This page covers some some cooling options for camper vans. They range from passive methods through forced ventilation and evaporative cooling to full air conditioners.
A lot of people doing camper van conversions want to be independent of shore power or generators, and generally, this is very doable. But, if you need air conditioning for your camper, it becomes much more difficult. Some methods for doing air conditioning on camper vans with no shore power or generator, and only batteries and solar are discussed below.
Definitely interested in hearing other ideas on how to cool camper van — please add a comment below.
Some features that will make your camper van more comfortable on warm days:
- Choose a reflective paint color like white.
- Insulate the van well — if you can include a reflective layer with an airspace in the insulation stackup, this helps with radiant heat transfer.
- Provide windows and/or vents for air circulation
- Use reflective shades in the windows to insulate and (more important) to avoid solar heat gain.
- Park in the shade — shade makes a very large difference in what the inside temperature will climb to. Cuts heat gain about in half.
While I have not seen anyone do this, some form of shade that you could deploy over the van to effectively shade it would be quite effective. Even a shade spaced 2 or 3 inches off the van should be very helpful. Got any ideas on how to do this?
These methods, plus a fan for forced ventilation (next section) may be enough for some climates.
Update July 2018 – A practical sunshade for the van:
This is an external sunshade developed my MSNomer of the ProMaster Forum. It is made from Tyvek and attached to the van with magnets.
By measuring the van skin temperatures on the outer skin of the van in in the sun and in the shade, I estimate that the heat gain to the van in the sun is about twice what it is in the shade. The Tyvek sunshade is probably not quite as good as being in the shade, but it should be close. The more of the van exterior you can cover the better, and if you can space it off the van a bit, that would be very good. Post on the PM forum describing the sunshade… MSNomer’s very good website…
Many camper vans and RVs use roof mounted powered fans to provide forced ventilation. These fans do a great job of getting the inside temperature down close to the outside temperature. Its good to combine the power fan with the passive cooling methods mentioned above to get the best effect.
The two most popular brands are the MaxxFan and the Fantastic Fan — there may be other good ones out there. Our MaxxFan has ten speeds, will blow air in or out, will automatically turn off and on to control temperature, and has a remote control — pretty fancy, and it does the job well.
One thing to bear in mind with these fans to work and actually circulate air, there have to be windows or vents for the fan to pull the air in from (or push it out to if the fan is in intake mode). Some people who do not want to have windows use floor vents for this purpose.
This is a test I did on cooling provided by our MaxxFan. In a nutshell, the fan was able to lower the inside temperature from 93F to 82F with an outside ambient temperature of 78F.
But, at best, the fan can only lower the temperature inside the van to what the outside temperature is, and it cannot lower humidity. So, if its really hot and humid outside, the inside of the van is not going to be comfortable. You will have to avoid these conditions, or go to one of the cooling methods listed below.
Evaporative cooling uses the evaporation of water to cool an air stream. Each pound of water evaporated removes nearly 1000 BTU from the air stream doing the evaporating. Evaporative coolers can be quite effective, and will reduce the temperature of a low humidity air stream by 20 or 30F. But, evaporative cooling is not effective when the humidity is high — see the chart below.
The big advantage of evaporative cooling is that it takes very little power to operate one compared to conventional compressor AC units. They can be operated on solar and batteries quite nicely and do not require either shore power or a noisy smelly generator.
Commercial Evaporative Coolers
TurboKool is a commercial unit that will cool about 750 cubic ft per minute of air by 20 to 30F depending on the ambient conditions. One of these units should effectively cool an insulated camper van. It has about the same footprint as a common RV roof AC, and installs in the same 14 inch square opening.
Evaporative coolers use water. There is a formula for estimating how much water an evaporative cooler will use here.
Gal Per Hour = CFM * deltaT * efic / 8700
CFM is the cooler airflow in cubic ft per minute.
deltaT is the inlet temperature – outlet temperature
efic is efficiency (they recommend 93%)
If you take the TurboKool commercial unit above, it puts out 750 cfm, and if you assume a 20F temperature drop, it would use (750)*(20)(0.93)/(8700) = 1.6 gallons per hour. This is on high speed, so maybe actual average use might be lower.
