Working on a project with MidAmerican Energy here in Iowa. Client has eight heat pump units serving a large retail space. During cold snaps, all units seem to switch to auxiliary heat at the same time, creating huge demand spikes. Last month hit 340kW vs normal 180kW. MidAmerican's demand charge is $15.20/kW so that extra 160kW cost them $2,432. Anyone have suggestions for better staging of heat pump auxiliary heat?
MidAmerican Energy demand charges - heat pump staging
Xcel Energy here in Minneapolis - same issue every winter. The key is adjusting the auxiliary heat lockout temperature on each unit so they don't all switch over at the same outdoor temp. We typically stagger them 2-3 degrees apart. Unit 1 might switch at 25°F, Unit 2 at 22°F, etc. Prevents the simultaneous switchover.
Hank - that's a great idea. Simple but effective. Do you worry about comfort issues in the zones that don't get auxiliary heat as early? I'm thinking if the building load is high and some units are still trying to heat with just the heat pump, those areas might get cold.
We haven't had comfort complaints with a 2-3 degree spread. The heat pumps are still working, just not getting the auxiliary boost immediately. You could also consider zone priority - maybe the main customer areas get aux heat at 25°F while storage or back office areas wait until 20°F. Depends on the building layout and use patterns.