Water cooled Air

[Sibling Chatty]

In the '50s before we had AC, my grandfather used rubber tubing tied off at the ends, filled with water and then frozen overnight to drape around his neck (and mine) when we worked at the cooperage. Old wooden building with a tin roof--if there was no breeze, 110 wasn't unheard of on a summer afternoon.

He actually used inner tubes from bicycle tires, cut in half and heat sealed on one end, tied on the other. He'd break up the ice so it would wrap, and with the fans on, it was tolerable.

I used to use my cold packs from the chiropractor's office for cooling down when my tumor burden was high. (Carcinoid causes a sensation of burning up from the inside out...among the less disgusting but more irritating side effects.) That gooshy gel stuff in a refreezable pad kinda thing....

[Sibling Zono (anon1mat0)]

Given that you will be able to get quicker freeze times out of containers with high surface areas, you could build an ultra-low tech system simply by placing a number of cold packs (ziplock bags filled with water, then frozen while laying flat on baking sheets work too) on a wire rack or shelf and blowing a fan past them.  No need for a pump or radiator.

Actually that is a wonderful idea! I can make the duct out of plywood to work as a rack for the trays at the same time. The condensed water would fall in the trays themselves and it would be relatively easy to check how long takes the ice to melt in the duct, and to freeze in the fridge.

Thx! 

[Aggie]

You're welcome!

I like projects.

[Bob in a quantum-state-of-faith]

The one I bought http://www.heatbusters.com/easifit/products/all-products/unico-star-85-heating-cooling does cool or heat..... and has no outside unit... what you get is what you see... but it wouldn't solve the cost element - or at least I suspect it wouldn't.... but maybe worth investigating how it works.

From the description: 

An elegant, self contained unit simply requiring two vents through an external wall,

The unit sucks air into the inside box with one vent, blows that across the condenser radiator and the now-hot air exits out the other vent.

It does provide a very clean look on the outside.

And, you can put these in temp, with an adapter plate in a window-- that is, the window shuts onto the plate, which has two holes for the two vents.

If you live on the first floor, and the unit is to be on an interior wall, you can vent under the house to the outside (assuming you're not on a slab).

I would imagine these are about as efficient as a quality window unit.

The size is everything, obviously, and too big is worse by far (for a number of reasons) than too small.


Why?  Because, too big will get the temperature down quickly.... too quickly, and leave in all that nasty humidity.  It's like being in a damp cave....


_______________________

Just thinking... my gut feeling says that in the middle of a Florida summer, a dehumidifier might be more effective than an evaporative cooling device.  It wouldn't reduce the actual ambient temperature, but by reducing humidity, it would improve your body's ability to evaporate heat away itself.  Effectively, it should reduce the humidex/"feels like" temperature.

Another part of my gut says that a normal freon-or-similar-based system is probably going to give you the biggest cool-for-the-buck of any active system.  Is it a viable option to just close the vents in the unoccupied rooms (and either switch the A/C system on & off manually, or wire in a switch to a second thermostat in the room you're in), or to get a small window air conditioner for the one room you need cooled?

You DO NOT want to close off too many rooms-- if you have central.  Your A/C unit DEPENDS on a certain load-- if you close off too many vents, it will freeze up and possibly ruin the compressor.  Not good.

If you just want a room or three cooled, and the rest ambient, then 2 or 3 window units is the way to go, if you've a medium-large house.

If you've a small one, the break-even point is at about 1 window unit, vs the whole house one.

Commercial de-humidifiers are basically a small window A/C unit.  They work pretty well, but unless plumbed, you have to empty them daily.

[Griffin NoName]

It does provide a very clean look on the outside.

It does indeed.

And mine seems effective. The few times I used it last summer.

[Aggie]

*thread resurrection*

As it's starting to warm up here, I'm mulling over what would be the best way to help keep this place cool in the summer.

