Rooftop Heat Pump Lockout Strategy (or lack of)

[Pirate1]

I touched upon this briefly when I installed a heat pump. After using it for a bit, I decided to revisit the instructions. Anyone have an idea of why they use the "strikeout" method? I don't know why it hurts to leave the heat pump run all night if it is keeping the temp at the set point. By reading this, if it doesn't exceed it and shut off, it will cause a strike? Huh? I am pretty sure my heat pump ran continuous one night but it kept the set temp right where it should have been.

http://www.rvcomfort.com/rvp/pdf_documents/t_stat_electric_heat_function.pdf

[dougrainer]

RVP has that 5 degree separation point. WHAT the system does is this. Once the system reaches your set point, the HP should be able to maintain that set temp without having a 5 degree or more drop. IF the outside temp and conditions are such that the inside of the RV drops more than that 5 degrees or ANYTHING that causes a more than 5 degree drop and this means even if the HP is on but the inside temp cannot be raised before the inside temp goes past that 5 degree threshold, the Furnace (or Aqua hot) will assist the HP. If the conditions are such that this happens so many times, the system determines that the HP is futile and the furnace (or Aqua hot) needs to be the primary heater, until those conditions change. In almost ALL circumstances, above 35 degrees, that strike rule will never happen. Doug

PS, Kudo's, somebody ACTUALLY read the instruction manual:B

[Jframpey]

Pirate wrote:
My home honeywell thermostat is set up for ac, heatpump, and emerg. heat. I wonder if it would consider the gas furnace as emerg. heat? I may investigate a new thermostat. Besides, my honeywell thermostat has a recirc mode and auto switches (2 deg separation of course) between heat and cool as needed.

https://customer.honeywell.com/en-US/pages/product.aspx?cat=HonECC%20Catalog&pid=TH8320U1008/U

Their are new thermostats that can be setup to use your gas furnace as the "emergency heat" making your system a "duel fuel" heat pump. These are the new popular systems and are considerably more efficient that electric resistance heaters.

The new thermostats can monitor the outside temperature and switch to the gas furnace when temperatures drop below the efficient heat pump temps.

[Jframpey]

And, as the outside temps drop, the heat pump becomes less efficient - at some point (30 F?) it can no longer extract enough heat to maintain the inside temps. It runs continuously! Blowing cool air. Brrrr. Better to have the electric strips or propane come on for 10 minutes and warm everything up.

[Pirate1]

Ductape wrote:
When you are pumping heat in, the inside coils are warmed and so the outside coils are being chilled. Running continuously in low temps the outside coils can freeze and ice up.

More sophisticated systems like the one we have at home monitor the outdoor coil temperature and will periodically defrost. The strikeout or timeout strategies are less sophisticated methods employed to keep your unit from turning into an ice block and self-destructing.

Ok, that makes sense. Thanks.

[Ductape]

When you are pumping heat in, the inside coils are warmed and so the outside coils are being chilled. Running continuously in low temps the outside coils can freeze and ice up.

More sophisticated systems like the one we have at home monitor the outdoor coil temperature and will periodically defrost. The strikeout or timeout strategies are less sophisticated methods employed to keep your unit from turning into an ice block and self-destructing.

[Pirate1]

My home honeywell thermostat is set up for ac, heatpump, and emerg. heat. I wonder if it would consider the gas furnace as emerg. heat? I may investigate a new thermostat. Besides, my honeywell thermostat has a recirc mode and auto switches (2 deg separation of course) between heat and cool as needed.

https://customer.honeywell.com/en-US/pages/product.aspx?cat=HonECC%20Catalog&pid=TH8320U1008/U

[Wayne_Dohnal]

I'm fairly confident that the strikeout algorithm is in the thermostat's software, so you're not going to change it. You could hot-wire at the thermostat output to keep it running, but then you'd lose temperature control. Another option would be to find another thermostat, but then you'd lose the gas heat/electric heat integration. You could do it with an additional thermostat, moving the electric heat control wire over to it.

I'm annoyed by the thermostat's insistence of running the gas heat when the spread between the current temp and desired temp gets too large. Sometimes I don't want the dang gas heat running and want to wait for the heat pump to do the job. The workaround of course is to chase the temp setting up as the heat pump runs, a pain in the neck.

As to "why", it's just somebody's bad idea of how it should work.