Page 228 - HVAC Pump Handbook

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The Use of Water in HVAC Systems

The Use of Water in HVAC Systems 225

The efficiency of boilers and chillers should not be compromised in
an effort to save pumping energy. Here lies one of the major responsi-
bilities of the water system designer, who must evaluate various con-
nections and pumping arrangements to acquire the optimal configu-
ration for a particular system.

Zone 2: Transportation of energy. Once the hot or chilled water has been
generated, it must be moved out to the heating or cooling coils. Com-
bining the pumps for this transportation with the pumps for the boil-
ers or chillers may or may not improve the efficiency of the entire
water system.
Often, the most efficient system of delivering the water to the end
uses is to develop the transportation pumps strictly for the purpose of
distributing the water and not to generate the energy. A number of
different pumping and piping arrangements are provided herein to
assist the designer in selecting the most efficient system for a particu-
lar water system.

Zone 3: Use of the energy. Water in hot and chilled water systems is
used by hot and chilled water coils, heat exchangers, and process
equipment. Most of these energy users are equipped with a control
valve to regulate the flow of water through them.
Some coils are operated without control valves and are called “wild”
coils. They are often equipped with face and bypass dampers that con-
trol the use of energy by them. The water flows continuously through
the coil, and the air flows around the coil on low heating or cooling
loads. Wild coils should not be used on systems with high pumping
heads and broad load ranges due to the pumping energy wasted by
them. Some designers use these coils on outside makeup air to pre-
vent freezing in the coil. There are other methods to prevent freezing
besides wild coils that control the flow and therefore conserve pumping
energy. The other problem with these uncontrolled coils is the return of
the water unused to the boilers and chillers. This raises the return
water temperature on hot water systems and lowers the return water
temperature on chilled water systems.
Much will be made of different coil connections to develop the effi-
ciencies or inefficiencies of the various systems that are used in
HVAC systems today. It is obvious that the three-way valve on a heat-
ing or cooling coil is a wasteful device like the wild coil with a face
and bypass damper. Water is bypassed around the coil and returned
to the boiler or chiller unused.
Sizing of coils from a standpoint of water friction loss is becoming a
very detailed task. From a standpoint of pumping energy, if the coil is
sized with too great a friction drop, energy is wasted. If the coil is

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