Geothermal Water Chiller

  As we are entering the warm months of the year, and knowing that her sheep (Pure breed Icelandic's) are heavily taxed by the heat, Deb ask'd if "they made something opposite of a deicer....a de-heater?" That was all it took to get me over engineering a solution.  In this case it was a very simple concept and didn't take much to implement a test system that is currently running. I installed a closed loop geothermal system through which I circulate water direct from the watering trough, through the loop and back.

  It was really such a simple idea that I am shocked I didn't find a ton of information regarding the concept, on the web.  But I have found nothing. Everything about cooling livestock had to do with putting water vapor in a fan.  That may work for short haired animals like cattle and horses, it doesn't work for a ball of wool panting in the shade.

  My first attempt utilizes 65 feet of 1/2 inch OD polyethylene (LDPE) tubing run around a hole dug 4-1/2 feet deep.  For circulation, I used an inexpensive submersible pond pump rated at 150gph at 1' of head.

  I started by purchasing the tubing, the pump, and two lengths of foam pipe insulation.  A total investment of less then $50.  In addition to the purchased supplies, we used fence wire to make 'staples' for holding the tubing prior to backfilling the hole, and the John Deere tractor to make digging easy.  Neither of these last two items is a requirement, but sure made the project easier.

  Along with the help of my two junior engineers (Ben and Colton), work began on a cool weekend morning, with the digging of the hole.  I had two goals in digging the hole.  First was to accommodate 65 feet of tubing spaced in what I thought would be a reasonable distance to avoid thermal exhaustion.  If the tubing is too close together, it will put more heat in the ground then can be absorbed, causing a decrease in efficiency. I also wanted to be deep enough so as to reduce the affect of surface temperature.  Staying below the frost line was only a secondary consideration as using this for winter de-icing was not the primary purpose. The hole ended up being a four foot oval, one foot wide and four and one half feet deep.  The auger in the picture is 12 inches wide and 4 feet long overall.  After running the auger in three times, we scooped out the loose dirt, and ran it in again.  At the end of the digging and cleaning out the hole, we were 4-1/2 feet deep, with water coming in at the bottom.

The next step was to put the tubing in the hole.  Ben started the job with the initial two loops in the bottom. Its hard to get in a hole that small, then touch your toes.

Ben is taller then I am(5'10").  You can get an idea of the fit from this picture.

Then Colton took over and completed the upper loops. You can see the 'staples' we made from fence brace wire, in the foreground of the picture.  These staples held the tubing in place prior to back filling the hole. Where the two ends of the loop come out of the ground we covered the tubing with pipe insulation.  This too was held in place with 'staples'.

With the hole back filled and watered in thoroughly, we set about connecting the pump output to one end of the tubing loop.  Using a heat gun, and a short length of clear PVC tubing, we warmed the end of the tubing until it would slide over the pump output.  A small hose clamp insured the connection would not come loose.  The PVC tubing with 1/2 ID fit perfect over the LDPE tubing that is 1/2 OD.  This connection allows me to slide the pump up and down the end of the LDPE giving some flexibility in placing the pump.

 We used the garden hose to fill the line and remove all the bubbles.  Removing the bubbles is an important step.  Because water seeks its own level, a small pump will circulate it without a problem.  However, if there is a bubble in the line, the pump has to be powerful enough to force it down into the hole and back out.  This is roughly the same as pumping up hill.  The little pump we were using didn't build enough pressure to push any left over bubbles down and out.  We had to fill the tubing twice before all the bubbles were out and the pump could perform.

For our initial setup, we put the pump and output end into a 5-gallon bucket.  We covered the tubing and cords with a section of four inch corrugated plastic drain tile.  The initial 24 hours proved it would work.  The water temperature in the bucket was 63 F. in the late afternoon.  It was sitting in full sunlight.  The high temp that day was almost 80.

I have now purchased a new watering trough to allow for more scientific statistic gathering.  I have two black water tubs exactly alike. They hold 25 gallons and sit in full sunlight.  One is running through the GWC, the other is not (my control group).  Since implementing this setup we have had a couple of cool, cloudy days.  The control group water temperature very closely mimics the air temperature on cloudy days.  The GWC however, is staying near the 60F mark.  Although I am most interested in cooling during the summer, it is obvious that the GWC will warm the water and prevent freezing during the winter.

I will publish a graph of the statistics I am gathering once I have some good sample data.

Current Hypothesis:  At this time, I expect I will be able to reduce the water temperature on a hot (80F +) day by 20 degrees when compared to the control group.  However, given the size of the tub and the lack of shade, I don't think I will be able to maintain the mid 60F temperature I would like.

Additional Test Parameters

• Create some kind of shade for the tub.  I expect this will make a significant difference.  Given the lack of natural shade in the area of water, it will have to be something I construct.
• Change the tubing size.  I used 1/2 OD LDPE tubing.  I think the volume of the tub (25 gallons) will require more circulation then I currently have.  In an effort to reduce the velocity of the water through the loop, I am going to try 3/4" OD on the next installation.
• Change the loop length.  In an additional effort to increase the heat exchange, I will double the loop length in the ground.  My next installation will be ~150".

Below are some sample results that I collected this past spring (2007).  The general thing to note here is that the blue line (water temp as run through geothermal) makes much shallower changes.  While the air temp and the control group (same size bucked without g.t. loop).

It is December (2007) and we are getting our first really cold spell.  We have been way below freezing overnight for several nights.  We got 4+ inches of snow yesterday and then the temp dropped to almost zero (F) overnight.  This morning I checked the g.t. bucket and found the water was completely free of ice.  Compare this to the other bucket that has been frozen over for days.  I need to take some more temperature readings and publish them.  I had a thermometer on the bucket, but one of the sheep decided that the wire looked tasty and chewed it in half.

Over the last couple of days, I have taken some water temperature measurements.  You will notice that the control group temp is not listed.  That is because it is frozen when the temp is below 32f.  I am currently tracking the differential between air temp and water temp in the geothermal (GT) bucket.  We have not gotten cold enough, or stayed cold enough, long enough, for any ice to form in this bucket.

Air Temp(f)	Water Temp(f)	Delta(f)
22.5	41.2	18.7
35.8	42.6	6.8
37.7	43.0	5.3

On another note, I added a shade for the bucket to sit under.  I built a little metal roof on a pallet and set the bucket on that.

I think another significant improvement could be made by insulating the bucket.  I need to find a bucket that will nest inside what I am currently using, creating a couple of inches that I can insulate.

~P.

Through my searching of the web, I have turned up the following links that correlate water temperature to animal health.  I knew the animals like cool water (not frozen) but these are studies that prove it.

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