[Equest-users] BEPU space heating calculation

Carol Gardner cmg750 at gmail.com
Thu Aug 26 05:38:53 PDT 2010


Let me take a crack at this. What John is saying is that eQUEST takes into
consideration all building components and their interactions. You can't just
pull out one and ask hey why doesn't this match my hand calc? In fact, if
you want eQUEST to match a hand calc, you shouldn't be using it: use the
hand calc.

Carol

On Wed, Aug 25, 2010 at 2:04 PM, Paul Riemer <Paul.Riemer at dunhameng.com>wrote:

>  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 | jaulbach at ptrenergy.com <%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
>
>
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-- 
Carol Gardner PE
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