Air Source VRF and Heat Pumps Indoors

[jonathan_vanl]

I am wondering if anyone has successfully developed a way to simulate a design with the "outdoor unit" components of air source VRF and heat pumps operating within a conditioned space.

I work primarily in extreme cold environment design (Winnipeg Manitoba) and it is standard practice to design a rooftop "penthouse" to locate the outdoor units within to allow them to operate in our low temperatures. The penthouses have large thermally broken louvres on the walls to allow for air movement into them in the summer and close up in low temperature. Once the temperature reaches a certain point in the winter, gas fired unit heaters are turned on to temper the space to an optimal value for the COP of the unit.

While some have suggested switching the system to all electric on a separate meter and calculating the energy input separately based on the direct electrical load minus the compressor heat, we would be losing out on the effect of the sheltered space and the heat gain from the building the penthouse shares a wall or floor/ceiling with and the fact that the unit heaters would still only turn on below a certain temperature.

I would hope this would eventually become an option within the ApacheHVAC parameters but likely won't be for a while so I was hoping someone else had also looked into this.

Thanks in advance!

[enerGwizz]

That's a tough one. I'm pretty sure you can't currently do this explicitly in VE. One option that could work, although pretty complicated, would be to run a second model with a modified weather file that represents the temp/humidity conditions of the penthouse space. Since the building loads would be affected, I'd make it a dummy model with a single space. Assign the sensible heat gain/loss from your system to the dummy space. The VRF system serving this space would theoretically meet your load and ambient conditions and should give you a better estimate of energy use. Those results could be applied to your other whole-building model.

This would take some work to dial it in between both models, since there are several variables in play that are impacted by others. However, once you have one working, I'd do some sensitivity studies and figure out an adjustment that you could use for all of these projects.