Refrigeration & Air Conditioning Technology, 8e - 37

Unit 2 Matter and Energy

Our purpose in discussing these topics is to help you
understand how to use power effectively and to understand
how power companies determine their methods of charging
money for power.

37

Some examples of conversions follow:
1. Converting electric heat rated in kilowatts (kW) to the
equivalent gas or oil heat rated in Btu/h. Suppose that we
want to know the capacity in Btu/h for a 20-kW electric
heater (a kilowatt is 1000 watts).

2.14 ELECTRICAL POWER-
THE WATT

1 kW 5 3413 Btu/h
20 kW 3 3413 Btu/kWh 5 68,260 Btu/h of heat energy

The unit of measurement for electrical power is the watt (W).
This is the unit used by power companies. When you get your
energy bill, you pay for kilowatt hours (kWh), which is the cost
for using 1000 watts of power for one hour. When converted
to electrical energy, 746 watts 5 1 horsepower (1 hp).
Fossil-fuel energy can be compared with electrical energy,
and one form of energy can be converted to the other. There
must be some basis, however, for conversion to make the
comparison. The examples we use to illustrate this will not
take efficiencies for the various fuels into account. Efficiencies of fossil fuels will be discussed in the corresponding
Units of this text.

2. Converting Btu/h to kW. Suppose that a gas or oil furnace has an output capacity of 100,000  Btu/h. Since
3413 Btu/h 5 1 kW, we have
100,000 Btu/h 4 3413 Btu/h/kW 5 29.3 kW
3. In other words, a 29.3-kW electric heating system would
be required to replace the 100,000-Btu/h furnace.
Contact your local utility company for rate comparisons
between different fuels. SAFETY PRECAUTION: Any device
that consumes power, such as an electric motor or gas furnace, is
potentially dangerous. These devices should only be handled or
adjusted by experienced people.●● ●

SUMMARY
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Matter takes up space, has mass, and can be in the form of
a solid, a liquid, or a gas.
The weight of a substance at rest on the earth is proportional to its mass.
Density is the weight of a substance per cubic foot.
Specific gravity is the property used to compare the density
of various substances.
Specific volume is the amount of space a pound of a vapor
or a gas will occupy.
Boyle's law states that the volume of a gas varies inversely
with the absolute pressure, provided the temperature
remains constant.
Charles' law states that at a constant pressure, the volume
of a gas varies directly as to the absolute temperature, and
at a constant volume the pressure of a gas varies directly
with the absolute temperature.

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Dalton's law states that the total pressure of a confined
mixture of non-reactive gases is the sum of the pressures
of each of the gases in the mixture.
Electrical energy and heat energy are two forms of energy
used in the HVAC/R industry.
Fossil fuels are purchased by the unit. Natural gas is metered
by the cubic foot; oil is purchased by the gallon; and coal
is purchased by the ton. Electricity is purchased from the
electric utility company by the kilowatt-hour (kWh).
Work is the amount of force necessary to move an object:
Work 5 Force 3 Distance.
One horsepower is the equivalent of lifting 33,000  lb to a
height of 1 ft in 1 min, or some combination totaling the same.
Watts are a measurement of electrical power. One horsepower equals 746 W.
3.413 Btu/h 5 1 W; 1 kW (1000 W) 5 3413 Btu/h.

REVIEW QUESTIONS
1. Matter is a substance that occupies space and has
A. color.
B. texture.
C. temperature.
D. mass.
2. What are the three states in which matter is commonly
found?
3.
is the term used for water when it is in the
solid state.

4. In what direction does a solid exert force?
5. In what direction does a liquid exert force?
6. Vapor exerts pressure in what direction?
A. Outward
B. Upward
C. Downward
D. All of the above
7. Define density.
8. Define specific gravity.



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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