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AHU Supply Air Temperature

asked 2016-02-19 07:26:45 -0500

Dustin gravatar image

Hi all,

I have the Control sequence for this building I am working on and have noticed something that I really have no clue how to implement in my design. I have a portion of it in my model but the other portion is not modelled and I am not even sure if I can model it.

The AHU SAT is initially based off of OAT. Then if the average deviation of space temperature and the space setpoint is big enough, the SAT is then further modified. I have the values for the SAT based on OAT and have implemented that in the model using the OutdoorAirReset Setpoint manager which is working fine. Just I am wondering if there is a way the implement the second portion of the control.

If anyone has any tips they are greatly appreciated.

Thanks

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what kind of system is this exactly? (eg: single zone/multizone, VAV/CV, terminal reheat/no reheat?)

Julien Marrec gravatar image Julien Marrec  ( 2016-02-19 08:44:22 -0500 )edit

Multizone VAV with no reheat. Radiant panels throughout the building supply the majority of the heating load.

Dustin gravatar image Dustin  ( 2016-02-19 09:39:45 -0500 )edit

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answered 2016-02-19 10:25:32 -0500

Without seeing your actual sequence of operation I can't be sure of the intent, but here are my two cents.

I'd say that the SAT being based off of OAT is irrelevant or at least should be, and you can talk to your MEP about it and propose another one.

Given the portion about looking at deviation of space temperature compared to setpoint, that makes me think there will be a BMS/EMS polling information from the spaces throughout the building. In this case, you should reset your discharge temperature so that the warmest zone can be adequately cooled, while minimizing the reheating done by your radiant panels in other zones.

In EnergyPlus, you should use a SetpointManager:Warmest to implement this strategy. The control temperature will be temperature, the strategy "MaximumTemperature", and you need to put in the bounds for discharge temp. The Minimum setpoint temperature is your design temperature for summer/cooling (typically 55F) and the maximum temperature should be the design temperature for winter/heating, whatever that is in your case (80F for example, or 70F maybe if you're sending neutral air and letting the radiant panels do the rest).

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Thanks for that I will have to give it a try.

Dustin gravatar image Dustin  ( 2016-02-19 11:53:37 -0500 )edit

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Asked: 2016-02-19 07:26:45 -0500

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Last updated: Feb 19 '16