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Earth tubes to water exchange hot climate home cooling
Last Post 11 Sep 2011 12:51 AM by zehboss. 26 Replies. |
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kit
New Member
Posts:8
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| 14 May 2011 08:56 AM |
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· I am about to build a home, in a hot, and somewhat humid climate. I want to integrate cooling into all external walls and ceiling. I found the idea of earth tubes interesting and at first I thought to run air cooled in the tubes, by forcing it trough with fans, in a loop from the earth tubes into an air space built between two layers of external walls of the house, and back to air tubes. But it seemed that extensive earth tubes would be necessary for continuous effectiveness, and also a complex wall system, and a lot of energy for fans to move the air. Then I thought maybe to run water instead. The water will be circulated by an electrical pump, through the 1'' tubes. These tubes will pass within 15 water filled 10'' pipes laid 6' deep in the ground. The water in 1'' tubes will be separate from the water in the 10'' pipes. The 10'' pipes, 40' long each, will lie horizontally 6' deep, below, or around the house. At each end these pipes will turn 90 degrees upwards, and come up vertically above ground level. These pipes will serve as an efficient exchanger of heat between earth and water carrying tubes, having a greater surface, and water being good at storing and transferring heat/coolth. The 1'' pipes, are the type used for irrigation in drip systems, and they will lay submerged within the buried 10'' pipes, and emerge from each end, and from there travel to house and back. The 1'' tubes then will travel in a zigzag pattern (without any fittings so as to minimize chances of leaks), on the back of internal wall and ceiling paneling in the house. The inner paneling will have a continuous opening at bottom and top, to let air circulate from rooms to behind paneling, thus passing over the water filled tubes, and out the top back in to room, thus collecting from coolth from the pipes. Heat will also flow from wall panels to pipes where they touch. The same system will be built for the ceiling. This system envelopes the home with a sort of radiator that both cools the walls creating a radiating cooling (and heating for winter) surface, and supplies the space with a continuous cool air flow. there will be a large amount of tubing in the house, the total inner surfaces walls ceiling, add up to 4000 sq feet, that will require 5000 linear feet of tubing. The tubing will cost 1,400 usd, and the 10'' piping will cost 1,200 usd (prices i got from dealers) seems like viable investment, even when adding cost for pump earthworks, and custom walls fopr home, etc. I plan to build an experimental room using this system so I can assess its effectiveness. If anyone has suggestions i would be happy to hear them. i wish i could do some calculations so as to assess length of tubing etc' , if anyone has any experience in calculating a system like this, in relatively simple terms, id'e love to be informed. thanks, kit |
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buck3647
New Member
Posts:85
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| 14 May 2011 09:03 AM |
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If you encapsulate your entire home exterior with closed cell foam You will not need to do all this extra work!
Completed encapsulating a mobile home in Ocala Florida with 3 LB closed cell foam now even in the 90 degree Florida heat the mobile stays cool and the Central AC has been removed
Foam
See before and after photos at SafeDomes dot com |
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kit
New Member
Posts:8
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| 14 May 2011 09:43 AM |
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Thanks, butI am afraid here we get 105 degrees and upward from june to october, insulation onely slows heat transfer but wont stop it, i have an insulated prefab, closed cell foam 4' thick walls, boiling hot all summer, so it takes a strong air conditioner to keep cool, the home Ime starting to build has 9 times the size of the prefab, it will need emense cooling, so I am seeking alternative green methodes... |
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kermit
New Member
Posts:30
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| 14 May 2011 12:42 PM |
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kit.....i'd boot the earth tube idea...
concentrate on insulation.....
you described your house as needing emense cooling...
