Water based air conditioning?

[Telco]

Has anyone ever tried anything like this? Since this board has a lot on hot water heating systems, thought I'd check here. Looks like this group has come up with the inverse of the wood fired boiler heating water for heat storage, they are burying water for cold storage. Opinions? Seems like the perfect setup, one could have heated or cooled air depending on the season with a simple turn of a valve. You could even extend the cooling ability of the tank by pumping water through underground loops.

 

[Corey]

I just scanned the article, but it looks like they are talking about simple loops of pipe underground and circulating water through them. It seems like a variant on the ground source heat pump - without the 'heat pump' part - just circulating water. You could probably get away with that in some places where the ground stays relatively cool and the summer heat load isn't that high (minnesota?)

But in a lot of places, I suspect the summer heat load would saturate the ground with heat, and the ground would warm up with the summer, then about August, no more cooling

One thing I'm surprised doesn't get brought up more often around here is a true absorption chiller. You could literally have a 'wood fired' air conditioner.

 

[reaperman]

I didnt read the above article. But I have a friend with a OWB, who rigged up his well water to run through his heat exchanger in the summer, which blew the cool air into his home ductwork. Then the exiting water was used to water his lawn. He found out his power bill was getting kind of high running his well pump constantly. He used it for a season and then installed central air.

 

[Yule log]

Cozy Heat,
I agree with you, if they can make an LP fired fridge for my camper, why can't we make a super-sized cooler for a home that uses hot water. A co-worker of mine has asked the same question. She has lots of horse manure and sawdust that she needs to get rid of. Burning unwanted biomass in a Goliath type gasifier would be a great way to cool ones home in the summer (if it is possible to do at a reasonable cost).

 

[Redox]

One thing that this system isn't going to address very well is moisture removal. You will need 45 degree water to really pull humidity out of the air. It might work in a very dry climate, but for most of the country, you will wind up with an indoor mold farm.

Where ground source heat pumps really shine is in their cooling performance. A 60 degree condenser is very efficient for a refrigeration system. Still, you could bury the pipe and see how it works and put in the heat pump later if it disappoints.

Re the absorption machines: These require very hot water (+200F) or steam to work. Some of them are even direct fired with a burner. There was a rush on before electricity became deregulated to install them, but after fuel prices began to shoot up, they became boat anchors. Most large buildings have gone back to electric chillers. Arkla/Servel was marketing a small direct fired absorber that would have worked well residentially, but only had a small niche market and never really caught on. I saw a used lot on Ebay a while back, but I don't think they ever sold. They really are thermodynamic losers. I think they needed a 250,000 BTU burner to make 5 tons of A/C, if memory serves.

I have only seen one chiller that was driven by a true steam turbine, but last I checked, they were running their Centravac (electric). Still, the idea is intriging. Anyone want to volunteer their Eko for a little science fair project? We might have to repaint it when we're done...

On a side note, a fair number of ice storage systems are out there, but they yanked the rug out from under them with deregulation.

 

[Telco]

So it sounds like it WOULD work, but isn't necessarily the best way to go. You'd need to be able to efficiently run a pump to move water constantly, and would need to have a separate humidity control installed in the HVAC system. Power usage for the air mover would be the same on either system, and for me at least power for the humidity control would be the same as I plan on installing an active humidity control in my house, so the difference would be between pumping water and pumping freon. Hmm, have to give this one some thought. A standard air conditioner would be a lot simpler to install, and would be guaranteed effective, while a water chiller would be more complicated, possibly not as effective, but safer since the coolant would be plain water. A busted line would require a simple splice and refill instead of a service call from an HVAC tech.

Luckily I have plenty of time to consider, since the land I was just trying for isn't going to happen. Decided that it would be too much of a financial strain right now. Not to mention that if gasoline goes up another dollar a gallon I can probably get similar land in the same area for half what it's going for now. It was beautiful land too, 20 acres in a squarish rectangular block out in the sticks, currently used as a hayfield so there's nothing at all growing on it but hay, on the south side of the access road and on the high side of a creek with the land on the far side of the creek being lower for a mile or more. It was 99 percent perfect, would just need a paved road to it to be 100 percent perfect!

 

[solarguy]

Something I've kicked around a couple of times is to use your well water much in the same way geo-thermal is used. Most drilled wells have temperatures in the 50-52 degree range during the summer. Just run the well water thru a hot water coil & you've got a chilled water system. When the well water temperature gets to warm, bleed it off. Just gotta build another house so I can put all this "yankee" stuff into play.

 

[Redox]

No, it really won't work. You will achieve some cooling, but this is not considered air conditioning. In order to get the dewpoint down, you need about 45 degree water, unless you can live with all the humidity, and you really can't. You need to keep the humidity under 50% to keep the mold at bay. The only practical way to do this is with refrigeration of some type. Adding multiple dehumidifiers would help, but you might as well run a real A/C unit for the current they use.

Water chillers have to put out 44-45 degree water at 2.4 GPM/ton. If you had a well that was 45 degrees (Canada?), you would need a 7 1/2 GPM well to cover the typical 3 ton load. You also need a chilled water coil which is deeper and circuited differently than a hot water coil.

