
be pumped from the cool, 35°F interior of the refrigerator to the warmer,
70°F air in the room in which the refrigerator is located.
REFRIGERATOR'S
COMPONENTS PUMP
OUT.
THE HEAT OUT
HEAT
AT
LEAKING
AKING IN

COOL AIR

1 TON OF ICE
(2000 LB)

REFRIGERATOR'S
REFRIGERA
HEAT-PUMPING
MECHANISM



Refrigeration & Air Conditioning Technology, 8e

Table of Contents for the Digital Edition of Refrigeration & Air Conditioning Technology, 8e

Contents
Refrigeration & Air Conditioning Technology, 8e - Cover1
Refrigeration & Air Conditioning Technology, 8e - Cover2
Refrigeration & Air Conditioning Technology, 8e - i
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Refrigeration & Air Conditioning Technology, 8e - Contents
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