# Air Conditioning Solution for Short Range EV



## JRP3 (Mar 7, 2008)

Try this experiment. On a hot day in your regular car turn the A/C on full blast and cool the car down, then turn it off and see how long it takes to warm back up. That's how I run my A/C in my ICE to save energy and it usually only takes a few minutes to heat up again.


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## AviatorBJP (Sep 17, 2011)

But it is not the air in the car that I am cooling down, its a relatively large volume of water, which has a huge heat capacity (4 times greater than air by mass) (and 4000 times greater by volume). A normal car doesn't do that.

Try this experiment: get a Styrofoam cooler and fill it with half ice half water, and see how long it stays cold.


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## JRP3 (Mar 7, 2008)

It stay's cool because it's a large solid mass not exposed to air or warm fluid running through it. You'll get some cooling for sure, I'm just not sure for how long.


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## Ziggythewiz (May 16, 2010)

Some is better than nothing. I think it sounds like an interesting experiment, but it's largely a question of physics. You should be able to calculate the thermal capacity and compare it to the BTUs of cooling typically needed before having to build anything.

For a short trip it doesn't matter if you can't get a lot of cooling. I got through a Houston summer (hottest on record) with no AC, largely because a 20 min drive isn't long enough to get too uncomfortable in the morning, and on the way home I can suck it up.


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## GizmoEV (Nov 28, 2009)

Since the humidity is likely low there you could probably do just fine with an evaporative cooling system.


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## Ziggythewiz (May 16, 2010)

Good point. Mobile swamp cooler, I've got one that somewhat resembles an R2 unit, barely uses more power than a fan.


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## AviatorBJP (Sep 17, 2011)

Evaporative cooler would be nice and simple. Yes, the location of this EV will be low humidity in the summer, so it should work great. But water in the tank will freeze in the winter without seasonal maintenance. It would also require a quick top off of water every few driving days.

I personally don't mind doing these things, but it would be nice to have a set it and forget it system; especially if I want to sell this thing in the future.


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## Ziggythewiz (May 16, 2010)

I don't think the goal of an EV should be to make it so someone else likes it. You will never get your money out of an EV (unless you're building it to spec). Build something you will love and want to keep. We're just suggesting options, the path you take is entirely up to you.


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## AviatorBJP (Sep 17, 2011)

Thanks for commenting Ziggythewiz,

I do plan on making several of these cars over my lifetime, and I don't plan on hoarding them all to myself. I feel like I should take a future owner into consideration. Not everyone is like you, a brave EV tinkerer willing to sit through the hottest summer Texas commute.

While working on my car I have been approached by so many people already, and the overwhelming response I get from them is positive. They are excited about possibly owning their own EVs one day, but they are also intimidated. I would like to alleviate some of that trepidation in the cars I design.

This first car is for my wife. She has asked for Air Conditioning, and I am trying to find a user-end-friendly, efficient method of meeting that request.


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## piotrsko (Dec 9, 2007)

you can go about 20 degrees lower than ambient with a thermocouple style of heater/cooler. running one way generates heat, reversing the polarity causes a cooling effect. couple that with your hot or cold reservoir, perhaps some sort of system could pan out.


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## Mark C (Jun 25, 2010)

Maybe I'm just missing something, but here goes anyway. I owned a 2008 Malibu Hybrid for a spell and it's AC unit was controlled to match the only hybrid function the car had, to stop and restart the engine when you stopped the car. When the engine shut off with the car stopped (in drive, foot on brake pedal, AC in auto mode), the AC compressor stopped too, but the cars circulating fan kicked up to high to circulate the air in the cabin. Since the maximum time the engine would stay off was 2 minutes, it worked very well.

Why don't you just use a standard automobile AC system and let the exposed shaft (on a motor with a dual shaft) drive the AC unit. Alternatively, use a small stand alone motor to drive the compressor. One could even buy a reman AC compressor, less the clutch and use the wiring that's designed to engage the clutch to activate the small electric motor that drives the compressor.


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## JRoque (Mar 9, 2010)

Hi. Interesting discussion here, especially for those of us that live in furnace-like So. Florida.

For the record, if I turn off my A/C compressor for more than 15 secs, I will quickly evaporate before I could reach and turn it back on. However, I have noticed on my home A/C that if I run the fan always the compressor remains off for a longer time on each cycle so there is something in there worth exploring.

