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Discussion Starter · #1 ·
Okay, pardon the attention-grabbing thread title, you'll see below why I said that... :)

So, many of you who have considered adding A/C to your conversion have run into the same thing as me:
A) compressor driven off motor: has problem you can't run it when not driving, which is a problem if you want a "remote cool" feature to get your car cooled down before you leave work for the drive home.
B) driven off dedicated motor: these seem to push your range down the most, according to hivemind knowledge I've gathered reading posts.
C) the so-interesting-I-laughed-when-I-saw-it-first-then-finally-read-about-it idea about using an actual box full of ice which pumps melted ice-water through a grill and blows air over it. Check it out here.

Idea C is great cause it's simple, super-cheap, and easy. Of course the problems it has is 1) you have to fill the box every morning with ice from your freezer and 2) the ice melts during the day.

Well, I have an idea to fix #1, but I'm not sure it's physically possible. :cool:

What if when you plug in your car to charge overnight, you actually create ice overnight so that it's automatically in the box the next morning without transferring it from your freezer? At first I thought about putting a quick-connect water line to the car every night, but that's a pain. Then I wondered, can you get enough water to condense out of the air and then freeze it? This might not work if you live in AZ, but most places there is actually a lot of water in the air. Is there a way to force it to condense, and then freeze it? Then it would require no water line, and would happen automatically from the power from your charger.

For those that can charge while at work, this also fixes problem #2 in that when you come back to your car to drive home, the ice is still frozen. And for those that can't charge at work, it might be possible that the ice is still there. I know we have a cooler for camping that can supposedly keep ice for 6 days at 80F as long as you don't open it. So if you build it in a high-quality cooler with a mostly-closed system, it is reasonable that it would still be frozen 8 hours later.

Thoughts?
 

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It would work in the same way that the frost will build up in your fridge icebox.

Two immediate issues:
As the frost builds up on your cooler pipes they will also become more insulated and less efficient.
Also you will end up driving around with the weight of a fridge system on board.

An advantage is that the system is basically a heat pump and so you could also use it to heat the cabin.

I think I would place a small freezer in the garage or near the front door of the house.
 

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  1. How much extra weight in ice will you have to haul around to produce enough cool for your daily need?
  2. How much extra weight will the components you need to re-freeze the ice add?
  3. How will that extra weight affect your range? Every stop and go will cost more energy and the added weight will result in higher friction between tire and road.
  4. How much more range would you get if you kept the old AC-system (which probably weight less since it's already optimized for automotive use + doesn't have to cool down to freezing point) and used the room for more batteries instead of ice? If you power it with a second motor you can still run it when the car's parked to take care of that initial cooling without having to power it from the pack.
  5. How much more will this complicate the conversion since you will have to reengineer the whole ventilation system?
  6. How much does the risk increase that the complete work load gets overwhelming so that the conversion will never be finished thanks to these plans? :D
 

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Okay, pardon the attention-grabbing thread title, you'll see below why I said that... :)

Then I wondered, can you get enough water to condense out of the air and then freeze it? This might not work if you live in AZ, but most places there is actually a lot of water in the air. Is there a way to force it to condense, and then freeze it? Then it would require no water line, and would happen automatically from the power from your charger.

Thoughts?
Thermodynamics is not with you. It takes a lot of energy to condense water [think of the reverse of making steam]. It would be simpler to just keep the melted ice in your cooler chest to be re-frozen on the next cycle.
Gerhard
 

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Discussion Starter · #5 ·
Hi guys,

Thanks for the replies. I think you're missing the detail that this is only running and consuming energy when you're plugged into wall outlet. I posted last night at about 1AM, so I'm sure I was unclear in my original post. :)

So, the idea is to make ice at night while charging, or in the middle of the day at work, again while charging. While actually driving around and using the A/C, you are only consuming the electricity of your regular blower motor, which you already do in the winter for your heat setup.

So let me answer some quotes directly.

  1. How much extra weight in ice will you have to haul around to produce enough cool for your daily need?
Good question. I don't know. The same as the amount that use the ice system directly.

  1. How much extra weight will the components you need to re-freeze the ice add?
  2. How will that extra weight affect your range? Every stop and go will cost more energy and the added weight will result in higher friction between tire and road.
I imagine some significant weight. But all A/C options are going to add weight. It is probably comparable to the weight of the compressor/condensor from factory A/C. I was thinking of ripping it off one of those old garage mini-fridges.

