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Ecosun: The world’s finest solar pool heater

There are several reasons why we believe the Ecosun® solar pool heating collector panel by Aquatherm® is the finest swimming pool heating system available on the market today. The Ecosun® panel offers the following specific advantages:

  • Best combination of thermal performance and structural integrity
  • Best solar panel design for efficient pool pump operation
  • Best design for real world performance
  • Best design for storm velocity winds
  • Strongest and most durable mounting system

Please take a moment and review our discussion of each of these advantages below, and we are confident you will agree that the Aquatherm® Ecosun® solar collector panel represesents the state-of-the-art in solar pool heating collector design and engineering.

Best combination of thermal performance and structural integrity

Since the early 1970s, polypropylene has proven to be a perfect material for swimming pool heating solar collectors because (1) unlike most plastics, polypropylene is stable at temperatures in the 90–240°F range, and (2) polypropylene does not react with chlorine or other common swimming pool chemicals.

But all plastics are very poor heat conductors. Polypropylene has about one thousandth the thermal conductivity of copper, so thicker solar collector fluid passageway walls equal lower efficiency. As a result, some solar pool heating collector manufacturers have succumbed to chasing the highest possible thermal performance ratings by making the fluid passageway walls of their solar collectors as thin as possible.

Thinning out the fluid passageway walls increases the risk that cyclical stresses caused by temperature extremes—during freezing weather and during no-flow stagnation conditions on a hot summer day—will cause the solar collector’s fluid passageways to crack and leak.

One competing solar collector has achieved a thermal performance rating that is about five percent higher than the Ecosun® collector. But at what cost? This particular competing collector weighs about 14 percent less than the same size Ecosun® collector—15.9 pounds versus 17.1 pounds for the Ecosun®—for the two collector models’ 4×10 foot panels. Five percent fewer Btus is insignificant (it’s actually within the margin of testing error, for you statistics buffs out there), but 1.2 pounds less plastic in a solar collector that weighs less than 17 pounds?

The Ecosun® collector has the same size header manifolds (two-inch) and about the same size parallel fluid passageway tubes (0.20–0.25 inch diameter) as the competing collector. But the Ecosun® collector has only about half the number of parallel fluid passageway tubes, so how can it possibly be heavier?

Folks, solar is modular. You can always add more collector surface area to your system, if you desire, to gain additional heating capacity. But you can’t make the solar collector you choose more rugged and durable after it’s been installed. So choose wisely.

Best solar panel design for efficient pool pump operation

Ecosun® solar collectors have an unimpeded flow design; water flows from the header manifolds directly into the parallel fluid passageways with minimal flow restriction. However, it’s important to understand that not every solar collector is designed this way. Some solar collectors employ a header flange manufacturing design for attaching the collector’s parallel fluid passageway tubes to the header manifolds.

A header flange, sometimes called a sub-header manifold or plenum, saves a few expensive and time-consuming steps in the process of manufacturing a polypropylene solar collector panel, but it also creates—as a byproduct—secondary water chambers at each end of the solar collector panel that restrict water flow and significantly increase the pool pump’s workload.

Two established solar pool heating collector manufacturers use the header flange technique to manufacture their solar collector panels. Technical data published by one of the manufacturers shows that its header flange design produces more than six times the flow restriction of the Aquatherm® Ecosun® solar collector (0.87 psi versus 0.13 psi, respectively, at the recommended flow rate of 4 gallons per minute for a 4×10 foot collector).

What does 0.87 psi really mean? Well, it’s a measure of friction loss, or flow restriction. By comparison, 100 feet of 1-1/2 inch Schedule 40 PVC pipe flowing at 4 gallons per minute produce a friction loss of 0.06 psi. So the header flange collector in the example above produces over 14 times the flow restriction produced by 100 feet of 1-1/2 inch Schedule 40 PVC pipe.

One of these manufacturers likes to call its header flange a metering plenum, claiming in its marketing materials that the additional flow restriction balances flow to a solar collector’s many parallel fluid passageways, resulting in more even—and thus better—heat transfer.

But this is a solution to a non-existent problem, because one of the most basic principles of fluid hydraulics is that flow will be balanced when all of the fluid pathways in a parallel piping arrangement are the same cross-sectional area and length. This is always the case in a solar collector array plumbed with opposite-end return.

And frankly, same-end return plumbing is usually fine as well, in a bank of up to perhaps six four-foot-wide solar panels, because another principle of fluid hydraulics is that a fluid always follows the path of least resistance. In plain terms, water flowing into a solar collector panel bank fills the entire length of the big two-inch diameter header manifold (low flow restriction) before rising into the very small diameter parallel flow passages of the solar panels (which each create a much greater flow restriction). Just to be safe, we always calibrate the flow up above the standard 1/10 gallon per square foot of solar collector surface area whenever available space or other constraints force us to use same-end return.

