Our pool is to cold even in summer so it's time for some solar heating. It only gets morning sun and is exposed to the wind. We have a flat (3-5degrees) metal roof with box gutters and parapets all round which leaves me concerned about possible leaks.
I'm still waiting for a few quotes to come in but to reduce the risk of leaks on the roof I'm most likely going for a one piece polypropylene panel system that are interconnected with barrel unions. I will need to cut into the existing filter system for a booster pump as there is no dedicated supply for the solar heating.
We have a PV system that feeds back to the grid at 52c a Kwh and when we're not producing our own power we purchase it from the grid at ~28c a Kwk. I've calculated our self consumption of the PV at ~10% which is great with such a high feed in tariff. I'm currently using a 3 speed eco pump on the low speed which is timed to run early morning and late afternoon to avoid using our PV power. Four hours on low is currently enough to manage our pools water quality. The booster pump for the solar heat collector will need to run during the day and I can use a discounted, timed, feed from the grid that does not draw from from our PV system.
From the schematics I've seen on the net a booster pump is normally plumbed into the existing system between the filter and chlorinator with a non-return between the inlet and outlet. This setup would mean that I need to run my main pump whenever the booster pump is required and it will probably need to run on the medium speed.
I would love to run both pumps independent but can this be done? The main pump can be run for four hours a day and the booster pump can be used only as required. Power wise the main pump would need to be on our main power feed and timed to run early morning and late afternoon as it's currently setup. The booster pump can go on the discounted feed that provides power during the day but cuts out during peak usage times, typically early morning and early afternoon or evening.
I guess the suction ends of both pumps can be connected to the same point with non-return valves to prevent each from sucking through the other. A simple relay switch can be used to avoid both pumps being on together. Due to the non-return on the booster pump I will need a solar heat collector bypass up near the roof line to ensure the panels drain out when the booster pump turns off.
My sticking point for this system is the return point where the booster pump and solar collector plumbing feeds back into the existing filter system just after the chlorinator. I would use a wee or a Y tee here but I think when the main pump is running and the booster pump is off with the panels drained out a venturi affect will suck air into the return line from the solar system. Would this be the case and is it something that I should be concerned about?
If I can successfully run both pumps off the same feed and return lines I will need a solar collector bypass to allow the panels to drain out via the hot return, but will a bypass work? I would be connecting the cold feed and hot return just below the roof line using a pair of 1.5 / 0.5" faucet tees and could reduce the 0.5" join a little more if required. In theory I think this should work but I've never seen it done before. When the booster pump is on the water will want to go strait ahead through the faucet tee with very little bypassing the collector but when the booster pump is off the non return will prevent flow back through the cold feed and water will drain out through the bypass, I hope. Has anyone used this application?
Sorry for such a long post and thanks in advance for and advice that is greatly appreciated.