Refrigeration & Air Conditioning Technology, 8e - 17

Unit 1

17

Heat, Temperature, and Pressure

Photo by Eugene Silberstein

Figure 1.2 Pressure gauge used to measure the system operating
pressures in air-conditioning and refrigeration equipment.

1.2 TEMPERaTURE
Temperature can be thought of as a description of the level of
heat and also may be referred to as heat intensity. Heat level
and heat intensity should not be confused with the amount of
heat, or heat content. As a substance receives more heat, its
molecular motion, and therefore its temperature, increases.
Most people know that the freezing point of water is
32  degrees Fahrenheit (32°F) and that the boiling point is
212  degrees Fahrenheit (212°F), figure  1.3. These points
are commonly indicated on a thermometer, which is an
instrument that measures temperature.
We must clarify the statements that water boils at 212°F
and freezes at 32°F. These temperatures are accurate when
Figure 1.3 The water in the container increases in temperature because
the molecules move faster as heat is applied. When the water temperature reaches 212°F, boiling will occur. The bubbles in the water are small
steam cells that, because they are lighter than water, rise to the top.

2128F

standard atmospheric conditions exist. For example, in
Denver, Colorado, which is about 5,600 miles above sea
level, water boils at about 203°F. At the top of Mt. Everest,
which is about 31,000 feet above sea level, water boils at
about 167°F. Standard conditions occur at sea level with the
barometer reading 29.92  in. Hg (14.696  psia); this topic is
covered in detail later in this unit as part of the discussion of
pressure. It is important to understand the concept of standard conditions because these are the conditions that will be
applied to actual practice later in this book.
Heat theory states that the lowest attainable temperature
is 2460°F. This is the temperature at which all molecular
motion stops and the temperature at which there is no heat
present. This temperature is referred to as absolute zero.
This is a theoretical temperature because molecular motion
has never been totally stopped; scientists have actually come
very close, dropping the temperature in a laboratory setting
to within one-millionth of a degree of absolute zero.
The Fahrenheit temperature scale is part of the English
measurement system used by the United States. This measurement system is also known as the I-P, or inch-pound, system.
The Celsius temperature scale is part of the International
System of Units (SI) or metric system used by most other
countries. Some important Fahrenheit and Celsius equivalent temperatures are provided in figure 1.4. A more detailed
conversion chart can be found in Appendix B of this book.
Figure 1.4 Relationship between Fahrenheit and Celsius temperatures.
TEMPERATURE OF STARS

54,0008F

30,0008C

TUNGSTEN LAMP
TEMPERATURE

5,0008F

2,7608C

BONFIRE TEMPERATURE

2,5008F

1,3708C

MERCURY BOILS

6748F

3578C

AVERAGE OVEN
TEMPERATURE

3508F

1778C

PURE WATER BOILS AT
SEA LEVEL

2128F

1008C

98.68F

378C

BODY TEMPERATURE
WATER

FLAME

PURE WATER FREEZES

ABSOLUTE ZERO
MOLECULAR MOTION STOPS

328F

-4608F

08C

-2738C



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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