I wonder if coupling a small (~1 HP) DC motor to the A/C compressor, but bypassing the clutch, will work. I believe compressors start hard so when using a small motor, some sort of flywheel effect is needed. True? Of course, removing the clutch would be ideal. Has anyone done this and if so, how large of a motor was needed?

JR


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## Roy Von Rogers (Mar 21, 2009)

This has come up so many times in here its getting funny. Look let me make it simple, if there was a more (better) efficient way to airconditioning, it would already be in your home or automobile.

Get a dc compressor and run your system just as original designed. Anything else is hogwash, for some dont seem to understand the process and the math involved.

To cool a glycol mixture first and then using it to cool your vehicle is kind of silly, for why waste energy cooling a medium and then using more energy circulating this medium to do what you did originally.


Refrigeration/hvac is all about heat removal, and there is no better method then using the refrigerant directly on an eveaporator to do that.

Btw I do this for a living in case some of you wonder about my qualifications.


Roy


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## spdas (Nov 28, 2009)

I totally agree with Roy, but if you want to experiment with a cheap 12v heat exchanger, try this:

http://www.ebay.com/itm/12-VOLT-BAT...492140?pt=Air_Conditioner&hash=item43aa17c06c


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## AviatorBJP (Sep 17, 2011)

Hi Roy,

I am not trying to build a more efficient machine here. I am just making a system that doesn't use massive amounts of battery pack power to cool the car. I am totally fine with using AC power from the wall to do that.

A 1 or 2 gallon per minute dc circulation pump is going to use much less power from the batteries than an independent 1 horsepower compressor pump. Electricity is cheap, but batteries are expensive. Therefore limiting the amount of draw on the batteries is critical to making a cost effective system, in my humble opinion.


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## redcelt007 (Oct 2, 2008)

Under the hood of my Mazda B2200, I mounted a small beverage cooler (ice chest) with a bilge pump fitted inside the cooler. I fill the cooler with ice and some water. The pump circulates the ice water through the heater core. I turn the heater on full and get cool air coming through the vents. Soon I will try dry ice. There is little or no danger of CO2 fumes entering the cabin since the cooler is under the hood. This kept me cool during the long Arkansas summer.


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## AviatorBJP (Sep 17, 2011)

hi redcelt007

That is essentially what I am going to do, but instead of adding ice to the reservoir when the car is parked, I have a little refrigeration unit chilling it while the car is plugged in. 

I am glad to hear that solution worked for you. Do you know about how long your ice chest provided cooling in your car? Oh, and about how many gallons of liquid did you keep in the chest?


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## redcelt007 (Oct 2, 2008)

The cooler can hold about 1.5 gallons of water. I fill the cooler with enough water to cover the pump intake. The rest of the cooler volume is filled with ice. We had a long period of temps over 100 degrees here in Little Rock this past summer. I could get about 15 minutes of driving in that kind of heat.


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## PhantomPholly (Aug 20, 2008)

There really is a system that will cool you for short periods of time that doesn't require you use onboard power.

However, it requires dry ice or other suitably cold phase-changing thermal mass storage. Despite water's very good phase-change properties, you really can't store much "cold" with Ice cooled only to zero degrees F.

Options are more mass, or colder total temperature delta, to extend the amount of time it will work. Mass works against EV range.

On the sillier side, carry a large can of O2 and put a slow blast of it on critical body areas. The temperature drops as it escapes the bottle (Boyles Law, or Charles' law?) so it comes out damned chilly. Until it runs out.


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## Ziggythewiz (May 16, 2010)

PhantomPholly said:


> On the sillier side, carry a large can of O2 and put a slow blast of it on critical body areas. The temperature drops as it escapes the bottle (Boyles Law, or Charles' law?) so it comes out damned chilly. Until it runs out.


If it's computer air you can spray it upside down and get instant freezer burn, even through clothes.


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## PhantomPholly (Aug 20, 2008)

Ziggythewiz said:


> If it's computer air you can spray it upside down and get instant freezer burn, even through clothes.


I won't ask how you know that...


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## JRP3 (Mar 7, 2008)




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## redcelt007 (Oct 2, 2008)

Just looked over this thread again and noticed I said "15 minutes of driving in that kind of heat". I should have said "15 minutes of cooling..." My apologies.


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