Heat pump water heater on exhaust

edit

Hi,

I'd like to model a system based on a heat pump system, using extracted air instead of outside air. The point is to recover the few degrees that are still rejected to the outside, even after going through the ERV.

Then, using a Heat pump water heater, I'd like to set my inlet air to the node after the ERV. Is there any way this is possible in openstudio, with or without a measure, or directly in the idf?

It looks like it could work using the "inlet air mixer fraction schedule" and putting (1-efficiency of heat recovery system), but then it isn't true when by-passing the ERV...

Thanks, JB