Refrigeration & Air Conditioning Technology, 8e - 40

40

Section 1 Theory of Heat

Figure 3.1 Ice boxes were made of wood at first, then metal. The boxes
were insulated with cork. If a cooling unit were placed where the ice was
located, this would constitute a refrigerator.
DRAIN FOR
MELTED
ELTED ICE

ICE BLOCK

Figure 3.2 The colder air falls out of the refrigerator because it is heavier
than the warmer air located outside. The cooler air is replaced with
warmer air at the top. This is referred to as heat leakage.
WARM AIR REPLACES
THE COLD AIR.

FOOD AT BOTTOM
(COLD AIR FALLS
TO FOOD, HEAT
FROM FOOD RISES.)

COLD AIR FALLS
OUT BECAUSE IT
IS HEAVIER.

did not have a freezer at this time, centralized frozen food
lockers were established so that a family could have its
own locker. Food that is frozen fresh is appealing because
it stays fresh for a longer period of time. Refrigerated and
frozen foods are so common now that most people take
them for granted.

3.2 REFRIGERATION
Refrigeration is the process of removing heat from a place
where it is not wanted and transferring that heat to a place
where it makes little or no difference. In the average household, the room temperature from summer to winter is normally between 70°F and 90°F. The temperature inside the
refrigerator fresh food section should be about 35°F. Heat
flows naturally from a warm level to a cold level. Therefore, heat in the room is trying to flow into the refrigerator;
it does so through the insulated walls, the door when it is
opened, and warm food placed in the refrigerator, Figure 3.2,
Figure 3.3, and Figure 3.4. For this reason, to increase the efficiency of the unit, it is always best to allow food to cool down
to room temperature before placing it in the refrigerator.

3.3 RATING REFRIGERATION
EQUIPMENT
Refrigeration equipment must have a capacity rating system so that equipment made by different manufacturers

Figure 3.3 Heat transfers through the walls into the box by conduction. The walls have insulation, but this does not stop the heat leakage
completely.
HEAT TRANSFERS
THROUGH THE WALLS
AND INSULATION
BECAUSE OF THE
WARMER ROOM
TEMPERATURE OF 708F.

358F

and different models can be compared. The method for
rating refrigeration equipment capacity goes back to the
days of using ice as the source for removing heat. It takes
144 Btu of heat energy to melt 1 lb of ice at 32°F. This same
figure is also used in the capacity rating of refrigeration
equipment.



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
Refrigeration & Air Conditioning Technology, 8e - ii
Refrigeration & Air Conditioning Technology, 8e - iii
Refrigeration & Air Conditioning Technology, 8e - Contents
Refrigeration & Air Conditioning Technology, 8e - v
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