Electric System: VAV reheat high heating load

asked 2017-12-12 15:16:50 -0500

hoffmann1320
241 ●2 ●7

updated 2017-12-13 08:21:10 -0500

Energy modeling a building that contains a packaged rooftop dx coil electric heat coil with VAV reheat in zone. Currently the Setpoint Manager: Warmest is used in the air loops to supply 55-60 degree are to the zones, and the VAV heat coils condition the air to the thermal zone tstat parameter. I am experiencing high heating loads(about 200k kbtu/yr) and low cooling loads (About 50k kbtu/yr) for the building. Is there a way to reset the SAT in the heating season to be higher so the building is not relying on the VAV box reheat coils to condition the air from 55 to 85-90 degrees.

Attached is the link to the Openstudio model as well as the mechanical spec sheet for the project, only pay attention to the circled tables on the mechanical spec sheet because they are relevant to this part of the site. Any insight into this would be greatly appreciated

https://drive.google.com/drive/folder...

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answered 2017-12-13 05:24:28 -0500

Julien Marrec

29017 ●85 ●74 http://www.effibem.com/

Unless I'm missing something here, the answer is contained in the question.

Change your SetpointManager:Warmest Maximum Setpoint Temperature to allow a higher reset temperature.

Obviously, this looks at the warmest zone... What this means is that you should ensure you don't have a zone or two that are calling for very high cooling loads (a server room for example), which would make the setpoint manager completely unable to drift its temperature back up and defeat the purpose.

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answered 2017-12-19 10:42:05 -0500

kramerica

1070 ●1 ●13 http://ambient-e.com/

You could also manually make a schedule using SetpointManager:Scheduled to have a SAT for winter and another SAT for summer. For instance, if you knew that from 10/15 to 4/15 the SAT was 60 ºF and the rest of the year it was 55 ºF you could do this. Or you could use SetpointManager:OutdoorAirReset if the SAT follows the outdoor temperature, ie over 75 ºF OA then SAT is 55 ºF, 50 ºF OA then SAT 60 ºF.