Page 226 - HVAC Pump Handbook

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The Use of Water in HVAC Systems

The Use of Water in HVAC Systems 223

If the annual loss to balance valves is 100,000 kW, recognizing
the heating value of this energy is achieved by multiplying
100,000(1 0.284), which gives a net energy loss of 71,600 kW/year.
On hot and chilled water systems, the advent of variable-speed
pumping and digital control has made possible the conversion of
constant-volume systems to variable-volume systems. This is
accomplished through the replacement of three-way control valves
by two-way valves and adjusting of the balance valves to the full-
open position. The procedure included herein for computing energy
losses of balance valves can be used to help determine the energy
savings that could be achieved by installing variable-speed pumps
with proper control, replacing the three-way valves with two-way
valves, and opening the balance valves.

8.2 Efficient Use of Water in HVAC Systems
The preceding discussion points the way to efficient use of water and
pumping energy in HVAC systems. The remainder of this chapter will
be used to develop the load range for a water system and to describe
the various uses of water in these systems.

8.2.1 Load range for a water system
All of this chapter has been devoted to an analysis of energy at
design load or maximum water flow. Unfortunately, in many
instances on actual water systems this is the last part of the analy-
sis. It is of utmost importance that the minimum load as well as the
maximum load be determined for a water system to achieve an accu-
rate consumption of energy. Part-load calculation is a subject of con-
siderable study by the American Society of Heating, Refrigerating,
and Air Conditioning Engineers (ASHRAE). Its Handbook on
Fundamentals describes the “bin” method for computing part-load
system flows. Using the formula for pipe friction, the system heads
can be calculated for these part-load conditions. Likewise, with
proper use of the affinity laws, the energy consumption of the pumps
can be computed from minimum to maximum load. In all the system
evaluations that will be discussed in this book, minimum load will
always be included when computing pumping system performance
and energy consumption.

8.2.2 Energy consumption and water uses in HVAC
The use of the energy consumers, as described in the previous section,
develops a possibility that the water system could have been designed
differently; this would have eliminated the need for their use and

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