  1. How much more range would you get if you kept the old AC-system (which probably weight less since it's already optimized for automotive use + doesn't have to cool down to freezing point) and used the room for more batteries instead of ice? If you power it with a second motor you can still run it when the car's parked to take care of that initial cooling without having to power it from the pack.
The problem I've seen with reusing the old system is you need such a powerful motor to run the compressor while driving. I've read here anywhere from 1/2 to a couple HP and a pretty respectable power inverter to run it. And those motors add quite a bit of weight. That's just to run the compressor, on top of your blower motor. The idea I'm proposing would add a motor but since it can run off wall power, no power inverter needed. When you're driving, you're not compressing anything, so just use your fan motor.

  1. How much more will this complicate the conversion since you will have to reengineer the whole ventilation system?
  2. How much does the risk increase that the complete work load gets overwhelming so that the conversion will never be finished thanks to these plans? :D
Hahaha, I dunno. It adds complication. I expect that, but it's also part of the fun.

Thermodynamics is not with you. It takes a lot of energy to condense water [think of the reverse of making steam]. It would be simpler to just keep the melted ice in your cooler chest to be re-frozen on the next cycle.
Gerhard
Again, I am not concerned with energy when plugged in to the wall, which is the only time I am condensing water or freezing anything. But that's a good idea, to keep the melted water around. Fill it once, or every month or something depending how long it takes to evaporate/sublimate. That's also a lot easier than pulling water from the air. :) I'm picturing how in Africa they're like collecting dew drops off leaves and squeezing them into a pouch. Trying to get it from the air is probably like that.

I'd be interested to see what someone thinks who has run the simple icebox system in their car already...
 

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Discussion Starter · #6 ·
It would work in the same way that the frost will build up in your fridge icebox.

Two immediate issues:
As the frost builds up on your cooler pipes they will also become more insulated and less efficient.
Also you will end up driving around with the weight of a fridge system on board.

An advantage is that the system is basically a heat pump and so you could also use it to heat the cabin.

I think I would place a small freezer in the garage or near the front door of the house.
Hi Woodsmith, sorry I missed your post.

Yeah, sounds like the creating it from the air won't work. You're right that I would be driving with added weight, which would reduce range, but range is also reduced when you run the compressor while driving, which this method wouldn't need to do. So I guess which one is better is still up in the air.
 

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I imagine some significant weight. But all A/C options are going to add weight. It is probably comparable to the weight of the compressor/condensor from factory A/C. I was thinking of ripping it off one of those old garage mini-fridges.
I think you're underestimating the weight and/or the power needed, here. An A/C in a car are pretty beefy to handle the amount of cooling needed and since space and weight is a problem, a car A/C is comparatively small for it's power.

A small mini fridge can't freeze water and even cooling down several gallons will take HOURS, possibly days since that's not what they're built for. If you only cool down the water to fridge temperatures (6-8C) there will be a lot less available cooling capacity compared with if you freeze the water since every kilo water stores 4.2 kJ per degree C. If you only have a useful temperature range of, say, 5-10C instead of 0-10C you need twice the amount of water. Naturally that means that if you can freeze the water to -10C instead you can half the amount of needed water compared to the 0-10C range, but -10C also demands a MUCH stronger compressor than both a fridge or a car A/C.

The problem I've seen with reusing the old system is you need such a powerful motor to run the compressor while driving. I've read here anywhere from 1/2 to a couple HP and a pretty respectable power inverter to run it. And those motors add quite a bit of weight. That's just to run the compressor, on top of your blower motor. The idea I'm proposing would add a motor but since it can run off wall power, no power inverter needed. When you're driving, you're not compressing anything, so just use your fan motor.
The big energy cost is the initial cooling down of the car which you can do when the car's still plugged in. Once that is done you don't need that much power to keep the car cool and even if it takes 1/2 HP to keep the car cool it's just ~370 Watt while the main motor will crave several kW to keep the car rolling. I also doubt that a system that contain several litres of water + a freezer system will weight less than the general car A/C when you start to count the kilos. Besides, even if we're optimistic and say that you have a temperature span of 20C you can tap it still means that 10 kilos of water will store about 230 Wh.

