Freon-free A/C cooling system

From what I remember of peliers, it works by passing a current through 2 plates of I don’t remember what, which makes one side very hot, and the other very cold.
This has been used in home grown computer cooling systems with some success, though I believe this method of cooling to be extremely inefficient, using a lot of power to get the desired effect.

I’m probably wrong, but consider the equivalent to incandescent light bulbs to fluorescent, in terms of efficiency. The incandescent being the peltier effect.

These kids didnt invent anything new, they just stuck it in a car instead of a computer.
and as i understand it, normal AC for the home dont use freon anymore

 

i think its great that the kids had the ingenuity to put this together, especially at their young age, but the article covering the award is pretty poorly written.

Of course GM said it couldn't be done: the analysis was in 1964 when peltier coolers had only recently been developed and their efficiency was poor and cost was ridiculously high. Ten years ago this wasn't even feasible because of the high cost of the cooler, but recent technology has helped to bring the cost of production down.

Another thing i believe they failed to realize was that while the cooler doesn't use gas for power, it uses battery power which must be regenerated with your alternator which is powered by gasoline. I am not sure how the peltier cooler's true energy efficiency compares to the standard AC's we use, but i have a feeling it won't save anything near to what they estimated, if it saves at all.

One more thing: i don't think the cooling will be nearly as adjustable or powerful as the air conditioners we use today either. That being said, i love how they eliminated the freon and i think this is a step in the right direction, and although they may be getting a little more credit that they deserve, its great to see kids working towards the right goals.

cheers

 

First cars do not use Freon in their air conditioning systems and have not for years. They generally use a non-cfc refrigerant called R-134a. Next, in normal use there should be practically zero loss of the R-134a to the environment.

 

It's been pretty much torn apart on Slashdot.

Basically, Peltiers make very efficient heaters (you get more heat than the energy you put in) but very poor coolers where efficiency ~10% is less than conventional gas-based heat pumps which get ~85% like your fridge at home.

Even with the ones made with modern semiconductors.

It's been pretty much a failure (including my experience) after a brief experiment in the CPU cooling industry. Simply, it generated more heat than it was sucking from the CPU which made case cooling extremely difficult. It's like trying to AC cool your car with the windows rolled up, and a space heater left on inside, or rolling a rock uphill.

Anybody serious about CPU cooling these days either get a cooler cpu, bigger heatsink, or switch to water-cooling which is basically your gas-exchange system that's used everywhere already.

And, where is the mass amount of electricity going to come from to run a peltier in a 12V automotive electrical system?

 

Actually, Peltier devices have a fairly good COP (Coefficient Of Performance which is a measurement of total power in vs. total power out). However, the trick to the high COP numbers is to make use of both the cooling and heating effect you get out of the device. When you consider cooling only and the heat as a throwaway then the numbers start to look pretty bad. The newer devices are getting better.

The great thing is that these two kids didn't know it "couldn't be done" (GM's opinion) so they went and did it. Its the basis on which our world moves forward in leaps instead of mini-steps based on some minor tweak of an existing device.

 

Individual Peltier chips have been around for awhile. Melcor is one of the bigger names (www.melcor.com) and they sell the chips and integrated assemblies, including A/C systems. For example, they have a 1200 BTU/hr system than runs off of 115 VAC and 7.3 amps. = 840 watts for ~ 350 watts worth of cooling. If this was a car system, it would require 70 amps DC at 12 volts. Of course, this is for only 1200 BTU.... This is at least 5 x less than a car system and 5x smaller the the smallest room air conditioners.

For a car, you need alot more cooling because the low R value, sun exposure, and general high temp reached by the interior when not occupied.

Overall, these kids should take the money and run because their idea is not new, not practical nor useful. Toyota made the right choice with an electric powered compressor.

I've considered a Peltier system for an aircraft application. It has a little more merit there, but not much. Either you need a a very heavy battery array or a very big alternator, if not both.

It would be much lighter and effective to pair a Toyota electric compressor with a AC inverter (compressor is AC powered) and a compact AC system from Vintage air.

