What's an AC with heat pump?

[hclarkx]

Originally Posted by wa8yxm

An "Air Conditioner" is any device that changes the condition of the air One air freshner used to advertise itself as the $1.89 Air Conditioner. But in standard practic when we say Air Conditioner we are talking about COOLING the air.

Now imagine if you were a window A/C installed backwards..So the outside was on the inside, IT would make the room WARMER by "Pumping" heat from outside to the Inside..

And this is what an A/C with Heat pump is.. A reversable A/C. only the "Reversing" is done with valves (Solenoids) inside the unit.

In teh Summer it "Pumps" heat out of the RV like any air conditioenr
In the Spring and fall it "Pumps" into the RV to help keep you warm
ANd in teh winter it just sits there and does nothing (one hopes you do not turn it on below freezing).

15,000 BTU will provide more cooling than 13,500 BTU. and I highly recommend it as the world warms. (I upgraded both my 13,500's to 15000 and it is still not enough.

Finally.. Warm air tends to rise. Your Heat Pump is at the top of the RV, of course the blower may push warm air down (Spring and fall) but the FURNACE ductwork is in the FLOOR, where a heater belongs.

That said. I'd much rather burn "Free" (included in teh site rental) electricity and relatively Expensive Propane.

Thanks for the replies. I am familiar with heatpumps; I have two mini-splits and two multi-splits doing the heating and cooling of my home. I was hoping something similar was available for RVs that has escaped me. I have seen mini-split home units used on RV trailers, but on a fifth wheel it's not so easy. Mostly I was hoping for cooling via a more efficient and maybe soft-start roof unit.



So, with a heatpump ruled out, I'm looking at the 11,200 BTU/Hr Coleman Mach 8 Cub. Supposedly my Honda 2000 will drive it up to maybe 5000 ft altitude. That will be enough. Since we avoid really hot weather, the 13,500 factory unit is over kill (cools only the living area of our 30' 5vr). It was severe underkill even when it's was 90F out until I bypassed the ducts and removed the blocking plate that forced air into the ducts. It's now overkill.



I may provide some kind of control to make the bedroom ducts usable since the bedroom gets no cooling from the factory unit throwing air straight down in the living area. The ducts would be used only before bedtime, not when it's glaringly hot out. This would make the smaller 11,200 unit do double duty, living area and bedroom.



The Mach 8 Cub is lower profile and that will shade my solar panels somewhat less. Hopefully it will be quieter as well.

[DHuse]

I'm totally confused. More than a few people have said the heat pump function pulls in the warm air from outside and forces the cooler air outside. If the temperature in the coach is 60* and the outside air is 50* where does this warmer air come from? I'm from the San Diego area and have never come across a heat pump. Thanks

[wingnut60]

You don't actually pull in air into the unit and push it into the coach. You pull air out of the coach and run it over an area that is cooled by compressed freon expanding for AC (cooling) and sending back thru the coach. Energy to compress the freon is supplied by the electric motor in the AC unit.
If you reverse the process, you can heat the coach by pulling air over the warmer area.
Cooling ability of most ACs is about 20d delta--air in will not be cooled more than 20d going out. If the coach is well insulated, the air inside will gradually get cooler as the incoming air is cooler than before and can be cooled more each volume turnover. At some point, the thermostat will cut the AC off when the set temp is reached. If the outside temp is extremely hot and the coach poorly insulated, the AC may never be able to reach a set temp.
Sorry I can't explain any better and perhaps I have some of this wrong. But any air-to-air conditioning unit will be less efficient as the ambient temps get very high or very low.

[docj]

Originally Posted by DHuse

I'm totally confused. More than a few people have said the heat pump function pulls in the warm air from outside and forces the cooler air outside. If the temperature in the coach is 60* and the outside air is 50* where does this warmer air come from? I'm from the San Diego area and have never come across a heat pump. Thanks

All air that is above absolute zero contains energy (heat). Just because the inside of the RV is at 60 degrees and the outside temp is at 50 degrees doesn't mean that a "machine" can't take energy from the air outside and move it inside.

The heat pump doesn't move air from one place to another, it moves heat from one place to another! The efficiency of a heat pump decreases as the temperature of the air outside decreases. That's logical since it gets harder and harder to extract heat from air that is colder and colder. At around ~40 degrees outside temp, most heat pumps become fairly useless.

The most important thing about a heat pump is that no matter what the outside temperature, it is a more efficient heat source than the same electricity would be if used in a space heater no matter what brand! All space heaters convert electricity to heat using the basic equation

Energy= current-squared x resistance

which is the same law that governs your toaster or any other heating appliance.