Lithium batteries store ~100Wh/kilo, so 10 kilos extra of batteries would mean about (or at least close to) 1kWh. On top of that a car A/C has a COP factor, meaning that for every Wh you put in it's multiplied by COP in cooling capacity, so if you have an A/C with COP 3 (not unrealistic) those 1kWh electrical energy in the batteries turns into a total cooling capacity of 3kWh. More than 3 times the cooling capacity of the frozen water.

"Ya can't change the laws of physics!"
-- Scotty. :D
 

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Discussion Starter · #8 ·
I think you're underestimating the weight and/or the power needed, here. An A/C in a car are pretty beefy to handle the amount of cooling needed and since space and weight is a problem, a car A/C is comparatively small for it's power.

The big energy cost is the initial cooling down of the car which you can do when the car's still plugged in. Once that is done you don't need that much power to keep the car cool and even if it takes 1/2 HP to keep the car cool it's just ~370 Watt while the main motor will crave several kW to keep the car rolling.
Qer, you're probably right - it's hard to beat a system that's been custom designed for lightness in that specific car. However that leaves me with one last question: If it's as simple as "hook a small dedicated motor to a stock A/C compressor," then why after poring over the pages and pages of forum posts on this topic isn't this the slam-dunk solution to the problem? I saw that suggested several places but it doesn't seem to be a universal position.

thanks
 

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If you don't end up in traffic jams on a daily basis I'd suggest you simply hook it up to the main motor, it's definitely the simplest solution. If you use a second motor for the AC it means you'll either have to use a PM-motor (which is inefficient) or a series wound motor (which essentially means you need a second controller) and then you have to control it in some way so it only runs when the AC needs it.

Normally there's an electric clutch that connects the AC compressor to the belt when needed, if you run the AC from a separate motor you could skip that one (or weld it permanently connected) and let the same signal control the motor instead. That solution would, of course, provide you with cooling even when the traffic comes to a complete dead stop so it might be worth the hazzle.

YMMV etc. ;)
 

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Hi Notailpipe

Lets run some numbers
Qer says that car AC has a COP of 3 and would use 1kw to cool and 1/3Kw to keep cold

So we need 3 Kw of cooling with 1 Kw to maintain temperature

Ice (water) has a latent heat of fusion of 334 Kj/Kg or in EV terms 0.09 Kwhrs /Kg -92whrs/Kg

So 10 Kg of ice will cool the car for 20 minutes and another 10 kg of ice will keep the car cool for an hour

Sound like it could work! - and at the same weight as lithium (100 wh/kg)

You don't need to carry the fridge with you - just have a fridge at home and another at work
 

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One of my uncles(a devoted camper) uses this Low-tech approach:

1) a thoroughly insulated, modified 24" commercial cooler filled with
2) several dozen rigid plastic freezer packs, pre-filled at the manufacturer and arranged into two 'cells' via plastic milk carton racks and zip ties, and
3)a deep freezer at home.

The modifications to the cooler are as follows:
1) a rectangle cut into the top of the cooler to make way for 2 3-inch, 12V computer fans, on-off switch and 2 12V, 2.4 Ahr Dewalt toolpacks(the originals were Ni-cad, the new ones are Lithium) and
2) a small insulated lid with a gasket and latch.

When ready to embark on an overnight stay, my uncle simply slaps two cells into the cooler, two fully charged Dewalt packs in place and loads the cooler on his Kawasaki for the trip ahead-at night, he simply opens the lid and flips the switch..

I'm no camper myself so I can't verify this directly, but he claims roughly nine hours of comfort in a lightly insulated tent with average night-time conditions of 89-92 Farenheit and mid-level humidity-followed by slightly less comfort for another four to five hours with extra batteries.

Might be worth a shot.
 

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Two really significant factors affect the typical oversizing of vehicle AC. The ability to quickly cool off an extremely overheated car left in the sun for an afternoon and the thermal gain even when driving from the amount of glass in a car. All vehicle AC units are capable of keeping areas of much greater volumetric space "cool" (yes it's all relative).

The small PV solar ventilation fans really help the first issue and glass tinting really helps the second issue. With these two things in place.... look for the ac out of a sub-compact car...even a smart car size if you can find it. This is adequate for normal running if you have addressed the first two issues I think.
 
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