Reset Based on Return Air- Equest

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I am trying to model existing building with Constant Volume Dual Duct (CVDD)
with ECONOMIZER. Currently building uses Siemens controller. Controller
resets mixed air, hot deck and cold deck supply air temperature based on
return air. I was wondering if it is possible to reset in E-quest based on
return air temperature instead of outside air temperature. E-quest allows me
to do the reset based on outside air. Has anyone modeled reset based on
return air temperature. If yes, can you please help me or give me
suggestions. Is it possible to have some kind of source code and then import
into E-quest? Thank you for your time and help.


Amol Mehta

Amol Mehta's picture
Joined: 2011-09-30
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I haven't run into an existing situation with SAT reset based on RAT, but I
always wondered how it could work. Such a reset should require a
proportional offset--a deviation from zone temperature setpoint--to reset
the SAT. Why implement a control that, in the absence of significant heat
gains or losses in the return air path, requires a deviation from setpoint
to have an impact?

Prompted by your inquiry, I did some quick on-line research, and it appears
my concern was warranted. This paper covers the topic quite well.

While it doesn't address the question about how to model a reset based on
RAT, the paper describes the issues with such a reset and concludes that an
OAT or hybrid reset is preferred.

William E. Koran, P.E.

Bill2's picture
Joined: 2011-09-30
Reputation: 0