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Rv mini split sizing

Bobert

Solar Enthusiast
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Jan 15, 2022
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I just installed a 9000 btu mini split in my 38’ travel trailer. It has been a game changer for my solar system. In my case the choice for size was easy as the only location that I could put a inside unit was only 30” wide. Only a handful of companies make a inside unit less than 30” wide and senville was the most readily available so I went with that. If I had the option to go larger I would have had trouble choosing what btu to go with because the size recommendations are so ambiguous especially for campers. If you use a mini split in your camper could you share how it is working for you. I think that would be helpful for those considering such an installation. Here’s my experience so far
I installed a 9000 btu Senville Leto mini split. It’s the 20.5 seer version.
I use it in my 38’ travel trailer the cabin measures about 35 feet long I have 2 slides and the ceilings are about 7’ high. The trailer was built in 2000 and I rebuilt it so the walls are 1 1/2” polyiso insulation 2” in the floors and 1” in the ceiling plus a bit of original fiberglass. We have a central living room with a bunkhouse at the front and bedroom at the rear. The living room is about 144 square feet when the slide is out. The 9000 btu mini split cools this area very well in spite of the fact that we don’t have tinted windows. If it’s in the 80s outside the living room will be around 70 even with the bedroom doors open. Once the sun is down the bedrooms are comfortable so it works for us. We replaced a very old 15000 btu roof unit with this mini split it was 22 years old and pretty well warn out it used about 1400 watts of power to operate and maxed out my 3500 watt inverter starting up. The roof top unit was slightly better at cooling the bedrooms but much worse in cooling the living room and even at 80 degrees the compressor would never shut off. The unit was loud enough to interfere with conversation in the camper on the inside and about as loud as my inverter generator on the outside. The mini split uses less than 800 watts on full blast and tapers off to about 250 watts overnight when it is mostly dehumidifying the air and not doing much cooling. Start up amperage is not an issue as this mini split gradually increases power consumption until it reaches the watts required for the cooling load placed on it. You can’t hear the unit inside unless it is on high and you are close to it and the outside unit is only slightly louder. One downside with this unit is that it continues to use over 200 watts of power when it is turned off using the remote so when it is not in use we turn off it’s breaker.
 
Is the sun hitting your RV? Do you have slide toppers?
This is incredibly good; I have 12k and 9k IDU's in my 38' 5th wheel and that's too weak when it's 90+ outside and sun's hitting the RV. Fine when it's in the 80's. Granted I have higher ceilings.
I also shut off my breaker if I need to conserve power and I'm not using the A/C - 2kWh/day lost to standby consumption! Ridiculous!
 
A temperature difference of 10°F, between inside/outside, low humidity, cloudy day, with nobody inside, no cooking...is doable with 9K.

A 9K is only capable of cooling about 450 sq ft on a 90F day, in a modern, well insulated home.
 
Is the sun hitting your RV? Do you have slide toppers?
This is incredibly good; I have 12k and 9k IDU's in my 38' 5th wheel and that's too weak when it's 90+ outside and sun's hitting the RV. Fine when it's in the 80's. Granted I have higher ceilings.
I also shut off my breaker if I need to conserve power and I'm not using the A/C - 2kWh/day lost to standby consumption! Ridiculous!
The reason it works for us is because we are fairly well insulated for a travel trailer, our actual square feet is 334 including the slides also our ceilings are only 7’ tall so the cubic feet is probably less than half of a similar length 5th wheel. The actual space that we must cool in the heat of the day is the living room at 144 square feet. We were close to 70 in that room at 90 outside and the bedrooms were much warmer close to 80 but way lower humidity than outside. Our layout gives us options to decrease square footage if the outside temperatures get ridiculously high. On the other hand we are a family of 6 with a large dog and 2 cats so body heat and cooking are major factors in our cooling requirements. We have clear glass windows that create quite a bit of heat also.
 
The reason it works for us is because we are fairly well insulated for a travel trailer, our actual square feet is 334 including the slides also our ceilings are only 7’ tall so the cubic feet is probably less than half of a similar length 5th wheel. The actual space that we must cool in the heat of the day is the living room at 144 square feet. We were close to 70 in that room at 90 outside and the bedrooms were much warmer close to 80 but way lower humidity than outside. Our layout gives us options to decrease square footage if the outside temperatures get ridiculously high. On the other hand we are a family of 6 with a large dog and 2 cats so body heat and cooking are major factors in our cooling requirements. We have clear glass windows that create quite a bit of heat also.
Yeah I'm pretty well insulated, too - plus tinted windows. And it's just me. You're lucky! That's fantastic!
 
