Chapter hvac engineering Fundamentals: Part 1 Introduction

349
Figur
e
10.23
P
ackage
heat
pump
cycles.
Equipment: Part 2
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350
Chapter Ten
Figure 10.24
Estimating heating and cooling loads versus outdoor temperature.
Figure 10.25
Heating load versus heat pump capacity.
buildings with 24-h occupancy, solar heat effects should be ignored.
Note that the net heat loss is less than the calculated heat loss be-
cause of internal heat gains due to people, lights, and other sources.
In Fig. 10.25, this net heating load is plotted against the heat pump
capacity from manufacturer’s data as a function of temperature. The
shaded area is the excess of load over capacity, requiring auxiliary
heat. Almost any fuel can be used for auxiliary heat, but electric re-
sistance is the most common.
In a water-to-air package heat pump, a water-to-air heat exchanger
is substituted for the outdoor coil. A central source for heating or cool-
ing the water can then, in effect, provide the auxiliary heat. Systems
of this type are used in apartment houses and hotels to allow maxi-
mum control of the room environment by the occupant. The system
arrangement is shown in Fig. 7.16. The water temperature is con-
trolled at a range of values—perhaps 70 to 85
⬚
F—which is suitable
Equipment: Part 2
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