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Why do I get 'Cooling Design Supply Air Temperature=[25.00]' and 'Heating Design Supply Air Temperature=[20.00]' severe errors? ?

My understanding is that I am setting the heating and cooling temperature setpoints. For instance, if the thermal zone is at 25C or hotter it will cool. My understanding maybe incorrect here.

The error I received in the eplusout.err file is the following:

Cooling Design Supply Air Temperature=[25.00]
**   ~~~   ** This is not allowed.  Please check and revise your input.
** Severe  ** Sizing:Zone="TZ - S6 - FCU 2" has invalid data.
**   ~~~   ** ... incorrect Zone Heating Design Supply Air Temperature=[20.00] is less than Zone Cooling Design Supply Air Temperature=[25.00]
**   ~~~   ** This is not allowed.  Please check and revise your input.
** Severe  ** Sizing:Zone="TZ - S6 - TOILETS" has invalid data.
**   ~~~   ** ... incorrect Zone Heating Design Supply Air Temperature=[20.00] is less than Zone Cooling Design Supply Air Temperature=[25.00]
**   ~~~   ** This is not allowed.  Please check and revise your input.
**  Fatal  ** Sizing:Zone: Errors found in getting input. Program terminates.

How should I resolve this issue? I changed the temperature setpoints but the issue persists.

Mike117's avatar
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Mike117
asked 2024-04-09 01:22:49 -0500
Aaron Boranian's avatar
14.1k
Aaron Boranian
updated 2024-04-09 08:10:56 -0500
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1 Answer

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Heating and cooling design supply air temperatures are not room setpoint temperatures (e.g. for thermal comfort). They are min/max user-set design temperatures required for airflow rate sizing for cooling and/or heating needs (e.g. fan-powered terminal units, or central HVAC). Cooling supply temperatures (e.g. 55F, or 13°C) need to be below desired room summer setpoints (e.g. 77F, or 25°C) in order to be effective. Heating supply temperatures (e.g. 88F, or 31°C) need to be above desired room winter setpoints (68F, or 20°C) to be effective. So heating supply temperatures can't be below cooling supply temperatures.

Zone heating/cooling setpoints are set through schedules.

Denis Bourgeois's avatar
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Denis Bourgeois
answered 2024-04-09 06:09:16 -0500, updated 2024-04-09 06:13:42 -0500
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Ah! I understand my error now. Thank you very much.

Mike117's avatar Mike117 (2024-04-09 11:57:27 -0500) edit
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