Is a Portable Air Conditioner with Water Cooling Feasible for Garage Use?

[Pengwuino]

One problem that came up for my father and my aunt was that they did not want to work (cleaning my grandfathers garage, he's in a nursing home now :-/) during the summer in the garage. Now i was wondering how feasible is a portable air conditioner? If say, at the 'hot coils', instead of air, you put a lot of water but not so much as to make it non-portable. Then after a while, you'd have to dump the water and refill it of course. But how long could you run the air conditioner before the water becomes too hot to work as a heat transfer unit. there's a big danger of course of pouring out like, 600 degree water ... a lot of which would vaporize as u begin pouring it. The water would be enclosed by a variation of a dewar flask i suppose to keep the water from leaking off too horribly. What does everything think about the feasibility of this lol.

 

[russ_watters]

The water will heat up relatively quickly, so this sort of thing wouldn't work (about as fast as if you put it on the stove at "medium"). There are, however, two kinds of portable air conditioners: water and air source. unfortunately, both need a heat sink. An air source portable has a duct that you send out a window to discharge heat. A water source unit is connected to a spigot and a drain (or just discharged outside)

 

[Pengwuino]

Ah so it would heat up pretty fast... dang. Wonder if you could setup somethign where you connect the unit to a faucet and water comes in and u drain out through another hose going back into the sink (but make it flush with the drain so the water doesn't make contact with the air in the sink)... or i don't know :D Maybe ill find anothe rway to eleviate working in a hot as hell garage in the summer with no a/c.

 

[brewnog]

You could look into an evaporative cooler. You fill them up with water, and they cool the air, but aren't suitable for applications where moisture is a problem unless you use them in conjunction with a dehumidifier.

 

[Pengwuino]

where does the hot air go though? actually wait, how does it work?

 

[brewnog]

The air is drawn through water-soaked pads within the machine, where it evaporates water. Since evaporation requires heat, the temperature of the air drops. This cooled air is then circulated around the room.

The problems arise when the input air is already damp, because it finds it difficult to hold more water so the air temperature cannot drop.

Air conditioners work on a closed cycle (which is why you close the windows and doors for them to work properly), evaporative coolers work on an open cycle (so you need somewhere for the heated up air to escape).

Wait for russ to get in here, he'll know much more about it.

Edit: oh, he's here already.

 

[Pengwuino]

Wait so these evaporative coolers need a place for the hot air to escape? I thought the air comes out cooler. And i don't understand this idea. I thought the air flowing over i guess these pads would transfer energy to the colder pads and come out at a cooler temperature. Why would it "evaporate", i thought that means it would get to like 100C.

 

[brewnog]

When the cold air comes out of the cooler, it will gradually get heated up by the air in the room. When it's been warmed up (by the heat inside your house) you ideally want to get rid of it, replacing it with more nice cool air from the cooler.

If you drag fresh, dry air (from outside) over some wet pads, the water evaporates into the air, cooling it down. You're right that the air flowing over the pads tranfers energy to the pads, this is how the air becomes colder. It's like when you sweat; the sweat evaporates off your body. This requires energy (in the form of heat), so you become colder.

As for water needing to be 100 degrees celsius before it will evaporate, well you know this isn't the case because a puddle will evaporate on a dry day. Water molecules on the surface will 'borrow' enough energy from the surrounding molecules to allow them to evaporate.

 

[Pengwuino]

I don't get it though, what does it mean to evaporate compared to vaporize?

 

[brewnog]

Same thing really. Evaporation is when a liquid changes into a gaseous state below its boiling point, which happens when the surface is exposed and unconfined. Vaporisation is just when a liquid changes from its liquid to its gaseous state.

 

[russ_watters]

Wonder if you could setup somethign where you connect the unit to a faucet and water comes in and u drain out through another hose going back into the sink (but make it flush with the drain so the water doesn't make contact with the air in the sink)...

That's the water source air conditioner I was describing. They aren't very common though.

Regarding evaporative coolers - they don't work unless the humidity is really low. But Pengwuino, evaporation happens at any temperature, yet the energy required to change phase is the same as with boiling. That energy absorbed (in the breaking of chemical bonds keeping water liquid) means the remaining water and the water vapor must lower their temperature to keep the system energy constant. This is how a cooling tower can cool water below ambient temperature.

 

[Pengwuino]

Whats a cooling tower and how does it work... i might have a project for that kind of concept :D

 

[brewnog]

Cooling towers are those massive stacks you see at power stations, which cool whatever substance has been forced through the turbines to generate power.

They work, in exactly the way, that Russ told you they work.

 

[Cliff_J]

Pengwuino - to your original question, think of the typical window mounted air conditioner, if it was a larger one (just big enough to keep a 2 car garage reasonably comforable) it would have something like a 12,000 BTU capacity.

In the industry, this would be called a one ton unit, and a home might have a 3 ton or 4 ton unit depending on its size. This ton rating means in a 24 hour period of operation it pumps enough heat to melt x tons of ice into water. So you could build a historic air conditioner with a large payload of ice, about 83 lbs per hour or so. (close enough, you could look up latent heat of fusion and do the exact math from 32F to 70F and so on...)

Ice has much more heat capacity than water - think of a ice filled drink on a hot day and how quickly it starts to warm up once the ice in it melts. So you'll need a lot of capacity to keep an volume as large as a garage pleasant in the summer.

Cliff

 

[russ_watters]

Cooling towers are those massive stacks you see at power stations, which cool whatever substance has been forced through the turbines to generate power.

They work, in exactly the way, that Russ told you they work.

They make them for building HVAC systems as well. I even saw one a guy made to water-cool a computer. It was a 3' high pvc pipe with a shower head at the top. It would be an interesting project to make that work for a water source air conditioner (heat pump).

