Water Cooling a house! I need some help!

[MyHeadHz]

So I'm building a small project.  It will be either a "pre-cooling" mist system or a direct evaporation system for my home AC unit.  The potential savings are well worth the effort.  And it's a project we could all use here!   My goal is to keep it around or under $100.

Back story: So I was cleaning my outside coil (summer here in the US), and noticed that while wet, it cooled much more quickly and to a much lower temperature.  So I looked around and found some people use "misters" for cooling.  However, these are ridiculously priced and gimmicky.

Would "pre-cooling" with a misting system be better/more efficient than spraying larger droplets directly on the coil radiator fins (basically a heatsink)?  It seems like having the water directly on the fins would make it more efficient to me.  However, everything I see available for purchase is a pre-cooling system.

So, because of the expense of such systems, I've decided to build my own.  XD  I wasn't able to find previous projects, so give me a link if you find one!  I've put the problems in a few categories:

1.  I will need some sort of control system (active, or passive) because I want it automatic.  To save water, and to make the system less of a hassle.  I have some spare raspberry pi's that I could use for this project.  It might be worth getting an arduino, though.  That might help for I/O reasons and power consumption.  An arduino might be able to run with a small solar panel.  What would be better?  I've seen passive valves with air paddles that activate when the coil fan is on.  This should work well enough, but I want to consider other options to see if I would get any advantages from a controller or something else.

2.  Water source and pipe/hose system.  ... I live in California.  Keeping water use (and energy use) down is important, and I may need to adapt the system to use a reservoir of some sort so that I could just filter and re-use waste water instead of tap water.  If I do a reservoir system, I would need a pump system as well.  I'm hoping to get by with just tap water, though.  Either way, I need a way to get some sort of water to the unit, in an unobtrusive way.  Keeping a garden hose hooked up to it would probably not be an option.

3.  Some sort of water-emiting device like a mister or sprayer.  I don't know which type would be better.  However, I have seen pre-made setups with small hoses and nozzles that I can probably adapt well... and go for pretty cheap.  Unfortunately, I see no flow data on devices I've seen so far.   Adjustability would be nice.  I suppose I might be able to add a control valve, BUT that might reduce sprayer efficiency above/below design flow rate... but without data, I can only guess/test :/

I am also considering a "trickle" system of some sort, to trickle water from the top of the coil down, instead of spraying or misting.  At the moment, I'm not sure what the advantages or disadvantages would be.  I would guess that spraying or misting systems would be more efficient, given the greater surface area.  But... if it was adjusted so that it all evaporated, and there was no runoff, would it be just as efficient then?

4.  Water filtration.  This will hopefully be simple to implement, with ready-made filters that take out calcium carbonate and minerals.

5.  Powering the device(s).  I either need a solar panel, battery system, or an unobtrusive way to power it from tapping into the A/C unit lines.  There is a 25v AC line, but I don't think there are any DC lines.  There is a window right by the unit, so I might be able to run a flat power cable under the window and out to the unit.  the power requirements will hopefully be either none (all passive) or minimal (just the arduino), but may be more.

So what do you think?  At the moment, I'm trying to decide between the above options to see which ones to go with so I can start building and designing.  I would greatly appreciate some input!

[ConKbot]

If you live somewhere not super dry (desert climate), then take your evaporator condensate, pipe it to a small reservoir near your ac condenser, and when the AC is on, run a small pump to feed water to misters.  With a float switch to shut off the pump when it's low.

No need for an arduino,  just steal the control signal out of the AC to run a relay when the AC is on, and no need for municipal water, so no California legal problems. 

If you can, keep the reservoir underground, or at least in the shade, so it stays cool and soaks up more heat when its sprayed.  Just make sure to find atomizer nozzles suited to the pressure your pump puts out.

