Refrigeration & Air Conditioning Technology, 8e - 16

unit 1
HeAt, teMPerAture, And PreSSure
O B J E C T I V E S
After studying this unit, you should be able to
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define temperature.
make conversions between the Fahrenheit and Celsius scales.
describe molecular motion at absolute zero.
define the British thermal unit.
describe heat flow between substances of different temperatures.
explain the transfer of heat by conduction, convection, and
radiation.
discuss sensible heat, latent heat, and specific heat.
state atmospheric pressure at sea level and explain why it
varies at different elevations.
describe two types of barometers.
explain psig and psia as they apply to pressure measurements.

✔●HVAC/R technicians are often exposed to very high and very low
temperatures. Be sure to wear gloves and other appropriate pieces of
personal protection equipment (PPE) to reduce the chances of getting injured.
✔●Many fluids that are used by the HVAC/R technicians are under pressure. Be sure to transport all pressure vessels vertically and be sure
they are properly secured.
✔●Make certain that all tanks are properly capped to prevent accidental
releases from the tanks.
✔●Make certain all test instruments are properly calibrated and fully
operational to ensure accurate pressure and temperature readings.

In our industry, accurate temperature readings are very
important because it is based on these temperature readings
that we make decisions regarding system operation. Therefore, it is important to use high-quality thermometers to take
these readings, figure 1.1. It should be noted that the terms
heat and temperature are not the same and cannot be used
interchangeably. The following pages provide more details
regarding heat and temperature.
Another term that must be understood is pressure. We
use the term atmospheric pressure when we refer to weather
conditions. We also refer to pressure when we talk about the
air in the tires of bicycles and cars. Information regarding the
pressures inside air-conditioning and refrigeration systems is
very important to the HVAC/R technician. System operating
pressures, along with various temperature readings, provide
valuable information to the technician that is used to properly evaluate and troubleshoot heating and cooling equipment. System pressures are obtained by using a refrigeration
gauge manifold, figure 1.2.
The terms heat, pressure, and temperature will be a part
of nearly all conversations relating to the HVAC/R industry,
so it's very important to understand them. The sections that
follow provide more insight into these concepts and how
they relate to each other.

Figure 1.1 Thermocouple thermometer used to take accurate temperature readings in heating, air-conditioning, and refrigeration systems.

The term heat can be applied to events in our lives that refer to
our comfort, food, weather, and many other things. How does
cold figure in? Cold is defined simply as the absence of heat.
We say, "It is hot outside" or "The coffee is hot; the ice cream
is cold." In the HVAC/R industry we must truly understand
what heat is and how heat energy moves from one substance
to another as well as between the molecules of a single substance. We use the words hot and cold as relative terms. When
we need to be more specific, we often refer to temperature. If
you are asked how hot it is outside, your answer will likely be
along the lines of "It's 85 degrees outside."

Photo by Eugene Silberstein

1.1 HEaT, TEMPERaTURE,
aND PRESSURE



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
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Refrigeration & Air Conditioning Technology, 8e - Cover4
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