Page 258 - HVAC Pump Handbook

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Configuring an HVAC Water System

Configuring an HVAC Water System 255

80
Design point

60

System head—ft. 40 Design flow
2160 GPM

Static head
20

0
0 500 1000 1500 2000 2500
System flow—GPM
Figure 9.5b Actual system head area.

This is elementary manual modeling of a water system. With com-
puters, such system head areas can be developed easily. Without a com-
puter, a simple procedure that works practically is to adjust the distrib-
ution friction at 50 percent water flow, i.e., 11 ft in our model building
at 50 percent load. This variable or distribution friction can be multi-
plied by 20 percent for the lower curve and then by 150 percent for the
upper curve. Drawing curves similar to Fig. 9.5a through these points
will generate an approximate system head area. This system head area
will give designers a rough idea of what the system head area will be,
and it will enable them to predict pump performance within this sys-
tem head area. A further discussion of the operation of pumps with the
system head area will be presented in Chap. 15.
Campus-type installations with a number of buildings, as shown in
Fig. 9.7a, create another dimension in system head areas and system
modeling. As demonstrated in this figure, there are buildings near the
central energy plant and buildings far from it. This figure has two of
our model buildings, building A near the central plant and building B
far from the central plant. It is obvious that the campus loop loss will

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