Page 276 - HVAC Pump Handbook

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Source: HVAC Pump Handbook

Chapter
10

Basics of Pump

Application for HVAC Systems

10.1 Introduction
The configuration of a hot or chilled water system was emphasized in
Chap. 9 to achieve the desired heating or cooling with a minimum of
flow and head. This chapter undertakes evaluation of the pumps
themselves to achieve optimal energy consumption for the pumps. It
was necessary for the readers to have a basic understanding of HVAC
water systems before initiating this application of pumps.
Before embarking on the actual application of pumps to HVAC
water systems, there should be a discussion of when to use constant-
speed pumps and when to use variable-speed pumps. With the rapid
reduction in the cost of variable-speed drives, there is almost no limit,
in terms of motor size, for the use of variable-speed pumps. Very low
head pumps, i.e., less than 50 ft, can still be constant-speed pumps
when applied to small systems. Otherwise, the rule should be constant-
speed pumps for constant-volume systems and variable-speed pumps
for variable-volume systems.
If a water system has a large variation in its flow, from less than 50
to 100 percent of design, it is probably a candidate for variable speed.
Likewise, if the flow rarely changes and there is little variation in
temperature or viscosity, this is a constant-speed pump application.
As was pointed out elsewhere, variable-speed pumping offers great
savings in maintenance as well as in energy. Further, variable-speed
pumps, if controlled properly, operate at the system’s flow and head
requirements, not necessarily at the design conditions. They eliminate
overpressuring, which causes operational problems as well as loss of
pumping energy.

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