(number one will be to get some curtains on the place, and perhaps some awnings over the south windows, but let's ignore that bit)

My bedroom in particular could probably benefit from some sort of jury-rigged system. I'm in a small house built circa 1946, with removable storm windows on the outside of the (original) interior windows.  The bedroom window is east-facing, and gets morning sunlight.  Since I like it dark, I've mounted fibreboard and a mirror on the interior of the storm window.  The house is in a slightly dodgy part of town, and aside from the effectiveness of the exterior-mounted 'curtain', I'm disinclined to remove the storm window in order to catch the night breezes.  There are, however, two ~3 cm diameter holes in the bottom portion of the frame of the storm window which will admit some air.

At the moment, those little holes do a fine job of admitting some cool night air, but during the summer it gets seriously hot (>40^oC during the day, and sometimes can remain above 30^oC at night).  The advantage relative to Zono's issue is that we are semi-desert in the summer and it's also very, very dry.

So, given that I have dry air and that the side of the house I'm on doesn't get sun except in the coolest part of the day, I'm wondering if I can concoct a little evaporative cooling system here.

Now, I still don't want the added humidity, so what I'm speculating about is a system that cools a set of coils through which air from the room to be cooled is passed.  Some sort of little tube or duct fan would be required to move air through the coils.  With the two holes in the window frame, I could pass the tubing in and out without any modifications.  

The coils themselves could be cooled in a couple of ways; one would be to be sew a tight-fitting terry-cloth cover out of an old towel to fit the stacked coil, and then use a small pond pump to circulate water over the cover.  Similar to Bob's cooling tower design in principle, but the towel has much more surface area for evaporation, and would also slow the passage of water to allow greater cooling.

What might also work is to place the coil inside a terracotta pot (a large planter with the bottom hole plugged off would do) full of water, which would function similar to a pot-in-pot refrigerator.  Essentially, this would be a water-to-air heat exchanger running through a large thermal mass of water, which itself is being cooled by evaporation (plus, cools down every night).  It may even work better in full sun, if the pot was fairly light in colour (perhaps whitewashed). The evaporation would occur entirely outside of the building, so there'd be no additional humidity to the air.  There's some potential for condensation to occur within the coils, but it wouldn't be hard to build a trap that could be drained out from the bottom of the coils (remember the hole in that pot? put it out through there).  A coil of copper tubing would be ideal as it would conduct heat well, but I've got a bunch of scrap 5/8" polyethylene tube kicking about. The stuff is (IIRC) about $30 for 100 ft, so it would be more economical to use a longer tube of cheaper material than a short copper coil, perhaps.  

EDIT: I took a peek and found some 1" HDPE tubing at ~$60/100 ft; smaller diameters will make better heat exchangers, but larger diameters will be easier to push air through. Am I correct in thinking that since air friction and energy transfer are proportional to surface area, it might not make much of a difference either way in terms of efficiency?

With a large, porous container, you could even stick this near a down-spout and have a combination air-conditioner/rain-barrel (hmm. should patent that, perhaps). Worst case, you'd have to top it up with water every morning - no big deal. I'd move the air through the coil from top to bottom, which should be counter-current to the temperature gradient and would make it no big deal if the pot wasn't totally full to the top of the coil.  If a terry-cloth jacket was used on the coil, having the water level low might actually help with the cooling. It could even be used as an intentional pre-stage; if the towel protrudes down into the water, it'll wick up enough moisture to stay wet.

Now, the biggest issue I can see with this is how to move the air through the tube.  The best thing I can see at the moment is perhaps electric ducted fan units used for RC aircraft, like this:


They don't make these things quite as small as I'd need, but they are cheap-cheap (under $20).  I imagine the system might be a little noisy, but probably no worse than a compressor (unless it whistled). Now, these suckers are meant to produce thrust, so I imagine they would be capable of compressing the air a bit.  If you mounted the fan outside the house, just before the cooling coil, then put a condenser to drop the diameter from whatever fit the fan to whatever diameter you were using for the coil, there would be a (slight?) increase in air temperature at that point. However, this heat would be removed as the air passed through the coil, and there would be an equal (slight) drop in temperature as the air was decompressed from the coil into the room. Bonus!

