Advantages/Disadvantages of Heat Pumps

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GaryB

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I've noticed that some of the mid (to high) level 5th wheels have heat pumps, at least as an option.  Although I know what a household heat pump is/does, what are the advantages and disadvantages to a heat pump in a 5th wheel, as compared to the standard roof A/C and furnace?

Thanks
Gary
 

John From Detroit

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The basic advantage to a heat pump is efficency,  Normally to cool our rigs we use the roof-top AC and to heat we use either electric heaters or propane. Normally we pay extra for propane, electric for the ac/heater some places charge for, and other places say "DO NOT USE ELECTRIC HEATERS"

At their very best a 1500 watt electric heater gives you the equivlent of 1500 watts of heat, at their worst, same amount of heat, they are 100% efficent (The reason for this is in an electrical system all losses are heat, so with a heater, all losses are desired product)

With a heat pump that same 1500 watts may well give you 30,000 watts worth of heat.

And that saves on propane, which we ALWAYS pay for
 

blueblood

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GaryB said:
I've noticed that some of the mid (to high) level 5th wheels have heat pumps, at least as an option.? Although I know what a household heat pump is/does, what are the advantages and disadvantages to a heat pump in a 5th wheel, as compared to the standard roof A/C and furnace?

Thanks
Gary

You can't get by without a furnace as well as a heat pump, (which is the way most motorhomes , if not all, come,)  if your going to be in places with temperature below 40 degree. 
 

Smoky

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Gary:

We almost never use our furnace.  Of course, we almost never are in anything less than high 30s temperature and even that is rare.  I still would want both a furnace and a heat pump.  the beauty of the heat pump is that you also have an air conditioner.  and in most campgrounds you are riding on someone else's electric bill rather than your own propane bill.  They do a GREAT and comfortable job of heating , and in our case with two of them, they give us better control of heat.

 

Ned

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John In Detroit said:
With a heat pump that same 1500 watts may well give you 30,000 watts worth of heat.

Interesting bit of physics.  What universe does this work in?
 

King

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My offhand calc said 22500 watts,  but what is the point of a heat pump if it is not better than simple electric heat?
Art
 

King

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Oops...  sorry, should have been 4500 to 6000 watts...  used a multiplier from memory...  should have looked it up.
Art
 

Gary RV_Wizard

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GaryB,
The pros and cons for a heat pump are the same in an Rv as a home - and I can't think of a single disadvantage except initial cost.  Perhaps there is a slight increase in future repair/maintenance costs - any extra componentry in a system always has a service cost, but in heat pumps it is pretty trivial and probably not worth worrying about.

In other words, buy the heat pump option if you can afford it.
 

Carl L

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Interesting bit of physics.  What universe does this work in?

It does sound a bit Stargate, but it is not.  It is just heat pump.  The pump works by extracting the heat in the surrounding envonment, compressing its vehicle and transmitting it to the radiator side.

See the Wikipedia article HERE.
 

Ned

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I know how a heat pump works, but turning 1500 watts of energy into 30,000 watts is more like warp drive technology :)
 

Gary RV_Wizard

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but turning 1500 watts of energy into 30,000 watts is more like warp drive technology

I think we have to allow for a bit for hyperbole  :eek:

But an a/c unit or heat pump does indeed use around 1500 wats of power (12-14 amps) to move about 13-15,000 btus (not watts) of thermal energy either out of or in to the coach interior to/from the surrounding air. So its not violating the energy conservation laws - it's just concentrating the heat in a more desirable place, i.e. either inside or outside of the RV living space.
 

Ned

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I understand all that, but that's not what was said.  I sit here with my electric cube heater keeping the whole living area very comfortable with a 46F outside temp running at 100% efficiency :)
 

BruceinFL

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The only thing I don't like about my roof mounted heat pump is that it blows the air from the ceiling vents, so the top gets warm but the floor is cold. With the propane furnace, the ducts are in the floor so the floor gets warm. Also the propane furnace has an outlet in the bathroom. To save propane, we use the heat pump with a higher thermostat setting and then when using the john or taking a shower, use the propane furnace.
 

Lorna

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Bruce

You are right about that.  The heat pumps just don't warm up the floor.
 

John From Detroit

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Ned said:
I know how a heat pump works, but turning 1500 watts of energy into 30,000 watts is more like warp drive technology :)

Well, I do admit to grabbing the numbers,  However the point is that since a heat pump does not turn electricity to heat, it "Pumps" existing heat, and thus it is more efficent than a resistive heater, you get more heat per kilowatt than a resistor can produce.

I'd have to do some research to figure out how much, and alas I lack one of the needed items to do it (the heat pump)

So you are not creating more enegery, (Which my earlier post, I will admit, does imply) you are simply using it better

For those who do not know how a heat pump works,  Imagine a window air conditioner, you turn it on and cold air blows out the room side, hot air blows out the outside...... Now, turn it around so the inside is out and the outside is in. (NOTE do not do this for real, just imagine) now the hot air is blowing INTO the room to keep you warm,  That is the simple version.