If you manage to get your dream piece of property, consider burying a slinky loop in the yard before you backfill and save up for a water source heat pump. you can take advantage of the cool ground and have very efficient air conditioning. I have a friend that uses his well for the heat pump, but he is reinjecting the water back into the same well. On a hot day, his tap water is preheated to 85-90 degrees, but the A/C is cheap. I'm not sure his install is code though, as most jurisdictions rule out reinjecting anything back into the ground due to the possibility of contamination. You could waste the warm water into the back yard, but you will probably wind up with a swamp there and deplete the aquifer.

I have tried to work out a system like this before, as my parents have a free flowing spring on their property, but it isn't cold enough.


Chris

 

[Telco]

Cool thanks. I couldn't really see a way to keep humidity under control even if you actually used an AC and just used something like this to precool the air. The AC wouldn't run long enough, so you'd need separate humidity control. Thanks for the tip on the water based geothermal, I'll see what I can turn up on that. Might just be the way to go. Since I'm in the preplanning mode and have a couple of years to work it out, I'm looking at any and all options to cut power use without cutting into our comfort and lifestyle. And so far I'm getting a long ways down the right path, thinking I might be able to live in a far more comfortable house than I do now when I get it all together, yet not be putting out about half my pay to keep it running.

 

[mayhem]

Isn't this basically just a swamp cooler we're talking about here? My sister uses one at her house is Joshua Tree, but they don't work well outside the desert.

 

[Telco]

No, a swamp cooler is evaporative cooling. A very fine mist is sprayed into the air to cool it. What I speak of is a closed loop system, would pump water through piping several feet in the ground where the ground temps are much lower than surface temps, then the water would be pumped through a heat exchanger of some sort to cool the air with a forced air system. Swamp coolers depend on very dry air to cause the water to evaporate, taking the heat with it.

 

[ISeeDeadBTUs]

I swear I read about some machine that was combining a swamp cooler with a dehumidifier to deliver cool, dry air. I can't remember what it was called or where I saw it though.

 

[Telco]

Interesting. Never heard of such a thing, but if it works...

(broken link removed to http://www.acdirect.com/xcart/product.php?productid=1286) is what I've been looking at doing for my place, eventually, would be nice to find this with some sort of ground loop instead of air exchange but if necessary I can do without a ground loop pump. Wonder how well it would work to water cool the outside unit with ground water pumped through a closed loop? The hot water would be primarily provided by solar, with a wood fired boiler backup, from a large storage tank in a shed just outside the house.

 

[tkirk22]

I have seen a setup on the net that used heatpipe technology to cool air for a short distance with the goal of removing water vapor. I don't know how well it works but it's out there. It had no moving parts and required no external power source.

 

[streeter69]

I have seen a setup on the net that used heatpipe technology to cool air for a short distance with the goal of removing water vapor. I don't know how well it works but it's out there. It had no moving parts and required no external power source.

I seen something like that online. It was part swamp cooler in that it used water to cool but did not give out the humidity of a swamp cooler. I found it researching solar panels and have yet to find the site again.

Doug

 

[tkirk22]

I have seen a setup on the net that used heatpipe technology to cool air for a short distance with the goal of removing water vapor. I don't know how well it works but it's out there. It had no moving parts and required no external power source.

I seen something like that online. It was part swamp cooler in that it used water to cool but did not give out the humidity of a swamp cooler. I found it researching solar panels and have yet to find the site again.

Doug

This was easier to find than I expected:
http://www.google.com/search?&q=heatpipe+dehumidifier

 

[Redox]

Heat pipes are just another form of heat exchanger and are only capable of moving heat up to a cool source. They cannot "magnify" the cooling effect eg: if you only have a 55F source, they cannot get any colder. The commercial units you are seeing take the heat from the incoming air and transfer it to the leaving air thus precooling the incoming air and "reheating" the leaving air. They are only good if you have a very large moisture (latent) load without a lot of cooling (sensible) load. They are mainly used for conditioning indoor swimming pools and other specialized applications.

Swamp coolers are basically a big humidifier that only work well in the desert. I wouldn't consider one unless the summer dry bulb temperature is less that 55F consistently and this rules out most of the US. The most efficient systems that I know of are the ground source heat pumps with either an underground loop or a well to dispose of the heat. Even a 70 degree ground is cooler than 90 degree air.

I once saw a prototype dessicant unit that used a gas burner to super dry the air without raising the temperature very much and then used a swamp cooler to reevaporate moisture for cooling. This was when gas was much cheaper and even then, it never got much past the prototype stage.

Unfortunately, nobody has been able to better Willis Carrier's invention very much. It still takes a lot of energy to cool a house properly. Absorption systems do work if you have a lot of waste heat available, but these units are cantankerous even when they are designed right, and a nightmare when they aren't.

Just my $.02 from the steamy mid-Atlantic...

Chris

 

[tkirk22]

Here's one idea that I have been kicking around but that I haven't researched yet. The main goals would be to provide some level of cooling and dehumidification in a large shop (not a home), and do it without spending a lot of money on a commercial ground source heat pump.

