Thermal Solar Pool Heater - summary

Since there's plenty of interest in the thermal pool heater that we made last summer, I thought I'd try and do a post just to summarize what we're using, and how it's holding up.  (My original post is here.)

Here's a silly MS Paint schematic of our system:

Simple schematic showing intake, pump, coils (2xparallel of 3 in series) and return.

Main components are the coils and pump.  The pump was picked up off this surplus site is:
Diamond brand; Model No 312233-01; Consuming 120 Volt and maxing at 7 Amps (nameplate), yielding 1/2 HP, in a CSA Enclosure 3, Made in Italy.  I see that it's available as of 04/30/12 for $95, though I seem to remember paying less.

This pump is MORE than enough power, but with two smaller pumps, we didn't quite have enough juice, so we figured we'd go a bit overkill on this one.  For those wondering, we don't submerge this pump, but rather, it sits by the side of the pool, and so the electric cord (which goes through a watertight gland) doesn't come into contact with the pool water).

Our roof is about 15 feet above the pool water level (note that we crest the apex of the roof, and the coils are on the far side, for sun exposure).

The pump is controlled on a time-of-day timer, though someday I'd like to trigger it with a light-activated system, or possibly a water-temperature-activated system.  On cloudy days, I try and remember to flip the switch on the pump itself, to prevent it from cooling the pool.

The timer is an all-weather system, with a rain/splash guard, not meant for submersion.
The one I bought is $11 from Amazon, click here to see it.

 The coils are arranged into two banks of three coils in series, the banks are in parallel, to slow the flow of water somewhat, to increase heating.  Our flow rate is measured at 15 L/min which is almost 240 gallons per hour.  In the summer, I've measured the temperature from the roof at over 130 F during startup, and continuous around 110, while incoming water is 80 degrees, so I don't feel the need to slow down the flow.  The coils are detailed in my past article, but since posting there, We spray painted the PVC pipe black, as well as the zip ties, to reduce with UV exposure weakening.  Also, a commenter recommended making the PVC crosses at different diameters (6 inches per side), so that it's easier to thread the flexible pipe onto the coil.  LOVE that idea, thanks Ariel!

What we failed to do was to glue the straight PVC pipes into the joiners at the middle of each coil, so that when we went to reposition them a bit, the coils became un-attached.  So if you do this, go ahead and use a primer and glue for PVC.  Totally easy, and worth the $5.

All of the water-filled connections are holding up just fine after all that daily cycling.  I had serious doubts about the push-to-seal type of joints employed by this pipe (remember, it's DIG corp, SKU # 642176 at Home Depot, $80 for 1000 ft).

Finally, go check out the 

Separately, we have a photovoltaic (PV) solar panel powering an attic fan to keep the attic cool in the summer.  This is a related effect to the above project, where the cool water from the pool actually cools the roof as well.  Bonus!  We enacted both projects at the same time, so it's hard to say which had a larger effect on the summer temperature in the house, but I would bet money that the fan had a larger effect -- it was noticeable.

Solar Thermal + Cheap = Inexpensive Pool Heater!

[UPDATE #3: Check out the newer post / summary here showing some of the improvements, as well as simple schematic, etc.]

[UPDATE: See end of article about materials used and height differential!  Also new pump notes!]

Just wanted to share pics and tidbits on how my roommate and I decided to heat our pool without breaking the bank.  While commercial estimates were coming in at between $5000 and $6000, we managed to heat our pool with a weekend of work and about $300 at Home Depot, and about $100/year in electricity.

I should also note that I didn't come up with this method, and that two good friends, JM and DB, did something very similar before me, and we all learned a bit from various websites, including Solar Pool Heating.

Being in southern California, our pool was about 73 degrees in the afternoons of late June.  This was certainly warm enough to enjoy, but we wanted to prepare for the winter (and to see how hot we could get it this summer!).  I'm happy to report that our temperature is now about 86 in the afternoon, and still rising daily.

We start with a submerged pump in the pool.  Since we happened to have two free, smaller pumps, we hooked them up in series.  They're driven by a 110 VAC outlet, and controlled by a simple daily lamp timer.

Pumps in Series (not req'd if you just get a bigger pump)

Primitive Control & Measurement

Next, the output of the pumps goes up onto the roof via some black drip irrigation tubing, 1/2" diameter, and coiled about 45 times to finish at around 6 or 7 feet in diameter.

2 of the 6 coils, the other four are on the south facing side of the roof for now.

There are a total of 6 coils, 500 feet each.  The pipe comes in rolls of 1000 feet at Home Depot for $80 (we used DIG corp, SKU # 642176), cut in half for more manageable handling.

6 Coils of pipe.  Roughly equal to one third of our pool top surface area.

The construction of each coil is designed to be inexpensive.  Just PVC and some zip ties.  Use a wooden block to space out the PVC as you start, and use zip ties liberally to keep the coils in order.  Get two spinning tables (lazy susans, office chairs, be creative!) and directly spool from the supply to the PVC.  Two people work best, though it is doable with one.

One pretty coil.

Sample coil showing PVC construction

We decided to split the water into two channels, and have each channel run through three coils, from one to the next.  We're still debating what the best speed is for the water, but this seems very reasonable.  I guess we could pump faster, though it is mid-day at mid-summer, so maybe we'll want that slow speed in the winter.