Eric

 

<div class='quotetop'>QUOTE(empannin\";p=\"109718)</div>

Eric:

Why not just use the manifold for bypass air and use that to run the Air Cycle machine - AKA "pack?" Turbojet and especially turbofan engines have used that for a long time now with good results.

Jay

 

Question:

I have a portable fridge that can be plugged into the 12V socket of a car. Does that use the Peltier system, or is it some other non-gas heat exchange method? How do those things work?

 

<div class='quotetop'>QUOTE(senna4ever\";p=\"110260)</div>

Yes, it does. If you mean something like a 12 vdc Coleman cooler/heater, it uses the thermoelectric or Peltier Effect. They can only cool to about 40 F below ambient temp.

As far as learning how they work, please go straight to the horse's mouth at Melcor, a large manufacturer of Peltier Modules:

http://www.melcor.com/handbook.html

 

Quick summary of thermoelectric devices is they convert current into a differential temperture between a cold side and hot side of a diode junction. The change in temp is related to the diode material and the amount of heat moved is a function of the current. Since they are moving heat from one side to the other side of a thin "chip" you still need to dissipate the heat, usually via a fan to the outside air.

As far as air-pack type coolers used on airplanes, usually these rely on the expansion of a large volume of air at a pressure << 50psi. This is available in jet engines from the compression stage. I think the efficiency is low but the systems are light in weight and not complex.

There is no source of air pressure at the right flow or pressure in a car and tanks would only last seconds. The other option would be a vortex tube sold commercially by Exair. These are alot of fun and are able to maintain a big delta T, but the flow rate is 10 CFM+ for even moderate cooling. My 5 HP compressor cannot keep up and my sizeable tank lasts ~ 20 seconds at full flow. It also screams like a banshee... (core rpm estimated in the millions)

If you had a plug in system you might be able to pre-cool if you were on a regular schedule (or pre-heat in cold climates)

There are some reversible chemical systems but the cooling duration would be very short. As I mentioned earlier, I have been investigating some exotic cooling solutions for an airplane kit but so far nothing seems as light and straightforward as a traditional AC system.

Have a nice day,

Eric

 

Thanks, jayman & empannin!

 

<div class='quotetop'>QUOTE(empannin\";p=\"110651)</div>

Eric:

Oh, sorry I thought you meant an aircraft powered by a turboprop or turbofan.

The few civilian piston aircraft I've seen with A/C - mostly twins - have had the regular compressor mounted to the motor.

The Air Cycle Machine is lower efficiency than a closed-loop refrigerant system, but it has so many advantages in terms of simplicity, long life, and weight savings, that they are exclusively used.

They only tap a small portion of the bypass air for the manifold, WRT thrust a modern carefully engineered high-bypass turbofan like a CFM-56 will lose an insignificant amount of thrust. The larger the turbofan the smaller the loss.

The only concern for an ACM is during critical thrust periods, such as takeoff. Pressure monitors in the manifold and the EPR will automatically trip or "bump" the packs off if needed.

On the ground, or optionally at takeoff, the APU can also run the packs at reduced capacity. The APU is also a turbofan, a microturbine motor. In this case all the bypass air is used to pressurize the manifold and run accessories, the shaft-driven generator runs the electrical bus.

The APU is also used to pressurize the manifold to "start" the turbofans by using the bleed air to rotate the fan. You may have felt a slight change in ear pressure when the flight crew starts the turbofans on the ground. That's because the tiny APU can't run both the packs and spin the fan at the same time, so the packs shut down and pressurization stops.

As far as your kit airplane, I knew a guy in Utah who built a KitFox with a Subaru motor from a junked Imprezza. Subaru motors are popular for kit airplane service. He was toying with the idea of taking the A/C out of the donor Subaru and putting it into his KitFox but I'm not sure if he was able to. I'll ask him when I get a chance.

Jay

 

Denso has developed a Hydrogen-based system with the benefit of being significantly lighter as well as less harmful to the environment. The spec of the H system appears very similar to the system in the Prius (also made by Denso.)

As for thermocouples, I made one in ten minutes in high school about a hundred years ago. And these kids "invented" what now? Good luck to them for making money, if not technology. : )