Questions Related to the Thermo-Siphon Principle

Q1. The heat source (collector) cannot be above the heat sink (pool) and still drive natural circulation.

Q2. Cool water inlet should be as low as possible. The warm water return should be just below the lowest normal water level.

Q3. You should not need a storage tank.

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Using smooth large diameter piping with few turns (and no sharp turns), natural circulation could be set up with with the collector beside your above ground pool.

All of the thermosiphon systems I have seen agree with that description: heat exchange tubes below reservoir liquid level. However, you still might be able to find info on the "Cricket" system. It had a "high" solar collector surmounted by a small reservoir, with some kind of "geysering" scheme to drive water to and from a larger tank below (such as the pool). I don't know how well it worked, though.

Alternatively, if a small circulating pump can be allowed, you could pump from the pool up to the roortop collector, and then drain back to the pool. Solar PV might work to drive the pump.

Good luck, and please keep us posted.

Your 3000 gallon pool has no pump? Is this a swimming pool for humans? How do you filter it? Normal plastic tube direct thermal panels need fairly good circulation, using the diagonal feed in bottom on one side, exhaust from top on other side. Multiple panels can be treated as one panel with bottom and top manifolds.

Solar heater works, for a long time. Thermosiphon feeding it in an elevated position works "in theory", does not in real life. Water has dissolved gas in it. As gas lifted, its pressure drops, gas separates and breaks the thermosiphon action.

Elevated solar heaters all have a feeding pump for this reason. Now, if you have a properly oriented slope below your pool....

I had a friend in the UK about 40 years ago that heated his (below ground) pool up from start of April through to the end of October by simply running the water over his tin roofed garage, after painting it black first.

The only changes he ever made was to cover it in with glass and added an extra rain collector.....then he could run it even when it rained.....but not at night!

The only energy it used was a very small 12 volt water pump, that could even be solar driven nowadays....

As a DIY enthusiast, he had everything just laying around except for the 22mm piping. He used copper if I remember correctly, but today I would use plastic.....

Yours being above ground, you would need even less energy to pump.....

try here http://www.supremeheating.com.au/

or here http://www.directpoolsupplies.com.au/category181_1.htm

As you will see a simple blanket on the pool will do some heating as well as keep out leaves.

multi channel black plastic pipe "thrown" on the roof that works in conjunction with the filter pump is another way. both are in the links.

Rather than composing six individual responses, I'll just respond to each of you in this single post (hope that doesn't violate the rules or protocol).

truth is not a compromise - Thanks for your thorough answers to my questions. This is exactly what I needed to get started.

Tornado - I have read about the cricket elsewhere, but I feel like it's more than I want to invest in time and effort (and $$?) - plus, it's copper (see below). But I appreciate your suggestion. Now that I have some design parameters, I plan to sketch this up and repost for a final critique.

ormondotvos - Yes, I have a circulation pump through the filter, but it's only rated for 10.5' of head at 110 watts. I'd question whether it would have sufficient reserve to filter the water AND push heated water out of the collector.

leveles - I guess you're saying what I suspected - i.e. that entrained air in the incoming water can serve to degrade the vacuum in the feed line, resulting in an interruption of flow into the collector. I guess that's why it's been suggested that a small pump pushing water into the collector would allow me to go with the roof-mount option.

Andy German - Yes, PVC would be used, as the chlorine in the water will react with any copper in the system.

JIMRAT - I do have a thermal blanket (basically bubble-wrap), but it's just an insulator, not an enhancer, since the pool is inside a small out-building and only gets limited sunlight through side windows.