AC Mod: Peltier Junctions

[abshnasko]

Hey, I have a 97 Civic EX that I've been working on lately, and I'm looking to do a few FE mods. I know that when running, the air conditioner sucks a lot of hp out of the engine, especially on a small car.

Would running a peltier cooler (or an array of) be more efficient than running the ac compressor? Here are some preliminary obseravtions:

Pros:
- less rotational energy needed from the belt
- less weight (how much does the entire ac system weigh? 100 lbs?)

cons:
- uses a lot of power. my guess is that you'd need 300-400watts of power, causing the alt. to raise resistance
- a lot of work to implement


Any thoughts?

[AndrewJ]

From wikipedia:

"Due to the relatively low efficiency, thermoelectric cooling is generally only used in environments where the solid state nature (no moving parts, maintenance-free) outweighs pure efficiency."

Sounds like it's not quite ideal for the automotive environment. Or, more accurately, the fuel efficiency environment. Remember if it's not good for efficiency, it's not gonna be good for fuel efficiency (so long as you're running it off the alternator)

And if you were to run it off it's own battery power, it would probably be more efficient to just remove the alternator and run the a/c off the belt.

Remember, you can always cycle the a/c to squeeze a bit more efficiency out of it. It's a bit more work, but it's free and won't require re-inventing the wheel.

[blackjackel]

it would be much more inefficient than your cars cooler... by a lot... trust me. I deal with this stuff over at overclockers forums, they use peltiers for cpu cooling vs regular old refrigerant loop.

HOWEVER.

You MAY use peltiers in combination with heatsinks on the exhaust, engine, and anywhere else there is heat to generate electricity!!!

[abshnasko]

Ok well maybe this changes the picture a little bit:

I have a solar panel array mounted on my roof and trunk (they're the flexi kind to they mold to my exterior, its quite nice), so I am running off of battery (alt-less) a lot of the time. If I use my peltiers instead of the ac, effectively I am simply releasing the power requirement from my belt, and placing the additional strain on my panels/deep-cycle grid.

And if you were to run it off it's own battery power, it would probably be more efficient to just remove the alternator and run the a/c off the belt.

How so? If I eliminate alt+ac, wouldnt that be better than eliminating just alt? Please clarify.


also, I am a computer guy too and I am familiar with their cpu-cooling applications... I'm not sure if power efficiency comes into play there. I go to college in blacksburg, va up in the appalachian mountains, so it gets pretty cold here during the winter... but im not sure that using the peltiers to generate power during one season is a cost-effective way to go either.

[AndrewJ]

the question is whither or not your pv/batt system can handle the extra load. If a belted a/c system can noticeably draw down your engine, and an electric system is (at best) half efficient, then you're gonna be placing one heck of a load on the batts.

[abshnasko]

My idea is to have sort of a scaled-down air conditioning system... most of my driving is city where I can just roll down the windows, but I live 5 hours away and drive home occasionally, and if its sunny I'd like to be able to use the ac. But also under ideal ac-use conditions, we also have ideal solar panel current. A single peltier junction (a small 2x2 in.) square draws 75 watts. If I can power a decent ac with 4 of them making a total draw of 300watts, would this be better than the belt-driven ac?

If the alt. is off then obviously, but since I'll probably need it on, so here's the question I'm looking to have answered: will an extra ~300watts of power use cause less load on the engine via alt. than a belt-driven ac?

[ttoyoda]

For peltiers, you have to put in an electrical wattage that is about equal to the heat (in watts) that you want to move. That is really bad efficiency.
From Here:
http://www.bry-air.com/tech-center/r...l/default.html
we see that
to convert Btu/Hr to Watts multiply by 0.293
just wildassguessing that you need 3000 btu/hr for ac that is 879 watts you need to move. The peltier will need ANOTHER 879 watts to do the work so you end up with 1758 watts which divided by 12 volts is 146.5 amps.
(ass-u-me-ing that i did not mess up the math)
And you dont even have a fan to blow the cold air yet.
If you wanted to use less btu/hr for cooling, run chilling tubes thru your seat.
Then you cool just your body, not the whole car.
Beware of frostbite if you try this.

[ebacherville]

Cool idea also remember that these work best if you can get the other side cooler.. the cooler the hot side the cooler the cool side.. they really will only drop any temp by about 30 -40 degrees.. thats in a very insulated closed space like a minifridge.. there great for heat sinks etc.. as there very directed cooling but for air cooling i doubt it will be better..

Also for cooling the car rolling the windows down is more efficient than AC.. especially if there just cracked to provide enough cooling to keep you comfortable.. typically ill just roll my window down about a inch to provide some circulation..

Also you could probably improve rolled down windows aerodynamics with some simple areomods to your window frames to deflect any air back outside of the car again.. usually the drag is where the air hits the rear pillar of the car window..

[JohnnyGrey]

You won't be able to move anywhere near the amount of BTUs your car's AC does.

I'd recommend tinting your windows instead.

http://www.gisdistributing.com/V_Koo...e_Poducts.html

That stuff blocks out most of the heat while letting visible light through so you won't get hassled by the cops. I put limo tint on the back side windows of my car and I'm going to do the back in limo tint too, but on the front windows, I'm going to use V-Kool. Sunlight produces about 1KW of heat per square meter, which is about the size of most rear windows. Every watt of energy you stop at the windows is probably 4 that you don't have to rob from the crank to maintain the same comfort level. You might even be able to get away with just the blower.

[abshnasko]

Thank you all for your input, but none of this is answering the question I asked which was:

so here's the question I'm looking to have answered: will an extra ~300watts of power use cause less load on the engine via alt. than a belt-driven ac?

I said that I wanted a "scaled-down version" of my current air conditioner, so I don't want to use 879 watts. I care about using 300 watts. If i used 300 watts of additional power, would that result in more or less fuel usage than running my belt-driven ac?

And I figure I can just use the existing AC radiator and pipe the heat from the hot side to that in order to keep them cool.