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Plumbing and Controlling Solar Swimming Pool Heating Systems
These diagrams are shown in the solar off mode. Worst case design conditions occur when solar is off. The isolation and drain valves allow the system to be isolated and drained (winterized) so the pool pump can be run through freezing conditions. These drains should be located at the lowest points in the plumbing and all piping including the bottom headers of the solar panels should slope (tilt) towards those drains so the water runs out by gravity. The check valve prevents the water from running backwards through the filter (backwashing it) when the pool pump is shut off. It also prevents the pump from losing its prime if it is above pool level. The vacuum breaker allows air to enter when solar shuts off. This allows the system to drain back to the pool and prevents negative pressure in the collectors and plumbing. Without it the collectors would always be full of water and reverse flows would be induced at night cooling the pool. At night solar panels lose heat to the night sky by radiation so if they are full of water you are likely to have a cooling effect if the collectors are full of water and not operating. There are many subtle ways your system can underperform but we'll make sure its all set up perfectly though simple checks done as part of each installation including do-it-yourself installations of course.
Tilting the collectors to drain is important and co-incidentally avoids air entrapment that can cause poor performance as depicted in this animation...
This animation explains a tricky concept that is a common source of frustration for solar installers. You have to let the air migrate up out of the system. Air in water wants to rise. You need that second return pipe to make sure all the air can rise up to the highest point where it can be flushed to the pool.
Note that most of our standard plumbing schemes include a bypass valve that allows us to not have to send all the water to solar when solar is on. With this capability your roof can be 400 feet away and we don't have any trouble handling it from a mechanical perspective even using 1.5" pipe all the way. Relative to pool system flows we don't need much for efficient collector operation. Collectors can operate at 2-9 GPM each. You need 2 to get good enough efficiency and over 9 GPM you're starting to see pressure from too much resistance to high flow. 400 feet of 1.5" PVC pipe with 10 panels needing 20 GPM won't develop a significant pressure drop. Smaller pipe means less air to flush thru upon startup and less surface area for heat loss thru piping. The industry standard for 4'x12' polypropylene grid style collectors is a 2" header and even we recommend 2" pool system plumbing always! That's the pipe coming out of the filter carrying the full flow. In these cases we often plumb with 2" but most of our collectors use 1.5" header pipes. If we plumb in 2" we split into banks of 1.5". Our Hot Sun solar collectors use 1.5" headers as do many of our Powerpro collectors.
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Check out the auto controls page for more information on the automatic controllers we use for our systems.
Go to the sizing page to review how to calculate the sizing for your system.