SYS-APM001-EN
Chilled-Water-Control Options
48
Critical valve reset
Often, pumps are controlled to maintain a constant-pressure differential at a
remote coil. Unless this coil serves the zone requiring the most cooling (the
critical zone), the pump provides more pressure than necessary and consumes
more power than necessary. Systems that have integrated air-side and chiller
plant control systems and contain valves with direct digital controls present an
opportunity for further pump operating-cost reduction. If a system is monitored
to determine the critical valve at each point in time, the pump's operating
pressure can be reset so that the critical zone's control valve is nearly open.
Integrated control allows a system-level controller to determine the critical zone
and reset the pump's set point dynamically, therefore reducing pump operating
costs.
The controllers know the position of their individual valves, which modulate to
maintain the required water flow through the coil. The building automation
system continually monitors the valve controllers, looking for the most open
valve. The controller resets the pump set point so that at least one valve, the
one requiring the highest inlet pressure, is nearly wide open. The result is that
the pump generates only enough pressure to get the required water flow
through this "critical" valve, thus saving pumping energy.
Chapter references
1 BSR/ASHRAE/IESNA 90.11999, "Energy standard for buildings except low-
rise residential buildings," Illuminating Engineering Society of North
America and American Society of Heating, Refrigerating and Air-
Conditioning Engineers, Inc., 1999.
Summary :
SYS-APM001-EN Chilled-Water-Control Options 48 Critical valve reset Often, pumps are controlled to maintain a constant-pressure differential at a remote coil. If a system is monitored to determine the critical valve at each point in time, the pump's operating pressure can be reset so that the critical zone's control valve is nearly open.
Tags :
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