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NC-2009 EAc1:Optimize Energy Performance

Baseline during unoccupied hours

Hans Wetterlund

Energy Analyst

WSP Sverige

LEEDuser Basic Member

4 thumbs up

September 20, 2013

In an EAp2 appeal we were denied a 87 % cooling energy saving. The reviewer consider it unlighty to have cooling demand during winter during unoccupied hours. However, the Baseline system shall have a supply air temperature of 15.3 degrees C and the return air temperature from the zones are about 20 degrees C. So obviously there is a cooling demand. As baseline has high U values in comparisson with Proposed (heated with radiators, nor air) the cooling savings becomes great. How should I address USGBC about this issue? I have some more building like this coming up and need general arguments. And also, why does the temperature have to be 15.3 degrees during unoccupied hours? Why just not recycle it directly back at an higher temperature (if you have a heating demand)?

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Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Fri, 09/20/2013 - 13:42

I am not aware of any specific requirements for unoccupied temperature settings within Appendix G. The baseline supply airflow is based on a delta T between supply air temperature and occupied space temperature. Unoccupied space temperature setting are typically the same or higher than the occupied setting so the delta is easily maintained. Perhaps I am not understanding your issue?

Hans Wetterlund

Energy Analyst

WSP Sverige

LEEDuser Basic Member

4 thumbs up

Fri, 09/20/2013 - 14:00

Thank you Marcus. It is probably me who have missunderstood the supply air temperature settings and HVAC systems for baseline. We never use recyceled air in our Project systems so I don´t have experiance of these systems. So can you tell me; In Baseline, during unoccupied hours, during heating demand, are any return air beeing cooled before reentering the zones? Or is it as I see most natural, that one just recycle the return air back to the zones and then heat it in the reheat coils

Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Fri, 09/20/2013 - 16:23

What is your baseline system type?

Hans Wetterlund

Energy Analyst

WSP Sverige

LEEDuser Basic Member

4 thumbs up

Mon, 09/23/2013 - 05:26

It´s System 7 - VAV with reheat

Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Mon, 09/23/2013 - 14:57

For a system 7 during unoccupied the outside air is shut down so all of the air is return air. If any of the zones call for cooling during unoccupied (which depends on the unoccupied temperature setting) then the air would be cooled.