roof mounted cab AC

[coachgeo]

here's one way to get AC in the cab... Not to sure if this is the way I would go....

Long term report will be interesting. cab AC (typical engine mount type) are like 5 times the power of the one he installed cause in general a cab/car is not a room.. but essentially a solar oven. To get max benefit of what he installed probably will have to massively insulate the cab from solar heat and engine heat. Mentioned on Youtube he should also consider a shore power box to plug it in and crank it up several hours prior to leaving on an adventure to overcome the heat built up by solar oven affect as it sat baking in the sun. Some solar shades on windows and windshield may help. Maybe he should consider permanent solar shade the rear side windows?

Time will tell.

 

[Awesomeness]

cab AC (typical engine mount type) are like 5 times the power of the one he installed

The engine mounted compressors have considerably more power available to them than electrically driven units. 1HP = 746W, so an engine mounted compressor stealing several HP (that you'll barely notice) is easily more powerful than a 2kW-running (~2.8HP) electric A/C. It's also far more efficient, because of all the losses in running an alternator, running that electricity through cabling/devices, and then driving an electric motor again. You probably end up having to rob 2HP from the engine to generate enough electricity for 1HP of running electric motor.

 

[deshet]

The engine mounted compressors have considerably more power available to them than electrically driven units. 1HP = 746W, so an engine mounted compressor stealing several HP (that you'll barely notice) is easily more powerful than a 2kW-running (~2.8HP) electric A/C. It's also far more efficient, because of all the losses in running an alternator, running that electricity through cabling/devices, and then driving an electric motor again. You probably end up having to rob 2HP from the engine to generate enough electricity for 1HP of running electric motor.

Those window units ACs are able to produce a lot of cooling. Some people hack them to build massive walkin freezers/fridges. I don't think the BTU load in the worse condition is enough to exhaust an average sized window unit, the smallest ones are 5000 BTU. It will likely cycle on an off too often. It is all based on BTU load. A real AC guy can calculate the worse case load. The engine driven units look better but at 25-40 times the price it is a decision.

A 1 ton house hole AC is 12,000 BTU. I have seen many 2000sq ft homes with only 2.0 ton units or 24,000 BTU of cooling. (12 BTU per sq ft) The Cab of a LMTV is less the 50 sq ft so a 5000 BTU window unit would provide 100 BTU per sq ft. The 5000 BTU units are usually under $150.00.


https://www.youtube.com/watch?v=alNft9J2wEg

This one show a lot more capability. 40 degrees in a 24' shipping container

https://www.youtube.com/watch?v=OG_-qNYuJhI


Thanks

 

[coachgeo]

Those window units ACs are able to produce a lot of cooling. Some people hack them to build massive walkin freezers/fridges. I don't think the BTU load in the worse condition is enough to exhaust an average sized window unit, the smallest ones are 5000 BTU. It will likely cycle on an off too often. It is all based on BTU load...... The engine driven units look better but at 25-40 times the price it is a decision.

Amen

A 1 ton house hole AC is 12,000 BTU...) The Cab of a LMTV is less the 50 sq ft so a 5000 BTU window unit would provide 100 BTU per sq ft. The 5000 BTU units are usually under $150.00...

Folk really should not use the home sq.foot/btu comparison to a cab. It is the most apples to oranges comparison one can use. Reality is the cab is a HOT OVEN and your trying to cool it to lower than room temperature.... be dammed the sq. footage.

that being said... compared to going with engine driven tyical NOS or otherwise Cab AC system it is still probably less costly (but looks more crude) to pay for insulating the holly haill out of the cab, and pay for a less costly lower btu ac system. The more hacked the less costly ..... ymmv

 

[Awesomeness]

Those window units ACs are able to produce a lot of cooling. Some people hack them to build massive walkin freezers/fridges. I don't think the BTU load in the worse condition is enough to exhaust an average sized window unit, the smallest ones are 5000 BTU. It will likely cycle on an off too often. It is all based on BTU load. A real AC guy can calculate the worse case load. The engine driven units look better but at 25-40 times the price it is a decision.
A 1 ton house hole AC is 12,000 BTU. I have seen many 2000sq ft homes with only 2.0 ton units or 24,000 BTU of cooling. (12 BTU per sq ft) The Cab of a LMTV is less the 50 sq ft so a 5000 BTU window unit would provide 100 BTU per sq ft. The 5000 BTU units are usually under $150.00.

