Air Conditioner?

[HarveyH42]

A few years ago I read an article about a solar icemaker. I read it mostly because I wonder how you can get cold from the hot sun. Was wondering if anyone has seen or heard about this in the air conditioning field? I know that electric fans would still need to be used to move the air, but they would be much cheaper than central air to run.

This is my biggest electrical draw. Yeah, its a comfort and convience, but I only had mine installed about 10 years ago. It's mighty rough in the summertime here.

I remember this icemaker wasn't that complex, but a little out of my field. I dealt with expanding gas. I know this is kind of a vague post, but I just don't remember enough details, and hoping for something to point me in the right direction.

 

[dknguyen]

Wouldn't it just be solar panels collecting energy to move heat against the temperature gradient?

 

[HarveyH42]

This link goes to pretty good description, but isn't the system as I remember. This is comercial, the other was a homebrewed system and gave details on construction from availiable parts and materials.

https://www.thesustainablevillage.com/servlet/display/product/detail/29150/

 

[Oznog]

That's the Servel cycle, "adsorption refrigeration". I did not misspell this. Some people still use the inappropriate but more widely used term "absorption". It was used in refrigerators which ran off of propane or natural gas before the compressor-based units were invented. It is still used for refrigerators in RVs, sailboats, or remote locations without electricity. I think it's also used in industrial settings for making cooling out of "waste heat" you don't need.

That Sustainable Village link looks way too good to be true, those numbers are pretty high. The page so lacks technical details that I don't give it a lot of credibility.

The adsorption cycle I remember also uses hydrogen as an important component. Hydrogen, anhydrous ammonia, water. It's a pretty neat-o cycle. It is not particularly efficient and the hardware must be large, its value is entirely that it operates off of heat which sometimes we can get a lot of. Spacewise, I'm fairly sure solar cells should be more effective though I'd want to run some numbers to back that up. But cost-wise, it could potentially be more competitive especially if you can find tubing as cheap scrap whereas cheap "scrap" solar cells are never available. The liquids are very cheap and are good for life. Be aware that calling around for volumes of anhydrous ammonia will arouse suspicion because it is a component desperately needed by illegal methamphetamine labs. It is not an illegal material however, it a common agricultural chemical. Still, if you grow weed, giving people the false idea you might have a meth lab might not be in your best interest.

Wikipedia also lists an interesting adsorption cycle using charcoal, methanol, and water.

 

[HarveyH42]

I just came across that site while looking for the homebrewed version. The 'village' thing is what suckered me in. I'm guessing the numbers are exagerated and the unit price is set for government purchases...

The one I was looking for used 55 gallon drums, PVC and copper tubing.

Bummer about the anhydrous ammonia. Between drugs and terrorist, what are we going to be left with. Should just legalize pot, seems to have several legitmate uses, and make everything elsa a capital offense (probably kill them eventually anyway).

Guess I'll keep looking, at least I know its not a 'Joe Cell" project....

 

[Oznog]

Well the first place to start is looking up the data on how a cycle actually works. You want to be REALLY careful about what materials are required. For example regular steel might corrode and poison the reaction (just a random thought).

You can look up the efficiency and temps required, and check and see how many BTU it takes to cool a house your size. You might want to build a model of your solar concentrator and even a smaller version of the system to test the principle.

Getting anhydrous ammonia really isn't that big of a problem, and it's not expensive either. You just need to be prepared to explain yourself and not act dodgy.

 

[HarveyH42]

Still looking for sites that deal with build your own. My searches so far have mostly been turning up ready made system to buy (expensive). Haven't come across any used to cool a house yet. Have to search for anhydrous ammonia, maybe that will help cut down on the hits some.

I don't think buying anhydrous ammonia will be an issue, I don't do anything with drugs, and nothing too illegal in the house. Having the police or FBI searching would be a huge waste of time.

 

[Oznog]

There is also a silica dessicant adsorption cycle.
The "swap cooler" evaporator cools the air by evaporating water, but in the process raises the humidity level. The air is too humid to cycle a second time, even though the sun's still warming the air in the house again, and in fact it will make the air too humid for a house anyways.

Now silica dessicant will fix this problem by reabsorbing the humidity, I think that's an endothermic (cooling) process too! Then heating the dessicant using air that doesn't mix with the house air will drive out the moisture again. So you either need to physically move the dessicant to the solar collector or use 4 valves to isolate the dessicant chamber from the a/c system airflow and route solar-heated air through it and exhaust it outside the house.

It is a slow process though. You should look up some estimates of how much dessicant and how much heat you'd need to do the job.

Be aware that air conditioners are pretty competitively efficient with its alternatives. There's a theoretical max of how much heat can be be pumped across a given temp differential for a given power input, and compressor-based systems are fairly high. The problem is simply that a crapload of cooling is needed. Usually the greatest gains can be had by simply increasing the insulation in the attic and/or walls, paint the house a lighter color, have a large tree shading the structure's south side, install "solar screens".

Anhydrous ammonia can burn you badly, btw. You will need to think about that, and the environmental consequences of a leak into the soil.

