[BLDG-SIM] static pressure reset control

Mark Mullins Mmullins at hecenergy.com
Fri Mar 17 05:05:31 PST 2000


In the "real "world" it is important to program the static pressure reset control strategy properly in order to get it to work.  If sp reset is a strategy that reduces the sp setpoint based on the most open VAV damper via an EMS, then it would only take one "rogue" damper that is stuck in the open position to defeat the control.  The damper could get stuck in the open position for a number of reasons:  the damper is simply inoperable and stuck, the temp sensor is reading high, the occupant has cranked down the thermostat, the vav box is undersized and unable to meet the load, etc.  These odds of any of these things happening of course increases as the number of zones increase.

In order to mitigate this effect, I would suggest adding two features to the sp reset controls sequence:
1.  Set a maximum or "not to exceed" sp setpoint.
2.  Base the current sp setpoint on an average of the most open two to four boxes, rather than just one.  This will reduce the effect of the rogue box.  The flaw with this is that if there is in fact no rogue box, then a warm room may become starved.  However, I would argue that if the VAV boxes are sized properly, it will simply take longer to cool the warm space.  If the boxes weren't  sized properly, the room would have been warm w/o sp reset anyway, and the underlying problem should be fixed.  

Mark J. Mullins, PE
Project Engineer
HEC Energy & Design Services, Inc.
24 Prime Parkway
Natick, MA  01760
(800) 325-4432 ext. 1229
mmullins at hecenergy.com


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