I’m currently working on a VRF system and am modeling it this way:
· The actual system uses Mitsubishi City Multi VRF units with heat recovery capability. I am not sure if this approach will work for other manufacturers of VRF systems.
· My model uses water source heat pumps (WSHP) for each zone. These should capture the ability of the VRF system to “shift” energy around when some zones are heating while others are cooling. The model is running without error, but I have not addressed the details of the energy portion yet. That part will go similar to the following…
o The WSHP fans will be assigned power (efficiency and pressure rise) to match the VRF fans.
o The WSHP heating and cooling coils will have a “simple” power consumption coefficient. If I can use 0 power, that will be best, since the VRFs don’t use power at each zone except for the fans. If I can’t use 0 due to some E+ restriction, I’ll probably make it equivalent to a COP as high as possible and then report that energy in a Custom Meter and use a Custom Decrement Meter so it can be removed from the total electricity use.
o The WSHPs have a gas boiler with efficiency of 1.0 for supplemental heat and an electric chiller with COP of 1.0 for supplemental cooling. The 1.0 efficiency / COP values are used for simplicity so that energy used by the boiler and chiller is essentially the same as the load.
o I will report the boiler and chiller energy and “post-process” their energy using the manufacturer’s part load efficiency equation. It occurs to me just now that I may be able to apply curve values which mimic the manufacture part load performance and avoid the post processing….
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