If you take one kilowatt-hour of energy and convert it into heat with a heater, a heat pump can generate 2-3 times as much heat from the same amount of energy. If you pay for the electricity you use during the winter then a heat pump may make sense for you.

Since I have elderly A/C's I've been comparing the cost of heat pump replacements to that of regular A/C's. The cost is a couple of hundred dollars higher, but it's ridiculous to talk of heat pump repairs costing up to $1,000 since that's the basic cost of a Dometic Penguin which is about the most expensive heat pump you can buy. You would never spend that much to repair one if you could replace it for the same cost.

Personally, I don't like heat pumps all that much because the temperature of the air coming off the coils is at or around skin temperature so you end up heating your house with air that can actually feel cool to the touch. Having had one house with a heat pump, we vowed to never have one again. However, living on a fixed income in a relatively mild climate, a heat pump makes a lot of sense as a way of keeping our monthly costs down.

[Mr_D]

In mild climate areas like where I live a heat pump is almost a given in new houses although natural gas heat is about a push in my area.
BTW: if you look up heat pump on WIKI you will find that anything that moves hot or cold from one area to another is a heat pump. So what people call an air conditioner is a heat pump too. In actuality it's not an air conditioner with heat pump. Just saying heat pump means it does both.

[JFNM]

Originally Posted by hclarkx

1) lower starting current (hope to run it on a Honda 2000 good for 1600W continuous).

If not familiar with a "soft start" kit, take a look at this:

https://www.microair.net/collections...nt=30176048267

[docj]

Originally Posted by Mr_D

BTW: if you look up heat pump on WIKI you will find that anything that moves hot or cold from one area to another is a heat pump. So what people call an air conditioner is a heat pump too.

With all due respect, there is no such thing as "cold". Cold is the absence of heat. An air conditioner most definitely is a heat pump. It moves the heat from inside the house to the outside. That's why when you put your hand into the air stream of the outside unit of a "split system" A/C it feels so hot. The heat from inside the house has been moved to the outside.

If we want to get technical, A/C's and heat pumps are Carnot engines operating against the Second Law of Thermodynamics. Normally heat flows from hotter to colder. In order to make heat flow in the other direction requires energy (electricity) which is why these devices can consume so much energy.

[harleyjt]

Personally, I don't like heat pumps all that much because the temperature of the air coming off the coils is at or around skin temperature so you end up heating your house with air that can actually feel cool to the touch. Having had one house with a heat pump, we vowed to never have one again. However, living on a fixed income in a relatively mild climate, a heat pump makes a lot of sense as a way of keeping our monthly costs down.

I have noticed the same thing in homes that have heat pumps for heating. However, interestingly enough, the Penguin heat pumps in my coach actually blow warm air. We have only used them a couple of times in the morning or evenings when it's chilly. We haven't done any trips in cold weather.
jt

[docj]

Originally Posted by harleyjt

I have noticed the same thing in homes that have heat pumps for heating. However, interestingly enough, the Penguin heat pumps in my coach actually blow warm air. We have only used them a couple of times in the morning or evenings when it's chilly. We haven't done any trips in cold weather.
jt

Thanks for posting that, that's good to know and probably will result in my buying a heatpump rather than an A/C when mine dies. From what I've read, the Coefficient of Performance (the efficiency) of a heat pump increases as the design output temperature decreases. So the designer will want to use as low an output temperature as possible so the manufacturer can quote the highest COP possible. This is probably more of a consideration for residential heatpumps than it is for those intended for RV use so Dometic chose to design for higher output temperature.

[Ray,IN]

Originally Posted by DHuse

I'm totally confused. More than a few people have said the heat pump function pulls in the warm air from outside and forces the cooler air outside. If the temperature in the coach is 60* and the outside air is 50* where does this warmer air come from? I'm from the San Diego area and have never come across a heat pump. Thanks

this explains:https://highperformancehvac.com/heat...nce-operation/

[snowman1]

I'm actually in the process of replacing both 18 year old Duo-Therm (Dometic) Penguins with new Penguin II's in our coach. The compressor in the front A/C is going out and vibrating something awful. Problem is, we have the older 4 button comfort control center (CCC) which is not compatible with the new Penguin II's. So we would have to order two new control boards for the new A/C and the older one in the back plus a newer 5 button CCC. The would pay for almost half the cost of a new second Penguin II which we have opted to do. Even though the back A/C runs perfectly, an 18 year old RV air conditioner is living on borrowed time. Of course we will upgrade to the new 12 button CCC2 which has more features built into it.

