This is the Canadian Zuba Central Air-to-Air heat pump made by Mitsubishi Electric. Its based off the same technology as City Multi, and can heat with COPs over 1.0 at -30C (-22F). The design day for the area of the install is -18C (0F), and the unit is supposed to have a COP over 1.8 at that temp.
This install is a small cottage, the existing heating source was electric baseboard heaters and this was a full retro with full new metal. HL calc came out at 36,000 BTU, and the 3 ton Mitsubishi unit puts out 40,000 BTU in heating. The heat pump should be able to carry 100% load without the electric backup heater ever firing.
All the bends were done with a tubing bender, there are 3 welds on the whole system.
So how cold will this unit actually run down to and still produce heat?
If you can not do it right, Why even do it at all?
The heat pump should be able to carry 100% load without the electric backup heater ever firing.
Did you calculate the balance point to make that determination?
How do you mean? There is no need for a balance point calculation with a 1.8 heat pump COP vs. the 1.0 COP of electricity. 1.8>1.0.
The heat loss matches the heat output of the unit. On a design day, the heat pump should run all day, and that is ideal. The electric heater is just a 100% capacity redundant heat source. I actually have the Em. Heat locked out through the Honeywell VisionPro thermostat to not fire unless the temperature drops below -15C (5F).