Low temperatures modelling heat pump with source terms
 

I am trying to model an air source heat pump acting as a heat sink for a residential building application. As a very simplified model, I created a box shaped fluid zone and adjusted the source terms (not a porous zone). The heat pump has a capacity of approximately 4kW. The pump performs as I expect but in the fluid zone representing the heat pump I get very low localized air temperatures, down to -10C or lower, while the air outside this region is closer to ambient (20C) temperatures.

Just trying to get a sense if this is reasonable or not.

Thanks,
-ian