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OpenStudio Cooling Load is Zero

asked 2021-05-26 14:14:30 -0500

Scott Crowner gravatar image

updated 2021-05-27 12:50:32 -0500

I'm running into this problem with a more complex OpenStudio model, but I've replicated the problem in a simple one-zone model. As far as HVAC goes, all I've done is make an air handling unit with two fans and water coils connected to district heating and district cooling. Its temperature is managed by a scheduled setpoint manager set a constant 12 C. The zone is served by the AHU with a VAV reheat. The zone's cooling setpoint is 21 C and the zone's heating setpoint is 20 C. The model runs, but only shows results for heating; no cooling. Perhaps there is a setting somewhere preventing the building from turning on cooling?

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I would look at the water coil heating and cooling energy variables (COIL SPECIFIC) (look in the .rdd file to find a list of the ones you may need). Check if the water coil cooling energy is 0, since this may indicate that there is no cooling energy from the coil to the air in the air loop. In other words, the water coil is never extracting any heat energy from the air.

The water coil is connected to a plant loop on the demand side, serving an air loop on the supply side to condition air before delivering it to the zone.

sashadf1 gravatar image sashadf1  ( 2021-05-27 08:28:54 -0500 )edit

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answered 2021-06-02 11:17:10 -0500

Scott Crowner gravatar image

Figured it out. I needed to hard-size the input and output air humidity ratios. Otherwise, the system makes a bad assumption and sets the cooling load to zero, as found in the error file.

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answered 2021-05-27 09:37:53 -0500

If you're autosizing the coil parameters, check your EIO file to check the capacity of your cooling coils.

If the capacity of your cooling coil is = 0, then you either have a problem with your zone loads (actual loads like people/lighting and thermostat design temps) or with your sizing parameters (Sizing:Zone/Sizing:System).

If the capacity of your cooling coil is > 0, then you have some sort of operational problem. Is your AHU making setpoint, or is it just blowing hot air because the cooling coil is not coming on?

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Asked: 2021-05-26 14:14:30 -0500

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Last updated: Jun 02