Battery Powered A/C
- Thread starter Broompilot
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I read that one but wasn't sure I was guesstimating correctly. My knowledge of electricicals is pretty much don't stick anything but a plug into an outlet.
Actually, 33 amps DC for 16,000 BTU's seems awfully, awfully efficient. Especially in light of the fact that the Red Dot units (the DC units, anyway) are manufactured by DC Airco in Europe, and you'd think that they would incorporate the uber-efficient specs of the Red Dot units into their own units. The DC Airco 9000 unit pulls 50 amps. And the Red Dot says the 33 amps includes 4 amps for the A/C clutch, which means it puts out 16,000 on only 29 amps constant. Again, that's awfully efficient. Whew-weee that's efficient. That's the equivalent of a 120V air conditioner putting out 16,000 BTU's on just 2.6 amps AC. Most window and RV rooftop 16,000 BTU units even the really, really efficient ones, will draw 10-12 amps. But, hey, DC air conditioners are getting more efficient all the time. We'll see. I do know that higher BTU units are more efficient than their lower counterparts, all other things being equal. But 200-300% more efficient? And as far as I can figure out, the Red Dot DC air conditioner specs haven't changed any at all since their introduction in 2004.
But, at a 33 amp draw on a 100 amp hour battery, The Peukert effect means that the battery will be drained dry in 1.72 hours (103.2 minutes). The Peukert Effect is an easy one to forget about, and it turns a 100 amp hour battery into a 56.77 amp hour battery, because the Perkert Corrected Amps of 33 amps becomes 58.13 amps.
More batteries, tho, and the Perkert Effect means more available amps, as the high amp draw isn't as severe on the batteries. 300 amp hours of batteries and a 33 amp draw means 236.81 available amp hours (41.81 Perkert Corrected amps) and the batteries will last 7.18 hours till they're dead, or 3.59 hours (3:35) to 50% DoD.
600 amp hours of batteries at a 33 amp draw will yield 583 amp hours of batteries, and a Perkert Corrected amp draw of 33.96 (so we're finally getting the battery bank to match the amp hour requirements insofar as Peukert Efficiency is concerned), and the batteries will last 17.67 till dry, or 8.835 hours (8 hrs, 50 minutes) to 50% DoD.
Because available amps slightly decreases every time they are discharged and recharged, 600 amp hours is the absolute minimum to go with for a 33 amp draw. No doubt there will be plenty of nights where the AC can be turned down and it won't draw 33 amps, but there will also be plenty of nights where that isn't the case. And of course, the 600 amp hours is just for the 33 amp draw. If you have a TV, computer, lights, fridge, whatever, you need to add those amp hour requirements to the battery bank. 700-800 amp hours is what most are gonna need (to go 8 hours between recharging).
In any case, the pricing on the Red Dot until will be interesting, particular when compared to what's at the end of this post. After DC Airco makes their profit, and Red Dot makes theirs, and Thermo King makes theirs, pricing should be interesting.
The key to efficient cooling (or heating, for that matter) is BTU's and airflow, with airflow being the most important, generally.
The Red Dot R-6100
BTU - 16,000
Airflow - 450 m3/h (cubic meters per hour, or 265 cubic feet per minute)
Weight - 44 lbs
Amp draw - 33 amps (constant 100% duty cycle)
DC Airco 9000
BTU - 9,000
Airflow - 530 m3/h
Weight - 88.2 lbs
Amp draw - 50 amps (full duty)
Amp Draw - 25 amps (50% duty)
DC Airco 4400
BTU - 4,400
Airflow - 400 m3/h
Weight - 66 lbs
Amp draw - 30 amps (100% duty)
Amp Draw - 15 amps (50% duty)
Dirna Bycool MiniCool Compact
BTU - 4,760
Airflow - 530 m3/h
Weight - 62 lbs
Amp draw - 17 amps (100% duty)
Amp Draw - 12.2 amps (50% duty)
A 12,000 BTU air conditioner (a 1-ton air conditioner, 12,000 BTU's will melt 1 ton of ice in 24 hours) with an airflow rate of 450 cubic meters per hour will keep a 500 square-foot room cool. That assumes a 10-foot ceiling. In a truck or a van, there won't likely be a 10-foot ceiling, but the reduced thickness of the walls and the inferior insulation of the vehicle compared to a home evens this all out.
