I am a homeowner looking for technical details so I can understand my HVAC system and properly diagnose faulty operation, etc. I am fairly knowledgeable but agree that HVAC DIY is not wise. I am having an 18 SEER Amana R410A split heat pump system installed by an HVAC contractor. This system is comprised of a 4-ton ASZ18 compressor, a White-Rodgers 1F95-1277 T-Stat, and a variable speed AEPF426016 air handler equipped with 20 kW of resistance heat strips (HKR-20CB kit). It’s replacing an 25-year-old Trane heat pump system that provided good service over the years but the Amana 18 SEER unit should provide a significant savings over the approx. 8 SEER unit it’s replacing. I live in the Chicago area where below zero operation occurs several times a year. The Trane compressor ran during all non-emergency heat demand. I was told that this is to prevent “dry” startups on very cold days. It was equipped with a hard start kit and a crankcase heater. I think my electric-energy-electric-utility costs have been relatively competitive with equivalent gas-energy-electric-utility homes in my area.
The new system has 2 stages for both heating and cooling (Y1 and Y2) and up to 4 stages of resistance heat (W1 and maybe W2). The Duel Fuel T-Stat option controls the second stage of auxiliary heat (W2) using an adjustable Outdoor Remote temperature setting but this option cuts off the compressor. The ASZ18 is efficient well below zero versus resistance heat so the compressor should continue to run. From the data I’ve seen for the ASZ18048, pure resistance heat will be more expensive to operate in subzero weather. I will not use this option unless below zero operation is an issue with respect to compressor life or the lifetime warranty on the Copeland compressor. Does this make sense? If not, please explain.
My contractor has explained that the auxiliary resistance heat consists of 4 stages of 5 kW heat strips controlled by time sequencing. As he explained, a T-Stat call for auxiliary heat (W1) will start a progressive process where additional stages of heat strips are energized after every 10 minutes that the T-Stat demand is not satisfied. I have not been able to find a written explanation of this process anywhere and the Amana/Goodman technical support people are not willing to discuss any of this with a lowly homeowner. From the schematics, I see that the heater strips have 2 circuits that can possibly be independently and externally controlled, which corresponds to the T-Stat and air handler terminals (W1 and W2). It’s not clear to me how the time sequencing operates. Is the progression 5, 10, 15, 20 kW? If the heat strips are controlled by W1 only, is the progression 10 then 20 kW (heat strip pairs only)? Would it make sense to use an independent outdoor thermostat to control W1 and/or W2 for subzero operation? Assuming my HVAC system is properly sized, what is the best auxiliary heat setup for my location and equipment? Is there a way to keep the compressor running if T-Stat W2 is used? Thanks for your help!!