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Old 01-13-2020, 02:13 PM   #1
Dom
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Here is the skinny on heat pumps

I use a heat pump to heat my shop in the winter. I only run it from 8 in the morning until 4 in the afternoon. I have been waiting until it got cold enough to post this to show how good they work. This morning at 9 am it was 0 F outside and 33F inside shop. when I checked it at 1130 it was 8F outside and 55 deg inside shop. Air temp coming out heat pump was 92F. Now I know someones gona say that's not very efficient but keep in mind, its my only source of heat and heat pumps are most efficient at 30 to 45F So all in all, if you have free electricity as in a campground, use your heat pump as long as you can
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Old 01-13-2020, 02:35 PM   #2
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Do you have heating coils in your blower system? If you do not and are pulling that kind of heat out of a heat pump I guess it must be one of the new inverters. Our hybrid inverter heats to -5 outside temp so building code where we are doesn't require emergency supplement heating coils. In our coach we have a Truma Combi gas/electric so we do run it on electric when plugged in.
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Old 01-13-2020, 02:41 PM   #3
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Do you have heating coils in your blower system? If you do not and are pulling that kind of heat out of a heat pump I guess it must be one of the new inverters. Our hybrid inverter heats to -5 outside temp so building code where we are doesn't require emergency supplement heating coils. In our coach we have a Truma Combi gas/electric so we do run it on electric when plugged in.
No just heat and air conditioning. Its about 4 years old and yes it is inverter type. But all in all heat pumps use refrigerant so even a strait compressor type would work, maybe not as efficient as inverter technology but when powers free, hey
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Old 01-13-2020, 06:17 PM   #4
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The standard-type 3-ton heat pump in our house works well down to around 30 F. It struggles a bit down to around 25 but still produces heat. Below that, not so much. It has auxiliary electric heat, but the house heats better with a pair of electric space heaters than with the aux heat on the pump, even though the aux heat has more btus.


We live in north-central Florida, so that's adequate for our needs and energy costs are modest. Would probably need something better for a colder climate.
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Old 01-13-2020, 07:04 PM   #5
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The standard-type 3-ton heat pump in our house works well down to around 30 F. It struggles a bit down to around 25 but still produces heat. Below that, not so much. It has auxiliary electric heat, but the house heats better with a pair of electric space heaters than with the aux heat on the pump, even though the aux heat has more btus.


We live in north-central Florida, so that's adequate for our needs and energy costs are modest. Would probably need something better for a colder climate.
How old is your heat pump? With the new refrigerants and technology they are very efficient
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Old 01-13-2020, 08:36 PM   #6
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Residential and RV heat pumps are two different critters. An RV heat pump really is only good down to 40 degF outside temperature.

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Old 01-13-2020, 08:40 PM   #7
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Residential and RV heat pumps are two different critters. An RV heat pump really is only good down to 40 degF outside temperature.

Ken
I am air conditioning technician and they are not different. Same refrigerant and same compressor.
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Old 01-14-2020, 12:33 AM   #8
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Here is all I have observed with running RV heat pumps...

1. They do appear to work OK down to 40* but below that they seem to struggle.

2. As temps get down to 40* they are more prone to having to go through defrost cycles. If it is relatively humid then defrost cycles might start at 45* or so. (I've actually seen defrost cycles at even 50* with very humid conditions but that is a bit unusual.)

3. If I am NOT paying for electricity, I will run them until the defrost cycles start getting to be annoying.

4. If I'm paying for electricity I will generally run on Oasis when temps are forecasted to be below 40*.

YMMV
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Old 01-14-2020, 09:22 AM   #9
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Here is all I have observed with running RV heat pumps...

1. They do appear to work OK down to 40* but below that they seem to struggle.

2. As temps get down to 40* they are more prone to having to go through defrost cycles. If it is relatively humid then defrost cycles might start at 45* or so. (I've actually seen defrost cycles at even 50* with very humid conditions but that is a bit unusual.)