 

[bryan1]

Oznog has described very well all the concepts of alternate refrigation and one I've looked at making is using Anhydrous Ammonia. Now I'm very skilled at machining and welding as one slipup when playing with this type of gas is you only get one chance then you will pushing up daisies. Simply googling will find plenty of projects using this gas and I've done a heap of research and when I can get some ammonia I'll be giving it a go. But remember if you don't do it right and have a properly sealed unit you will be asking for trouble. Any project I do I'll be keeping to myself as I don't want to be responsible if someone makes up my design wrong and kills themselves.
As far as using solar panels just do the maths say your using a 2hp aircon thats 1500 watts and upto 5 times that when the unit starts or cycles. Without a decent deep cycle battery bank and huge inverter forget it. Now to give an idea of the cost just to run a 2 hp aircon, my house array has 14 new gen 65 watt solar panels ($8,400) an MPPT ($2,500) 12- 2 volt 600 amp/hour batteries($10,000) and a 2400 watt sinewave inverter ($3,500). Now for me to run the aircon all day I would need to either let the batteries go flat or run the genset to keep them topped up and at $1.40 a litre for fuel it's pricey. Anyway I've got a couple of evaporitive coolers that serve us well and I'm making one that works on 12 volts DC.

Anyway enough of me ranting

Cheers Bryan

 

[Overclocked]

The only thing I can think of that converts heat into cold is a Pelt, but it requires alot of power (4 to 8 amps depending on wattage) and needs a somewhat high voltage (12 to 16V) inrelation to a solar cell.

 

[Oznog]

The Peltier is widely misunderstood. It is terribly inefficient relative to a compressor-based system. It is also much more limited in how much temp differential it is capable of creating. To put it another way, if you need to make a space 10 deg cooler than the outside air it will require much more power than a conventional A/C. If you want to make it 30 deg cooler than the outside, it may require 10x more power still.

 

[HarveyH42]

Aren't Peltier junctions also used to generate electricity? I'm guessing that it's very low yield as I've only read about it's heating/cooling effect these past ten years or so.

I lived in this house for 5-6 years before buying central AC. Mid-summer was toughest, fans didn't help that much. Typically, a 10-20 degree temperature would be fine most of the years. I'm guessing both of these methods aren't suitable for cooling a house. Solar power is much too expensive for me, unless I could figure some way to get George Bush to help out on it...

 

[Overclocked]

Aren't Peltier junctions also used to generate electricity? I'm guessing that it's very low yield as I've only read about it's heating/cooling effect these past ten years or so.

I lived in this house for 5-6 years before buying central AC. Mid-summer was toughest, fans didn't help that much. Typically, a 10-20 degree temperature would be fine most of the years. I'm guessing both of these methods aren't suitable for cooling a house. Solar power is much too expensive for me, unless I could figure some way to get George Bush to help out on it...

Yes they can also generate electricity by either heat or cold. They could be another way to generate electricity, but I dont know how too much. They may rival Solar Panels

 

[HarveyH42]

I don't remember too much. It was new and expensive, but had cool posibilities.
The basics were teo dissimilar metals bonded together, by cooling one side, and heating the other, you get an electrical current. By applying a DC current one side gets hot, other cold. The voltage and current need/generated didn't stick in my head, but that was many years ago. I'm sure if it was feasiable for power generation, someone would be doing it. The junction isn't too complicated to form.

 

[Overclocked]

I don't remember too much. It was new and expensive, but had cool posibilities.
The basics were teo dissimilar metals bonded together, by cooling one side, and heating the other, you get an electrical current. By applying a DC current one side gets hot, other cold. The voltage and current need/generated didn't stick in my head, but that was many years ago. I'm sure if it was feasiable for power generation, someone would be doing it. The junction isn't too complicated to form.

Its a PN Junction, Watts of the pelt are proportional to consumed current. Of course, they do have low voltage low current Pelts, but they are only like 8W or so.

 

[Oznog]

Generating power from a Peltier device is "Seebeck Effect", not Peltier Effect, though essentially they are two ways of looking at the same equation. Any Peltier device can be a Seebeck Thermoelectric Generator but devices specifically made to generate power can be more efficient because they can tolerate higher temperatures. There's a company called High-Z on the net that makes them.

There used to be a page detailing all the equations but I think it's long gone. It wasn't that great... I mean like a really high temp differential tuned to the device's max could generate like fews watts of power for a device, less power for a lesser temp differential. Probably under a watt for a solar-heated device of typical Peltier size. Also the device does conduct substantial heat across it so a solar heating plate with the cold side in the shade would heat up the cold side pretty quickly. In short it did not seem practical to compete with solar cells.

 

[HarveyH42]

Wonder if you could generate enough power to run a well pump, use the water to cool the cold side. Basically free hot water for your house...

 

[HarveyH42]

www.homepower.com/files/solarice.pdf

This is the article I remembered seeing! Can't believe its 1996... Wonder what the price tag would be 10 years later. $510.00 wouldn't be too bad to play with...

 

[davew1301]

Hi guys,
What HarveyH42 is describing is a thermocouple! There are several instances of them being used in multiple series to power valve radios about 50-60 years ago from a gas flame (so my old Dad used to tell me) but I've never seen one in the flesh.

DaveW

 

[Paul Obrien]

I did read a book "Modern Theromelectrics" published in the 80s that wasextremely informativer. Yes, Peltiers are very inefficeint 1-2% at the time maybe better today. There was a mention of a Russian generator that used a kerosene lamp with a vast number of junctions in the flue used to drive a radio, probably a cold cathode valve job. There were examples of military generators and air conditions in the book also. The nuclear devices used in heart pacemakers and spacecraft also use Peltier devices. A very interesting book.