Page 221 - HVAC Pump Handbook

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The Use of Water in HVAC Systems

218 The HVAC World

loads. Motor horsepower is, therefore, a plus for heating loads and is a
deduction when computing the total heating load for a building. It is
an added load on chilled water systems and must be included in the
total cooling load of a building. It is important that we watch for
energy wasters, particularly on chilled water systems. Following is an
evaluation of such mechanical devices that are used on hot and
chilled water systems. Appreciable energy is used to circulate water to
all the terminal units that are on such a system. The HVAC industry
is full of various devices that regulate the flow of water to achieve a
desired flow distribution of hot or chilled water in a building.

Typical energy consumers

1. Balance valves, manual and automatic
2. Pressure-regulating valves
3. Pressure-reducing valves
4. Three-way temperature-control valves
5. Most crossover bridges

The most popular of the preceding are balance valves; many of
them may be installed in a single building. Usually, a manual-type
balance valve has two ports that are used to measure the pressure
loss across the valve. Each manufacturer publishes a table for the
valve that will provide the flow in gallons per minute at the measured
pressure loss.

8.1.4 Energy losses for an element of a
water system
All the calculations and formulas in this chapter are based on electric
motor–driven pumps. Following are calculations that can be used to
determine how much energy is being consumed by any element in or
part of a water system such as a single balance valve on a hot or
chilled water system. This procedure also can be used for pressure-
reducing and pressure-regulating valves, but it may be difficult to
accurately determine the flow through these valves.
The basic formula for computing pump horsepower also computes
the energy loss hP for part of a system such as a balance valve. This
v
formula is as follows, where Q is the flow in gallons per minute
v
through the part of a system being evaluated or for a balance valve;
likewise, H is the loss in feet of head for that part of a system or for a
v
balance valve.

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