Peltier Device for superheating and cooling Aircon Gas

Hello All,

My name is Luc, just joined the forum, mainly to get more knowledge and information about airconditioners in a drive to lower my energy bills.

In search for alternatives for aircon's or improving their efficiency, I first came across Peltier Devices but soon found out that they are very in-efficient.
Another solution I found was assisted solar, where gas is superheated before the compressor by a solar heat-collector.

That's where a light went off as in...
Combine the Peltier's Hot/Cold functionality with a PV-module (connected to battery and charger for night use) and use the hot side to pre-heat the gas before the compressor. Then use the cold side of the Peltier to cool down the post-compressor gas in the condenser...

So you'd be using both sides. Peltier sandwiched between 2 heat-sinks, with 1 heat-sink attached to the incoming line and the 2nd heat-sink attached to the outgoing line of the compressor..

I am very tempted to try this on an old fridge-unit that I have, stripped and on a sled. It's filled up and functional, so it's easy for me to start.
But before that, I want to know some expert-opinions on this.

Hope you guys can get me on the way a with.

Thanks and regards,
Luc

It's a non starter Luc.

Any heat you add to the already superheated suction gas, above the 'useful' 3K before the compressor, will require additional compressor input power to deal with it, thereby making your system less efficient.

As the compressor is cooled by the cold suction gas, any 'additional' superheat will reduce the cooling effect and cause your compressor to run hotter, which will then consume more power.

If you can use your Peltier to cool the discharge gas prior to the condenser, then you will effectively lower the head pressure and system efficiency improves. Basically, you would be increasing your condenser surface, however, I don't think that your Peltier would be able to deal with such high temperatures.

Thanks Frank..clears things up a bit.
Does make me wonder though...where do these retro-fit solar aids get their improvement then?

But coming back to the Peltier... super-cooling the condensor stage might be an option. But it will be a matter of measuring how much the cooling for the Peltier on the hot side will take.
Using a small Peltier chip, clamped to a CPU cooling device with copper/aluminum heat-sink and a clamp around the pipe, attached with some heat-sink paste that transfers the cold side to the compressor outlet will not be too difficult.
Then doing the same to a larger heatsink/radiator that is clamped to the front of the compressor / condensor unit outside...(there's a big fan running in there anyway.) that should do the trick.

To make sure the Peltier runs only when the compressor is on, I'll need an always off relay that switches on when 220 power is applied to the compressor. That will then turn on the Peltier's 12v circuit.
Peltier's can really run cold, as long as you manage to cool off the hot side properly.

(It would of course make sense to have the Peltier's hot side pre-heat a hot-water system, but that's another story)

Will have a look at getting some small Peltiers and over the course of the next few weeks I hope to have some time to test this with a simple "Kill-a-Watt" meter!

Cheers,
Luc

What if the cold end of the Peltier were connected to the evaporator, in some way?

Been thinking of that also, but it's more work and likely less efficient, as you have to somehow build that in and loose the heat on the hot side. You could have the device outside, but that would mean a long transfer for the cold side making it even less efficient. You want to keep the device as close to the delivery point as possible..
Cheers,
Luc

Thought it over again...need to order some Peltier devices..
But....

Peltier devices work on Temperature differences.
So..if a hot side is connected to a cooler temperature vessel and a cold side is connected to a hot vessel, it will generate electricity...

So with that in mind, if we'd connect a load and get hot temperature from past compressor and cool temperature from pre-compressor, then we would have electricity.

Then..it's not much,..but putting a computer fan, like 12v, on that current would pull energy from the system and as such keep the peltier unit going, thus save the compressor energy...
And we'd pull energy the correct way...heating up the gas intake minimally but the output side is very hot so loading it would cool it down..

And it would be completely automatic, balanced it would stop...only when the evaporator signals temperature rise, the compressor starts and that's where the politer kicks in...

I am very curious to experts opinion on this..
Cheers,
Luc

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Why not consider using the Peltier device in reverse.

You are wanting to use them in heat mode, why not use
them in power generation mode. A Peltier will convert
electricity into temperature difference or using temperature
difference, it will create electricity.

Install your peltier devices to the discharge and suction and then
use the electricity to supplement what you use.

Regards

Rob

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Quote:

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Originally Posted by Rob White

.

Why not consider using the Peltier device in reverse.

You are wanting to use them in heat mode, why not use
them in power generation mode. A Peltier will convert
electricity into temperature difference or using temperature
difference, it will create electricity.

Install your peltier devices to the discharge and suction and then
use the electricity to supplement what you use.

Regards

Rob

.

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Hello Rob, that's indeed exactly what I thought just now and described in my previous post. See if I have time to order some devices and start measuring first.
Then maybe get my aircon guy in to modify my test-bed and put in some check valves to still test the original idea.

Will update on test results as soon as possible.
Thanks....!
Luc

Ordered 4 devices, 40x40mm, 89w with a DeltaT-Max of 67'C, 12v, max 10A.

I'll first check on the passive cooling by trying to generate electricity. See how much that will give.
Have a large amount of very big heat-sinks, copper tubing and all the bits and pieces from old Telcom Base Stations at work so with some drilling, sanding and soldering, I should come quite a distance.

Hopefully next weekend.
Cheers,
Luc

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Sounds interesting.

Keep us informed as to your progress :)

Rob

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Hello again, been a long time as work and renovation of the house kept me busy.
Am going to try working on the peltiers the coming weeks, and got some test plans in my head.

Main question I still have is: if you cool the gas before it goes into the compressor. Does that reduce the workload for the compressor?
Or does it only work when I'd cool the hot gas outlet from the compressor before the condenser?

My target is to make an easy to install, retrofit unit that I could clamp on the copper pipe and power it with a small solar/battery combo.

Thanks in advance,
Luc

Well... Lifted the top of our old compressor unit that will go in the new house for now. Very simple to get post compressor and pre condenser, so next will be to open up our new Panasonic and have a look at the layout there. Need to do some temp-checks and then get parts made. (Clamp, copper plates and heatsink. Bolt it all on and connect to a power supply and Kill-A-Watt meter.
Very curious on that.

At the same time, I put a 'swamp cooler' behind the compressor unit. Still measuring, but seems to really help getting energy use down. Verdict out next week with hard figures I hope.
Very simple, a small planter box, an old mozzy-screen, small aquarium pump, hose, PVC pipe with small holes. Connect to compressor so it start and stop with compressor. Water comes from evaporator unit and is very cold. Spraying it on the mozzy screen cools the air that hits the condenser coil.
It is about 10cm behind it to leave enough space for air flow.
See next week how that helps as it's over 50 baht a night currently.
Cheers,
Luc

It will reduce the load of your compressor when cooling at the inlet. The gas has a bigger specific weight. You will pump more kg's refrigerant/m³

Thanks Peter.. Got some other setbacks to deal with again, but got the plan firmed up on how to easily build and attach the peltier to the compressor. Will try both sides to get a comparison. With the amps used on the meter, it's easy to get solid confirmation once it's running.
As mentioned earlier on the thread, the heat post-compressor might be too much to deal with.
Getting the not too hot gas from the evaporator at the inlet to the compressor to go down another couple of degrees might be easier, especially when you factor in the battery and solar panel that will drive it.

Swamp cooler gave a very promising 10% less energy consumed this morning, but will check again tomorrow around the same time..