People don't understand them ... the older units do start dropping off as the temps fall ....BUT -- Installers would have them set up with the resistance heat coming on way too early.
Energy is saved when you lower the temp in the heating season or raise the temp in AC season --- not when you do large setbacks. Setbacks force the equipment to run on high if VS -- with the heat pumps the only way to get extra heat is for the resistance to come on.
So you turn down the heat at night .. well --- when the thermostat tells the system to come on the only way it can bring the temp up quickly is to run the aux -- partial or full. That aux is resistance heat and costing 2/3 times more $$. I have seen some set up at 45 cut off -- so the heat pump is not even running when it's 40 degrees.
If you do a set back at night -- and that causes the unit to need aux heat in the morning -- the warm up is costing many times more money vs just letting the system run.
so that's where a "heat pump aware" thermostat comes in.
For example, my go to thermostat is the Honeywell Prestige redlink system. when you hook up a heatpump, it will let you use a setting called "intelligent recovery", which does the following:
aims to be the requested temperature AT the set time, not starting operation at set time
avoids the use of aux heat entirely when coming out of setback
adjusts delivered setback vs requested setback if it can't recover in time (if it's unusually cold outside)
installer set-able aux lockout (thermostat will NOT call for aux heat above X outside temperature) - based on load calculations and system size.
the fuzzy logic uses past performance (it has a downloadable internal datalog) to base it's future behavior on.
the ROI on an expensive thermostat ($400-500 with all the sensors) is sometimes under one month.
That's impressive. Did he have to run a backup heating system like oil or propane? Or is the HP the only heating he has?
the new system is a communicating system, so the backup heat is PWM controlled electric resistance heat. it can do the bulk of the work with the compressor (which has 64 "stages" and "overdrive" (spinning compressor above nameplate rating for cold weather compensation) and provide a comfortable discharge temp by running the aux heat just enough.
The ductless splits/mini splits are a whole different animal, and have been for some time compared to the whole house units.
I still don't think I'd heat my home with a heat pump efficiently compared to my propane fired boiler.
that depends on the price of fuel. in CT, the price per BTU delivered for mid-winter deliveries of propane can be quite high. works great if you can buy in bulk in the summer when there's no demand. my gas price is substantially lower in the summer than it is in the winter. electricity is less variable.
really it all comes down to what is your price per BTU delivered to the home. without doing the math it's just assumptions and fear mongering by vendors.
factors include furnace efficiency (80% or 95%+ furnace?), COP of the heat pump at low temperatures, unnecessary use of aux heat, unnecessary defrost cycles (timer based systems waste substantial energy when the dewpoint is below outdoor coil temps), and so on.
energy waste is another issue entirely (how much heat do you dump out of leaks?).
