Page 18 - HVAC Pump Handbook

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Physical Data for HVAC System Design

Physical Data for HVAC System Design 15

the principal cities. Indoor air quality must be verified as well, both
from a chemical content basis as well as from a temperature basis.
Heat generation in the equipment rooms must be removed by ventila-
tion or mechanical cooling to ensure that the design standards of the
equipment are not exceeded.

2.2.2 Operating pressures
Gauge pressure is the water or steam pressure that is measured by a
gauge on a piece of HVAC equipment. Following is the basic equation
for gauge, absolute, and atmospheric pressures.
psia psig P (2.1)
e
2
where psia absolute pressure, lb/in (psi)
2
psig gauge pressure, lb/in (psi)
2
P atmospheric pressure, lb/in (psi)
e
For example, if a water system is operating at 75 psig pressure at an
altitude of 1000 ft, from Table 2.1, the atmospheric pressure is 14.2
2
lb/in , so the absolute pressure is 89.2 psia.

TABLE 2.1 Variation of Atmospheric Pressure
with Altitude
Average
Average pressure P ,
a
pressure P , ft H O,
e 2
Altitude, ft PSIA up to 85°F
0 14.7 34.0
500 14.4 33.3
1,000 14.2 32.8
1,500 13.9 32.1
2,000 13.7 31.6
2,500 13.4 31.0
3,000 13.2 30.5
4,000 12.7 29.3
5,000 12.2 28.2
6,000 11.8 27.3
7,000 11.3 26.1
8,000 10.9 25.2
9,000 10.5 24.3
10,000 10.1 23.3
15,000 8.3 19.2
20,000 6.7 15.5

SOURCE: Cameron Hydraulic Data, 15th ed., Ingersoll
Rand, Woodcliff Lake, NJ, 1977, p. 7–4; used with per-
mission.

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