3. If I am NOT paying for electricity, I will run them until the defrost cycles start getting to be annoying.

4. If I'm paying for electricity I will generally run on Oasis when temps are forecasted to be below 40*.

YMMV
Well said. On my particular heat pump in my Southwind, It does not have a heat strip, so will work on the compressor heat source until very cold outside. When we were traveling through Washington and Oregon in late January, temps were about 25f in the day, and 15 t0 20 at night. Heat pump kept coach not bad with a little help from one small electric heater. I did not want to use propane as I wasn't sure where we would get propane refill on our trip. Plus I wasn't paying for electricity
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Old 01-14-2020, 10:55 AM   #10
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So while on this subject I am wondering how much cost difference there is between running heat pumps (with strips) versus the small electric heaters. I have my Coach on my own RV lot so I will be paying for the electric. Thanks.
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Old 01-14-2020, 12:15 PM   #11
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Originally Posted by Dom View Post
I use a heat pump to heat my shop in the winter. I only run it from 8 in the morning until 4 in the afternoon. I have been waiting until it got cold enough to post this to show how good they work. This morning at 9 am it was 0 F outside and 33F inside shop. when I checked it at 1130 it was 8F outside and 55 deg inside shop. Air temp coming out heat pump was 92F. Now I know someones gona say that's not very efficient but keep in mind, its my only source of heat and heat pumps are most efficient at 30 to 45F So all in all, if you have free electricity as in a campground, use your heat pump as long as you can
Interesting information, however it is not the entire story. How much of that was solar heating =sunshine? That is really an unknown, so your figures are slanted.
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Old 01-14-2020, 02:06 PM   #12
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Quote:
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I am air conditioning technician and they are not different. Same refrigerant and same compressor.
Spent 40 plus years as a professional engineer industrial refrigeration and many heat pump applications. You are correct that the refrigerant and compressor are the same, but it ends there. The residential unit is more sophisticated with better controls and with a back up heat source. The RV heat pump is very basic.

The Coleman units have a temperature switch embedded in the outdoor coil set for 18 to 20 degF. This coil operates approximately 20 degF below the ambient temperature, so once you hit 38 to 40 DegF , it will shut off the compressor and goes into a sequence that will start the furnace. It will cycle through this sequence 3 times and lock out the heat pump. You have to shut off the system to get it to reset. There is not back up heat or defrost in the unit.

With the outdoor coil running so cold it will ice over and ice is a great insulator and the heat transfer is gone.

An A/C unit or heat pump is nothing more than a device to move heat from one source to another. In the A/C mode, if picks up the heat indoor and rejects the heat out door through the condenser. In heat pump mode or reverse cycle mode, it is removing the available heat from the outside air and putting it indoors.

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Old 01-14-2020, 02:49 PM   #13
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Interesting information, however it is not the entire story. How much of that was solar heating =sunshine? That is really an unknown, so your figures are slanted.
No solar heat as it was already dark when we stopped at night
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Old 01-14-2020, 03:03 PM   #14
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RV - Basement AC Questions & Expectations

In my 2004 Itasca "Horizon" 40AD I have a 2-ton (24,0000 BTU) Coleman Mach "Basement AC", and it has a 2-stage compressor type AC and Heat Pump.

I get the impression the above comments refer to roof-top AC/Heat Pumps more commonly found in RVs, but maybe this makes no-matter. Either way, I have some questions I hope a AC expert can answer:

1) Do the same rules apply to RV "Basement ACs" with a heat pump as they do to RV "Roof-Top" ACs? I.e., below 40F my heat pump will struggle?

2) Do I need more than -5F for the second stage of the heat pump to turn on? (I read this somewhere.)

3) I believe my Basement AC takes R-410a. Is this stuff still available? If so, can I buy it myself? And does anyone know how much "weight" my Coleman Mach need after evacuating the unit? And how often does a basement AC need a recharge?

4) In AC mode, if it's 100F outside, doe that mean the most I can expect to cool the inside of my RV down to is 80F? (-20F with AC on)

5) In Heat Pump mode, if it's 40F outside, does that mean the most I can expect to heat the inside of my RV to is 60F? (+20F with HP on)

6) I have read about "Electric Floor Heaters" using up the available oxygen content in a closed room. It this a concern when placing these things in a RV?

7) What type of heat source is safer: RV style Heat Pumps or gas furnace?

8) I have avoided running my heat pump, because I did not want to shorten the life of my basement AC. Is that true? Does running your basement AC create more "work" for the compressor vs. running in "cold mode", or is this fiction? ...And by more work, does that mean you shorten the life of the unit and/or increase the probability of needing maintenance?

8) Are RV-Basement ACs more robust than RV-Roof-Top ACs or is it the other way around? ...Or the same?

9) Does the type of refrigerant determine the life of the compressor? I.e., will R-410a compressor last longer than R-11 or R-134a, presumably due to better lubrication factors?

Thanks for sharing your expertise with us!
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