Cooling coil of Unitary System doesn't follow setpoint

asked 2023-03-09 09:11:05 -0500

Bárbara Torregrosa's avatar

updated 2023-03-09 09:52:35 -0500

Hello. I built an idf file in energyplus v22.2 to simulate a cooling-only central VAV system with two boxes with reheat.

I have two versions of the VAV system:

(1) One is inspired in the VAV System template with SetPointManager:Warmest. I used a Single Speed DX cooling coil. This file works as expected.

(2) The second one is very similar, but I used a AirLoopHVAC:UnitarySystem with control type=Setpoint, instead of the Fan+CoilSystem configuration from the VAV template.

The idf files can be downloaded here

The problem is that in the second file with the Unitary System, the cooling coil turns on at full speed in winter, when there's no cooling load. However, in the first file, the cooling coil remains switched off, as expected. The thermostat settings and the setpoint managers are the same in both files.

I have used the Unitary System configuration with VAV boxes successfully with central cooling and heating coils and setpoint managers Warmest-Coldest. But when I try to simulate a cooling-only system, I get these weird results.

I would appreciatte very much if anyone could tell me how to configure the Unitary System correctly for central cooling only, with variable volume fan and setpoint control type. Or maybe this configuration is just not possible. Thank you.

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