A/C ideal

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A/C ideal

Postby stjohn » Fri Mar 31, 2006 6:47 am

This may be a silly thought but why could you not refit a 3way rv refridge
to be a air conditioner would run on 12 volt 120 ac and propane if it will freeze meat and keep beer cold it should keep 100 cubic feet prety cool

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Postby GeorgeTelford » Fri Mar 31, 2006 7:52 am

Hi Mike,

no it would not work, for a set amount of heat removal you require a certain amount of energy to carry it away

Remember cold is the Abscence of heat, cold is not created heat is merely removed.

If you were to put a small mains fridge inside a tear with the fridge door wide open, the temperature would actually rise because heat removed would be exited at back of fridge into the tear, but even if you vented the back outside the tear the temperature would hardly move.
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Postby JunkMan » Fri Mar 31, 2006 9:46 am

RV fridges don't work the same as a regular fridge. If you put warm stuff in them, it takes forever for it to cool down. We normally load warm sodas in them in the evening so they will be cold then next day. Ideally, you should cool everything down before loading the fridge.
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Re: A/C ideal

Postby Steve_Cox » Fri Mar 31, 2006 10:17 am

stjohn wrote:This may be a silly thought but why could you not refit a 3way rv refridge
to be a air conditioner would run on 12 volt 120 ac and propane if it will freeze meat and keep beer cold it should keep 100 cubic feet prety cool

Mike


Mike,

You are on the path to making a small air conditioner, these just arn't the right components. 12 volt and propane, probably not gonna find the right stuff to build it, but 120 volt 60 hz, parts are available, it is just a matter of cost. a wine closet cooler would be about right, but they are expensive. It's that $78 Walmart special that's keeping the development of a TearDrop AC down. In the UK they have 2000 btu units for small caravans, but they are 50 hz. I talked to a rep from a boat air conditioning manufacturer at a local boat show not too long ago, he said they could build what we want for around $1200, it would be a split unit. So with that in mind I figure a knowledgable person could build it for maybe $300 or so, maybe less. I wonder what the demand would be if someone came up with a AC designed just for TDs, and how much people would be willing to pay.

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Postby SteveH » Fri Mar 31, 2006 10:54 am

Does anyone know if there are quick disconnect connectors available that could be used without loosing all the refrigerant? With something like that, an automotive under-dash evaporator could be used inside the tear and the compressor (small one) and condenser could be placed outside the trailer. The compressor and condenser inside the trailer is the problem as I see it.
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Just a thought !

Postby An Ol Timer » Fri Mar 31, 2006 11:02 am

I've been thinking this A/C thing for awhile and I've been wondering about this scenario. First the small units that some people are using are perfect except for being too large as far as output goes and therefore defeating some of the things that it is used for. You get too much cooling and not enough humidity removal. Too short of a heat/cool cycle. Why not let the unit run normally but thru a split plenum which would dump a portion back to the outside and the rest to the tear interior. Say a 60/40 split dumping 3k back to the outside and 2k to the tear. Now with the controls placed in the tear it's interior would be the controlling factor in the run time. I know that this would be a waste of 60% power but it is an alternative. The split plenum could be adjustable as far as the split ratio.
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Postby critter » Fri Mar 31, 2006 2:23 pm

hey all,
how bout just sit the thing outside in a box and hook a dryer hose to a vent to the side of the tear vent to put part of the cold air in the tear.then maybe just waterprof the rest of the unit somehow.would this work.ive been thinkin bout this.yall say that the small ac's put out way too much so just put 2vents in the frt of the box and only hook 1 to the tear.maybe get 1 w/remote?
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Postby Ira » Fri Mar 31, 2006 2:37 pm

critter wrote:hey all,
how bout just sit the thing outside in a box and hook a dryer hose to a vent to the side of the tear vent to put part of the cold air in the tear.then maybe just waterprof the rest of the unit somehow.would this work.ive been thinkin bout this.yall say that the small ac's put out way too much so just put 2vents in the frt of the box and only hook 1 to the tear.maybe get 1 w/remote?


I don't think that's gonna solve the constant cycling/on-off problem. Having not USED mine yet (one day Lord, please), I don't think it's the "too cold" problem that has tortured many. It's that constant cycling.
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Postby critter » Fri Mar 31, 2006 2:53 pm

hey ira,
i dont understand,what would make it cycle so much?why would this be a problem?
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Postby stjohn » Fri Mar 31, 2006 4:07 pm

Thanks guys just enough info to keep me awake all night again pondering
the possabllities :shock: :? :D

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Postby An Ol Timer » Fri Mar 31, 2006 4:08 pm

Exactly like I said above, dump your excess overboard and put the controller in the tear to solve the fast cycling problem. This could all be accomplished with a plenum between the face of the A/C unit and the tear and it probably wouldn't have to be more than 6 to 8" deep. Put in a damper to vary the flow to the tear.

