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cooling design supply air temperature error

asked 2016-02-14 19:17:40 -0500

Coolmint gravatar image

updated 2016-02-15 10:56:45 -0500

Hi everyone, I'm using EnergyPlus. I've designed zones and used unitary system template. I set zone heating setpoint off and zone cooling setpoint for 24C at HVACTemplate:Thermostat (just for cooling and no heating). The error :

* Severe * UpdateZoneSizing: Cooling supply air temperature (calculated) within 2C of zone temperature * ~~~ * ...check zone thermostat set point and design supply air temperatures * ~~~ * ...zone name = L1_GUEST_LOUNGE * ~~~ * ...design sensible cooling load = 49979.41 W * ~~~ * ...thermostat set point temp = 0.000 C * ~~~ * ...zone temperature = 12.927 C * ~~~ * ...supply air temperature = 12.800 C * ~~~ * ...temperature difference = -0.12726 C * ~~~ * ...calculated volume flow rate = 394045.60338 m3/s * ~~~ * ...calculated mass flow rate = 473653.03659 kg/s

When I change cooling design supply air temperature from 12,8C to 34,6C, Its still coming error.

* Severe * UpdateZoneSizing: Cooling supply air temperature (calculated) within 2C of zone temperature * ~~~ * ...check zone thermostat set point and design supply air temperatures * ~~~ * ...zone name = L1_GUEST_LOUNGE * ~~~ * ...design sensible cooling load = 97227.21 W * ~~~ * ...thermostat set point temp = 0.000 C * ~~~ * ...zone temperature = 34.603 C * ~~~ * ...supply air temperature = 34.600 C * ~~~ * ...temperature difference = -2.99108E-003 C * ~~~ * ...calculated volume flow rate = 13529.78784 m3/s * ~~~ * ...calculated mass flow rate = 16263.15594 kg/s

What should I do to fix this error? Please help me. I'm in hurry for my project. Thank you.

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Your gravatar matches your handle. Well done!

__AmirRoth__ gravatar image__AmirRoth__ ( 2016-02-14 20:13:51 -0500 )edit

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answered 2016-02-14 23:08:51 -0500

This error occurs when the calculated cooling supply air temperature is too close to the zone's air temperature (in this case, within 2 deg C). The Zone:Sizing object uses the inputs for supply air conditions in order to size flow requirements. Your two error messages show the change in setting cooling design supply air temp from 12.8 C to 34.6 C, but the thermostat set point temperature is 0 deg C for both! You said that you are using the Template Thermostat object, so I'm guessing something is wrong with that. Some things to check:

  • Did you happen to enter the value 24 on the "Cooling Setpoint Schedule Name" field instead of the "Constant Cooling Setpoint" field?
  • The Template Thermostat object can only be referenced by specific Zone HVAC Template objects. Make sure your unitary system template object matches the list on the Template Thermostat Input / Output Reference page I made a link to above.
  • Make sure that the unitary system template object is connected to the zone L1_GUEST_LOUNGE correctly
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  • I did, I have enter to cooling setpoint schedule name.
    • I think they matched
    • I sure

Would you like to help me to see whats wrong in IDF file? IDF file

Coolmint gravatar imageCoolmint ( 2016-02-15 03:49:42 -0500 )edit

I think the problem is about schedule compact that I have made. What value should I fill below the time in schedule compact? 24 or 1?

Coolmint gravatar imageCoolmint ( 2016-02-15 04:39:10 -0500 )edit
1

Your "Cooling Schedule" that sets cooling setpoint temperature changes values between 0 and 24 on Weekdays and the Summer Design Day, which is the design day used for cooling sizing. Setting cooling setpoint to 0 means that you want the room to be cooled to 0. If you want to have reduced cooling use during specific periods, you should RAISE the setpoint temperature higher than 24 (known as cooling setup temperature). You have already applied an availability schedule to the VAV system template to be off until 08:00, on until 17:00, then off again until 24:00.

Aaron Boranian gravatar imageAaron Boranian ( 2016-02-15 10:39:28 -0500 )edit
1

Had to continue due to character restriction ... For Summer Design Day, the availability schedule should be on the entire day. Likewise, the cooling setpoint temperature for Summer Design Day should be 24 C the entire day. In general, Summer Design Day and Winter Design Day schedules should be constant (applies to setpoints, availability, etc.). After changing '0' to '27' in the "Cooling Schedule" to model 27C setup, your model runs without the errors. You still have errors for a zone without a floor surface and non-convex geometry (affects solar gains of internal surfaces).

Aaron Boranian gravatar imageAaron Boranian ( 2016-02-15 10:54:40 -0500 )edit

Would you like to help me edit my IDF file? I've changed as you suggest but still have this errors :( Thank you so much.

Coolmint gravatar imageCoolmint ( 2016-02-16 21:55:32 -0500 )edit

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Asked: 2016-02-14 19:17:40 -0500

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Last updated: Feb 14 '16