Adding a heat pump alongside a natural gas furnace
I recently replaced our 30-year old air conditioner with an air-source heat pump.
It mostly went smoothly, except that I noticed it could only run for six or seven minutes at a time, and it made loud hissing and gurgling sounds as it was about to shutdown. This is known as “short-cycling.” The HVAC company sent out a technician who measured the coolant pressures as the heat pump was operating, and he determined that the pressures were far too high. He had to remove a substantial amount of coolant to bring the pressures into the proper range. He noted that since we have a very short run of copper tubing between our heat pump and HVAC system, even the coolant that came pre-charged in the heat pump may have been excessive. Since he adjusted the pressure, the heat pump has been working well.
Since I kept our high-efficiency natural gas furnace as well, that required me to decide a temperature threshold for switching between the dual fuel options (natural gas and electricity). See https://github.com/mdlemay/heat-pump-analysis/blob/main/heat-pumps.ipynb for more on that.