So, if you used it for 12 hours in a day, it would need 19 gallons. A lot of camper vans don’t have huge fresh water tanks, so this could be a problem if there is not a source of water around the campground. The water does not have to be drinking water, so taking it right out of the river or other non-potable supplies would be OK.
The efficiency is quite impressive. Judging by the reviews, the TurboKool when operating in low humidity conditions provides about the same level of cooling as a conventional roof top RV AC unit. The TurboKool uses about 50 watts while the roof top AC is more like 1000 watts, so, the TurboKool is about 20 times more energy efficient. This makes it very practical to operate on solar and batteries. The key caveat that it needs low humidity conditions.
SouthWest Solar makes some evaporative cooling units that might be adapted for using in cooling camper vans.
DIY Evaporative Coolers
RD’s design uses his Fantastic Fan roof fan to push air through a watered pad and then blow out the holes in the outer bucket. On a 93F outside day, the air coming out at the cooler was 63F, and it was able to cool the whole van down to 85F. Total cost $20.
This section discusses “true” (compressor based) air conditioners — the ones that require a whole lot of electrical power to run, but provide good cooling even in hot and humid conditions.
Because these units use a lot of power, efficiency is quite important.
Air conditioning units vary quite a bit in efficiency. If you want to be able to operate your AC independent of shore power or generators, then efficiency is very important. AC units draw a lot of power and most camper van conversions won’t be capable of running a conventional AC unit for very long, but the more efficient it is, the more likely you will be able to run a while on batteries and solar. All of the methods listed above under Passive Cooling (insulation, reflective shades, light color van, and shade) make the job of the AC unit much easier and will reduce the power used and extend how long your batteries will last.
While efficiency for AC units is stated in different ways, I’ve tried to give the EER (Energy Efficiency Ratio) for each of the AC units discussed below. The EER is defined as the cooling output in BTU per hour divided by the power input in watt-hours per hour. The EER test is normally done with an outside air temp of 95F, and an inside air temperature of 80F dry bulb and 67F wet bulb.
So, for example, if an AC unit produces 8000 BTU/hr of cooling while using 800 watts, the EER would be (8000 BTU/hr) / (800 watt-hrs/hr) = 10 EER. Choosing an AC unit with a higher EER will reduce power consumption.
RV Roof Air Conditioners
RV roof air conditioners have been around for many years and are the most common way of air conditioning RVs. Some RVs use one roof AC, while larger ones use two or even three. They come in ratings from about 8000 BTU/hr to about 16,000 BTU per hours. Here are some examples.
|AC Unit||Cooling (BTU/hr)||power (watts)||EER|
|Coleman Mach 3 PS||13,500||1090||12.4|
|Coleman Mach 3 Plus||13,500||1190||11.3|
The Mach 3 PS, where PS stands for power save, is recent design aimed at efficiency, and the 12.4 EER is good for RV roof ACs.
Splits and Outdoor
Climate Right offers some interesting outdoor and mini-split ACs that are intended for trailers, tear drops, kiosks, etc. — could work out for a camper van.
This is a unique split AC. It has an inside and outside unit (like all splits), and the two are permanently connected together. To use it, you open a window in the van, and from the outside you pass the inside unit through the window and hang the outside unit on the window sill.
For travel, you take it off and store it inside the RV.
It only runs on 220 VAC. Provides 2400 BTU/hr cooling, which is kind of low. The EER is about 7 — not so great.
This interesting post on the Transit Forum shows how one person was able to convert the very efficient Midea window AC (SEER 15) into a mini-split.
12 volt split AC
These Cruise-n-Comfort air conditioners run directly from 12 volts, so don’t have to deal with the inefficiency of the inverter. On these units, the condenser is mounted outside the vehicle and the evaporator is mounted inside.
They are pricey at about $4K.
A DC Powered Mini-Split
This DC powered mini-split from Hotspot Energy looks promising. It runs on 48 volts DC, so no inverter is required to convert the battery/solar DC to AC – this results in an about 15% gain in efficiency.
The SEER is listed as 19.2, which is quite good for an RV air conditioner. Price is about $2100 for just the Mini-Split – they also sell kits that include solar panels and batteries.
Adapting Window Air Conditioners
Small AC units made to fit in a window and provide air conditioning for a room are commonly available, compact, cheap and fairly efficient. The most efficient ones have EERs around 15. There are several schemes for adapting these units to camper vans. The Energy Star Room AC ratings allow you to compare EERs – note that the ratings give CEERs, which account for standby power use that is not included in the EER ratings. Right now, the Midea brand appears to have the best CEERs.