earth tubes are just another form of cooling
if you use super insulation it won't need immense cooling, it will need very minimal cooling.... something on the order of a couple of $200 window units
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acwizard
Basic Member
Posts:265
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| 14 May 2011 01:49 PM |
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The amount of pump energy needed to move water in the proposed piping would not be cost effective. A geothermal heat pump system would be a much better choice.Add some solar to this system and then set back and enjoy the energy savings. |
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kit
New Member
Posts:8
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| 15 May 2011 09:23 AM |
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thank you for your comments, it seems that my idea is novel, maybe faulty too, that is what I am trying to find out, of course I prefer to find out the easy way,  . So, yes, I am planning much insulation in any case. I think the novel part is the idea of not using a conventional heat exchanger, The system would require only slightly stronger pump or pumps than used for any radiant floor system for circulating the water, And water cooling pipes in the house would be cheaper than radiant floor system because they would carry water only at ambient temperatures a heat exchanger and geothermal system are not cheap, require energy, and demand maintenance and replacement in the long run. the house would require at least 4 separate air conditioners if air conditioning were to be the cooling method, for the house is divided into 4 distinct and separate zones, that is, three sides of a large courtyard, and a separate floor below. I was thinking that with proper insulation, hopefully, retrieving coolth from pipes underground, and dissipating it in house, without enhancement via a heat exchanger, might be enough to keep the house cool. If this works out I will certainly attempt to use solar panells for powering the pump, after all, i need it mostly when the sun is shinning, so then a battery bank may be excluded too. my deliberation remains upon the viability of the system, with this water running through long pipes in the ground, then equaly long pipes runing through house , will it work or not. |
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Alton
Veteran Member
Posts:2164
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| 15 May 2011 10:35 AM |
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What will you use to reduce humidity within the house? |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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acwizard
Basic Member
Posts:265
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| 15 May 2011 12:16 PM |
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Until you actually sit down and calculate pump horsepower your idea is like living in fantasyland.As Alton questioned, how do you plan to control humidity.I've been doing a/c for over 30 years and your idea is full of flaws.The closest thing out there is radiant cooilng, chilled beams, water to water heat pumps. One can build a super insulated structure, sealup all the windows and have the belief that their home is state of the art. Ventilation is as important if not the most important part of maintaining any indoor air quality. Fans are needed if windows are closed.Remember if your idea was feasable then there would already be thousands of homes constructed using this technology. |
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kit
New Member
Posts:8
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| 15 May 2011 04:45 PM |
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Yes, I have calculated pump horsepower. As I said in my last response I found out that I will need a similar pump, or pumps, as would be needed in a radiant floor system/geothermal system assuming the amount of piping, head loss and gpm I planned so far are correct for the cooling load.
The house will be well aerated, the climate hot, i checked, and it seems none of the surfaces will be reaching dew point at any time. Does a house with radiant floors in such a climate tend to condensation? again, the idea is to cool the entire inner surface of the walls and ceiling, thus radiating coolth, the walls will be insulated well too, and totaly shaded on all sides on the outside, the house is planned to receive prevailing westerly winds, it will be well ventilated, the whole idea is to rely more on a cool radiating interior, rather than on cooling the air with air conditioning and airtight house.
Heat exchangers in a geothermal heating cooling system, as I understand, and I am no specialist, couples with earth heat sink, discharging the heat they absorb from the house into the earth. In the house the heat exchanger connects to radiators, radiant floors, radiant wall/ceiling mats etc', or, support HVACs systems. I am trying to do without a heat exchanger, by replacing their method of powerfully cooling a segment of the house and using much energy, with a much less powerful cooler, but a cooler that cools most surfaces of the house, with very little energy. you may ask: how do I expect to cool a house which, however one looks at it, needs (for example) 100,000 btu/hr of cooling, that is energy. I answer: I want the cave effect, if there were a cave below ground, of similar size as the house, in the same climate, it probably would not need any cooling at all. Thus, if I can bring enough coolth up from the earth, maybe it can work. And thanks to Alton's referring me' in the recent past, to Lee Porter Butler's work and innovation in this general field. http://www.trianglemodernisthouses.com/butler.htm
All I'm trying to find out is if an extensive use of radiant surfaces - all walls and ceilings, 4000 sq ft, cooled to the temperature of the earth here, 20-23 c, just by a multitude of water tubes set 6'' o.c. in all walls and ceilings, will do the job, if it will, maybe there will be thousands of homes constructed using this technology, Though I doubt it. and yes, i am a dreamer, but i have built a couple of comfortable low energy homes that work, and now i am exploring this new option. thank you again for any comments.
kit
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Bruce Frey
Basic Member
Posts:429
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| 23 May 2011 05:20 PM |
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Two or so years ago there was a thread (in the ICF Forum by Manfred, IIRC) about doing something like you describe with PEX embedded in assymetrical ICF walls connected to a ground loop. His idea, I think, was to use this as "virtual insulation" in a heating dominant environment. He never posted whether or not it was actually built.
