Page 25 - HVAC Pump Handbook

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Physical Data for HVAC System Design

22 The Basic Tools

be best to locate an air separator near the suctions of the distribu-
tion pumps with air vents at the high points where the system pres-
sure is the lowest. For heating systems with high supply water tem-
peratures, it may be advisable to add a dip tube and an air vent at
the water discharge from the heater or boiler. These tables also
demonstrate that it is wise to have manual or automatic air vents at
the top of a building where the system pressure is the lowest. A de-
tailed discussion of air removal from HVAC water systems is included
in Chap. 9.

Air solubility and water system pressure. The solubility of air in
water increases appreciably with the pressure on the water system
as can be seen from Table 2.5. Figure 2.1 demonstrates this; 45°F
chilled water can have seven times as much dissolved air at 100 psig
pressure as can a system operating at 0 pressure. It is, therefore,
important that water systems be operated at the lowest possible
pressure without losing pressure at the top of a building or water

Figure 2.1 Solubility of air in water.

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