December 16, 2019

Lennox 10HPB18 Service Application Manual SAM Section 18 HEAT PUMP

Lennox 10HPB18 Service Application Manual SAM Section 18 HEAT PUMP - page 1

Service Application Manual 

SAM Chapter 620-56A 

Section 18 

 

HEAT PUMP REVERSING VALVE APPLICATION 

By: V. V. Solomon 

Mgr. Ed./Training 

Emerson Electric Company 

Alco Controls Division 

 

INTRODUCTION 

When the Arab nations cut back on oil exports (late 1973), it became apparent to the free world what 

scientists had known for years, i.e., that fossil fuels will eventually be depleted and thus energy-saving 

devices must be put into use immediately, and new sources of energy be made available as soon as 

possible. 

To this end the Refrigeration and Air Conditioning Industry came forth immediately and informed the 

Federal Government that they had one such energy saving machine! The "Heat Pump" was then 

described as a device that could under certain conditions deliver 3 times as much heat energy as it took 

to operate itself. This is in contrast to a modern hot air gas-fired furnace which under the best of 

conditions will deliver only 7/10 or 70% of a heat energy unit for each one unit expended to operate itself. 

With the blessing of the various energy conservation agencies (Federal Government) and a growth factor 

of 200-300% reported each year by heat pump manufacturers there is no doubt of an immediate demand 

for competent service engineers as there is not enough to keep up with the accelerated growth pattern. 

Let us now look into the heart of a reverse cycle heat pump system and observe the one main difference 

in hardware between it and a conventional air conditioner. The term "Heat Pump" can be applied to any 

refrigeration system since the basic function of a refrigeration system, is the transfer (pumping) of heat 

from one medium to another. Figure 1 shows a basic compression refrigeration cycle, consisting of a 

compressor (a "pump") two heat exchangers (condenser and evaporator) and an expansion device. After 

the low pressure gas returns from the evaporator, it is "pumped" by the compressor to a high level of 

pressure and temperature. As it flows through the first heat exchanger (condenser), it is condensed to a 

liquid under high pressure by rejecting heat through the condenser to the surrounding medium, which, for 

example, may be air or water. The high pressure liquid then flows through the expansion device, 

expanding it to a mixture of liquid and vapor at a low pressure and temperature. This mixture flowing 

Through the second heat exchanger (evaporator) and absorbing heat from its surrounding medium is 

evaporated to a low pressure gas. Finally, the low pressure gas returns to the pump, and the cycle is 

repeated. Thus, the system transfers heat from one medium to another. 

 

Basic compression refrigeration cycle 

1

 

 




Service Application Manual  SAM Chapter 620-56A  Section 18    HEAT PUMP REVERSING VALVE APPLICATION  By: V. V. Solomon  Mgr. Ed./Training  Emerson Electric Company  Alco Controls Division    INTRODUCTION  When the Arab nations cut back on oil exports (late 1973), it became apparent to the free world what  scientists had known for years, i.e., that fossil fuels will eventually be depleted and thus energy-saving  devices must be put into use immediately, and new sources of energy be made available as soon as  possible.  To this end the Refrigeration and Air Conditioning Industry came forth immediately and informed the  Federal Government that they had one such energy saving machine! The “Heat Pump” was then  described as a device that could under

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