Hot Water Beach And Cathedral Cove

The coromandel peninsula in New Zealand is just east of Auckland and is stunningly beautiful.  It presents miles and miles of winding coastline, peppered with small and large islands, some rocky, most with vegetation.  Pictures don’t do it justice!

There are many neat rocky artifacts, including this large natural rock arch in Cathedral Cove:
 

Nearby Stingray Bay was wonderfully picturesque, though we didn’t have time or wetsuits to figure out if it lives up to its name:

On the east side of the peninsula is Hot Water Beach, a thermally active area which has hot springs coming out of the ground near the coast, on the beach and even in the water.  The water is scaldingly hot in some places.

We ended up digging a pool near one of these hot water jets (comes out of the sand) and would use a bucket to mix refreshingly cold sea water with the hot fresh water.  We had a relaxing soak for about an hour, before the tide started to come in!

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!