[promacjoe]

An AC unit works because it changes the state of Freon. As you compress the Freon, you are also compressing the heat within that Freon. the condenser extracts that heat. And in doing so, converts the Freon from a gas to a liquid. in the evaporator the pressure is reduced by either an expansion valve or an orifice tube. As the pressure is lowered, the temperature of the Freon is greatly reduced. But at this point it is still a liquid. By blowing air across the evaporator, the cold Freon evaporates, changing the liquid into a gas, and is returned to the compressor. This cycle is repeated over and over again.


Basically It takes 1 BTU to change the temperature of 1 pound of water 1°. But it takes 144 BTU to change the state of 1 pound of water, Without changing the temperature 1°.

Running water over the condenser, will condense this Freon almost immediately. However for each pound of water that you run through the condenser, You might only gain about 60 to 70 BTUs per pound of water. This is because not all of the water will contact the condenser directly. The fan will pull much of that water away from the condenser. That water will have no effect on the temperature. the evaporator has a second effect. It removes moisture from the inside air. This water can be used to precool the Freon.

PS, simply spraying water into a fan, Will decrease the temperatures several degrees depending on the humidity. This will have an effect, but it may not be as dramatic as you might hope.

something else you might try, is putting a fence around the condenser to shaded from the sun. But make sure you do not put it to close, the condenser has to have room to breathe and you need to be able to get to it to service it. Also make sure you leave a gap at the bottom between the fence and the ground. This is to prevent hot air that is forced out of the top of the condenser back into the intake of the condenser. You want the cooler air be pulled in to the condenser, not the hot air. simply shading the condenser, can have a big effect on your utility bill.

good luck.

[Mechatrommer]

you need a descent size motor/compressor (submersible or closed tank system) to generate the said mist, added with control circuit, water tight outdoor enclosure for the circuit and water system, fitting, mist piping and nozzle, and water supply system, i doubt you can hit below $100 mark.

[dmills]

There are a couple of gotchas with these systems (One of which is **Really** nasty).

Firstly you want to evaporate the water before it hits the condenser tubes, spraying the tubes directly will cause pitting and eventually a leak.

Secondly, keeping a tank of warmish grey water and then pumping it thru spray heads at ~30 degrees C or so has public health implications, legionella is not fun, there is a reason most of these systems run on mains water and do not recirculate.

Regards, Dan.

[Seekonk]

Take a look at any evaporator in a humidifier and look at what happens over time when you evaporate water with any minerals in it.  Soon you will have no air flow.

[oldway]

When we have cheap water in abundance, the roof from the house or factory can be sprayed with water during the hottest hours of the day.

It's very effective and energy efficient.

This solution is sometimes used in tropical/equatorial countries.

But it seems that this is not possible in your case.

[BradC]

I did it differently and replaced my condenser with a *big* brazed plate heat exchanger. I extract water from my bore at 20C and poke it back in the ground at 24C. Sort of a hybrid between open and closed loop Geothermal.

It was expensive, it has been complex and to be honest has raised a lot of issues with bacteria, iron fouling, pump longevity and filter problems.
I paid about 2k for the heat exchanger and did the rest of the work myself. Granted, it's *very* efficient. I achieve and end to end COP exceeding 5 (ie 5KW heat removed for each 1KW of electricity) but it is a nightmare to maintain and keep running well.

As the others have said, you can't spray water onto your condenser becuase it will cause corrosion *and* deposit any minerals in the water causing a nasty insulating condenser fouling. The most efficient way to do it is put a set of evaporative cooler pads in front of your condenser and use those to pre-cool the air. The combination of cooler air and higher humidity will make the condenser more efficient, however you'll likely not gain enough efficiency to overcome the extra loss in both water and pump power to keep the evap system running.

[bitslice]

4.  Water filtration.  This will hopefully be simple to implement, with ready-made filters that take out calcium carbonate and minerals.

Just repeating this for the last 2/3 posters.

I'd thought the same as you guys and was going to suggest recirculating distilled water, but it looks like the OP has it covered.


In the UK we'd also have acid rain to consider if reusing rainwater

[vodka]

When we have cheap water in abundance, the roof from the house or factory can be sprayed with water during the hottest hours of the day.