My boss's water source air conditioner is made by http://www.koldwave.com/products.html and they still make portable water source A/C units.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=42910&item=3880270229&rd=1&ssPageName=WDVW has one - 12,500 BTU (typo in the title says 100,000), for $225, opening bid.

With an open system, you'd use a lot of water (about 3 gal/min). For my boss, that's not a big deal - he has well water, so he doesn't pay for it - but if you wanted to do something like this and feel like a little project, bulding a cooling tower could be fun. I can help with the performance calculations, if you want.

http://www.madshrimps.be/gotofaqlink.php?linkid=1524 is the cooling tower a guy made for his computer.

edit: I just discussed this with my boss - we may do this just for fun (yes, we're nerds).

 

[gschjetne]

I may be a novice in this field, but has anyone considered using a cooler based on the stirling cycle? It's most often used to cool superconductors in infrared sensors (I would think), but I suppose they could operate with most temperature deltas.

Something that has been bothering me about stirling cycle cooling is what the further cooling requirements are, and what part of the machine gets cold and what gets hot. Is it the side where heat is normally applied that gets cold, or is it the other one?

 

[brewnog]

The side to which heat is supplied is the side which gets cooled, but is still warmer than the side to which heat is rejected. I think...

 

[Artman]

Where are you located (just generally, such as SW USA, or NE USA, UK, etc.)?

How long of a project are we talking about here? Several days, a week, a month?

How big is the space to be cooled? (Again, generally speaking.) Also, how full is the space? This might effect air movement.

I have some ideas, but it depends on the specifics.

 

[Nenad]

to superconduct, to cool at those temperatures, you would use a conventional ac unit but more heavy duty. You have a compressor in the condensing unit and a cooling coil. This is how it was done in the early 1900's when super cooling first came out. Basically, as new substances were being developed that could evaporate at lower and lower temperatures, these were used as coolant and the substance being supercooled would be the substance loosing heat. Once this new super cooled substance evaporates and cools, then it is used to supercool a substance that evaporates at an even lower pressure. It sounds confucing but its one big cycle.
Im not sure how they o it now, but this is the simplest method I've heard of.
Regards,

Nenad

 

[minger]

Nenad, seems your referring to a Cascading Refrigeration Cycle.

 

[Nenad]

I don't know what its called exaktly, but its probably that.

Regards,

Nenad

 

[willib]

.
Pengwuino or someone else brought up a sterling engine.. i have an attic which gets really hot up there in the summer.. how could i use this heat to do something useful ?? like generate electricity?

 

[Pengwuino]

Sterling engines are very slow and not at all powerful so i don't believe you could make much electricity with the heat up there.

 

[xJuggleboy]

.
Pengwuino or somone else brought up a sterling engine.. i have an attic which gets really hot up there in the summer.. how could i use this heat to do something useful ?? like generate electricity?

THe answer to that is Hydrides! Warm air heats a hydride rasing the pressure of hydrogen which can be used to do lots of stuff... Running a fule cell or charging a battery... A few other things but those are the easy ones

*Edit

Before anyone brings it up... It would be very expencive... ANd recharging the hydride would cause you a bit of a problem... But that wasint your question

 

[M-Funf]

"Dry" Air Evaporative cooler.

You could also make a "dry-air" evaporative cooler. This was invented some time ago, and my father's company manufactured these until about 15 years ago. Basically, it's an evaporative cooler with a twist:

Instead of using a wet fiber/wet cardboard medium and blow air across that, wrap some thin wall PVC tubing with material. Run water over them and recycle it back to the top. Draw outside air across those tubes and exhaust that air back outside. Draw air THROUGH the tubes. This air will be cooled as it passes through the tubes into the space to be cooled.

It's not as efficient, but it is as dry as the outside air...

Good Luck!

 

[DaveC426913]

I don't get it though, what does it mean to evaporate compared to vaporize?

Boiling temperatures are not required to turn water into vapour. Water will naturally turn into vapour. What's why pools, puddles, spills and drops of sweat all eventually evaporate and disappear.

When you sweat, the liquid on your skin evaporates into the drier air. The process of evaporation is 'endothermic', meaning it requires heat. The heat is drawn from the water, and hence from your body as the water turns to vapour.

The net effect of water evaporating off your skin is a loss of heat, and thus a cooling feeling.

 

[DaveC426913]

While this topic is under discussion, something I've thought of but never verified:

Air conditioners cannot work well if the air temperature outside is too high, correct? If the outdoor ambient temperature is too near the temperature from the radiating fins, they won't be able to dump their heat efficiently, correct?

Any numbers on this?

 

[willib]

While this topic is under discussion, something I've thought of but never verified:

Air conditioners cannot work well if the air temperature outside is too high, correct? If the outdoor ambient temperature is too near the temperature from the radiating fins, they won't be able to dump their heat efficiently, correct?

Any numbers on this?

i have no data on that , but that is why on most window units , the fan that circulates the cold air on the inside , also cools the fins on the outside and on some units it also scoops water from condensation , from the inside , and sprays the fins with that thus lowering the fins temp even more..

 

[Averagesupernova]

Regarding air conditioning working in VERY hot temperatures:

Window type air conditioners are based on absorption. Air outside is used to 'absorb' heat from the condenser coil. Naturally, if the air is almost as warm as the condenser coils very little heat will be transferred out of the coils. If this happens, the evaporator coils (cool side) will not get any cooler than room temp.

 

[russ_watters]

A lot of commercial system manufacturers publish performance data at various temperatures. Here's one: Random Liebert Condenser. At 20 degrees dT, it has 80% of its capacity at 25 degrees dT.