EEM neglible change in different Runs

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I am running an EEM wizard where I changing the Roof R-Value from R-42 to R-24.

Here are my results. (almost the same) Am I missing something.
Base Results:
[cid:image001.jpg at 01CE1366.4A1560B0]

EEM with Roof R-24.
[cid:image002.jpg at 01CE1366.4A1560B0]

MICHAEL RAIVA, P.Eng., LEED(r) AP, CCGD(r)

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Is there a plenum zone, while you are also using ducted return?

David

David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP

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Yes I have both a plenum zone and ducted return.

MICHAEL RAIVA, P.Eng., LEED(r) AP, CCGD(r)

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I think the results are probably as eQUEST intended then.

Heat gain would be transferred directly to the conditioned zones if there was no plenum zone, and heat would be transferred to the AHU airstream if the system was plenum return.

With a plenum combined with ducted return, eQUEST is going to model the heat as moving through an insulation value to enter the conditioned spaces, so you will definitely see a diminishing return on roof insulation.

I believe there are some variables to allow a higher percentage of heat transfer through the return ductwork. There probably isn't a lot of insulation value to tweak in terms of allowing heat to conduct from the plenum space into the occupied zone space, although you might review your assumptions in case the heat transfer coefficients might be adjusted to allow more connection between plenum zone and conditioned zone if you think it to be more accurate.

David

David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP

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How many stories does your building have?

Also - you might want to try reducing it down to R 10 or something lower - just to see what the sensitivity is - you might be into diminishing returns for the added insulation.

Vikram Sami, LEED AP BD+C

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