[Equest-users] Benefit to modeling duct losses in cold climates?

[Joe Huang]

Chris,

I don't understand your concern.  You say that eQUEST models duct losses in terms of how 
(they) affect unconditioned zones, but isn't that what Plenums are? As far as I know, when 
eQUEST/DOE-2.2 models duct losses, they degrade the HVAC output to the conditioned spaces, 
and add those losses into the Plenum spaces.
Am I missing something here?

Joe

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
yjhuang at whiteboxtechnologies.com
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On 3/24/2015 4:33 PM, Chris Baker wrote:
>
> So I haven’t yet modeled my current project with duct losses.  This is a 13,000 sf 
> building in Alaska (Climate zone 8).
>
> Equest only models duct losses in terms of how it affects unconditioned zones (it does 
> not model duct losses to conditioned areas).
>
> But over the course of an Alaskan winter (October thru March) any duct losses would act 
> to somewhat heat the plenum space.
>
> So would there be a benefit in thermal performance over that period?
>
> Has anyone experimented with this?
>
> This would obviously add an additional load requirement to the air-side systems and the 
> pumps/air systems would obviously use slightly more power
>
> (especially for PSZ systems) to make up for any duct losses.
>
> I think the only potential benefit would be thermal performance but I’m not sure if 
> equest takes into account thermal energy in a plenum (unconditioned space)
>
> when it models the thermal performance of a conditioned space beneath it during the 
> course of 1 model year.
>
>
> If it does, I think the only potential benefits during winter months would be in 
> extremely cold climates like Alaska.
>
> Otherwise you are just adding more heating and power loads on the pumps, fans, etc…  
> Which over the course of 1 year would have an impact.
>
> HOWEVER…
>
> If you model proposed duct losses the same as baseline might there be a greater overall 
> cost savings in proposed model while keeping the baseline ashrae compliant?
>
> ASHRAE (at least the 2013 version) has equations for determining duct losses in the 
> baseline model.
>
> The proposed building would obviously retain the thermal energy more efficiently than 
> the baseline and it might be an overall benefit in cost savings in terms of heating costs
>
> Regardless of how much additional energy is used to make up for the duct losses on the 
> system.
>
> Both models would act to contain the heat expelled by the duct losses but the proposed 
> model would do a better job, basically, than baseline even though the duct losses are 
> the same.
>
> Chris Baker
> CCI CAD Drafter
>
>
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