Do you plan to make this a "continuoulsy conditioned" (or nearly so) house?
If you do a great job on the shell with lots of insulation, tight construction and good shading shading you can really minimize the load. Intuitively, I think what you describe is possible, but getting the calculations right (especially the earth part) will be complex. I am not convinced it is practical, however. You will still need to deal with ventilation and latent somehow.
Bruce |
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kit
New Member
Posts:8
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| 28 May 2011 07:57 AM |
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Bruce thanks for your reply
I am doing much research on this, I find that geothermal systems combined with - in wall/ in ceiling - cooling/heating - by water pipes, are becoming an important and fast developing industry, in Europe and also starting in the US. and Canada and Australia, they offer much savings compared with air to air solutions.
It seems though, that all systems rely on mechanical heat exchangers that use energy to cool or heat the water before it enters the radiant surfaces in the building.
My wish is to see if I can rely only on whatever coolth/warmth i can derive from the earth, and if necessary, use air conditioning as a backup.
I think my idea for a system is different in one respect - that I want to put cooling tubes in all external walls and in ceilings, this makes a bigger job in construction, but has a greater cooling/heating effect than a system that tries to work only from one surface, or from radiators .
in a way this acts as insulation too, for it brings the inner surface of walls and ceiling within comfort zone temperatures, thus lowering the temperature difference and minimizing heat transfer in either direction through the walls.
Different parts of the house can be activated separately as needed, and the pump can be controlled by a thermostat in correlation with indoor temp.
the system relies on cooling and heating by radiation like most radiant floor systems.
I want an uncomplicated system, one that has very little things that can go wrong with it, and I am willing to compromise with not having a super controlled temperature environment.
Conventional geothermal systems are very expensive to install, they do show savings in energy, but than i think of each time something goes wrong, a pump fails, a heat exchanger fails, and the costs are large.
the attitude of using highly mechanized systems reminds me of , for example, heating and cooling a space station, there u have no choice.
Here on earth there is an abundance of energy under our feet, waiting to be used, so maybe instead of making a system small, with a highly sophisticated expensive geothermal unit, I can make it with a larger simpler concept.
In the Australian hot regions many homes are built, or rather excavated underground, they maintain constant comfortable temp year round with no cooling or heating systems at all, so, if one wants to use this source above ground, maybe it can be done without to much machinery.
the more I delve into trying to do the calculations , it gets more complicated, I have yet to give up on that, but in the mean time I will build a model room , on location, and check the system experimentally.
Kit
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jonr
Senior Member
Posts:5341
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| 28 May 2011 09:11 AM |
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You are basically talking about using pipes and water to move ground heat/cooling to the walls - same principals as an underground house. I believe that it can be done and would run cost effectively. But just adding more insulation is simpler and cheaper.
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acwizard
Basic Member
Posts:265
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| 28 May 2011 12:04 PM |
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In order for this to work, the entire home would need to be conditioned to several degrees above the dewpoint. It is the same as if you were using chilled beams. |
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exipnos
New Member
Posts:6
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| 08 Jun 2011 05:37 AM |
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I have been thinking in exactly the same ideas. There was a post long time ago about a well insulated passive house that used a similar method and it resulted in an even more energy efficient house.
I believe the whole thing will come down to a proper calculation of surface area needed and a solution to deal with humidity control.
I recently built a house with an air/water heatpump with underfloor heating. While I also have water/air radiators connected to the same heatpump for summer cooling, one summer I ran the underfloor heating but with cool water. It worked great for many days (all floors are tiled). But when needing higher cooling and it reached the dew point it obviously did no longer work since the tiles started to collect moisture.
Water circulating pumps are indeed not very expensive to run. Invest as well in high insulation. In no expert but for me it sounds like it should work, I hope some of our resident experts can provide more expert advice.