That's pretty much all wishful thinking, and ignoring the obvious that vehicles routinely come with 20,000-30,000 BTU heating/cooling systems for a reason. There really isn't a need to speculate on how or why that's what it takes, or compare to well insulated houses and fridges, because you can see empirically that the A/C in your daily driver isn't overkill. The people who have designed this stuff hundreds of times over have established that is what it reasonably takes.

Keep in mind that 5000 BTU home window unit also runs on like 15A @ 110VAC, or 1650W. That's 137.5A @ 12VDC, so you're still outrunning even a beefy upgraded alternator, or what you could get from solar on the roof of an M1079, or both combined really. And that's not even factoring in that if you have to run it through a DC-to-AC inverter you're probably losing another 20% efficiency. Even the alternator upgrades are a couple grand too. Even if the 5000 BTU A/C was 100% efficient (and it's probably nowhere close), 5000 BTU = 1.46 kWh (in terms of unit conversion), which aligns with those amperage draws.

While I would love for there to be some easy and cheap solution for you to find, I think you should have been really skeptical of one the second you started looking around and started to seeing how expensive and how much power all this stuff uses (in it's conventional off the shelf form). It's like posting up that you want to make your car get 100MPG... if it was that easy, all the cars would come that way (conspiracy theories about the gov't keeping us dependent on oil aside). You just can't escape the physics of it. Maybe a fantastic insulating strategy would help you be able to use a very small A/C unit?

 

[coachgeo]

That's pretty much all wishful thinking, and ignoring the obvious that vehicles routinely come with 20,000-30,000 BTU heating/cooling systems for a reason. There really isn't a need to speculate on how or why that's what it takes, or compare to well insulated houses and fridges, because you can see empirically that the A/C in your daily driver isn't overkill. The people who have designed this stuff hundreds of times over have established that is what it reasonably takes....

Agree and disagree. For reasons that are beyond me.... vehicle companies seem to have avoided insulating the shiatt out of vehicles in order to reduce the BTU needs to cool/heat an automobile. Probably cost reasons. Reduced BTU setup may be not really much cost thus probably do not create profit benefit after they insulate necessary amount to get the comfort that public demands and the interior space public demands. Overland trucks are bigger and giving up some real estate might be worth it for lower cost (and fuel consumption) for driving smaller than typical automotive AC systems.

There is no reason to assume that the engineers who design them, do it in a way that logical from mostly an engineering standpoint. More likely they are assigned to design vehicles around parameters expected by the company "bean counters". Figrue that the accountants and others at the top have more part in final designs than the engineers (unfortunately).

 

[Awesomeness]

Agree and disagree. For reasons that escape me.... vehicle companies seem to have avoided insulating the shiatt out of vehicles in order to reduce the BTU needs to cool/heat an automobile. Probably cost factor. Reduced cost of less powerful AC/Heat systems probably do not create profit after they insulate necessary to get the comfort that public demands and the interior space public demands. Overland trucks are bigger and giving up some realstate might be worth it for lower cost (and fuel consumption) for driving typical automotive AC systems

The rebutal is that vehicle companies have been insulating vehicles in order to reduce road noise. They also do not have the cost issues, because they can engineer an engine-driven A/C system, and the cost is factored in from the start (plus economy of scale). However, if they could get by with a 5000 BTU system, they would. Production vehicles are some of the most highly engineered systems on the planet... they don't just throw money at them for no reason.

My point was that I would be foolish to start off by saying "They don't know what they're doing - they're doing it wrong. I can do better.", and instead, I would be seeking to understand why they are using such large systems. Insulation seems an obvious place to poke, both from outside heating and heat from the engine. Perhaps the production automakers have other requirements that we can avoid (e.g. needing to operate to 120° in the California desert, needing to have a particular lifespan on the system where instead we could throw out a $150 window A/C unit every year, etc.). I still don't think it's going to be that easy.

 

[deshet]

I put an inverter in for a client of mine that installed a Coleman unit on theirs. It will run you out of the cab even without insulating the cab any. I'll see if I can find some pictures.

I trust that Shark Bait is being honest when he says that he installed a roof top unit that will freeze the cab.
I would not install a window unit but I am leaning towards a roof top unit.
Most rooftop units are around 13,500 BTU and they will produce way more then enough cooling. I have a decent amount of experience with these and have a coleman unit that is still going strong from 1988. The cab won't need anything for these to cool it down.

My floor is insulated. It will be replaced to reduce sound but I have some insulation already.

The army actually installed a window unit in the box of my M1079 Truck Van and it will cool it down quickly in a 100 degree day in mins.