It takes some work to adapt these window ACs to use in a camper van, but people have worked out some ways to do it — some listed below.
One new window AC from Midea seems particularly well suited for van conversions in that it uses the same kind of more efficient design that is used in a lot of mini-splits. This not only makes the unit quieter, but also efficient enough that it might be possible to run it off batteries and solar (at least for some conditions). I would say that this is one of the best options for AC for a camper van with a chance of running on solar and batteries. It seems well suited to a backdoor mount.
Mounting methods for window ACs range from replacing a van window with an adapter plate that the AC unit is mounted on, to mounting the unit inside the van and then arranging for a flow of outside air over the AC condenser. Examples below.
Haier Energy Star window AC, EER 12.3.
Window AC example 1:
Wbullivant on the ProMaster Forum worked out a way to install a 5K BTU window AC in the bed platform of his ProMaster van conversion. Its a very nice installation that does not take up much space. He uses two 4 inch vents that go through the floor to circulate air though the condenser coil on the AC. If he AC was installed in a window, outside air could circulate freely around the condenser coil to cool it, but since on his mounting, the condenser coil is inside the van, and the 4 inch vents are required to circulate outside air to cool the condenser.
He used a Frigidaire similar to this one with one… with an EER of 12.2.
I did some testing on a window AC that we had lying around… It is pretty clear from the testing that restricting the cooling airflow to the condenser coil on the AC can have a major impact on efficiency of the unit and maybe even on its ability to operate at all. Time spent on getting good ventilation to the AC condenser is well spent. The testing at the link above provides some data that will help with sizing the venting.
Winow AC Example 2:
Here is another use of a window AC on a van conversion. It mounts the AC unit near the bottom of one of the back doors. The result is not aesthetically bad, is strong enough to support the AC unit, and does not interfere with other uses. It also takes up essentially no interior space in the van.
Window AC example 3:
Here is yet another idea for mounting a window AC unit. The AC unit sits on a counter top while traveling, but slides outward through a hatch in the van sidewall when stopped. No rerouting of the air flow is needed as when the AC is in the slid out position, it is just like it was installed in a window. A marine hatch cover is used to close up the opening when in travel mode. The slide is a regular hardware store slide. Some garage door rubber weather stripping is used to seal the edges of the opening when the AC is in the out position.
Window AC Example 4:
Pretty slick arrangement.
Thanks to Mark and Lissa for finding this scheme — see comment section below.
Here is another nice install of a window AC.
The window AC pulls in and out on drawer slides.
Full description in the ProMaster Forum post…
With a portable AC unit, the entire unit is inside the room being cooled and hoses are used to pull in ambient air and to exhaust the hot air that comes from cooling the condenser coil. The appealing thing for a camper van is that the unit is easily removed from the van when its not needed, but on the negative side, they take up space, are noisy, and are not as efficient.
Portable AC units are not as efficient as window AC units and are noisy– this is a quote from Consumer Reports in 2008:
While portable A/Cs might be convenient, those we tested delivered only about half of their cooling capacity—that means they operated with an energy-efficiency ratio (EER) of about 5 or 6. Compare that with the minimum EER of just under 10 for the window air conditioners we’ve recently test (we tested window models with an EER as high as 12).
If you are trying to operate from batteries/solar, the lower efficiency will cut operating time significantly.
Operating on Solar and Batteries
The section provides a little data on what it takes to air condition a camper van using solar and batteries.
Efficiency and Energy Use
The table below compares an example or two of each of the above AC units on how much cooling it provides and how energy efficient they are.
EER is an efficiency rating — the higher the better.
|Coleman Mach 3 PS||Roof||13,500||1190||11.3||325||104|
|Coleman Mach 3 Plus||Roof||13,500||1595||8.5||325||140|
|Climate Right ductless minisplit||mini-split||12,000||1241||9.7||323||109|
|Fridgadaire FFRE0533S1 5000BTU||Window||5,000||410||12.2||124||36|
|Haier Window 5400 Btu||Window||5,400||440||12.3||180||39|
Cooling output on high in BTU per hour.
Power consumption in watts at high cool.