As far as running any RV roof top A/C, heat pump or not, 11,200 btu or 13.5K btu, 5000 ft elevation or sea level, that is simply not going to happen with a 2000 watt generator. Even if you turned everything else over to propane and used a candle at night. No way, no how. Read the specs on any A/C units you are considering in the various online owners manuals. Minimum generator to run one A/C unit is 3.5kw which you won't even get by paralleling two 2000 watt units. Honda now makes a EU 2200 watt inverter generator but you'll still need two and you would be at the max operating wattage (3600 watts).

Hate to be the bearer of bad news, but you need to come up with a different system for generating electricity for your RV. I would step up to a Yamaha 4500 watt inverter genny and use a ramp to wheel it in and out of your pickup bed. You could use a winch if you are not able to roll it in or out. They are heavy at 150 lbs but they are excellent genny's, electric start and virtually bulletproof. Good luck.

[hclarkx]

Originally Posted by snowman1

I'm actually in the process of replacing both 18 year old Duo-Therm (Dometic) Penguins with new Penguin II's in our coach. The compressor in the front A/C is going out and vibrating something awful. Problem is, we have the older 4 button comfort control center (CCC) which is not compatible with the new Penguin II's. So we would have to order two new control boards for the new A/C and the older one in the back plus a newer 5 button CCC. The would pay for almost half the cost of a new second Penguin II which we have opted to do. Even though the back A/C runs perfectly, an 18 year old RV air conditioner is living on borrowed time. Of course we will upgrade to the new 12 button CCC2 which has more features built into it.

As far as running any RV roof top A/C, heat pump or not, 11,200 btu or 13.5K btu, 5000 ft elevation or sea level, that is simply not going to happen with a 2000 watt generator. Even if you turned everything else over to propane and used a candle at night. No way, no how. Read the specs on any A/C units you are considering in the various online owners manuals. Minimum generator to run one A/C unit is 3.5kw which you won't even get by paralleling two 2000 watt units. Honda now makes a EU 2200 watt inverter generator but you'll still need two and you would be at the max operating wattage (3600 watts).

Hate to be the bearer of bad news, but you need to come up with a different system for generating electricity for your RV. I would step up to a Yamaha 4500 watt inverter genny and use a ramp to wheel it in and out of your pickup bed. You could use a winch if you are not able to roll it in or out. They are heavy at 150 lbs but they are excellent genny's, electric start and virtually bulletproof. Good luck.

I question what you are saying. My Honda EU2000 (1600W, not 2000W) will start and run my 13.5 Dometic at 5000 feet (no soft start or any other help). It will run only a few minutes before the inverter (probably) overheats because the continuous draw is over 1600W. But, lots of users are running 11.2K Mach Cubs by Coleman on this generator at 5000 feet (1270W normal and up to 1550W under "severe desert" conditions). They probably aren't doing so in "severe desert heat" because the EU2000 can't do 1550W at 5000 feet. But like most of us, I'd never RV in such conditions (90F is my limit). So, my new unit will be 9K, enough to make our 30' rig pretty comfortable in 90F conditions and well within the rating of the EU2000 at 5000 feet (and higher).


As for other loads, my A/C can be fed from the EU2000 while the rest of the RV is served by a 900W inverter (enough for the microwave and coffee maker and toaster and similar).

[hclarkx]

Originally Posted by wingnut60

These are air-to-air devices, and if the air it is drawing in is too hot or too cold, the unit performance will suffer accordingly. At 40d or thereabouts for heating, and 90-05 and above for cooling, seems to be where they stumble. Some of the units are tied into the furnace, and when they won't heat correctly, they turn the furnace on.

I have to wonder what's up with the makers of heat pumps for RVs. I have mini-splits in my home that work down to -5F without special defrosting and such. Optional ones with defrosting run down to -15F. They are not very efficient and don't operate at their ratings, but they definitely keep the house from freezing. I wonder why the RV industry can't achieve this?

[hclarkx]

Originally Posted by harleyjt

Personally, I don't like heat pumps all that much because the temperature of the air coming off the coils is at or around skin temperature so you end up heating your house with air that can actually feel cool to the touch. Having had one house with a heat pump, we vowed to never have one again. However, living on a fixed income in a relatively mild climate, a heat pump makes a lot of sense as a way of keeping our monthly costs down.

I have noticed the same thing in homes that have heat pumps for heating. However, interestingly enough, the Penguin heat pumps in my coach actually blow warm air. We have only used them a couple of times in the morning or evenings when it's chilly. We haven't done any trips in cold weather.
jt

I'm not sure the RV industry will catch up, but I have heat pumps in my home ("mini-splits") that produce 110F output that isn't far off of conventional gas fired heating and easily as comfortable (and quieter). And with COP of 4.5 or 5 under non extreme conditions.