Think of a commercial unit that is serving several different areas of say a manufacturing plant. You can't satisfy each individual area so you get your roof top unit sized and running proper and then you vary the flow to each area. One area will have the thermostat and a smart manager will have it in a locked cage.
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Postby BrwBier » Fri Mar 31, 2006 5:20 pm

I have an alternet idea, come to Wisconsin in the summer and camp near Lake Michigan. Then go to a warm state to camp in the winter. No A/C or heat needed.
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Mike has the right idea.

Postby Guy » Fri Mar 31, 2006 6:42 pm

Dear All,

You may think that Mike's idea is off base, and George Telford. you know a lot about electrical, but you fall a little bit short on the refrigeration side.

A number of high end refrigeration companies, especially in the fishery business do have adapters which, in essense, do exactly as Mike is suggesting.

Here is one of the premier marine companies on the cutting edge of R&D for refrigeration and cooling.


http://www.glacierbay.com/marine_air_conditioning_systems.asp

If you really read their site wellyou will see how and why it is practical and practicable. And don't miss the discussion about aerogel. There is another company that manufactures it, called Aspen Aerogel but it is in Massachuesetts near TomS.


http://www.aerogel.com/

BTW, both companies were extremely encouraging about how they could help with Teardrops4vets.
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Postby GeorgeTelford » Fri Mar 31, 2006 7:19 pm

Hi Guy

There are some basic physics laws involved here, to remove a set amount of heat requires a minimum amount of energy, I guarantee that a 3 way fridge cannot remove enough heat to be worthwhile inside a tear, it has enough trouble keeping the contents of its tiny insides cool.

Think about it, If it were that easy then then big rigs would have Aircon running on LPG gas for boondooking, unfortunately it will not work (adapting a 3 way fridge).

The adaptor on the site you linked to is for a full on compressor fridge not the type being discussed here.

BTW I have done some design work on refridgeration and insulation to make a more efficient fridge for camping. I do understand the physics involved.
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Postby Artificer » Sat Apr 01, 2006 8:48 am

The idea isn't totally silly. I don't think its practical, but it is doable. First, you need to determine how many BTU's the refrigeration system needs. 5000 seems to be too much. Pet-cools run 2000BTU's, and I've heard 2nd(3rd?) hand that someone is running one in a teardrop in Meixco. So... 1500-2000BTU/hr seems to be a good goal.

The little LP powered fridges you see only put out around 250btu/hr. Thats why they take so long to cool down. You can find a propane unit that has the capacity, such as this freezer. 1700BTU's, but it costs $1700. These units also have several drawbacks. They are large, and they only run when perfectly level. These units also use 3 liquid/gases. (Ammonia, water, hydrogen) Any leaks, and they stop working. For $1800 (or $2500 for the DC breaze) you have a 12v off the shelf unit.

Your idea about disconecting the refrigerant line is not going to work. The best you can do is to have a water/glycol heat transfer system. The AC system sits outside, and the water line runs to the heat exchanger inside the trailer. This water system can be used with any of the AC units, if done right. You could also expand it to use it as a heating system.

I've been thinking about this a lot recently, and I've come up with seveal solutions. Some easy, some almost imposible for an individual. With some hard work and injinuity, you can also get a propane powered A/C system.

Easiest is to get a wall AC unit and duct it in. You can find examples all over the forums. The Pet-Cool is a sweet system, with the only drawback of using AC power, and more expensive than a wall unit. Good thing about it is that it will not cycle on/off as much.

Ammonia/water absorption system. (Lithium bromide/water as well) I'm not talking the gravity system the refrigerators use, but the pump driven type that industry uses. Most of you cooling power comes from the propane heater, so electrical power useage can be as small as 20-35 watts. DC power drives 2 fans and a pump. This system can be as large as you design it to be. A/C, refrigerator, FREEZER all in one unit. Its not a project for the timid. As soon as I get my trailer done, this is what I'll be working on.

Duplex Stirling cycle refrigeration. Stirling cycle engines are called external combustion engines. Heat one end, cool the other, and they work. Starting site for information is
here These engines also work inreverse. Apply mechanical movement, and you get cooling. The duplex system ties two of these back to back, so you use heat to get cooling. They're not as efficient as a compressor, but then again... you get propane powered A/C. You can add a small generator to the system so you have power for water pump and fans so this unit is outside of the trailer. Hmmm... throw the hot end in the campfire?

There is another cycle, like the duplex stirling, but I'm suffering a brain fart. Something like ve.... it doesn't have a piston, just two displacers. After a starting nudge (or small drive motor) this thing will move heat from the cold end to the ambiant temperature heat exchanger.

An article on direct thermally driven heat pumps is at
here

A more advanced heat pump is the free piston duplex stirling cooler. It doesn't have any connecting rods between the displacers and piston. Heat one end, cool the middle, and the other end gets cold. Add alternator coils and a magnet to the piston, and you also have electrical generation. How about a generator that's as loud as a furnace/water heater?

As I said in the begingin, its not totally silly to think about propane powered A/C, but you're not going to get it with a few modifications to a small refrigerator.
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