Yeah I'm pretty well insulated, too - plus tinted windows. And it's just me. You're lucky! That's fantastic!
In 2008 I was 36 years old single never married and no prospects. I never would have guessed by the time I turned 50 I would be married to a wonderful woman and that we would have 4 children. I am certainly blessed. Thanks.
 
Is the sun hitting your RV? Do you have slide toppers?
This is incredibly good; I have 12k and 9k IDU's in my 38' 5th wheel and that's too weak when it's 90+ outside and sun's hitting the RV. Fine when it's in the 80's. Granted I have higher ceilings.
I also shut off my breaker if I need to conserve power and I'm not using the A/C - 2kWh/day lost to standby consumption! Ridiculous!
Yes I emailed senville and asked what’s up with the 200w idle consumption. Fortunately I have extensive experience with electrical systems and figured out how to turn the breaker off.
 
Yes I emailed senville and asked what’s up with the 200w idle consumption. Fortunately I have extensive experience with electrical systems and figured out how to turn the breaker off.
Hello - thanks for the heads-up on the idle consumption issue. Did Senville ever clarify why it's so high? We have been cooling and dehumidifying the upper floor of our house with a 8000 BTU window air conditioner for the past few years. Our shoes no longer grow sweaters as they did in the "good old days" with open windows and no AC. Our main room is about 600sf, and with a 60w floor fan the adjacent 2 bedrooms stay comfortable at night for sleeping. The AC unit shuts off by midnight or so after the outdoor temp dips into the 60s or 70s. Summer high temps sometimes get into the 90s, and the humidity is very high. The house is fairly well insulated with good shading over windows. We are preparing to upgrade to a mini split, and I'm wondering if a 9000 BTU single zone unit would work as well or better than the 8000 BTU window AC for cooling and dehimidification. Is this like comparing apples and oranges?
Thanks for any input.
 
Hello - thanks for the heads-up on the idle consumption issue. Did Senville ever clarify why it's so high? We have been cooling and dehumidifying the upper floor of our house with a 8000 BTU window air conditioner for the past few years. Our shoes no longer grow sweaters as they did in the "good old days" with open windows and no AC. Our main room is about 600sf, and with a 60w floor fan the adjacent 2 bedrooms stay comfortable at night for sleeping. The AC unit shuts off by midnight or so after the outdoor temp dips into the 60s or 70s. Summer high temps sometimes get into the 90s, and the humidity is very high. The house is fairly well insulated with good shading over windows. We are preparing to upgrade to a mini split, and I'm wondering if a 9000 BTU single zone unit would work as well or better than the 8000 BTU window AC for cooling and dehimidification. Is this like comparing apples and oranges?
Thanks for any input.
If I recall correctly senville said that the mini split uses power in order to be ready for an instant on. It didn’t seem like a good enough reason for 200w of lost energy but disconnecting it from power doesn’t hurt it so it’s not a dealbreaker for me.

Btus are btus 9000 btu should cool better than 8000. The advantages of a mini split is lower power use and more consistent cooling. A high. Seer rating mini split will slow down rather than cycle on and off giving you even cooling and dehumidification. The mini split is also very quiet.
 
I found a thread on another site about mini split phantom loads.
One of the contributors suggests the 200w idle consumption is likely from the heater inside the compressor (crankcase heater), which stays on to prevent compressor damage. When the outdoor temp is below 68 F, the heater "is necessary because liquid refrigerant will migrate in the system to the coldest point and collect there... It is not a phantom load if you intend on operating the system anytime in the next 12 hours, In fact it is necessary to insure proper operation of the system... If you are not planning on operating the system for long periods of time you can turn off the circuit breaker so long as you to turn on the breaker 12 hours before you start up the compressor."
In the same thread a Mitsubishi controls engineer suggested the 200w figure was about 3 times too high - an error related to power factor and the meter being used. Other people confirmed this after trying different meters.
So, maybe the phantom load isn't that bad after all, especially if a pan heater in not in use.
 
