This article is part of a series: The 12 Days of Solar Pool Heating. 

Solar pool heating performance is about so much more than just the panel. While panel performance is important, and iSwim Solar Pool Heating Panels are among the top rated panels in terms of BTU heating output, the system performance is what’s key to a warm pool.

On Day 1 we discussed how important flow rate is for maximizing solar heating performance, and why the iSwim full flow tube design increases flow rate. On Day 3 we explained how using 2 inch plumbing and valves throughout the system further reduces restriction, increasing flow, making (any) panels more efficient. Combining these two design features is key to our success in proper system design that results in the best performance among brands and installers. Additional installation techniques such as minimizing fittings and using two 45 degree fittings rather than a 90 degree fitting further sets us apart.

Solar thermal panels rely on the temperature differential, also known as Delta T, or ΔT. The higher the difference in temperature between the pool water and the collector surface, a greater heat transfer results. By keeping water moving quickly through the panels it picks up more heat than if the water moved slower and the temperature difference were to decrease. To some this is counter-intuitive. Many think heating the water up as much as possible in the panels is desirable, but the opposite is true. A small temperature rise with a lot of flow will result in better heating performance overall. Better system design and installation is required to maximize flow rate in any given setting.

The other advantage of less system restriction and more flow is energy savings. If you have a single speed pump you can run it fewer hours to get the same pool water turnover. If you have a variable speed pump you can run it at a lower speed to get the same flow rate and turnover compared to a system with higher restriction. The way I think of this is comparing it to a delivery truck. More cargo is like more restriction. It takes more fuel to get to the same place at the same speed when carrying a heavier load.

The final key to performance is in system planning. When multiple roofs or banks of panels are required, balancing flow across the collector array makes each panel perform as well as possible. Using opposite end feed and return, common high return plumbing, and balancing valves where needed will greatly improve system balance and maximize performance across all panels.

Unfortunately, it is impossible to compare solar pool heaters with a single number or rating. Every pool and every system is different. We start with highly rated panels, but look at the system as a whole when designing and installing solar pool heating panels.

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