I am considering a swamp cooler for use in NV and AZ this winter during the day.  Another way to get more bang for you enegery buck since it uses different laws to give you a lot of cool for a little price... And humidity in the bargin
 

Pat

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BiFL:

Exactly.  I was wondering if somebody else had the same problem I do, which is a ceiling mounted a/c-heat pump, so all that lovely warmth is up above the floor, the cat, and most of the furniture.

BTW, the 40 degree thing:  My manual says that the heat pump works down to low 30s.  Then it kicks off and the furnace kicks on, until outside ambient temp gets to the low 40s.  I have run the heat pump with ambient temp in the low 30s.  Still works.

My big plus for the heat pump is that it provides a backup system.  I have the furnace, the heat pump, and, if all esle fails, a Vornado space heater tucked away somewhere.  Problem with the space heater is that it tends to overheat and turn off.  I think high temp runs on 1500 watts, which really maxes out whatever circuit it's on.  Medium just isn't adequate in the cold winter.  I have a small but well insulated motorhome.

--pat
 

Bob Buchanan

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GaryB said:
Although I know what a household heat pump is/does, what are the advantages and disadvantages to a heat pump in a 5th wheel, as compared to the standard roof A/C and furnace?

Interesting thread, Gary. I wasn't aware that RVs came with heat pumps. I had one once in an apartment complex. At the time I had never heard of one -- so when the repair guy came to fix mine that didn't work when I moved in -- I asked him "how" it worked. He responded, "I don't know, I just fix them". Anyway, after finding out their usefulness, it made sense for an apartment complex. The builder did not have to spend as much money installing both an air conditioner "and" a furnace in each unit. They did install a cheapo electric heaters for far less than the cost of a furnace to supplement the INefficient side of a heat pump.

From what I read here, rigs with heat pumps also have fully efficient propane furnaces -- so the idea seems to be to give the RVer more choices on how to save on energy costs -- as RVRoamer and John pointed out. Also, John's example of turning a window air conditioner around is a good analogy of "the results" of how it works. And that also demonstrates the only potential drawback.

My A/C is the biggest energy hog on board my RV.? It's the one item I am the most careful of if I am paying for it's running cost. For example, I only have a 20amp circuit where i am now parked so cannot run any other electric items requiring big watts. When dry camping, the genset "must" be running to do Air. And a Heat Pump, either way it is running, is an Air Conditioner -- and requires the same energy to operate. Turned one way it is cooling the inside of the rig -- while turned the other way, it is attempting to air condition "the world" outside.

Air conditioning the world involves each of those little molecules (of whatever type of liquid is used in the Pump) sucking energy in the form of heat from the environment as it becomes a vapor to later release inside the rig during condensation. The? colder it is outside the less energy for the little molecules to suck up. And that is the downside of a heat pump. The colder it is outside (and the corresponding need for heat inside), the less efficient the unit becomes. The hotter it is outside, the more efficient the heat production is inside.?

But going back to John's original response, we all want to use park power when available, and our own propane and genset when it is not. If an RV has a propane furnace as well as a heat pump, I would agree with RV Roamer in that if the cost is not that much more, and you understand exactly how it works, I would see it as an asset to give more alternatives in energy cost savings. That would be considering the incremental cost over just Air and a furnace. How much incremental cost would one be looking at that they would have to amortize in energy cost savings vs. just an air conditioner and furnace? "Rarely" do I need more to heat my Class A than one of those little "cube" type CW heaters.
 

Gary RV_Wizard

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An RV A/C with heat pump costs  a couple hundred $ more than a vanilla a/c. When buying a new RV, option pricing varies from an insignificant difference to big bucks, depending on factory option pricing policies.  Some rigs with two roof a/c unis may have one heat pump and one regular a/c.  That gives you a convenient source of heat for cool mornings without much extra cost.
 

BernieD

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RV Roamer said:
An RV A/C with heat pump costs  a couple hundred $ more than a vanilla a/c. When buying a new RV, option pricing varies from an insignificant difference to big bucks, depending on factory option pricing policies.  Some rigs with two roof a/c unis may have one heat pump and one regular a/c.  That gives you a convenient source of heat for cool mornings without much extra cost.

Gary

The "factory list price" for our heat pump upgrades was $854. Of course, this was before negotiated discount ;) The upgrade included both A/C units being upgraded to 15k btu from 13,500 and heat pumps on both. We also have the advantage of only needing to run one or the other when appropriate. In the evening while up front, we usually only have the back unit on. At nite when sleeping, only the front. Since we only have a single furnace and heat zone, the whole coach is heated and the furnace works a lot harder.
 

Shayne

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We had a Coachman with a heat pumps and furnace,  This unit has 2 furnaces.  Like this a bunch better.
 

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