High Efficiency Air Conditioning Units for non-generator powered campers

[IdaSHO]

As mentioned, the amount of temperature drop has a lot to do with it.
Here are a few fun ways to look at an old nasty camper, traditional truck camper, and a very well insulated IDACAMPER.
And let assume 90 degree temps, and you want to condition the camper to 70 degrees. So, a 20 degree drop.



Crappy truck camper, zero insulation, and many leaks.

Width = 7'
Length = 10' (simple clean number to work with)
height = 7'
Insulation = POOR

RESULT= You will need 5,174 BTU/hour or 1,516 watt.



Typical modern truck camper, with minimal insulation, non-insulated windows, and a few leaks.

Width = 7'
Length = 10' (simple clean number to work with)
height = 7'
Insulation = NORMAL

RESULT= You will need 2,464 BTU/hour or 722 watt




Then a well insulated and insulated windows, tightly built IDACAMPER of the same dimensions.

Width = 7'
Length = 10' (simple clean number to work with)
height = 7'
Insulation = GOOD

RESULT= You will need 1,478 BTU/hour or 433 watt.


This is yet another reason why I seem to harp about the insulation capability of a camper, if the intention is extended or full time use.
Every time you add R-value, you dramatically increase the overall efficiency of the camper.

The result is market reduction in energy usage, that translates into reduced operating costs.
And when traveling full-time with little to zero income, operating costs are EVERYTHING.

 

[MNtal]

So with that being said what R value do you think someone should shoot for when building a Camper?

R7 or Better?

 

[IdaSHO]

I run 1.5" XPS (extruded polystyrene) that boasts a R-value of 5 per inch.

So walls are R 7.5 plus whatever small insulation values the marine ply exterior and interior paneling provides.

Thats floor, walls, ceiling. And the entire camper, tanks, batteries, etc, are within the insulated shell to create a true 4-season unit that you can comfortably operate in sub-zero temps without mechanical worries.



I find 1.5" of XPS to be the best back for the buck, and provides a nice middle ground between insulation capacity and wall thickness.

Remember, every time you increase the wall thickness, you encroach upon the interior, essentially shrinking your camper.

So for typical sized campers, I treat it as the standard. For larger rigs, I encourage thicker walls.

 

[MNtal]

I have 2" wide wall framing in my Box and was planning for 1/2" Insulation layer inside that with a 1/8"-1/4" thick marine ply paneling inside that. Outside is a .100" Aluminum Skin on the walls and .125" Skin Roof.
.
Using the XPS Foam I could see R12.5 in the Walls and R10 in the Ceiling. Ceiling height is lousy in the ambulance module boxes.
.
/Hijack

 

[IdaSHO]

If you already have thick wall cavities, I would certainly fill the entire cavity with XPS, so long as it doesnt blow the budget.

I hate to see ANY air gaps within walls. Simply asking for mold/rot issues.

 

[campo]

Hi idaSHO
Nice to discuss. Remember that I use normally European standards and am not native English.
Like for Fahrenheit to Celsius I have to google. But I have no problems at all to understand you.
.
Your calculator tool is nice and easy to use.
The idea of this tool was to calculate houses and not extremely small cubic camper boxes. Keep that in mind and make the necessary correction. On the result side I am missing some 500 Watt (1.700 BTU/h). This is what I suggest to add for the 2 persons on board, the obligatory ventilation to breathe and some electrical devices in the volume (like the fridge, inverter,..) Don’t forget that some air means comfort and an RV is not a submarine.
.
In my personal calculations I use only for the most extreme summer situation 45°C to 28°C (113°F to 82°F). As I say, that is maximum, good for calculation, not usual in our climate zone. What means a delta T of 17°C or 31°F. I calculate always more than one situation, and of course heating in winter.
.
Then you have also to pull down the interior components, not only the air volume, mostly wooden furniture, the first time. We call it heat load.
When starting up the AC you will need something like 2 to 3 times your calculated need to obtain the desired interior temperature.

