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

[Eric O'Neill]

Cyrus,

 

I would suggest doing some basic verification. ASHRAE fundamentals has a
few chapters with a lot of good info on heating and cooling loads that
you can serve as a double check. I wouldn't suggest just accepting the
results on blind faith. There are quite a few inputs to a model, and
although sometimes things can be mentally justified (like what I did in
my previous response), they aren't necessarily theoretically justified
(if you have an economizer, then my example makes no sense). Do some
hand calculations, and make some predictions and test and verify various
settings. I would also suggest doing some hourly reports for both
simulations, and lining up the 8760 data next to each other and see if
the corresponding discrepancies between the simulated insulation
differences line up when you would expect them to.  

 

In terms of selecting an insulation value through eQuest, I would be
careful about the validity of that sort of prediction. The model is only
as good as your inputs. The simulations should be used as a reasonable
estimate for the savings of a specific ECM, however, using it to
identify a peak savings value seems contrary to what energy modeling
should be used for. Appendix G states (under G1.2 note 2) "Neither the
proposed building performance nor the baseline building performance are
predictions of actual energy consumption or costs". I think the
intention of this is to say we should be using the energy model to give
us an analysis of certain measures, but should not be used as a design
tool.

 

Also, make sure your utility rates are set up properly. If there is peak
demand savings on a ratcheted utility rate for the higher insulation, it
might use more total energy, but if your demand is high enough, the
bills could potentially be lower (which is how LEED EAcr1 judges the
effectiveness of the measures). 

 

Eric 

From: Cyrus Grimes [mailto:cgrimes at dynamix-ltd.com] 
Sent: Friday, December 19, 2008 10:15 AM
To: Eric O'Neill
Cc: equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Increase in roof insulation increases
cooling load.

 

This is a school and 70% of the rooms have about 25 kids. I was
skeptical at first I guess I will concede. I just don't have the
confidence in Equest yet. I guess I can play around with the insulation
and fin the preferred insulative value for the roof, do you suppose such
a prediction would be valid?

 

               Cyrus Grimes, LEED(r) AP               .     

                    Mechanical Engineer

Phone (614) 443-1178 ext. 274

 

From: Eric O'Neill [mailto:elo at MichaelsEngineering.com] 
Sent: Friday, December 19, 2008 11:03 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

1108 City Park Avenue, 3rd Floor

Columbus, Ohio 43206

 

Phone (614) 443-1178 ext. 274

Fax: (614) 443-1594

e-mail: cgrimes at dynamix-ltd.com

 

 www.dynamix-ltd.com

P Please consider the environment before printing this e-mail note

 

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