Page 26 - HVAC Pump Handbook

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Physical Data for HVAC System Design

Physical Data for HVAC System Design 23

system. Ten psig is adequate pressure at the top of most buildings
or water systems.

2.4.5 Velocity of sound in water
The velocity of sound in water is important, as it can indicate the
speed of pressure waves in water systems. The speed of sound in
water is faster than in air (Fig. 2.2). These waves are generated by
manual or automatic valves opening or closing or by pumps being
started or stopped. Also, noisy pumps operating near the shutoff con-
dition or far out on their curve can transmit noise through the con-
nected water system.

2.4.6 Pressure variations in water of a
HVAC system
Figure 2.3 describes the results of a test conducted on a HVAC
chilled water system to determine the variations in differential pres-
sures across coil control valves throughout one day. This figure
demonstrates that HVAC water systems with a number of coil control
valves can be a restless place. This figure indicates the need for prop-
erly designed and sized coil control valves along with adequate con-
trol response.

Figure 2.2 Velocity of sound in water. (From Karassik et al., Pump Handbook, 3rd ed.,
McGraw-Hill, used with permission.)

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