 

[LeishaShannon]

Changing quickly the cheap AC unit when it breaks down ?
I don’t think so.

I guess thats another advantage of domestic splits. Ours took 2 of us ~2 hours to install and there are domestic AC installers in every major town who could replace it with a similar model.

 

[DiploStrat]

:Wow1:

Hi idaSHO
... am not native English.
...
Then you have also to pull down the interior components, not only the air volume, mostly wooden furniture, the first time. We call it heat load.
When starting up the AC you will need something like 2 to 3 times your calculated need to obtain the desired interior temperature.

The first part is not a problem, your English is better than my Flemish!

The second part is important to note. Some of the sleeper cab A/C manufacturers have taken to adding a clarification that "the A/C is for maintaining a comfortable temperature, not for the initial pull down." They suggest using the cab A/C for this.

This is worth noting for a camper; in severe heat, you are probably going to have run the A/C for several hours while driving to achieve an initial cool off. Else, you may have to wait until later at night, say 10PM before attempting to run the A/C.

On days when you start out driving, this may not be an issue, but if you are camped for several days in Tamanrasset ... :Wow1:

 

[LeishaShannon]

I forgot to mention, I came across the dometic "harrier" on another forum. Its a roof top RV AC that uses inverter (variable speed compressor) technology. The COP is still miles off an efficient domestic unit but might be a good option for some:

http://mygenerator.com.au/media/160318_DOMETIC-Harrier-Brochure.pdf

 

[Coachgeo]

on the Split units.... can you disconnect the lines say with a quick disconnect like item orr? My truck would be used as a TRUCK most times with the camper box removed.

 

[IdaSHO]

The second part is important to note. Some of the sleeper cab A/C manufacturers have taken to adding a clarification that "the A/C is for maintaining a comfortable temperature, not for the initial pull down." They suggest using the cab A/C for this.

This is worth noting for a camper; in severe heat, you are probably going to have run the A/C for several hours while driving to achieve an initial cool off. Else, you may have to wait until later at night, say 10PM before attempting to run the A/C.

100% correct.

And I should also comment on the point made about a camper not being a submarine.
No, not a submarine, but it SHOULD be treated like an ice chest.

Unlike a home, a camper cannot rely on thermal mass. Weight is the enemy, so the camper must be built like an ice chest.
Insulated well, and sealed up tight.

With regards to cooling with an AC unit, air exchange will only work against you.
Humidity of the interior air is the only reason you should worry about air exchange.
Winter travel for instance, every time you breath you dump moisture into the air.
And with a good sealed burn furnace, the humidity doesnt have anywhere to go.
The result is moisture condensing on the coldest parts of the interior, like windows, and potentially freezing creating ice dams.
So the easiest thing to do to remedy the problem is crack a window, and turn on an exhaust fan.

AC units actively dry the air, so the need for air exchange simply isnt there.
Obviously a small amount of air exchange is needed, simply from a breathable air and dangerous carbon monoxide standpoint.
But the actual volume of air needed to keep things in the green is small, when compare to cold weather problems.

 

[campo]

:Wow1:

…. Some of the sleeper cab A/C manufacturers have taken to adding a clarification that "the A/C is for maintaining a comfortable temperature, not for the initial pull down." They suggest using the cab A/C for this.
.This is worth noting for a camper; in severe heat, you are probably going to have run the A/C for several hours while driving to achieve an initial cool off. Else, you may have to wait until later at night, say 10PM before attempting to run the A/C.
.On days when you start out driving, this may not be an issue, but if you are camped for several days in Tamanrasset ... :Wow1:[/COLOR]

.
Hi Diplostrat
.
I do agree with you. In fact you need 3 different AC systems. It would be optimal if you could combine them in one unit.
Thats why I tested with 4 AC systems on my rig ...

Campo

 

[campo]

…. I came across the dometic "harrier" on another forum. Its a roof top RV AC that uses inverter (variable speed compressor) technology. The COP is still miles off an efficient domestic unit but might be a good option for some:

http://mygenerator.com.au/media/160318_DOMETIC-Harrier-Brochure.pdf

Hi LeishaShannon !