The pipes are held together with simple press compression fittings.  I'm astounded at how they don't leak air at all.  I think they're magic.

Sample joint

 Then the water returns to the pool.   I just measured the water coming out of the hose at 2pm to be 114 degrees F.

UPDATE: We have had an issue lately with the black tubing on the roof collapsing due to the vacuum being pulled by the water wanting to flow down both ends of the tube when the pump is off.  Not sure the solution yet, maybe a more powerful pump to overcome this when it kicks on, or maybe a second pump on the roof?  Maybe the black tubing is just not structural enough.  Thoughts and suggestions?

UPDATE #2:  Thanks for the suggestions in your comments.  We upgraded to a surplus pump that is definitely oversized -- one half horsepower!  The flow rate is high, but we still get excellent thermal transfer; the water comes out nice and hot despite it being fall now.  We followed Dan's suggestion and bought a pump here.  The pump 'inflated' the hoses just fine and we have been running for a few days without incident.  Will re-update here, if we run into trouble!

HMI - Part III

To pick up where I left off in my second HMI post, we had finished our main altitude adjustment period as well as completed most of our lectures and practice work on the nearby Rathong glacier. It was time for our final exercise: an altitude gain day with option of summiting a peak, weather permitting. The goal was to reach approximately 18,000 feet (previous high altitude was 15,500 feet on the glacier) -- and the summit of BC Roy Peak.

Panorama, hiking up from base camp to BC Roy Peak (appears at approximately

We set off at the not-so-alpine-start time of a late 6 am, and after crossing a river with tons of yelling and confusion and passing handfuls of sand to step on slippery rocks, started up the peaks north of camp. We hiked at a ridiculous climb rate of 40 ft/minute and continued for about 2 hours. Resting every hour or so, we made it to the snow/ice and put on crampons and other cold weather gear. Ropes were fixed and we used our ascenders (Jumars) as safety as we climbed the final ~2000 ft on snow, in mostly clear, sunny weather. As we reached the final resting spot (and a possible base camp for higher peaks) in a beautifully protected cirque, we organized into teams to try for the summit.

Celebrating at the summit of BC Roy Peak. I have no idea why I'm making the Peace Sign. It seemed like the thing to do. When in Rome, I guess.

I gathered the three remaining members of my team (of originally 10 people) and we picked up two more friends, so 5 of us were roped up together. I led the final couple hundred feet, kicking my own steps apart from other teams that were headed up the same peak. It was really cool to be given the responsibility to pick a safe route and be asked to do the work of kicking steps in the snow/ice. The final altimiter reading at the top of BC Roy peak was 17,765 feet.


(I misheard the altitude reading, and as you can see there was lots of excitement at the top.)

After summiting (er... doing an altitude gain exercise), our time at Base Camp came to a close. We played a few games of soccer and cricket, had a lecture or two more, and then headed out.
Cricket at (allegedly) the world's highest cricket pitch, 14,400 ft.

The solar panel array at Base Camp that I didn't know existed -- I didn't bring my camera battery charger!

My friend liked to cuddle in the hut. He took a particular liking to me because (aside from feeding him), he knew that I, the sole White Dude, would always treat him well. My Indian counterparts were equally divided between petting him gently and kicking him -- confusing for me, let alone a dog! Street dogs in India have it tough.



Up at base camp there wasn't much to do, and because of the altitude we were asked not to sleep more than 8 hours per day -- luckily most of the Indians on the trip enjoyed singing continuously for hours upon hours.


Another nightmarish multi-day trek with 100 people (all hiking together, no gaps, etc.) later, we were back in Darjeeling at HMI.

We had a climbing competition on the outdoor wall (see last post) that I completely biff'd on... but the wouldn't let you study the route before starting your climb, so I'm writing that off as "bad practice." And we all then had a cross country competition. The race, for me, was more of race for the toilets, as my bowels weren't in the best shape. Still, I managed to take second place! The race was about 5 km, at 7000 feet, with hills, and my time was about 21 mins.

Finally, there was a graduation ceremony, where we all dressed up in matching pullovers. The presiding speaker (in addition to the Principal of HMI), was Nawang Gombu(wikipedia). Mr. Gombu(news article) was the first person to summit Mt. Everest twice, and lives in the Darjeeling area.
Each student was presented a pin. Additionally, three medals were given for boys and girls each in the Sport Climbing and Cross Country competitions. Additional awards were for "Best Technical Student" and "Best Overall Student."

Me receiving my mountaineering pin from Mr. Gombu. He also presented me with my "Best Overall Student" and 2nd place cross country awards!

The team I led for a month, with our excellent instructor. "Rope 6" from left: Ashish, Ajeet, Holden, Saikat, Juna Sir (instructor), Hiten (in front), and Tumpa.

With that, the course finished, and we went our separate ways! I have to say that despite my concerns for the safety, organization, and discipline in the course, I am glad that I attended. Though I didn't learn many new things, I really did reinforce and get clarity on those skills I already possessed. I was able to help the other students with their knots, first aid, and mountain skills. I was recommended to take the Advanced Mountaineering Course and will consider that in the future!


And finally, here's a picture of my most-favoritest brillo pad salesman in the world (to date) showing off his wares. You'd think that displaying one of the many identical packs would be enough... and I really do wonder how many pads he sells in one day (in this miniscule town in Sikkim that has 3 streets (named "Street 1," "Street 2," and "Street 3")?