There are charts for determining the BTU's needed for a given space, but quick and dirty (and fairly accurate) is the square feet times 35. The Sprinter's interior is roughly 100 square feet, so 100 times 35 is 3500 BTU's. Insulation is a huge factor in a van or truck, the more the better. So, 3500 isn't likely to keep a Sprinter cool on a hot day in the Laredo sun on an asphalt parking lot.
You are a factor, as well, as each person will pump out about 1600 BTU's of heat (200 Watts). Two people will put out 3200 BTU's, even more if they're gettin' busy, so you frisky team drivers better factor that in.
If you're a solo in a very well insulated van or truck, or in a truck with a rather small sleeper, the DC Airco 4400 might work, but it's airflow is reduced, so it's really only well suited to cabs only.
Solos in well insulated vans and trucks could almost certainly use the Minicool Compact at 4,760 BTU's, with its higher airflow.
Team drivers and drivers of vehicles that aren't extremely well insulated would need at least a 9000 BTU unit.
BTW, the weight of the Red Dot until makes me wonder if it doesn't employ a split compressor, housed elsewhere. Particularly when I read here (Red Dot Rooftop Units from Harold Electric) where it says the price of the unit from them is $1330 but to call for complete system pricing including a 20-foot hose, and that the "Complete System Pricing includes all component parts needed except Compressor Drive Belts, Drive Pulley, and miscellaneous small hardware."
Hose, compressor drive belts, pulley? Gives me pause.
greg334
Veteran Expediter
Er.... Red dot unit draws 33amps for a very good reason, it is a split system that uses the engine to run the compressor, which is purchased separately.
The majority of the current is from the fan, 33 amps runs right in line with what a 12 volt blower should be running at, the clutch current is about 4 amps.
The compressor is the key, equally too is the insulation in the sleeper/van. Compressor technology has come a long way but there is nothing around the physics of the system. But if one is to really plan the insulation out carefully, maybe using a combination of things, then there is a savings in heat removal technology. Oh by the way, don't forget that the floor is a main source of heat in the summer time - heat rises.
The majority of the current is from the fan, 33 amps runs right in line with what a 12 volt blower should be running at, the clutch current is about 4 amps.
The compressor is the key, equally too is the insulation in the sleeper/van. Compressor technology has come a long way but there is nothing around the physics of the system. But if one is to really plan the insulation out carefully, maybe using a combination of things, then there is a savings in heat removal technology. Oh by the way, don't forget that the floor is a main source of heat in the summer time - heat rises.
raylawrence
Expert Expediter
Turtle, you sure know you batteries and math! In most cases, 12 volt battery powered air conditioning is going to be a compromise of cooling performance in order to reduce the maintainance concerns of an APU. In all cases, a very good insulation package and a reduction in the size of area you are cooling will make you much happier with your 12 volt battery powered AC system.
As a positive for the battery powered systems, they are very quiet and use no fuel at all. Very environmentally friendly.
As a positive for the battery powered systems, they are very quiet and use no fuel at all. Very environmentally friendly.
Battery powered systems are only environmentally freindly IF you first assume that the batteries are manufactured in a environmentally proper system. IF the used batteries are recyled in the same way. The history is kind of weak in those reguards.
raylawrence
Expert Expediter
Your concerns are definately valid. That is why choosing a high quality avanced AGM battery with plenty of reserve capacity will reduce the number of times the batteries would need to be replaced. The least amount of times the battery is deep discharged will increase its life.
greg334
Veteran Expediter
So Ray, I don't know if you answered my question in the other thread but you guy service Webasto heaters, A/C units and EFoy Fuel cells?
