Do I understand this system correctly?
As I posted earlier I'm looking to install all-new HVAC to replace a 15 year-old York system that is having problems.
I am in St. Louis and am looking at a Trane dual-fuel singl-stage heat pump (probably XR15 or XL15i) mated with an 80% efficiency furnace with a variable-speed fan (e.g TUD2B080AV93?). Installation difficulties make the 90% not very arractive.
So tell me if I understand how a system like this will operate. If my summary below is true how would a two-stage heat pump change the equation?
Here's how I think I understand the system:
1) Around some Temperate Tmax (say, 110 degrees F) the A/C system and fan inside will go full-bore and barely keep up.
2) Cooler than that, but above, say 75 degrees and the A/C will run but the variable-speed fan in side will run slower? This will give good dehumidification when mated with a good thermostat (i.e. Honeywell IAQ).
3) Between 65 or so and the setpoint (around 25 degrees?) the heat pump will supply heat. The variable speed fan mostly runs at low speed. As the temperate drops the fan spends more time on high speed.
4) Below the setpoint the gas switches on. The furnace supplies much hotter air so once again the fan spends a lot of time running on a low-speed fan setting.
5) As the temperature drops below the setpoint the furnace runs more and more on the high fan setting.
6) below that we all freeze to death :)