I'm not sure what the power consumption is, but since they're for battery-powered aircraft, you might be able to run one with a small, cheap hobby-size solar panel.  If so, it's possible that you could plunk the entire unit outside of a small room and run it entirely by the sun, which would be adequate for taking the edge off the hottest part of the day.  I imagine you wouldn't move enough air to get things really cold, but from what I've heard about the pot-in-pot refrigerators (some designs can generate temperatures as low as 6C), it's not impossible that this could be effective as a small-scale cooling system.

Hmmm...  any glaring errors in all that?

[The Meromorph]

You might want to look at computer cooling fans (cheap, readily available, fairly high volume, designed for long continuous running) instead of expensive, ultra- lightweight model aircraft fans... 

[Aggie]

This was my first thought (simply to put a small computer fan against the holes in the window), but would a computer fan be appropriate for driving air through 100 feet of small-diameter tubing? I.e, can they work continuously with a significant load?

For the price, they'd certainly be worth a try.  It'd be easier to build a square duct for the fan-box than to size tubing for the little RC ducted fans.

[Bob in a quantum-state-of-faith]

If you use small diameter tubing?  (not a bad idea, actually)

You are going to need multiple paths to get any worthwhile airflow.   8 or 10 is not out of the question here-- or more.

The easiest way to push air through multiple tubes at the same time, is to plumb them all into a single box-- make it airtight.  Now cut a hole in the opposite end of the box from where the tubes all come in-- mount a fan there.  Or possibly two holes and two fans.

The fans will pressurize the box, with will then force the air through the multiple tubes.  Coming out the other end?  You could split them up to dump the cooler output air anywhere you like-- but keep in mind, a small diameter tube won't have much volume coming out, even if at relatively high velocity.

Such a setup might work for a single room, which was your goal, right? 

Another thing you'll want to do:  on the return-path for your tubes, after the air's been cooled?   Insulation.  A goodly bit, too-- once it's cooled down, but still outside?  I'll pick up heat quickly, if you don't insulate those tubes.  The tubes going from inside to the barrel ought to be insulated too-- no point in adding needless heat to your barrel, as once the system is up and running, the inside will be cooler than the outside air temp, so any point you can prevent unneeded heat is a must.

Finally?  Heat rises, cool air falls:  place your box-with-fans-and-tubes up high in the room-- near the ceiling.   (on the inside, there's no need to insulate your tubes-- the air will be nearly the same temp at that point). 

Now-- were to put your output, cooler air-tubes?   High or low?  Both have advantages.   But your goal is to mix-up the total air in the room.  So, since these are cheap, and small?   (and once back inside, no need to insulate once again)  I'd either string them across the ceiling to the opposite wall from the intake, exiting high (or at the ceiling), or dump them near the floor, if on the same wall as the intake box.

The opposite wall has the nice effect of forcing a circular motion in the room:  the cool air will naturally fall down, causing warmer air to rise up to be collected by the intake box.

But the same wall-but low-down, would work nearly as well, as it'd blow across the room, letting the warming air rise up to the ceiling, where it'd be drawn in by the intake fans.

Of course-- you could just dump the air anywhere, and intake nearby, and then use an ordinary room fan (or fans) to mix-up the air to a relatively constant temperature.   That would work too, and mean less tubing all over.

------------------

As for your clay pot?  You're going to need one that is large.  Really, really large-- I'm talking 30 gallon size or so here.  The surface area of evaporation has to be big, since you are depending on a purely passive system, on the evaporation side of things-- i.e the wind, etc, to move the outside air past your pot.   Normal evaporation will create modest air currents, but not nearly as much as you need, here.

