Water-Source VRF Openstudio

asked 2022-02-02 14:05:16 -0600

Lindsey Gaunt
161 ●2 ●6

updated 2022-02-03 09:46:56 -0600

14155 ●83 ●24 http://bigladdersoftware.com/

I'm using OS application v1.1 to model a water source VRF system serving a multifamily highrise. Each VRF unit is connected to a condenser water loop that operates between 60F and 90F. I've enabled heat recovery so the unit can operated in both heating and cooling mode depending on the zones' needs.

The problem I'm running into is I'm getting a ton of unmet heating hours in every zone served by this system all around the same time of year. The space temperature drops well below the thermostat setpoint but the heating coil doesn't seem to turn on unless the outside air drops below 40F. Only then does the heating coil engage and operate until outside air temp reaches ~55F.

The min and max heating mode operation are set to -4F and 86F and the Performance Curve Output Variables indicate that the coils have available capacity. I've also tried turning the crankcase heater and defrost on and off with no luck. Are there any other variables that are outside air dependent? Or maybe that is just a coincidence that I'm seeing that pattern and something else is controlling the heating operation.

Here's a pic of the current operation: image description

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Comments

1) I would check the manufacturers literature to see if that max OA temp in heating mode is reasonable. 2) If this is a water source VRF then the model should be looking at the inlet water temperature, not the OA temp. Check your results to see if the inlet water temp is high (up around 38C). Maybe the plant has control issues.