Regards,
Kosta |
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HHH
New Member
Posts:81
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kpittman
New Member
Posts:1
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| 28 Jul 2011 10:48 PM |
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First of all.... heat radiates, cold does not. Cold will attract heat. This system works quite well with water running through tubes buried in the earth then emergiing at a heat exchanger. A simple A-coil or even an auto radiator will exchange heat rapidly. If the water column begins and ends at a fill tank or reservoir, you are not pumping more than a couple of feet of height differential between inlet and outlet. A small outdoor fountain pump is plenty adequate. The idea is to create flow, not pressure. A massive volume of water flow is not required and not really desireable. You want to cool the air, removing the heat from inside and depositing it into the ground. The buried pipes work as the outside heat exchanger.
I've seen one system where instead of burying the lines, they were routed into an abandoned coal mine on the property. The floor of the mine has water 6 inches deep that runs out year round. If the volume is too high or the blower fan is not just right the heat exchanger will actually freeze up. This is not a closed system, it simply takes ground water from the mine at about 46 degrees f and circulates through the heat exchanger, then dumping it into the creek where it was going anyway. It cools both the house and the garage. |
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zehboss
Basic Member
Posts:216
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| 05 Aug 2011 04:14 AM |
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I have built a house with heated and cooled walls and floors using PEX tubing and a ground loop and insulated hot reservoir heated with solar thermal and cooled with ground water.
Where are you building? Specific climate data needs to be understood before any of your questions can be answered. In many areas, like the high desserts you get high dihedrals dry air making the problem easy to solve.
Brian
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Brock
Advanced Member
Posts:599
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| 26 Aug 2011 10:49 AM |
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In our house I have the option of circulating the 5 ton field through a coil in the furnace. We are at 44* north, Green Bay WI and I can tell you by this time of year, mid August I have no real cooling left in the field. When I start the cooling season I have about 45* incoming ground water temps and now I have 65* incoming temps. I do let it run all day with the fan on and it does help a bit and it continues to warm up the field for the coming winter So in a warmer climate I would think you have little to no cooling. At night I use the heat pump to cool / dehumidify the house and heat our indoor pool. Unless the ground is about 50* or less I get no dehumidification, just a bit of cooling. So it sort of works and is better than nothing, but if I didn't already have the field and coil it certainly wouldn't have been worth the cost. Bottom line, like everyone else has mentioned, insulate, insulate, insulate. Then worry about cooling. |
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| Green Bay, WI. - 4 ton horizontal goethermal, 16k gallon indoor pool, 3kw solar PV setup, 2 ton air to air HP, 3400 sq ft |
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Dana1
Senior Member
Posts:6991
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| 26 Aug 2011 02:42 PM |
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Brock- I wonder what the COP is of the pumping & air handler power is when running with 65F incoming water:
The delta-T on the water with say, 78F incoming air on the cooling coil has to be well under 10F, probably not better than 5F.
If you're running 100W of pump at 2gpm and 500W of air handler, and getting a delta-T of 5F on the water through the coil- that's ~5KBTU/hr or ~1.5kw of heat removed for 600w of power input, a COP 2.5-ish, which is pretty lousy (better window-shakers would beat it with some margin, and better mini-splits would beat it 2 to1.) But if it's actually 4gpm & 10F delta-T on water through the coil that's ~20KBTU/hr or 6kwh of cooling for 600W of power, a COP of 10.
Taking the actual power, delta-T, and flow measurements on the real system would tell you the in coming temp at which it's time to give up and kick on the compressor. I'd bet the COP was very decent in June, but may be sub-par on efficiency with 65F water on the coil. |
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Brock
Advanced Member
Posts:599
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| 02 Sep 2011 03:10 PM |
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I am sure the COP is low. Today for example, the incoming water temp is 62 and leaving at 65, air coming in at 74 and leaving at 66. The air handler is running in speed 2 of 5 and pulling 120w with the one circ pump running at 100w. So it's not much, but again I get a tiny bit of cooling and hopefully warming up the ground a bit My situation is during the day we have on peak rates at $.22 so I run this mostly during the day with solar pv and then when we hit off peak rates, currently $.07 I start the heat pump heating the pool and cooling / dehumidifying the house. |
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| Green Bay, WI. - 4 ton horizontal goethermal, 16k gallon indoor pool, 3kw solar PV setup, 2 ton air to air HP, 3400 sq ft |
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