Now you could opt for a ridiculously large pot to get the needed surface area... or... you could go multiple, small pots-- say one pot for each of your 10 tubes?    Then a system of cisterns to deliver (and top-up) your rainwater to each?    The nice thing about piping the air in insulated tubes, is that you can put your pots low to the ground, and have your cistern (say a used 55 gallon barrel?  Up on blocks? ) higher than your pots, and let gravity deliver the water.  A simple float-valve (like you'd find in a toilet water tank) will admit enough water to keep the pot full.    Coil the tube inside the pot, and then back out-- no insulation while in the pot, obviously.

You'd still want larger (than smaller) pots, though, for the thermal mass of more water in the system, since you are also depending on nighttime cool-down.   

-------------------

Have you considered a simpler option?    Move water instead of air?    Inside your house, set up a used radiator (a junkyard find) from a car, with a normal air-fan blowing across it into the room.   You'll want this sitting in a trough, say those nice things that wallpaper people use to get pre-pasted wallpaper wet would work-- for it's apt to get cool enough to gather moisture, some.   Since you're dry, not enough to really worry, but enough you don't want it just sitting there.

Okay-- from the radiator, you plumb water, driven by a pump of some kind-- a simple pond-pump outside in your cooling pot would do (and gets the noise outside, it does).   Plumb your water lines to the inlet & outlets of the radiator-- likely you'll need to cobble up reducers, as the radiator's openings will be rather large, but your system will be using rather smallish tubes.  Again, insulate the lines-- why add needless heat?

Now it gets simple:  dump the "hot" water into the top of your pot, through the terry-cloth cover.  And draw the coolest water from the bottom of the pot(s), via the pump sitting on the bottom(s).    Again, you'll need a system of make-up water from a cistern.    I would insulate the cistern well, to avoid daytime heat-pickup.   Since you're using rainwater, it'll already be clean, so no mineral build-up, and the rain will come down as "cold", why add unwanted heat? 

But you're just cooling the water, not the air this way-- and cooling it directly, too.  If your location is dry enough?  You ought to be able to get the water cool enough to be effective.

And here's a thought:  you could make a fountain somewhere with this water.... the fountain will spray up into the air, really cooling the water (but evaporating it faster, too).   

[Aggie]

I don't like the idea of moving water for my particular application for a couple of reasons:

1. Water. Potentially water, water everywhere if something goes haywire, but also the condensation on the radiator inside the room.

2. Energy use. Instead of a single blower fan, I now have to run a water pump plus an indoor fan.  That fan inside is going to be noisy for sleeping (the small fan driving the tubes may be worse, but perhaps not so bad after passing through the tubing, plus the unit'll be outdoors).  As for moving water... that stuff's HEAVY! No chance of avoiding a plug-in.

3. Indoor real-estate.  I've got a small room, and there's no practical place to put the radiator.  With the air unit, I'd only have the hoses coming in.  Since I'm effectively trying to spot-cool the bed, which is adjacent to the window (vent holes are near my torso - perfect), I'm not even that concerned about running the hoses beyond the window.  Perhaps I'd put the intake hose up to the ceiling, but I could stick to 1" diameter tubing for that and do any manifolding downstream of the fan-box (which I'll need anyways).  For night-time comfort (my only goal here - I love the heat in the day), only the bottom 4 ft or so of the room needs to be cooled, and hot air trapped near the ceiling is a non-issue. There are small, easily removable basement windows adjacent to where I'd be doing the install, so I could even source the air from the basement or get really fancy and put a coroplast air-to-air precooler down there.  

(of course, the lowest-tech version would be just to bury my cooling 'coil' in a long, deep trench underground.  I've got a glazed-pottery pot of kimchi using traditional ground-based refrigeration on the north side of the house. Hmm.. that could benefit from a damp cloth cap once it starts warming up).