I found a thread on another site about mini split phantom loads.
One of the contributors suggests the 200w idle consumption is likely from the heater inside the compressor (crankcase heater), which stays on to prevent compressor damage. When the outdoor temp is below 68 F, the heater "is necessary because liquid refrigerant will migrate in the system to the coldest point and collect there... It is not a phantom load if you intend on operating the system anytime in the next 12 hours, In fact it is necessary to insure proper operation of the system... If you are not planning on operating the system for long periods of time you can turn off the circuit breaker so long as you to turn on the breaker 12 hours before you start up the compressor."
In the same thread a Mitsubishi controls engineer suggested the 200w figure was about 3 times too high - an error related to power factor and the meter being used. Other people confirmed this after trying different meters.
So, maybe the phantom load isn't that bad after all, especially if a pan heater in not in use.
I can’t seem to find the email that I got from senville but if I recall the spokesman that responded assured me that no harm would come if the power was manually removed from the unit but that it would increase the time before the unit would start cooling or heating also that no pan heater was involved. No turn it on 12 hours before startup in cold temps warning was in the installation manual either. It seems a poor design to require a heater that does not automatically lock out until the compressor is warm enough when the heat pump is likely to be used when cold temperature related power outages are most likely (actually quite frequent in some places) the “phantom”power consumption was showing up on my AOI inverter and so I don’t know if that reading was accurate or not but it flattened my batteries at a rate consistent with a 200w draw so I assumed it was nearly accurate.
 
I have a 12k BTU mini split heat pump in my new DIY motorhome. My indoor unit is mounted up at the front of cabin. Without proper circulation, the back of the cabin struggles to maintain ideal temperature in extreme temperatures. Most RVs use ducts for both the heating and cooling. Moving tons of air obviously has its drawbacks, but one advantage is that it properly distributes throughout the RV. RVs are very...rectangular. They aren't great for circulation without some help. All that to say, location and circulation probably make as much of a difference as the size of the mini split. A small fan might defeat the point of the "ductless" mini split, but it can help quite a bit if you place your indoor unit in a bad location.

Another big difference is insulation, but that's probably obvious to everyone. Regardless, I'll always suggest in better insulation before better HVAC equipment. That's not always very easy in an RV though.

I should also note, I've only used my mini split for a couple months so far, and 95% of it has been in heat pump mode. These things are unbelievable! It can heat my setup with very little energy so long as temperatures are 20+F. I found it a bit more efficient to supplement it with a space heater once it reached single digit temperatures (F). But as another disclaimer: my DIY motorhome is built on a refrigerated box truck, so the insulation is significantly better than a standard travel trailer.
 
I plan on putting a panasonic 12k inverter mini split in our 35 foot 5th wheel. I will then pull the two ac's off the roof and fill in with insulation. Henrys kool koat to decrease the temps from sun and seal the roof from leaks. Supposedly Henrys will drop roof temp by 15 degrees. I will then add through the wall quiet fans to the bedroom and bathroom as circulation to the front of the camper isn’t that great.
 
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I plan on putting a panasonic 12k inverter mini split in our 35 foot 5th wheel. I will then pull the two ac's off the roof and fill in with insulation. Henrys kool koat to decrease the temps from sun and seal the roof from leaks. Supposedly Henrys will drop roof temp by 15 degrees. I will then add through the wall quiet fans to the bedroom and bathroom as circulation to the front of the camper isn’t that great.
I have a 28' TT (2018 Imagine 2800BH). The only available wall space that wasn't on a slide-out was in the front bedroom. Two years ago I installed a 12k BTU LG mini-split. It cools and heats the interior pretty well, but as others have suggested you need lots of air movement to circulate the air to the opposite end of the camper. I use a Vornado floor fan for this and it does work. The A/C struggles to keep up when the outside temps are 90+ or if the camper is in full sun.

With a 35' 5th wheel it might work if you put the air handler in the center, but if it were me I'd install a dual-zone mini-split and put one air handler in the back and the other in the front. This will require 240V for a multi-headed outdoor compressor.
 
Catch the cold air pooling out aways a bit in front of the evaporator and most any small fan directed flat across the floor makes a conveyor belt to 'mound' up cold air on the far side & gets more hot air back to the evaporator... 1915 farmhouse with afternoon/evening sun heated walls that would be an oven once the heat got through the walls & rock plaster between 9pm & midnight was tamed doing that by a 5k Btu window unit & $10 walmart table fan from 30' away : )
 
9k seems so small for a 38' I thought most people were doing 12k systems in 25-35' units. Sounds like multi-zone might be the solution for you.

Also 200 watts for an "off-state" seems like a lot! Did you figure out what was causing that?
I'm getting ready to put in a mini split on my 26' and have been debating back and forth between a 9k and 12k. It doesn't seem to be an exact science and I think Im right on the border.

Im really worried about undersized because of the cost of a reinstall if it isn't sufficient. I've had bad experiences with oversized central AC in a house and know generally you don't want to oversize due to short cycling. However, that's supposed to a relatively benign issue with mild oversizing on the newer inverter split ACs
 
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