EER Energy Efficiency Ratio — ratio of cooling output in BTU to electrical power to run in watts. Higher is better.
Flow is airflow from outlet vent in high speed in cubic ft per minute.
Battery Drain is the number of amp-hrs that would be drained from a 12 volt battery with the AC run continuously on high.
How much cooling is needed?
This depends on a lot of things — like:
- How hot and humid is it outside
- How big is your van
- How well insulated is your van
- Are windows insulated and have reflective shades
- Can you park in shade vs direct sun
Some have reported descent cooling of insulated camper vans with 5000 BTU/hr AC units, while some have reported only getting satisfactory cooling with larger (say 13,000 BTU/hr) units.
My van is a 136 wheel base (18 ft overall length) high roof ProMaster. It is insulated with 1 inch of polyurethane foam insulation (floor, ceiling, and walls),, and the windows are insulated with Reflectex plugs that reflect and insulate. The calculated heat gain with an outside temperature of 95F and inside temperature of 75F is only about 1600 BTU/hr. To this we need to add the heat gains inside the van — each human adds about 500 BTU/hr and pets also add heat, things like refrigerators, inverters, lights .. also add some heat to the interior. So, allowing 1500 BTU/hr for these gains, the total heat that the AC must remove on a 95F day might be about 3000 BTU/hr. This analysis assumes that your are parked in the shade — that is, no direct gain from the sun. In addition, while a capacity of 3000 BTU/hr might be enough to meet the steady state demand, more capacity will be needed to initially cool the van down. So, while this seems to support the idea that a 5000 BTU/hr AC unit might do the job most of the time for a well insulated van, it might come up short some of the time.
Note that the heat loss from a non-insulated version of my van under the same conditions is 7500 BTU/hr — 4.5 times as much as the insulated version.
Another thing to keep in mind is that solar gain from windows or windshield in direct sun can be very large. Ten sqft of window area with 80% transmittance in direct sun will gain about 2200 BTU/hr — more than doubling the heat gain of the basic van. So, be sure to use reflective window shades.
Operating on Batteries and Solar
If you want to have any hope of operating your conventional air conditioning on batteries and solar, you will have to
- Insulate the van well
- Use an efficient AC unit
- Have a large battery pack and solar array
If we assume 95F outside and 75F inside and the well insulated van described above with the internal gains used above, and parked in the shade. Then the steady state cooling need is about 3000 BTU/hr. If we assume an efficient 5K BTU/hr AC unit with an EER of 12, and we assume an inverter efficiency of 95%, then the steady state power usage is:
Power to AC = (3000 BTU/hr) / (12 EER) = 250 watts, or 250 / 0.95 = 263 watts from the battery — this is about 22 amps on average from the 12 volt battery. This basically assuming that the 5K BTU AC unit runs 60% of the time. So, under this fairly optimistic scenario, 22 amp-hrs are removed from the battery each hour. If you had a 440 amp-hr battery pack (eg 4 golf cart batteries), and discharge it to 20%, and assume 4 amp-hrs of other uses (eg fridge, lights, …), then you could get (440 amp-hrs)*(0.8) / (22 amps + 4 amps) = 13.5 hours of van operation with AC out of a fully charged battery. Not too unreasonable.
Its practical to install about 600 watts of solar on a camper van roof — maybe more with the longer vans. PVWatts says that on average in (say) Truth or Consequences, NM in mid summer, with horizontal PV panels, you should average about 110 KWH per month, or 3.67 KWH per day, or the equivalent of 305 amp-hrs per day, which is a bit short of the 350 amp-hrs required to charge from 20% up to full charge. Maybe 700 watts of PV in a good solar location would do it.
Note that there is a bit of a disconnect in the above in that it assumes the PV panels are in the sun and the van is in the shade.
Its clear that its a tough challenge to run AC on batteries and solar, but with a lot of care it might be done — especially if you don’t camp in really extreme hot weather. Of course, some engine running to supplement battery charging could be used.
This is one area where the high capacity of lithium batteries would be a big plus.
Another option to get more charging would be to install a 2nd alternator designed to produce high charge rates for the house battery.
It also points out that if evaporative cooling can work in the climate you use the van it, its a HUGE advantage in getting to an AC system that will operate from a battery pack and solar.
Comments, Suggestions, Ideas?