I'd start with a loop of air filled cooling tubes buried several feet in the ground. Near those tubes I would run water cooling tubes.
The air output from the tubes would be run into the return of an old air conditioning unit. The condenser of that air unit would be in a water bath that gets fed by the underground water cooling tubes.

So in short, the building air would get some precooling by the ground loops and the condenser would be cooled by the water loops.

As I said I haven't looked into the idea much. One problem I foresee is the evaporator freezing up too easily. The other may be that it would take more power to push air through the ground tubes than I get back in the form of cool air. I also don't know how well an OEM condenser would handle being bathed in water.

So go ahead guys. Pick my idea apart ;-)

 

[Redox]

Nobody else seems to be chiming in, so I'll give you my .02. First off, using outside air isn't very efficient because you have to cool it more than the return air from the space. The space should already be dehumidified and be easier to cool. Think of a furnace to heat your house with the return air outside. These are used in commercial applications (like restaurants) where it is necessary to ventilate the building and are energy hogs. Better to recirculate!

Using a ground loop warms up the ground, so that your 55 degree ground will be much warmer by the end of the summer. You are going to need a compressor, but this will still be more efficient than using 90 degree air outside. This is where the ground source heat pumps really shine. After the ground has been warming up all summer, you can then heat the house with it.

Ground source heat pumps (I think geothermal is a misnomer) are way overpriced because their demand is limited. All they are is a regular heat pump with a refrigerant-to-water heat exchanger instead of a refrigerant-to-air heat exchanger. The fan is replaced by a pump and may use a few more watts, but shouldn't be too bad.

If you had a ground loop, you could play around with converting an old window shaker to water cooling by spraying the water over the condenser and varying the flow rate to prevent freezup. Cut off the old condenser fan, close up the box to keep the water clean, pump it back into the ground loop and you have the poor man's heat pump! This is not the most efficient way to do it, but it will work fairly well. To do it properly, you would want to use a real water heat exchanger and maybe a water regulating valve and an expansion valve instead of the cap tubes, but this isn't really a homeowner type project, unless you are used to doing refrigeration work.

If I could only dig up the entire yard..........

Chris

 

[Gooserider]

I've seen other versions of this approach that use buried pipes filled with air... While I don't think they would be enough by themselves, I think that might be a good basis to work on making a more efficient system - the way the setup that I've seen described is supposed to work is to bury a series of loops using 4" PVC pipe, or possibly other equivalents - each loop being about 100' long - alternatively a bunch of nested "horseshoe" shaped loops with a slight variation in length but trying to keep them as even as possible, probably about 4-5 loops, with about 10' average separation between them.

Careful attention must be paid to the pipe slopes so that any water condensing in the pipes will drain out to one of the plenums - trapped water could become a 'mold farm' otherwise.

The loops should all end in a pair of plenums, one as intake and one return - If you have an HRV plumb it so the incoming air can be introduced into the "intake" plenum, along with optionally a general air intake blower from the outside.

The author suggested that there should be a secondary intake blower to slightly pressurize the house, just enough to ensure that it is the source of all "make-up" air and thus avoiding drafts.

In the summer, the "intake" plenum connects to the HVAC return, and the "return" plenum connects to the HVAC intake plumbing so that all air that goes through the AC coil has been pre-chilled by passing through the ground. The HRV blower air also gets pre-cooled additionally in the same way.

In the winter use the loops to pre-heat the "makeup blower" air, and possibly the HRV air, but probably directly connect the HVAC return and supply plenums normally as the pipes would probably otherwise tend to cool the already partially heated return air.

The claim was that it would greatly reduce the need for the AC compressor to run as it would not be having to work as hard to cool the air, and reduce heating demands because you would only be having to heat 50* makeup air instead of outside air temp air... Don't know if it would have enough payback to justify installing that sort of system by itself, but perhaps if one were already doing a lot of digging for some other reason it might be a decent add-on.

Gooserider

 

[Redox]

Hmm. Had to think about this one for a while. I suspect that if the building you are conditioning did require a lot of outdoor air for makeup, this would help. Since most residences in the US already have enough infiltration, outside air is generally unnecessary. An exception would be a "superinsulated" house that needs an ERV for fresh air. In this case, the quantity of air would be small and this precooler might help, but I suspect you might only be saving $100 or so a year making the payback lengthy. In a large commercial installation, you would need maybe a thousand feet of pipe per ton to do anything useful, and I suspect the additional fan horsepower would be a big negative. Commercial stuff is usually spec'ed on first cost basis and usually (for light commercial) not even as efficient as residential equipment. We're still trying to convince building owners that speed drives are a good idea! Even ERVs are a new concept, but I am not seeing a lot of activity for the most part. Homeowners usually are a little more concerned with energy consumption than commercial building owners, though. I'm still convinced that a GSHP is the best bang for the buck.

As far as I know, ASHRAE hasn't commissioned any studies on the concept yet. Maybe we could get a grant to play around with it?

Respectfully submitted,
Chris