Good Sam Club Open Roads Forum: Mini Split Air Conditioner / Heat pump
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 > Mini Split Air Conditioner / Heat pump

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MrWizard

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Posted: 01/04/18 10:57am Link  |  Quote  |  Print  |  Notify Moderator

Most of us have no experience, with a mini split cooling and heating

Which may be more efficient and produce more btu cooling for less energy use

But.. that does not change the circumstances of solar and battery Calculations

If it only uses 4 amps at 120v then power consumed and needed will be less than 14kwHrs

But you said '10 amps' and you said Texas summer

Please keep us informed of your progress


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pnichols

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Posted: 01/04/18 12:09pm Link  |  Quote  |  Print  |  Notify Moderator

Heat pumps are way more efficient at power consumption per BTU of heat output than electric resistance based heaters.

HOWEVER, heat pumps still have a compressor - just like an air conditioner (usually a heat pump is an air conditioner "run in reverse" when you have the unit set to it's heating mode) - so when drycamping you still need the instantaneous high current spike capability to start it in heat pump mode as when starting it in air conditioning mode. What this means is - is you still need a fairly healthy power system when drycamping in order to heat or cool with a heat pump unit in an RV.

Personally, I see no reason to have a heat pump system in an RV except for electrical hookup campground use in which you are charged for your electricity consumption and in which cold temperatures aren't below around 35 degrees. In this situation heat pump heating would be less expensive than electrical resistance heater heating and maybe less expensive than propane furnace heating. I guess for more "flexibility" in choosing from a wide variety of camping situations that might present themselves - having an RV with a heat pump system along with a propane furnace instead of an air conditioning system with only a propane furnace - could be the smarter way to go.


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Chris Bryant

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Posted: 01/04/18 01:19pm Link  |  Quote  |  Print  |  Notify Moderator

I doubt you will get much more efficient than this 24 vdc mini-split, spec'd at 13k btu/hr drawing 816 watts. I don't believe it will reverse cycle though.
Looking at all of the DC air conditioners, ~850 watts for 13k btu/hr seems to be the standard. Note that most of these figures are effective watts- averaged over time- IOW, the unit draws 1300 watts but they factor in the duty cycle to come up with the lower number.


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time2roll

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Posted: 01/04/18 04:11pm Link  |  Quote  |  Print  |  Notify Moderator

Walkdog wrote:

I've come to the conclusion that nobody here knows anything about minisplit air conditioners vs the regular stand topside airconditioner that come stand with a RV.
What is to know?
They are inherently more efficient than RV air conditioners is the biggest difference.

As far as amp draw that will depend on load and heat. No one can give you an exact number. Takes a lot of energy to move the heat out of your poorly insulated RV sitting in the sun.

You can limit the cooling or add more solar panels and battery until it works for you in most conditions. I expect 1500 watts solar and 12,000 watt/hours battery would be about minimum. Is that even realistic for your RV?


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pnichols

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Posted: 01/04/18 05:03pm Link  |  Quote  |  Print  |  Notify Moderator

time2roll wrote:

They are inherently more efficient than RV air conditioners is the biggest difference.


Huh???

Please explain.

For example ... why would a split 13.5K RV A/C be more efficient than a single package (on the roof or otherwise) 13.5K RV A/C .... especially with regards to a single package on the roof RV A/C with interior ducts distributed shooting down from the ceiling throughout the coach area?

Kindof related .... we specifically went with a 4 ton single package heat pump for our stick house because efficiency losses were less and reliability was better than having an outside-the-house condenser section connected via leakable, rottable, and rodent edible hoses to the inside-the-house evaporator section.

A split system seems to violate K.I.S.S. -> keeping it simple by having everything built and held together right inside the same metal enclosure with all interconnecting tubes made of metal and short in length.

DrewE

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Posted: 01/04/18 05:38pm Link  |  Quote  |  Print  |  Notify Moderator

pnichols wrote:

time2roll wrote:

They are inherently more efficient than RV air conditioners is the biggest difference.


Huh???

Please explain.

For example ... why would a split 13.5K RV A/C be more efficient than a single package (on the roof or otherwise) 13.5K RV A/C .... especially with regards to a single package on the roof RV A/C with interior ducts distributed shooting down from the ceiling throughout the coach area?


The mini splits generally use more modern motor and compressor designs, with variable speed compressors and fans. (I think these are multiphase induction motors with variable frequency drives, usually...but that's rather immaterial). I think a good part of their better efficiency comes from being able to modulate the amount of cooling, rather than being always full-on or full-off, which I suspect lets the condenser work more efficiently--a lower coolant flow means greater cooling in the condenser, and hence more cooling for the energy input. There's no inherent reason why a traditional RV air conditioner could not incorporate many of these features, but at present they do not do so.