I'm not convinced that multiple small tubes is going to be better than one large-ish one (1" diameter), provided a longer length of the large-diameter stuff was used.  The key factor for cooling is going to be surface area, but that's also going to determine the amount of friction limiting the airflow.  Sure, if I had a air-water exchange tapped into a small but well-chilled water cooler or the like, it'd make sense to do multiple small tubes, but since I need a very large pot (I'm thinking about stacking and sealing two planters in the 36 - 48" range, with the top one inverted, or just finding an alternate construction material* to build a box with the same properties). I'll have the capacity to use a very long coil...  100 ft would not be an issue.  The coil would sit towards the outside of the cavity in the cooler, which would place it close to the evaporating surface.  Plus, with the need for a condensation trap, it'd be wise to stick to a single tube.  I concur on the size - I was picturing something similar to a barrel (55 gal).


Now, if you want to take the multiple-paths evaporative cooler to an extreme, the best way to do this would be to construct a panel cooler using a sheet of coroplast, and cover it with terrycloth (get some cheap beach towels).  You'd need to rig a manifold for either end of the coroplast (not too difficult, I think) and would still need a fountain-pump plus a little drip manifold and catch tray to keep the terrycloth wet, but that sucker would cool air like crazy. You could set up as many of these panels as you needed in a parallel configuration at one end of a porch lllllll , blow a fan through the fins to give you cool (damp) air on the porch plus boost evaporation rates, and pass air through the coroplast to give you cool, dry air indoors. In a dry climate, this should work quite well and still be heaps cheaper than phase-change cooling. If they were mounted vertically, any condensation inside the panels could be collected and trapped in the bottom manifold.

Here's one more spin on this idea...  get some soaker hose - the kind designed to work at low pressures - and inside this hose insert a smaller-diameter polyethylene tubing to carry your airflow.  You'll need to do some jury-rigging to make sure you can still get the soaker hooked up to a tap (some y-joints and a little sealant should do the trick).  Now, either hook it up to a water supply using a pressure regulator, or simply have a gravity-fed reservoir to create enough flow to keep the surface of the soaker hose moist (the reservoir could be a self-cooling terracotta pot).  Gravity-fed will probably be better - you'd want less than 10 psi, probably much less, to keep the hose from actively weeping. This could be either set up as a freestanding coil or wound into a panel.  Black soaker hose would probably work in a shady spot, but hypothetically, a light-coloured hose could be used in full sunlight, with the caveat that most light-coloured plastics aren't UV-stable.





*hey, how about unglazed clay tiles as an outer 'skin' for the cooler? You could up the surface area considerably by building a box that was wide and tall but thin - say, four units W & H by one unit deep. There is likely an equilibrium point between what's going to heat up fast due to ambient temperature and what's going to cool down faster by evaporation, but if this idea works in the first place, presumably more surface area is a good thing.  A triangular prism, set on end, might be a good choice, too.

Are cinder blocks water-tight?

[Sibling Zono (anon1mat0)]

Question, is this for the land you were planning to buy, or in a place where you can do stuff in the roof/garden? I was looking a bit and it turns out that wind turbines are starting to go down in price enough to be economical mid term, for instance this:

http://homegardenoutdoors.com/product/26539_Home-Wind-Turbine-2kw-48V-wind-generator-for-home-use.html

is capable of generating up to 2KW and costs about ~U$1700. That should be able to power a small AC window unit and you should recover your investment in about two years.

The other thing was discussed before, can you bury the pot/tank? IIRC once underground the water temp would remain at a low temperature and depending on the size of the tank you should be able to pump water in/out without much trouble.

The last thing that popped into my mind was measuring wind speed in the shadowed part of the house, possibly near to the roof wind speeds may be higher and you may be able to duct that cooler air inside (while pumping out hot air from the roof).

[Aggie]

This is for the house I'm in (rental), on a small lot. I've got more-or-less free range to do anything that doesn't require putting big holes in house (holes in the ground are OK).

I'm mostly trying to cool my bedroom, but my roommate lives in the 'attic' (finished loft under the roof) and could use a way to cool her space too.  I'm not interested in major investments for this place, at this point, and we aren't seriously considering putting in a real AC unit. We are both lizards who love the heat*, but I prefer a cool room to sleep in.

