Quote:
Originally Posted by jimhoward
You are getting into some fine detail here that I don't know for sure. I don't think the speed it set directly by outside air temperature, I think it is set indirectly by it according to demand. If the thermostat is asking for cooling constantly it will increase the speed. If it asks for cooling less because the house isn't heating up so fast, it will reduce the speed.
Yes, the set point at the thermostat is what you will get regardless of single, multistage or variable speed. Its only a matter of whether the control system is bang-bang (off/on) or proportional.
I think the premise behind multi-stage or variable speed unit is that they are indeed more efficient. To the extent that you are correct then there would be no advantage beyond the ability to zone more easily.
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It is also beneficial for humidity control. On very humid days, the temperature may be at setpoint but the humidity may still be too high.
With single stage control the programming will bring on the heaters which will increase the compressor runtiime and raise your electric bill.
With variable speed it lowers the fan speed so that the air spends more time traveling through the cooling coils increasing the dehumidification rate. The heaters will probably never be used for dehumidification.
In other words:
Enhanced Dehumidification
When temperatures are at their highest outside, once your home is comfortable, it is more energy efficient for the HVAC system to dehumidify the air rather than air conditioning it and decrease the temperature. A variable HVAC option removes up to 400% more moisture than a standard system. This means less cycling, longer run times, and optimized compressor and blower speeds.
Why does variable speed air conditioning make sense?