[Equest-users] BEPU space heating calculation

[Paul Riemer]

John,
Internal gains figure into Ben 's approach by choosing a HDD number based on a balance point temperature that is below the actual space set point.
The balance point temperature is a theoretical temperature at which the building does not require heating because the internal gains offset the envelope loads.
To say it accounts for solar gain is a stretch but hey it is just a hand calc.
Ben does not state which HDD base he chose, but there are published values for temps like 55F, 60F, 65F etc.

Ben,
It is good you are checking your results but I would ask do you believe your baseline model?  Try your HDD calc on the your building U rather than the differential.  How does that gas consumption compare to your baseline model heating gas consumption?
Does a different HDD base fit your model better?

If you think your baseline model is okay, when you changed the U did you also change your shading coefficient?   A lower SC would eliminate some passive solar heating.
A daylighting interaction could be another possibility.

You'll figure it out.
Paul Riemer
Dunham



From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of John Aulbach
Sent: Wednesday, August 25, 2010 3:38 PM
To: Ben Pressman; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] BEPU space heating calculation

Ben - dumb question.

How is internal load figuring into this equation? And solar gain from the sun?

I NEVER get an exact U x A x dT savings, as eQuest takes ALL factors into consideration.

John R. Aulbach, PE, CEM
Senior Energy Engineer
________________________________
Partner Energy
1990 E. Grand Avenue, El Segundo, CA 90245
W: 888-826-1216, X254| D: 310-765-7295 | F: 310-817-2745
www.ptrenergy.com<http://www.ptrenergy.com/> | jaulbach at ptrenergy.com<mailto:%7C%20jaulbach at ptrenergy.com>


________________________________
From: Ben Pressman <bpressman at practicalenergy.net>
To: equest-users at lists.onebuilding.org
Sent: Wed, August 25, 2010 1:32:04 PM
Subject: [Equest-users] BEPU space heating calculation

I have a Window Glass EEM run that upgrades the windows in a 1970s school building from single-paned to double-paned, tinted, and argon-filled; a decrease in U-factor from 1.04 to 0.35. The LV-D report shows a decrease in building U-factor from 0.176 to 0.142 which, based on an HDD calculation:

(0.176-0.142)*24hrs*(estimated HDD for my area)*A/eff = 1217 therms

of savings, or 24.7% of the overall energy usage of my baseline model. The BEPU report, however, shows almost no energy savings. How can this be? Is there some way to see what schedule, or number of degree days the calculation in the BEPU is using? Has anyone had this sort of problem?

Thanks,
Ben

-- Ben Pressman
Project Engineer
Practical Energy Solutions
770 E. Market Street, Suite 250
West Chester, PA 19382
ph  610.430.1382
cell  610.733.9518
web  www.practicalenergy.net<http://www.practicalenergy.net/>


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