*first priority will be some screens to replace the storm windows; there's a few here but not enough


Digging a hole to sink a small cistern is possible, but as stated before, it'd be easier to just directly cool the air line in the ground.  A pot of water in the ground will give some heat up to the earth, but I suspect the cooling effect may be somewhat limited (short of using a metal container with fins to conduct faster).  Evaporative cooling should do better in responding to the hottest days, and the bonus will be the nightly chill-down.  I've some ideas on how to augment the night-time cooling by radiating heat to space, but that's beyond what I'm trying to achieve at the moment.

[Bob in a quantum-state-of-faith]

Clay pots are fantastic coolers, if the volume-to-surface is right.  A tall, skinny pot for example, would expose a lot of "skin" to the evaporative air compared to the volume of water.  

On the other hand, anything in the shade would work well enough, as you don't want direct sunlight heating up the water anyway.

100 feet of pipe buried 3 feet deep would work quite well, with air or water (running through the pipe).   If you can get below the ground-water table?  Fantastic... but even if not, it ought to work well.

I would pour sand around your pipe, then re-bury it.  The sand will let the pipe move a bit, and I think will work better than plain dirt.

[Aggie]

Ah, but unless you're below the water table, the sand will reduce contact and transmission of heat. Better to put it in with a clay slurry, I would imagine.  Clay's HEAVY and would have a lot of thermal mass, even in the immediate vicinity of the pipe.

Also, at the depth I'm interested in, it's all clay.   Groundwater appears to be deeper, from the few holes I've dug.

I am more interested in the evaporative model at the moment, due to portability. This could be used in some otherwise unlikely places such as vehicles and RVs.

I haven't been able to get a straight answer on whether the process is more effective in direct sunlight or in the shade. I think it would depend strongly on the wetting rate of the outer surface... if you could keep a constant film of moisture on the outside of the vessel, I think the cooling from the increased evaporation might outweigh the amount of incoming infrared.  I think the key here would be a light-coloured surface; either a white terrycloth or a whitewashed clay surface.  If it was dark, the intercepted visible light will cause direct heating. The actual goal of the process is to evaporate as much water as possible over the course of the day, without having any just leak down and drip. You also don't want the outer surface of the pot to be too cold...  if it's cold enough to cause condensation, you're now heating instead of cooling. There will be an equilibrium point based on humidity, I suspect.

I need to get some waterproof temperature loggers (these have been on my wishlist for a while), and a bunch of bench-scale (12") flower pots to test out various configurations. A heavy felt gasket between the two pots might be ideal, rather than sealing them off completely; there's no harm and probably some advantage in allowing a little extra wicking of water, provided it didn't cause bulk flow.  If the clay itself wasn't working fast enough, a fabric cover could also be connected to the inner reservoir with a few wicks (the same way that a towel left draped over the edge of the tub can effectively transfer water from tub to floor.  If using this kind of a cover, the clay pots wouldn't be strictly necessary; a fabric-coated metal barrel or even a galvanized steel trashcan would probably work great. Aluminum would be ideal to prevent rusting, of course.  The covers would tend to get a bit funky over time, but they'd also be machine washable.

Hmm...  an old flannelette sheet might be ideal here. Terrycloth would be good in terms of surface area, but would likely wick too much water and create pooling at the base of the tub.  

I can get some food-grade plastic barrels for pretty cheap, but I'm not sure how well this stuff conducts heat compared to pottery or metal.

[Bob in a quantum-state-of-faith]

Shade.  Definitely, definitely shade.

In the sun?  Your pot's static temperature will quickly rise to well over the ambient air temperature, due to infra-red radiation absorption.   This won't affect the water's evaporation rate much, if at all-- it's only a few percent with respect to the latent heat of evaporation after all.

But a 10 degree rise in temp of your air is quite noticeable.

However, the evaporative rate of your water is more affected by the relative humidity, than a few degrees one way or another of temperature.   

Fortunately, humidity is like water-- it will quickly "float" to the driest spots from a higher location.   

So put that pot in the shade!