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Outside Dry bulb Temperature is 32F on Summer Design Day

asked 2019-10-11 17:57:04 -0500

Ranjani gravatar image

updated 2019-10-12 18:34:31 -0500

I am working on a standard office building energy analysis located in Seattle. I am trying to calculate the peak load reduction between Baseline and proposed design. However, looking at the facility component report I see that both buildings are peaking on 8/21 @ 3.40 and 5.00 PM respectively but the outdoor dry bulb temperature is 32F. Seattle weather file shows that the Outdoor DB is 84 F on Peak Summer Day Why is the facility load report show 32F? Does this impact the peak load reduction? Attached are the facility load reports. C:\fakepath\Baseline.JPG C:\fakepath\Proposed.JPG

Thanks for the help.

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It's also strange that the Zone Dry Bulb Temperature is 32F and the Supply Air Temperature is 75F. I would expect these values to be about 75-78F and 55-60F respectively. If you can, it would be helpful to upload the .idf file also.

anchapin gravatar imageanchapin ( 2019-10-14 07:34:22 -0500 )edit

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answered 2019-10-14 10:55:12 -0500

updated 2019-10-14 10:57:42 -0500

32 F = 0 C, which means the outside fields are all zero and the zone values are default conditions as well. My guess is that it is related to this commit that fixes unit conversion for this output table in the E+ 9.2 release.

I'm assuming you're using E+ v9.1 or earlier. Since you requested the output html report in IP units, the conversions and reporting for the load component report happened before it accessed the air loop and facility variables, leaving you with the blank initialized constants (0 values).

Your options are to 1) update to EnergyPlus v9.2 (included in the OpenStudio v2.9.0 release if you are using OS), or 2) keep the EnergyPlus output tables in the default SI units.

Also peak load terminology: Peak load generally refers to design day sizing. If you are looking at peak load in the annual run period, which is what the facility load component summary report does, mention 'peak load during the annual run period' or something to that effect. Otherwise people will assume you are talking about design days.

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answered 2019-10-13 09:19:25 -0500

sspielman gravatar image

That is odd. Are you looking at the .epw weather file or the .ddy design day file? The design day file should be used to calculate peaks.

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Asked: 2019-10-11 17:57:04 -0500

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Last updated: Oct 14