Anyone know how to create an unloading curve for a residential split system? I was recently asked to do a life cycle cost analysis for an apartment complex owned by a unversity. They wanted me to model three different options. 15 SEER AC with 90% gas furnance, 15 SEER Heat Pump with backup 90% gas furnance, and 19 SEER Heat Pump with backup 95% gas furnance. The 19 SEER unit has the exact same EER number as the 15 SEER unit. The 19 SEER unit has two compressors to get to the higher SEER number. I think the only way to model this is to make a new unloading curve. I called the CDS help line and they understood the problem but couldn't help.