The fancy motors also mean that the startup current requirements are a good bit lower out of the box (i.e. without a separate soft start device). That's not an efficiency question, per se, but it is a very nice feature when running off a generator or inverter.

It also wouldn't hurt that you don't have a big hole in the ceiling with not much more than a sheet metal plate separating the evaporator and cold air from the hot outside air and motor and compressor and condenser.

RV air conditioners are among the least energy efficient ones available these days, I believe. Many window air conditioners do at least a little better. Probably most of the portable units with a hose going out a window would be even less efficient, I suspect, but that's about it.





pnichols

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Posted: 01/04/18 06:03pm Link  |  Quote  |  Print  |  Notify Moderator

DrewE wrote:

The mini splits generally use more modern motor and compressor designs, with variable speed compressors and fans. (I think these are multiphase induction motors with variable frequency drives, usually...but that's rather immaterial). I think a good part of their better efficiency comes from being able to modulate the amount of cooling, rather than being always full-on or full-off, which I suspect lets the condenser work more efficiently--a lower coolant flow means greater cooling in the condenser, and hence more cooling for the energy input. There's no inherent reason why a traditional RV air conditioner could not incorporate many of these features, but at present they do not do so.


What you say above is what I thought that the situation might be. As usual, many aspects of "modern" RV's still wind up being old technology.

FWIW, our stick house single package heat pump has a variable speed scroll compressor - which runs at 100% volumetric efficiency - and a variable speed air distribution fan, both of which in combination leads to reduced energy consumption. It's sound out the registers varies from whisper quiet to a rushing wind, all automatically controlled.

There's no reasons, beyond cheaping out, that RV heat pumps and air conditioners couldn't be made the same way .... thus MAYBE allowing an EU2000i Honda generator to power an RV's 13.5K heat pump at nearly all altitudes.

time2roll

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Posted: 01/04/18 06:54pm Link  |  Quote  |  Print  |  Notify Moderator

pnichols wrote:

time2roll wrote:

They are inherently more efficient than RV air conditioners is the biggest difference.


Huh???

Please explain.

For example ... why would a split 13.5K RV A/C be more efficient than a single package (on the roof or otherwise) 13.5K RV A/C .... especially with regards to a single package on the roof RV A/C with interior ducts distributed shooting down from the ceiling throughout the coach area?

Kindof related .... we specifically went with a 4 ton single package heat pump for our stick house because efficiency losses were less and reliability was better than having an outside-the-house condenser section connected via leakable, rottable, and rodent edible hoses to the inside-the-house evaporator section.How does the heat even get outside? Largest window style unit I have seen is just 2 tons... 4 tons seems like a monster. Or is this a through-the-wall unit?

A split system seems to violate K.I.S.S. -> keeping it simple by having everything built and held together right inside the same metal enclosure with all interconnecting tubes made of metal and short in length.
Start by comparing SEER ratings.

Next ANY ducting through the sun heated ceiling cavity is losing monster heat.

Most ducting leaks like a sieve. Why does cold air blow out of my outlets? More heat loss.

Have you checked your plenum divider? Mine barely divided anything and allowed a lot of air to just circulate in the unit.

More compact design will tend to be lower efficiency and lower SEER rating. This can be observed with home units that have higher rating have a larger condenser.

Mini-split cooling unit is fully contained in the RV. Just a couple coolant tubes and some control wires to connect to the condenser outside. No 14" x 14" hole to cause more heat transfer issues.

MrWizard

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Posted: 01/04/18 06:55pm Link  |  Quote  |  Print  |  Notify Moderator

I wish RV A/C was more efficient
But none of that changes the physics of solar and batteries, electrical creation
10 amps 120v is is 1200 Watts aka approx 100 amps of battery draw to the inverter, didn't make any difference what type of device is drawing that 1200w

The OP saw amps, and thought solar would run it
He didn't realize it's all about Watts amps times volts is Watts
He needs at least ten times the power he thought he needed

10 amp 120v =1200 Watts
100 amps 12v = 1200 Watts

cewillis

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Posted: 01/04/18 09:42pm Link  |  Quote  |  Print  |  Notify Moderator

Walkdog wrote:

I've come to the conclusion that nobody here knows anything about minisplit air conditioners vs the regular stand topside airconditioner that come stand with a RV.

I think you're mostly right -- no shortage of opinion anyway.
I was seriously looking at a 12v (or 48v -- they had both) mini-split actually made for big rigs years ago, but they were just too expensive.
There is one advertised on Ebay that's about the right size, but no clue about the quality.


Cal


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