[Equest-users] FW: Increase in roof insulation increases cooling load.

[Keith Swartz]

Cyrus,

Are the loads you are referring to peak (tons and MBH) or annual consumption (kWh, therms)? If it is annual consumption, then Eric's explanation below makes sense. I have that experienced that in models as well, although the effect is less pronounced with economizer control. But still in those cases the peaks have been less extreme.

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________________________________
From: Eric O'Neill [mailto:elo at MichaelsEngineering.com]
Sent: Friday, December 19, 2008 10:03 AM
To: Cyrus Grimes
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Increase in roof insulation increases cooling load.

Cyrus,

Depending on your internal gains, the increased levels of roofing insulation may make it more difficult for the system to reject the heat. I generally find this response when modeling auditoriums or rooms with high levels of internal gains. The system ends up working overtime to displace the heat that would normally have escaped after the internal loads subsided and/or ambient conditions cooled off. For instance, on a 45 degree day, the building might break even with a high internal gain and low roof insulation, but with the higher roof insulation, the internal gains dominate and cooling is required. It really depends on the scenario, but without more information, I can only say that it's plausible.

Eric
From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Cyrus Grimes
Sent: Friday, December 19, 2008 9:34 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Increase in roof insulation increases cooling load.

In a parametric run the roofing insulation was increased from U= 0.063 to U=0.033. by increasing the thickness of the "Insul Bd 2in (HF-B3)" of the built up roof from 0.28 to 0.64.

In my results the HVAC cooling load increased by 4% and my heating load decreased by 4%. Overall the net change was -1% energy savings.

Is this reasonable?
 Any suggestions?

thanks

                  Cyrus Grimes, LEED(r) AP               .
                    Mechanical Engineer

Corporate Office
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