The engine mounted AC on my 4x4 Born Free could not keep the rear of the Van cool going down the road. The roof mounted unit could cooled everything but required generator power.

 

[Shark Bait]

I found these that I had taken after they converted it into a wash it ruck.You can almost see the roof top unit on it.

 

[deshet]

I found these that I had taken after they converted it into a wash it ruck.View attachment 733721View attachment 733722You can almost see the roof top unit on it.

Did you install a battery bank or just use the truck batteries?

Thanks

 

[Shark Bait]

Did you install a battery bank or just use the truck batteries?

Thanks

Theyre using the 12 volt side of the truck batteries.

 

[coachgeo]

Theyre using the 12 volt side of the truck batteries.

Is there a reason the 12v side was used.... beyond they only had a 12v invertor?

 

[Shark Bait]

Is there a reason the 12v side was used.... beyond they only had a 12v invertor?

That's what they wanted.

 

[Pointman0853]

Crank vs. Batteries...

So, how does Tesla, Volt, etc. get it done?

Pointman

 

[Awesomeness]

Crank vs. Batteries...

So, how does Tesla, Volt, etc. get it done?

Pointman

They do it with batteries/electricity, but as I said above 1HP = 746W, so the 10,000W the A/C is drawing is nothing compared to the 223,800W (300HP) the motors draw. So they don't really care much.

 

[scottmandu]

EV's also have far more battery reserve than the LMTVs.

 

[deshet]

The original truck that I posted a link to has a 6000 watt inverter.
The inverter that Shark Bait installed is 3000 watt inverter. 12v DC to AC

I am not following the last few posts maybe some content was edited out....
It seems that my original question has been answered and the reliability is there for the roof top units. I also have several high end inverters already.

The equation below never changes......

Power(watts) = current(amps) x voltage
_2400watts__=200 amp alternator x 12 volts
_2400watts_=100 amp alternator x 24 volts

Thanks everyone

 

[Awesomeness]

I am not following the last few posts maybe some content was edited out....

No content was edited out. That part of the discussion was about why the engine driven compressors are so much more common, or work so much better. The reason is that the engine is a HUGE 200kW energy supply, so drawing of 10-20kW is barely noticed. With electrical compressors, the available power source (e.g. batteries and alternator) are a much smaller 20kW source, plus all the conversions (e.g. motor -> alternator -> electric motor -> compressor) is a less efficient system (results in less cooling from each watt of energy originally drawn from the engine, so for example you may be drawing 10kW from the engine in order to get 5kW of cooling).

There are obviously cases where people are making it work. The point is that you can make it work a whole lot easier, overkill really, by using the engine driven compressors. Using an electric system requires much more careful planning, and solving a number of other issues (e.g. insulation).

 

[markf]

So im thinking of a CAB AC on an LMTV. using a 9000BTU Mini-split (seer rating of 20) and a 24V to 110 pure sine inverter rated for 1500W (which is overrated to cover turn on current draw) Tie into the 24V battery Bank charged via the 100A dual voltage alternator (I estimate something like 33A run current. Just have to make sure the inverter is turned off when the truck is not running, or its parasitic draw will kill the battery bank. The full power cooling draw of the unit is 6.8A at 110V or 748w. From the 24V battery bank (or Alternator) thats 34 amp draw with 90% efficiency through the inverter. only issue might be longevity of the unit off road. has anyone done this configuration before (under $1000)

 

[Ronmar]

Well you don’t really have 100A available. The batteries need to get back to full charge. A 240AH bank is looking for 25% of the AH capacity from the alternator(AGM’s are looking for 45%), So those 60 amps are spoken for until the batteries are charged. Since the bank is so large this could take a while depending on how discharged they might get… Then there are the operational loads pulled out of that(lights are 26-34A). The alt can only really deliver 60A on the 12V side, so that side is already loaded 100-150% to charge batteries depending on if the lights are on… this leaves the remaining power available out of the alt to feed the 12-24 batts also overloaded simply feeding the batteries… This mismatched battery to alternator relationship is why these trucks have so many power/battery/alt problems…

The question I would ask is do you really want to add load to an already marginal system and further risk a VERY expensive alternator for 9KBTU(Marginal capacity for a large truck cab)? Now you could add another 24V alt to feed this beast, but then you are starting to approach the cost of a good compressor driven system that will deliver 20-30KBTU… There are A/C kits that will far exceed that 9KBTU capacity for under $1K…