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

[Carol Gardner]

But what about the case where you can't input the over-sizing in the systems
side because all the necessary inputs are grayed out?

On Tue, Jul 26, 2011 at 2:17 PM, Bruce Easterbrook <bruce5 at bellnet.ca>wrote:

>  No.  Your over sizing will carry from the terminal units to the plant but
> not the other way around.  Note Bills note about the system variance.  This
> will also apply to the plant.  It is a little awkward though and over sizes
> everything.
> Bruce
>
> On 26/07/2011 02:11 PM, Arunabha Sau wrote:
>
> 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,
>>
>>
>>
>> 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.”
>>
>>
>>
>> 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.
>>
>>
>>
>> Regards,
>>
>> Bill
>>
>>
>>
>> [image: Senior Energy Engineer]
>>
>>
>>
>> *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!
>>
>>
>>
>>
>>
>> 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?
>>
>>
>>
>> I appreciate your help.
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> Much thanks,
>>
>> Aru
>>
>
>
>
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-- 
Carol Gardner PE
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