I have a SEER 18 heat pump for cooling which can reverse for heating in the winter but it also has a natural gas burner. Based on the installer's advice we set the system to use the heat pump if the outside air is 40F or above and switch to natural gas below 40F.
The problem was that when the power was out the electronics in the system could not communicate with the thermostat in the house. My Nest thermostat literally said there was no system connected. I wish there was some kind of UPS to power those electronics and the blower fan.
There is, an inverter sized for the load with an auto transfer switch attached to a set of 100ah batteries will do what you're looking for. And that is what a UPS is on the inside. They just tend to use terribly small batteries.
Such setups are easy to build if you want it and running a 100-200w blower doesn't require too many batteries either. However, if you need to run a compressor, the number of batteries required to power that for 6hours would start to get cost prohibitive.
This guy has accumulated essentially everything you could want to know about such setups, at any voltage, any reasonable power range, in various applications: backup systems, full off-grid, mobile power.
For a 240v load, there are inverters that output 220v or you can use one inverter to power each hot line, just buy the batteries at the same time from the same manufacturer and ensure they will stay balanced. In your case you could also use a cheaper manual transfer switch if you don't mind going into the closet to flip it when the power goes out.
What model do you have? I currently have a boiler for hydronic baseboards and would like to move to a more all in-one-solution for heating/cooling that is predominantly electric. My goal is to move all my gas appliances to electric with solar but it would be great to have gas backup and gas for those cooler days.
The heat pump will be a 240VAC load. Consumer-level computer UPSes in the US are 120VAC.
The 24VAC transformer for the control circuitry will be on one of the 120VAC legs, but it's likely the installer didn't specifically wire it to allow partial powering of just the transformer and electronics board.
Hm... you might be able to get away with ordering a EU UPS then, those are 240V, you'll have to add a center tap transformer and maybe mess around a bit with it to get it to output 60 Hz (that will only improve efficiency).
I think if you’re just looking to run the fossil fuel equipment from the UPS, you can do it by just ensuring that and all the transformers and controls are on that phase.
That will take an HVAC person who knows who things work rather than just following colors on a wiring diagram. Probably easier and more supportable than trying to import and mod an out of region unit.
I have a SEER 18 heat pump for cooling which can reverse for heating in the winter but it also has a natural gas burner. Based on the installer's advice we set the system to use the heat pump if the outside air is 40F or above and switch to natural gas below 40F.
The problem was that when the power was out the electronics in the system could not communicate with the thermostat in the house. My Nest thermostat literally said there was no system connected. I wish there was some kind of UPS to power those electronics and the blower fan.