AC with heat pumps.

[garyb1st]

On one relatively cool morning, probably mid 50's in the coach, we turned on the furnace.  The thermostat works both the furnace and the air conditioners.  The furnace came on as usual and began heating the coach.  However, after a few minutes, the AC started.  That never happened before.  When I looked at the thermostat, the setting of the AC units were not on off.  They indicated heat. I know AC's with heat pumps exist, but I didn't know if ours had them. 

So if we actually do have them, how effective are they?  Are there temperature limits when I can use them?  (seems I read once that they're only good to a point)  Would it make more sense to just use our stand alone space heaters? 

 

[Tom]

I don't recall the "limits", but within their operating range heat pumps work very well. We're hooked to shore power, and on these chilly mornings (some around freezing), they bring (and maintain) the coach interior temperature to very comfortable in a few minutes.

Think of the heat pumps as the A/C units working in reverse.

 

[jayc2640]

We have a heat pump on one of our air conditioners.  From what I've observed, the heat pump is good down to temps in the upper 30s.  Anything below that, we need to go to the furnace.

 

[Tom]

FWIW our prior coach had "heat strips" in the A/C units. They worked much like a small electric fan heater with a heating element. They helped take the chill off, but weren't anywhere near as effective as our current heat pumps.

A quick google search turned up varying answers for the lower ambient temperature where heat pumps will continue to work. Some said 30F and others 20F. Our owners manual says 20F, although it does allude to issues closer to 30F. Check your manual.

 

[garyb1st]

Thanks for the replies.  Next time we're out in relatively cold weather, I'll give them a real try. 

 

[Back2PA]

I had heat pumps previously, they do a pretty good job. While mine actually worked down to the low 30s, after frying a connection I was told by an RV AC guy I shouldn't use them below about 40 as it puts considerable strain on them

 

[SeilerBird]

The A/C in my fiver also has a heat pump and it works fantastic here in Florida. It never gets too cold for the heat pump not to work.

 

[Tom]

[quote author=Back2PA]... after frying a connection ... [/quote]

Scott, just curious - which connection did you fry?

 

[Kevin Means]

That's kind of a nice surprise to stumble across 'eh Gary? Ours work well, and I agree with Tom... they're kind of like working the AC in reverse (Just as noisy too.) Of course they only work on AC, so we don't use them when boondocking, but when we are hooked up to power, they'll heat the coach up fast.

Kev

 

[WILDEBILL308]

On one relatively cool morning, probably mid 50's in the coach, we turned on the furnace.  The thermostat works both the furnace and the air conditioners.  The furnace came on as usual and began heating the coach.  However, after a few minutes, the AC started.  That never happened before.  When I looked at the thermostat, the setting of the AC units were not on off.  They indicated heat. I know AC's with heat pumps exist, but I didn't know if ours had them. 

So if we actually do have them, how effective are they?  Are there temperature limits when I can use them?  (seems I read once that they're only good to a point)  Would it make more sense to just use our stand alone space heaters?

You have gotten some good answers, but here is what I think happened.
When you used the thermostat to call for heat you were below the temp where the thermostat was set to use the heat pumps. The gas furnace came on and warmed the coach up enough so it could switch to the heat pumps.
I have had this happen  in reverse. It started with the heat pumps but the temp was to low and it automatically switched to gas heat. 
Bill

 

[Back2PA]

Scott, just curious - which connection did you fry?

Tom, it was the main power wire, I was lucky the rig didn't burn. Details are in this post

 

[Back2PA]

You have gotten some good answers, but here is what I think happened.
When you used the thermostat to call for heat you were below the temp where the thermostat was set to use the heat pumps. The gas furnace came on and warmed the coach up enough so it could switch to the heat pumps.
I have had this happen  in reverse. It started with the heat pumps but the temp was to low and it automatically switched to gas heat. 
Bill

Bill, pretty sure the sensor which determines whether it's too cold to use the heat pumps is mounted outside so as to sample outside air, not cabin air.

 

[lynnmor]

I have a heat strip in the AC.  When temperatures are low enough, both the heat strip and furnace will run till it warms the air, perhaps that is what you have.

 

[Tom]

[quote author=Back2PA] it was the main power wire...[/quote]

Thanks Scott. Looks like it was the 'main power wire' to the A/C. I was trying to figure out if it was your main power cord. A poor connection to either can quickly build up heat under high current load.

Coincidentally, on the drive home from dinner last evening, the other couple mentioned that they'd replaced 6 a/c units on their prior coach. I was too busy driving to think of asking if any failures happened at the low temps we're discussing here.

 

[TheBar]

This graph shows how heat pumps become inefficient below 35. They still work but do not save electricity below that point. 

 

[Tom]

[quote author=TheBar]This graph shows how heat pumps become inefficient below 35. They still work but do not save electricity below that point.[/quote]

I don't think we were talking about 'saving electricity'. Meanwhile, for clarification, one source for that graph states "Every house and heat pump will have the capacity and load lines in different places, so don't take the numbers in this graph as absolute".

 

[TheBar]

So if we actually do have them, how effective are they?  Are there temperature limits when I can use them?  (seems I read once that they're only good to a point)  Would it make more sense to just use our stand alone space heaters?

Sorry, I posted the graph in response to the OP statement quoted above to show the efficiency at different temperatures.

 

[Tom]

Thanks for the clarification.

 

[WILDEBILL308]

Bill, pretty sure the sensor which determines whether it's too cold to use the heat pumps is mounted outside so as to sample outside air, not cabin air.

And your point is? I never said it wasn't sampling outside air.
Bill

 

[Larry N.]

On one relatively cool morning, probably mid 50's in the coach, we turned on the furnace.  The thermostat works both the furnace and the air conditioners.  The furnace came on as usual and began heating the coach.  However, after a few minutes, the AC started.  That never happened before.  When I looked at the thermostat, the setting of the AC units were not on off.  They indicated heat. I know AC's with heat pumps exist, but I didn't know if ours had them. 

So if we actually do have them, how effective are they?  Are there temperature limits when I can use them?  (seems I read once that they're only good to a point)  Would it make more sense to just use our stand alone space heaters?

One thing I've often noticed is that some thermostats have two heat settings, one of which operates the heat pump and the other operates the propane furnace (or Aqua Hot, if equipped). Of course many don't but it's another thing you could check.