Header flange solar collectors allow the manufacturer to produce a solar collector less expensively. But all they really do for you is create more pressure for your pool pump to push against.

Best design for real world performance

As we all know, there is often a difference between rated performance and real world performance. To cite a familiar example, a variety of factors can cause your family car to achieve dramatically different mileage than its EPA fuel efficiency test results suggest.

So it is with solar collectors, and particularly solar collectors designed specifically for swimming pool heating. Such “low temperature” solar collectors usually do not have glazing or insulation to isolate their energy-absorbing fluid passageways from the outside air. As a result, their thermal efficiency can deteriorate rapidly as the air temperature falls or the wind speed increases.

This efficiency deterioration is not reflected in the instantaneous thermal performance ratings typically used in the marketplace to compare solar collectors. These instantaneous ratings, presented as a single number in Btus per square foot of collector surface, assume a wind speed of only 3.5 mph.

However, as wind speed increases, differences in individual solar pool heating collector shapes and surface configurations can have a tremendous impact on actual, real world thermal performance. Here’s why:

When air moves across any surface, it encounters friction. This friction causes a layer of slower moving air to form near the surface. This boundary layer of slower moving air acts as an insulating barrier, reducing the rate of convective heat transfer between a warm surface and colder air moving above it. Rough surfaces encourage the formation of boundary layers; smooth surfaces do not.

This explains why, other factors being equal, an unglazed solar pool heating collector with a smooth flat plate surface will tend to perform worse than a flat plate collector with an irregular surface in moderate to high winds, even though the two collectors may have identical thermal performance ratings.

Worst of all, though, are loose tube and serially plumbed pipe collector systems that allow air to flow freely all around the circumference of the tubes or pipes. Any sailor or pilot can tell you that air flowing past a smooth, convex curved surface accelerates. This phenomenon is called the Bernoulli Effect.

The Bernoulli Effect dramatically increases the rate of heat loss experienced by a loose tube or serial pipe solar collector when the surrounding air is cooler than the water circulating through the collector’s fluid passageways. These types of solar collectors will generally become much less efficient, in windy conditions, than comparably rated “flat plate” collectors.

Ecosun® solar collector fluid passageways are extruded with a web of polypropylene in the spacing between each tube, so that air can’t circulate freely around the individual tubes. Additionally, the outer surface of each Ecosun® parallel fluid passageway is fluted, creating an irregular surface of small ridges that encourage boundary layer formation when the wind speed increases, discouraging convective cooling. (Incidentally, the fluting also adds stiffness to the fluid passageway tubes; the extra material mass also improves the collector’s freeze resistance.)

Best design for storm velocity winds

While it is desirable to have a solid collector panel surface in order to prevent free air circulation around the fluid passageway tubes (see “real world performance” above), tremendous aerodynamic forces can be exerted on a solid collector panel during gale-force winds or hurricanes. Air moving across the top of the collector at high speed causes the pressure on the top side of the collector to fall, creating aerodynamic lift.

The Ecosun® solar collector panel has a unique slitted web design, with small strategically placed slits in the webbing between the fluid passageway tubes. These slits provide pressure relief (reducing aerodynamic lift) during potentially destructive storm winds. However, the size and placement of these slits substantially prevents convection losses of the sort associated with loose tube and serial pipe solar collectors.

Strongest and most durable mounting system

The Ecosun® coated stainless steel mounting system is incomparably superior to the industry standard—nylon strapping—for strength, long material life, and appearance.

While the nylon strapping material that holds down most solar collectors has more than adequate design strength to withstand the force of hurricane windloads, it deteriorates over time. Solar pool heating system manufacturers are quick to point out that their nylon hold-down strapping systems are treated with UV inhibitors, chemical additives that protect the strapping material against the effects of prolonged exposure to sunlight (in much the same way that sunscreen protects your skin).

But UV inhibitors can’t protect nylon against moisture. After working with tens of thousands of solar pool heating collectors over two decades, our people have learned that prolonged exposure to moisture can weaken and rot nylon strapping material in just a few short years.

Aquatherm’s® coated stainless steel collector hold-down straps are much more expensive than nylon, and take longer to install because they are more difficult for the installation technicians to handle. But they will last as long as your solar collectors, and they will retain their design strength even after exposure to years of wind, rain, and sunlight.

Which hold-down strapping material would you prefer?

Seeing, holding and touching is believing

The durability and design strengths of the Aquatherm® Ecosun® solar collector are plainly obvious when you have the opportunity to hold a section of an actual Ecosun® collector in your hands—and compare it with samples of competing collector products. When you compare the real thing, Ecosun’s® heft, rigidity, tube fluting, and unique slitted web design become the obvious choice for heating your pool.

So call us at or complete our quick form to get a free estimate, and one of our experienced design consultants will make it possible for you to see, hold and touch the world’s finest solar pool heating collector panel firsthand.

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