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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