I'm modeling a ground loop heat exchanger to provide condenser water to a large water-to-water heat pump which will be capable of providing simultaneous heating and chilled water to AHU coils in the building. The Water-to-water Heat Pump being designed around is similar to that manufactured by Multistack, Heat-Harvester, Climacool, etc.

I've successfully created a 2-pipe water loop with a water-to-water heat pump that gets its' condenser water from a ground loop heat exchanger (lake/well). When assigned to Fan Coils in the building this system appears to work just fine. However, no simultaneous heating/cooling capability.

So, I've now added a chilled water loop with a second water-to-water heat pump that gets its' condenser water from a seperate ground loop heat exchanger. I then assigned the cooling coils to the chilled water loop and the heating coils to the 2-pipe water loop. Trouble is I get the error that reads, "the chilled water loop has no load". If I manage to get this error to go away then my zones have 5,000 + hours of unmet heating loads.

I've been searching the archives and I see that this has come up several times but with no real solution other than "it should be able to be done". I'm posting the question again in hopes that someone who has successfully modeled this system can point the rest of us in the right direction. This type of system is coming up more and more (I have 4 projects considering them now) and as we strive toward greater building efficiency we are going to HAVE to be able to successfully model these system types.

Tim Dion, LEED(r) AP