As for battery technology, Ultracaps seem to be more of a long term solution. They can be brought down to zero voltage while charging doesn't take hours. The drawback is cost.
As for battery technology, Ultracaps seem to be more of a long term solution. They can be brought down to zero voltage while charging doesn't take hours. The drawback is cost.
I have an Arctic Breeze system that I have been very happy with. 3 group 31 Freightliner AGM batteries and it runs nearly 8 hours (I have a genset/charger system to extend that time). It works well and is all 12v basic automotive components (cheap to fix). Ray from Espar of Michigan sells them, they are made in North America not China or some other far off land. I like it and bought it because it only draws 900 watts MAX at start up and 600 when the compressor is running (40~60% of the time).
I see more and more battery only stuff, it is the way to go I think. Ray had lots of cool stuff at the Expo.
I see more and more battery only stuff, it is the way to go I think. Ray had lots of cool stuff at the Expo.
greg334
Veteran Expediter
I think that a/c system also uses the Danfoss 12 volt compressor which depending on the model has it components sourced from China or Korea. I know they are assembled here, and they are a good product but they can be flakey when they fail.
Not to knock all these 12 volts systems but it seems to me that they all have their origins traced back to marine applications. I mean I sourced all my components for my fridge which is a small A/C unit in itself from marine supplies and looking at one today in pieces, I see the same components my fridge had. It is not a bad thing but when you spend 3 grand on a unit that someone can put together for say 1000 with the help of one of the marine A/C books out there, it makes you wonder.
Now I Ray about Wabesto, how 'bout it, you service them?
Not to knock all these 12 volts systems but it seems to me that they all have their origins traced back to marine applications. I mean I sourced all my components for my fridge which is a small A/C unit in itself from marine supplies and looking at one today in pieces, I see the same components my fridge had. It is not a bad thing but when you spend 3 grand on a unit that someone can put together for say 1000 with the help of one of the marine A/C books out there, it makes you wonder.
Now I Ray about Wabesto, how 'bout it, you service them?
greg334
Veteran Expediter
Piper, I was wrong (yes fan club I get some things wrong) I was reading the wrong notes when I looked it up.
I remember that one now, that's an open compressor design. Which makes even more sense if you have the van that can spare the weight.
Do you know which motor they put in it to run the thing?
I remember that one now, that's an open compressor design. Which makes even more sense if you have the van that can spare the weight.
Do you know which motor they put in it to run the thing?
raylawrence
Expert Expediter
sorry, Greg. we haven't ever work on the Webasto product
raylawrence
Expert Expediter
The 12 volt motor in the Arctic Breeze is from the U.S. It has 4 replacable brushes and a stainless steel armature for lower amp draw and longer life.
greg334
Veteran Expediter
Thanks Ray, that sounds like a doable thing to get rid of the high cost Danfoss compressor.
Do you know who makes it or if is a custom job or something that you can get off the shelf?
The reason I ask is I am wondering what size is it and how it can be adapted to other applications.
Do you know who makes it or if is a custom job or something that you can get off the shelf?
The reason I ask is I am wondering what size is it and how it can be adapted to other applications.
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Ya, I guess it is, as 746 watts is 1 hp. That draw is a worst case scenario, compessor locked kinda draw. I rarely see it, usually I see the number closer to 5-600 watts when it is starts up (and that includes the condensor and evap fans). They did tell me once, and I have completely forgotten, where they originally found the motor but they are a custom built deal now. It is basically a very high quality, high torque, DC motor that is about the size of a loaf of bread. It turns fairly slow (< 500rpm) and is very quiet. They did a great job of matching all these typically high speed components up, running them at low speed and getting the balance of refrigerant and evaporator right. When I first saw the system I thought there was no way it should work because it was so slow speed, but it does!