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Using a negative temperature in design supply temperature?

asked 2015-03-19 11:29:57 -0500

kcschultz2012 gravatar image

updated 2015-08-11 17:32:07 -0500

We are trying to model a refrigerated/freezer warehouse in OpenStudio/EnergyPlus. We are using the ideal load scenario (Thermal zones section of OpenStudio). When running our model, we get a fatal error that results from the supply air temperature being set below freezing. The error file is listed below.

Has anyone encountered this problem before? Are you aware if we can input the supply temperature as below freezing?

* Warning * IP: Note -- Some missing fields have been filled with defaults. See the audit output file for details.

* Severe * Sizing:Zone="FREEZER", invalid data.
* ~~~ * ... incorrect Zone Cooling Design Supply Air Temperature=[-5.56], value should not be negative.

* Severe * Sizing:Zone="FREEZER", invalid data.
* ~~~ * ... incorrect Zone Heating Design Supply Air Temperature=[-7.78], value should not be negative.

* Fatal * Sizing:Zone: Errors found in getting input. Program terminates.

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Here is a related thread that takes about a default limit of 13C for zone temperature for ideal air loads.

Others who have more experience will know for sure, but you may have to model this as a walk in refrigerator vs. a conditioned thermal zone.

David Goldwasser gravatar image David Goldwasser  ( 2015-03-19 13:44:16 -0500 )edit

The severe error is triggered by not being allowed to set negative values for supply temperatures in the Sizing:Zone objects. The EnergyPlus workaround could be to set "Do zone sizing calculation" in the Simulation Control object to No and than to set negative value in "Minimum Cooling Supply Air Temperature" field in the ZoneHVAC:IdealLoadsAirSystem object.

Ivan Korolija gravatar image Ivan Korolija  ( 2015-03-19 13:47:59 -0500 )edit

The above worked, but is there a good way of going from that updated IDF file back into Open Studio? I tried importing it but all of the schedules and construction sets disappeared, and the only foreseeable thing to do would be to go back and manually add all of the missing schedules. Any other/better ideas?

kcschultz2012 gravatar image kcschultz2012  ( 2015-03-24 20:41:35 -0500 )edit

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answered 2015-03-23 09:32:27 -0500

Archmage gravatar image

See the input object called Refrigeration:Chiller, it is intended for warehouse applications. The usual EnergyPlus air-based models for HVAC are not going to work very well compared to the refrigeration system models that are intended for this applicaiton.

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answered 2015-12-23 02:03:35 -0500

TianZhichao gravatar image

You may set Field: Zone Cooling Design Supply Air Temperature Input Method= TemperatureDifference, then supply air temperature will change automatically and zone temperature can below zero.

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Asked: 2015-03-19 11:29:57 -0500

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Last updated: Aug 11 '15