Page 275 - HVAC Pump Handbook

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Configuring an HVAC Water System

272 The HVAC World

Valve position indicator-
transmitter
To pump speed
control
From pumps

To pump ∆P
speed control T
To pumps

Set point is adjusted by Air-handling
valve position to hold unit coil
valve to 80 to 85% open
Figure 9.15 Valve position control on air-handling unit coil.

the heat exchange is adjusted so that the control valve is always 80 to
85 percent open. For example, if the set point is 20 ft at design load, it
may be only 5 ft at minimum load. Not only is friction loss reduced
through the control valve, but the constant pressure established for
the system is reduced by the lower set point. Similar control can be
utilized on large air-handling units, Fig. 9.15, where high set points
such as 35 ft are required for them, and only 15 ft is required for the
other coils. The set point for the large air handler may be down near
the 15 ft for other coils much of the time when part-load conditions
exist on the air-handling unit.

9.11 Bibliography
James B. Rishel, Variable Water Volume Is Hydro-Electronics, SYSTECON, Inc., West
Chester, Ohio, 1982.
James B. Rishel, The Water Management Manual, SYSTECON, Inc., West Chester,
Ohio, 1992.
James B. Rishel, “Simplifying Contemporary HVAC PIPING,” ASHRAE JOURNAL,
Vol. 47, No.2, pp.16–25, FEBRUARY 2005.

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