www.davidwilbur.com

That's not a bad looking pool, is it? Seems inviting, doesn't it. Unfortunately, during most of the swimming season the water temperature is in excess of 86 degrees and often it is over 90 degrees. At those temperatures, the pool is not very refreshing and feels like warm bath water. Because of this, I spend lots of time and money maintaining a pool I am reluctant to use. There had to be a solution to this problem. Something that would let me reclaim my pool during the hot, humid, summer monsoon season here in Phoenix.

One day, while getting out of the pool because it was too warm, the wind started blowing. The wind evaporated the film of water on my body and I was actually cold even though it was 110+ degrees out that day. I thought, why can't I do that to the whole pool?...

After much research, I came upon "cooling towers." They are used in industry all the time to cool water. Why couldn't I cool the pool water using a smaller version of an industrial cooling tower? After looking over several websites about cooling towers and several regarding swimming pool cooling (all of which were modified "aerators"), I decided that a mechanical draft, counter-flow, cooling tower would be the easiest to undertake.

I checked around on craigslist and found someone locally who was selling HDPE barrels that were supposedly used for soda pop ingredients. Food grade? Not bad, and only $10 each. I went over and picked two of them up, brought them home and started cutting them into my version of a cooling tower. As it turns out the "ingredient" was phosphoric acid and I had to take some care to dilute and neuralize the acid. Fortunately I discovered this early and was not injured by the residual acid in the barrels.

I cut one barrel in half and then cut air inlets into the sides. On top of this is stacked another barrel with four quarter circle shaped holes in it to leave a cross of material remaining (need picture of this). This allows me to put fill material in the bottom of the top barrel and not have it fall out. Above the fill material in the top barrel is enough space to install a water distribution system. A "weather resistant" fan will sit on top of the barrel to exhaust hot humid air and draw in cooler dryer air from the bottom.

I went to the local building center to pick up fill material and a fan. The material I ended up with was evaporative cooler pad ("swamp cooler"). It turns out that this was not such a good fill material. Air does not travel through large amounts of it well and it absorbs a LOT of water and gets heavy. It works well in a swamp cooler where you are trying to cool a lot of air with a small amount of water. In my cooling tower I am trying to cool a large amount of water with a huge amount of air.

I built a manifold out of several pieces of pipe and drilled holes in it to distribute water over the cooler pads. I then held the fan on temporarily with masking tape. I took the whole thing out back to the pool and set it up.

The inlet side of the cooling tower is attached to the fitting that normally holds little aerator in the side of the pool. As it is shown in the pictures, the water is returned to the pool by a small submersible pump. This version was slow to get going as the water was absorbed by the large amount of fill material. Once it did get wet, the water coming out the bottom was cool in spots and warm in other spots. I think this is because the water and air were "channeling" and the air was not in contact with the water most of the time. After a while, the fill material collapsed and the whole thing stopped working. Back to the drawing board on the fill material.

While the system was failing to work properly and visions of better fill materials started filling my mind, I noticed that I was using an electric powered pump to pump the water up over a 5 inch tall barrier and back to the pool. This seemed silly to me. Besides the pump was not mine and I had to return it. I decided to add a piece of pipe and let gravity return the water to the pool in the next version. I returned to the building center to get more PVC pipe and fittings to make the rotating water arm and to search for a better fill material. I had recently read that industrial cooling towers stretch spherical water droplets (bad surface area to volume ratio) in to long streams (good surface area to volume ratio) to improve the cooling. This obviously meant a non-absorbent material.

While at the building supply store, I came across a better, non-absorbent and definitely more colorful material -- Temporary fencing for construction sites. I wadded a bunch of the fencing up and stuffed into the top barrel in place of the swamp cooler pads. I was so anxious to try the new fill material that I skipped making the rotating water arm and just used the fixed manifold. Performance was better as the water was "streaming" a bit more. There was also an improvement in air flow, but it wasn't dramatic. The water was still cold in spots and warm in spots as is dropped into the catch basin. I was only measuring a couple degrees difference in the basin water temperature and the pool water temperature. Not good enough. From what I had been reading, I should be able to get all the water near the ambient wet-bulb temperature.

At this point, my wife tells me that her brother, an actual rocket scientist (propulsion engineer, venus radar mapper), previously worked for a company that designed industrial cooling towers. He lives in England, but I soon had an opportunity to speak to him on the phone. The thing I left that conversation with was "corrugated plastic". He said that they used corrugated plastic blocks, with the layers biased at an angle for the fill material. I was soon at the building supply store and buying 10 sheets (26" x 8') of white corrugated PVC roofing. I'm not sure what situation you would normally use it for, but it was perfect for what I needed. I cut sheets out at an angle to the corrugations, and stacked it with the layers alternating the corrugations. Afterward, I cut the stack into a circular shape to fit the barrel and glued all the sheets together into a block with standard clear PVC cement. (need picture here)

Before reassembling the tower, I finished the rotating water arm. The "X" fitting is drilled through to accept the vertical pipe. The "X" fitting will be slid down over the holes to allow water to be piped into the arms. Holes are drilled along the sides of the arms and the arms are rotatated a bit. The force of the water exiting the small holes in the arms starts the whole assembly rotating like a propeller, evenly distributing the water over the fill material. It works like those twirling lawn sprinklers you put on the end of a hose, but upside down.

Below are pictures of the pool cooler operating in it's final configuration. This version has the corrugated PVC fill material, the rotating water distribution arm, gravity water return, and I added a vavle to allow the incoming water to be slowed in case the gravity return is undersized (it worked fine without adjusting the valve). I have measured differences of 10-12 degrees between the basin temperature and the pool temperature. When run overnight, it will drop my 15,000 gallon pool from 91 degrees down to 80 degrees by morning. When I leave it running continuously on the weekends, the pool rarely exceeds 85 degrees during the day. Sitting in the pool near the cooler outlet, the water almost feels "cold" at times.

I just realized I should be giving my wife a photo credit here. Many of the pictures on this page were taken by her! 6/23/2008

 

 

 

 

 

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Steve's version of the DIY pool cooler