[Equest-users] Oversizing..AHU or Plant?

[Arunabha Sau]

Thanks Bill. Awesome clarification. I appreciate your time.
So I was wondering, if you oversize the Plant does the AHU get oversized too
by default, in eQuest?
Any thoughts?


Much thanks,
Aru


2011/7/26 Bishop, Bill <wbishop at pathfinder-ea.com>

> Aru,****
>
> ** **
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> I don't think the intention of G3.1.2.2 is met by oversizing only the plant
> and not the systems. The 90.1 User's Manual does not specify what is to be
> oversized either, although it does describe a chiller when discussing the
> differences in equipment sizing between the ECB and PRM:****
>
> "For instance, if a chiller in the proposed building is 50% oversized, then
> the chiller in the budget building is also 50% oversized. However with the
> building performance rating method, equipment in the baseline building is
> oversized by a fixed amount in all cases."****
>
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>
> In eQUEST, setting the system Cool Sizing Ratio to 1.15 and Heat Sizing
> Ratio to 1.25 will also increase the autosized capacities of the plant. I
> believe this is how most Appendix G modelers (including myself) address the
> G3.1.2.2 requirement.****
>
> ** **
>
> Note that you could also achieve the same cooling and heating capacity
> oversizing by setting the overall system Sizing Ratio to 1.15, the Cool
> Sizing ratio to 1.00 and the Heat Sizing Ratio to 1.087. (1.15x1.087≈1.25).
> However, this oversizes the system airflow by 15%, and G3.1.2.8, which
> specifies how design airflow rates are determined, does not mention
> oversizing. I have had models where unmet heating/cooling hours could only
> be reduced sufficiently by increasing the system airflow as a last resort.
> ****
>
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> Regards,****
>
> Bill****
>
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>
> [image: Senior Energy Engineer]****
>
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>
> *From:* equest-users-bounces at lists.onebuilding.org [mailto:
> equest-users-bounces at lists.onebuilding.org] *On Behalf Of *Arunabha Sau
> *Sent:* Monday, July 25, 2011 7:47 PM
> *To:* equest-users at lists.onebuilding.org
> *Subject:* [Equest-users] Oversizing..AHU or Plant?****
>
> ** **
>
> Howdy!****
>
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>
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> So, I just saw a project which has applied its oversizing factors (1.15 for
> cooling and 1.25 for heating) to the plant rather than the air handlers.
>  ASHRAE 90.1 Appendix G page 180, G3.1.2.2 Equipment capacities  does not
> specify where the oversizing should occur.  Have you seen this method used
> before?  Is it an acceptable and accurate way of meeting the baseline
> modeling requirements?****
>
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>
> I appreciate your help.****
>
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> Much thanks,****
>
> Aru****
>
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