Refrigeration & Air Conditioning Technology, 8e - 34

34

Section 1 Theory of Heat

containers. The temperature of the gas is lowered to 80°F.
What is the pressure in the combined containers?
P1 5 50 psig 1 14.696 (atmospheric pressure)
or 64.696 psia
V1 5 20 ft3
T1 5 100°F 1 460°R 5 560°R
P2 5 unknown
V2 5 50 ft3
T2 5 80°F 1 460°R or 540°R
The formula is mathematically rearranged to solve for the
unknown P2.
P2 5
P2 5

P1 3 V1 3 T2
T1 3 V2
64.696 psia 3 20 ft3 3 5408R
5608R 3 50 ft3

P2 5 24.95 psia 2 14.696 (Atmospheric pressure)
5 10.26 psig

2.7 ENERGY
Using energy properly to operate equipment is a major goal
of the HVAC/R industry. Energy in the form of electricity
drives the motors; heat energy from the fossil fuels of natural gas, oil, and coal heats homes and industry. What is this
energy and how is it used?
The only new energy we get is from the sun heating the
earth. Most of the energy we use is converted to usable heat
from something already here (e.g., fossil fuels). This conversion from fuel to heat can be direct or indirect. An example
of direct conversion is a gas furnace, which converts the gas
to usable heat by combustion. The gas is burned in a combustion chamber, and heat from combustion is transferred to circulated air by conduction through the thin steel walls of the
furnace's heat exchanger. The heated air is then distributed
throughout the heated space, Figure 2.9.
Figure 2.9 A high-efficiency furnace with burners on top of the heat
exchanger.

DALTON'S LAW

AIR FILTER

John Dalton, an English mathematics professor, made the
discovery in the early 1800s that the atmosphere is made
up of several different gases. He found that each gas created its own pressure and that the total pressure was the
sum of these individual pressures. Officially called Dalton's
Law of Partial Pressures, Dalton's law states that the total
pressure of a confined mixture of non-reacting (inert)
gases is the sum of the pressures of each of the gases in the
mixture. For example, if one cubic foot of nitrogen and
one cubic foot of oxygen are placed in a closed one cubic
foot container, the pressure on the container will be the
total pressure of the nitrogen as if it were in the container
by itself added to the oxygen pressure in the container by
itself, Figure 2.8.

ELECTRONIC
CONTROL BOARD

SEALED
COMBUSTION
SYSTEM

SECONDARY
CONDENSING
HEAT EXCHANGER

CONDENSING HEAT
EXCHANGER

Figure 2.8 Dalton's law of partial pressures. The total pressure is the sum
of the individual pressures of each gas.

OXYGEN

PRESSURE
GAUGE
(40 psig)

NITROGEN

PRESSURE
GAUGE
(70 psig)

MIXTURE OF OXYGEN
AND NITROGEN

Source: Bryant Heating and Cooling Systems

PRESSURE
GAUGE
(30 psig)



Refrigeration & Air Conditioning Technology, 8e

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

Contents
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Refrigeration & Air Conditioning Technology, 8e - Contents
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