That's contrary to conventional wisdom when it comes to heat pumps. If your system is right sized, then on cold mornings, it's not going to have a lot of extra capacity to quickly raise the temperature from 58F back to 64F. More of an issue when the outdoor design temperature is 20F or 30F than when it's 40F.
Cheers, Wayne
So yesterday morning, the inside temperature dropped to 59°F and the outside temperature was 37-38°F and the heat pump took about 80 minutes to bring the temperature up to the set point of 64°F. Today, the inside temperature was 61°F and the outside temperature was 48°F and the heat pump took only about 35 minutes to bring the temperature up. Per the performance charts I have on my model, the unit has a capacity of about 18-20% more when it's 48°F out compared to 37-38°F.
I agree that the thermostat controls the auxiliary heat but many systems don't have the option to adjust the tolerances and if you have a proprietary communicating system you loose too much functionality by going with a non-OEM thermostat. If
hh9oolu has 5 zones it is likely he has a communicating system and possibly a variable speed outside unit. But my point to
Ahh9oolu was that he may need to investigate how his system works to see if he is inadvertently kicking in the auxiliary heat.
My Carrier Infinity system has what it calls "Smart" setback. Basically, this means that it starts to ramp up to the new temperature 90 minutes before the time of the new temperature. If the heat pump starts falling behind during the ramp up it will call for auxiliary heat. And the 90 minute ramp isn't adjustable. I found out by trial and error the heat pump could only recover from a 4 degree setback during the colder days of the year before it made a call for auxiliary heat. And once a call for auxiliary heat is made it continues using auxiliary heat until the cycle is complete. So I had to take this into account if wanted to use a setback temperature above my furnace lockout temperature. And if my wife turned up the room temperature by more than 2 degrees it would bump it into auxiliary heating mode. This wasn't adjustable either.
That's pretty bad, and what it sounds like you need is a new thermostat that knows how to "speak" the Carrier Infinity protocol and doesn't do idiotic calls for auxiliary heat when it's not required. But in the long run, there needs to be a standard interface for communicating with variable speed systems. Instead of using a mess of wires that you screw in individually, they should use a 16 pin connector
like this and have all of the signals put in standard places on it. The standard could allow up to 100 different compressor speeds by using just 7 Y wires, Y0-Y6, by signaling the desired compressor operating speed in binary, i.e. 1 = 1% is binary 0000001 so power Y0 and leave Y1-Y6 floating. 50 = 50% = binary 0110010 so power Y5, Y4, and Y1. 100 = 100% = binary 1100100 so power Y7, Y6, and Y2. You could use an 8th pin as an error check/parity bit to make sure that all of the wires are connected and the thermostat/HVAC system should throw an error if it gets a nonsensical value. Since all of the signals run through the air handler, the air handler could intercept the signals coming from the thermostat and set its fan accordingly. Or you could have separate signals for the fan speed (for dehumidification purposes) encoded in the same manner.
And that is the reason why most HVAC installers don't bother with proper load calculations and simply to apply a rule of thumb that tends to oversize equipment by 50-100%, despite the fact that those systems provide less comfort than the right sized system.
Part of the problem is that if you size a system appropriately for winter in Tahoe, or Minnesota, or any extremely cold place, it's going to be grotesquely oversized for cooling especially in those climates. If you size a system appropriately for cooling in Phoenix, it's going to be grotesquely oversized for heating.
That said, I'm hopeful that new variable speed systems get you the best of both worlds - ability to dial down the power during periods of low heating/cooling requirements, but still able to really move the BTUs if necessary.
I don't really have a desire to get a variable speed system or even a multi stage system. These systems are supposed to not cycle which supposedly increases comfort but here in the SF Bay Area, the outdoor temperature often crosses through my indoor set point. Actually if you look at the ASHRAE design temperatures in my area, the 1% temperature for cooling is only 31°C and if you actually designed the system for that, you'd be uncomfortable during heat waves (which is why you turn on the AC to begin with around here). There are often days in July and August where I don't need to use the AC at all. And even during the worst heat waves, the temperature usually goes below my indoor set point of 78°F after around midnight. So after around 9pm or so, even a variable speed system is going to start cycling because a variable speed system can only go down to around 20-30% capacity, and then you're back to where you would have been with a single stage system, only with added complexity and increased maintenance costs if anything goes wrong.