But it is not  a A/C system , it is a nebulization

This solution is sometimes used in tropical/equatorial countries

USA and Europe too is used .

I'd thought the same as you guys and was going to suggest recirculating distilled water, but it looks like the OP has it covered.

Other option , It is changing the heat pump system(compressor) by an absortion system instead of use of electricity , you could use the solar energy for cooling the water.

[promacjoe]

If you really want to lower your energy bill, There is a few things you can do besides creating an elaborate system that may or may not work properly.

1: If you have not done so already, installed energy-efficient windows and doors. make sure that they are properly insulated.

2: use spray foam around the door jams, windows and fireplace brick to frame. many contractors are cheap. They do not like to use spray foam. Too messy and cost too much. Also use weatherstripping between the door and door jams.

the above suggestions will also help prevent dust and dirt from migrating into your home. I know it has helped reduce the dust in my house.

3: when you replace your roof, Add roof insulation to the roof itself. This includes a thermal reflective barrier that reflects heat away from the attic area. If you don't want to replace the roof you may want to add ridge vents to the roof. This will help promote air circulation in your attic.

4: increase the insulation in your attic area.


Check with your local power company, see if they have a energy assessment program in your area. You may be able to get help with some of these improvements through tax credits. Other incentives may be available as well.

[Back2Volts]

Take a look at any evaporator in a humidifier and look at what happens over time when you evaporate water with any minerals in it.  Soon you will have no air flow.

This!   I had to replace the evaporator (wick ?) in my AC humidifier because it was a solid block of limestone.

[jitter]

I wasn't aware of pre-coolers for AC, but that's what you get when living in a temperate climate, extreme weather happens, but not too often. But interesting, nevertheless.
For my small apartment, a 12,000 BTU unit suffices, and I effectively only run it a small part of the year (hotter days of July and August).

Living close to the sea, we have some reasonably humid weather, and I was wondering if the misting system will be less effective in humid climates and more effective in dry climates.
According to the Köppen climate system, North Western Europe and South Eastern USA have comparable climates, albeit that our summers are classified as "warm" rather than "hot" (Cfb vs Cfa).

So, I was wondering if the pre-cooling system does a good job in, say, California, but not such a good job in, say, Louisiana...
Any insight?

[CM800]

Why not just watercool yourself?

Try this?

that could be a fun little project.

[jitter]

Hmm, doesn't look like...

+

... is that much more portable than this  :

[CM800]

Hmm, doesn't look like...

+

... is that much more portable than this  :

Bah, that and a few meters of hosepipe will be fine

[Siwastaja]

The air conditioner is a heat pump - it transfers heat from the evaporator side (inside the house) to the condenser side (outside air). The whole idea is that it can pump the heat to the unnatural direction - from colder to hotter.

You seem to assume that this pumping is somehow much more efficient (or can increase the heat transfer power of the machine) when you can make the hot side cooler. While this indeed is true, you should dig a bit further on this; it's well possible that the cooling cycle is already working very well, even in the hot weather, and further watercooling the condenser wouldn't bring you that much extra cooling power nor efficiency.

Cheap AC units integrating the evaporator and condenser in one case usually use a small pump to recirculate the condensed water on the condenser block to help cooling it (by water evaporation), but this is necessary for a few reasons: first, they are size constrained so can't use large condenser blocks and thus need this extra cooling; also, as they suck in air from the outside and push the heated air back through a flexible tubing, they also tend to ventilate the room too much, sucking in hot outside air more than necessary (negating the rule of closing the windows when air conditioning the room!); using the water to help with cooling makes the amount of air required smaller, minimizing the effect. It also removes the nuisance of emptying out the water.

In a dedicated outside unit, there is no such a limit on the condenser size or the amount of air pushed through it by the fan, so this extra cooling by water evaporation is not needed; they are designed to cool well even without it.

Water tends to make any dust in the outside air sticky, necessitating more frequent cleaning of the condenser coil; otherwise, the cooling effect might soon get a lot worse than originally.

[Circlotron]

I achieve and end to end COP exceeding 5