Answered Heat Pumps in cold weather

[MapNerd]

Setting up the coach to spend the night outside if the service center and I decided that rather then burn fuel, I’d just let the heat pumps do the work of keeping everything from freezing up since we’re not staying in the coach.

odd thing though, the heat is coming out of the lower registers rather than the overhead vents. The few times I’ve used the heat pumps, the heat has always come from the overhead vents. Also, if I go outside I don’t hear my three rooftop ACs running which is where I thought the heat pumps would be.

what am I missing?

 

[Neal]

Is your tstat in "HP" or "Auto"? Remember, HP's don't work below about 40-45 so the system is likely automatically switching over to furnace. I seem to recall I saw this same thing happen. I rarely use my HP, I prefer the furnace.

 

[MapNerd]

It’s set to HP. I didn’t know they don’t work below 45-degrees. You’d think they would write that in the manual somewhere?

 

[TJ&LadyDi]

It’s set to HP. I didn’t know they don’t work below 45-degrees. You’d think they would write that in the manual somewhere?

@Neal is correct; the heat pumps will cease to work below 40-45 degrees (mine have worked down to 38 degrees, but not efficiently). As for that information not being in the owner's manual, it is just one of a whole bunch of things that should be covered, but are not. RV owners manuals seem to me to be written for the sole purpose of being able to say an owners manual was provided.

TJ

 

[MapNerd]

At least it switches over automagically so the unit doesn’t freeze up. I’ll forgive them for the 20m I spent poking the panel randomly.
I do wish there was an electric heat source for colder weather though. Don’t like burning fuel to keep the unit warm when there’s a 50amp connection right there.

 

[skychs]

We use the fireplace a lot when it's cold. It provides direct hot air into the den area. If it had a thermostat I would run it at night. It's quiet and very effective. The more we use it the more we enjoy it.

 

[Neal]

At least it switches over automagically so the unit doesn’t freeze up. I’ll forgive them for the 20m I spent poking the panel randomly.
I do wish there was an electric heat source for colder weather though. Don’t like burning fuel to keep the unit warm when there’s a 50amp connection right there.

And there is. Turn on AC I/II and furnace and you have heat. All electric.

 

[MapNerd]

And there is. Turn on AC I/II and furnace and you have heat. All electric.

Interesting. So next rookie question - what’s more efficient on the road. Running the generator for electric heat or running the furnace. I tend to think the furnace.

 

[Neal]

Turn the furnace on but it won’t run as the engine heats the fluid. Some say turn on AC 1 but that makes no sense to me as there is no shore power. Don’t run Gen.

 

[docj]

Is your tstat in "HP" or "Auto"? Remember, HP's don't work below about 40-45 so the system is likely automatically switching over to furnace. I seem to recall I saw this same thing happen. I rarely use my HP, I prefer the furnace.

At least some newer HP's do pretty well at colder temps. We've tested our new Coleman Mach 8+ units down as low as ~40F and they can still keep the coach at the set temperature. In another couple of days we're going to have a chance to take them down to ~35F and we'll see how they do. We have electric heaters as backup.

When people say that "heat pumps can't work below ~40 degrees" that's more of a reflection of how most heat pumps are designed to operate than it is a statement of "fact." In theory all that's required for a heat pump to operate properly is for the refrigerant temperature to be less than the ambient outdoor temperature. If a system can be designed so that this is the case, then it can absorb heat from the outside air even at rather low temperatures. Here's an example of a Mitsubishi HP system designed to operate down to -13F Low temperature heat pump