The variable electrical driven compressor idea is super.
We allways need to check if variable speed means also variable power consumption...
The electrical power consumption 6,8A/230V is as you mention still very high for this 3,1 kW cooling AC.
and I see no minimal power consumption on the specs.
.
The AC unit on the roof is not possible and not desired in my case and many other expedition vehicles. (solar panels and off road height)
.
My idea is to build an electrical 12/24V Volt +/- 2,4 kW maximum cooling unit (day and driving) that can regulate down to extremely silent 600 to 800 Watt (night and bedroom only compartment)..

Less than 30 dB(A) in your bedroom. 50dB(A) is really unacceptable.
In a version with components that can be used on and off road. Not a plastic house AC unit.
Of course split and weather resistant.
.
We do not really need the inverter principle because heating in winter with electricity is unacceptable for a very mobile expedition RV.

 

[campo]

We know that we need cooling capacity to cover the thermal losses through the walls.
The better word could be the outer peel of the box, because sometimes insulation is doubled by internal walls or furniture.
That’s the one where you calculated in your example +/- 500 (433) Watt for your standardized dimension (like IDACAMPER) in good isolation.

…Then a well insulated and insulated windows, tightly built IDACAMPER of the same dimensions….
Insulation = GOOD
RESULT= You will need 1,478 BTU/hour or 433 watt.

.
There is more:
A lot more thermal capacity will be needed for the first pull down/heat up starting from cold/warm outside temperatures. I agree that it is not always necessary this “first pull down”.
Depends on the situation. But if you only run the AC before going to bed in the evening than you will be confronted with this problem.
Remember that we have something like a mass of 300kg (660 lbs) stuff, equipment and furniture inside.
Let’s calculate with only … wood to make it easy.
I calculated that you need 2.290 Watt to cool down or heat up 300kg wood with 22°C
(Pull down a mass of +/- 660 lbs wood with 40°F is thermal need 7800 BTU/h)
.
Of course this thermal "first pull down" need depends on the individual situation and exact parameters.
Remember that I tested it, did some measurements and also tried to "evaluate" the result.
What I measured in my practical experience is that I need 1/4 hour before the AC system is cooling after a start-up.
The RV interior temperature feels comfortable some 3/4 hour later.
Conclusion is that, if you do only start to cool the box late in the evening before going to bed, you'll lose approximately 1 hour battery capacity just to start up your AC process.
.
We also have the ventilation losses.
Yes it is not a submarine. We will have to make some breathing refreshments.
In a submarine breathing air is produced on board and minimised to the max.
A person sleeping or living in a small RV wants some more comfort than a mariner in a submarine environment,
Classical values are 25 m³/h air refreshment for a room. Another classical value is 2 refreshments/hour with one open window or 20 air refreshments/h with 2 diagonal opened windows,
The smaller the room is (like a RV bedroom) the more refreshments per hour you will have to make, so don't use house or office refreshment values, you'll need lot's more in a compact RV environment,
Degree of humidity is important for comfort feeling but comes only after having adapted the air refreshments.
Air refreshments (ventilation) is obligatory to breath and for comfort.
The theory is that we ventilate more in normal conditions and less in extreme, to gain on battery consumption.
For the calculations it is easy to average the calorific thermal losses at 500 Watt for 2 persons living on board.
These 2 persons generate body heat (125 Watt per person) of course it depends from the moment (reading a book it is only 70 Watt for the tiny lady and can be 120 Watt for a fat man)
The 500 Watts is a value for body heat for 2 persons + ventilation + classical on board equipment like fridge, inverter, light, small and big battery charger's and much more that you might forget like the warm water boiler,
Included in this 500 Watt is here the necessary but minimalised ventilation to breath in reduced comfort conditions.
(Remember this is all about … we want to save on batteries)

 

[campo]

This is where we did the extreme overnight AC test with a maximum value +43°C (109°F) night temperature
in july some 250 km south of Marrakech, Marokko
.
.

.

.