Solar Heating is Flexible

Up until just a few years ago, solar swimming pool heating was far and away the largest use of "solar energy". The reason is simple and straightforward. It makes economic sense. It competes head on against very inexpensive natural gas for heating swimming pools. The unglazed (no glass over the collector) plastic collector is low cost per area exposed to the sun and when heating low temperature water like a swimming pool (or even pre-heating domestic hot water) the efficiency is high. In other words a large portion of the solar energy exposed to the collector is collected and delivered as energy to the load. This simple and obvious combination makes for the most cost effective and therefore most viable solar energy solution. Over the last 37 years this solar energy market has thrived but there have been ups and downs.

The first low cost unglazed solar collectors for swimming pool heating were introduced around 1969 under the trade name "Solaroll". The product was made of a synthetic rubber called EPDM. It was a flexible collector. It thrived. In 1972 "Fafco" introduced the first rigid collector. This collector, still in production today, was made of a type of polypropylene. The header pipes are permanently attached to the absorber sections in the factory resulting in fixed size collectors. 4x12 has become the most common size. The advantages to this design are that they are low cost to manufacture and low cost to install. Solaroll by comparison, required the installer, dealer, or homeowner to attach all the headers to the flexible fin-tubing after cutting the fin-tubing to length. This extra work traded off with the extra capability in terms of being able to fit the collector to the space. In addition these original flexible collectors could be used in areas where freezing was an issue. If water is trapped inside a rigid collector and it freezes the tubes break and the remedies require sealing off entire flow cores. The flexible Solaroll on the other hand could be mounted flat on a roof where water will not drain out. It could freeze solid with water in it. This was the state of the art in the industry 30 years ago? What happened since? Solaroll no longer exists and Fafco was mimicked over and over again and today 75% of all solar pool heating is done with rigid polypropylene boards floating around under straps. Most in the industry can tell you flexible EPDM synthetic rubber collectors like Solaroll had a fatal flaw. Chlorine in the swimming pools caused the flexible material to break down. One of the big chemical companies proposed a solution. It was a polypropylene based flexible extrusion called Santoprene. As the story goes, it broke down faster than EPDM and the result was an industry calamity. From this point forward the rigid polypropylene collector industry thrived.

But the rigid 4x12 panels were limiting. They couldn't be applied to flat roofs without fear of freeze damage. Available space could not be fully utilized and what could be less esthetically appealing than big black rectangles on a rooftop? Where there is demand there is supply. The epdm rubber tubing collectors came back, slowly and gradually. Its been 30 years since the major fallout. Hot Sun installed a 2000 sq ft system in North Carolina using EPDM and it took only 3 years in the field for the system to start churning black crud into the pool.

Luckily Hot Sun had decided this was risky and had already switched to a plastic based alternative. The experience in North Carolina was the final straw and we went 100% non EPDM after that point... because we could! There is an undeniable appeal to using EPDM. Its tough. It usually lasts long enough that these issues occur well into the lifespan when most people don't even remember who they bought their systems from. Hot Sun's solution is not without its downsides too. There is no perfect answer. We have to use a mechanical or an adhesive connection to join the tubing and the headers. It takes more time to assemble. Theoretically flexible plastic is not as strong as flexible epdm so we have to be more careful with system pressure but what we've found are better and better thermoplastics such that today our flexible plastic is as strong as most competing epdm products with one major distinction. Powerstrip is guaranteed not to break down for 25 years. Some manufacturers of some EPDM products can't have water left in them over winter due to "freezing issues". That mindbender really means that if you leave water in the epdm tubing and it heats up the black crud will come off the solar panel and go into the pool. Freezing seems to trigger the release, we think just due to the physical stretching. We don't believe anyone else has even tried to resolve the issues with epdm in the solar business. My point is we can guarantee it won't happen for 25 years. EPDM solar manufacturers can't guarantee it won't happen in 10. The seal manufacturers have certainly acknowledged this problem. Here we're talking about chlorine in drinking water (much lower concentrations) and city water temperatures. The effect is thought to double with every 10 degree increase in temperature. The solutions are special compounds that are very expensive and even then the effect is just reduced.

Pool Mechancial Systems and Solar Pool Heating

Ken Wright is president of Hot Sun Industries Inc, a San Diego based manufacturer and distributor of solar swimming pool heating technology. This blog chronicles the ongoing struggle of one entrepreneur and his noble staff attempting to take a technology approach to solar pool heating…..technology in concert with a swimming pool industry sometimes set in its ways. Hot Sun’s main web site is www.h2otsun.com Welcome to our blog. I trust you'll find our experiences in the field worthy of publication.

Since many of my readers will be our solar dealers looking for on-going training and many solar energy people have no specific swimming pool knowledge it is necessary that we first cover some of the basics of how swimming pools normally work. We all know that a pool mechanical system in its simplest form consists of a pump drawing water from the skimmer baskets and the bottom drain, pumping the water through a filter and returning it through "inlets" to the pool. Its normally all plumbed up with 2" and 1.5" pvc pipe. The pump runs long enough each day to theoretically turn the water over at least once a day. On commercial pools where the health department oversees things generally the requirement is that pools are turned over once in 6 hours. Filters are either sand, cartridge or diatomaceous earth. Sand filters are my favorite. They restrict flow more than the others but they are simpler and easier to clean. "Backwashing" is running the pool water backwards through the filter dumping dirty water to drain. Cartridge filters use a removable paper cartridge so the restriction is minimal when the filter is clean but cleaning requires removal and manual work with a hose. DE filters (diatomaceous earth) are just cartridge filters with a special compound packed in so that the water is treated with the magic earth. These filters also boast of finer particle filtration. Its all nonsense as far as I'm concerned. The job of the chlorine is to oxidize the contaminants into particles that can be filtered out. Pools with sand filters are every bit as crystal clear as pools with DE as far as I could ever tell but then again I've only visited about 15,000 pools in my career. Pool service guys have spent their careers dicking around with this more than we have so if they say DE makes sense in your area I defer to them.

Historically it has been the case that the pool construction industry hasn't been at all concerned with pool pump electricity operating cost. The pool builders are excellent tradespeople. I don't know how to build a pool any better than they know how to configure a mechanical system taking into consideration pressure and flow. Pool builders should not be insulted when an engineer or someone qualified tells them that all they need is a 3/4HP pump for filtering a residential pool but they are. The pool industry is missing oversight. There are no engineers. If I was the engineer working for a major pool company i would specify 3/4 HP or 1/2 HP as the filtering pump power on every pool. My job would then be done because there isn't anything else that requires a mechancial engineering degree. Everything else is pretty much OK just handled by the trades.
Seriously. The idea that you need 1.5HP to filter a residential pool is bordering on the insane. I still fight with pool builders to this day over basic pool pump sizing. Title 20 law in California (Jan 2008) has gone a long way to solve this problem for me by not allowing more than 3/4HP by law. Its a good law. How else can you get past widespread industry misconception? To be fair its just that energy is cheap so why bother trying to save any of it. If one aspirin cures your headache then take 5. That's the thinking and it isn't always the pool builder's fault. He's just not trained to argue it. Energy conservation has only been on the average guy's radar now for a few years.

I spent the first 24 years of my career as a solar pool heating technician, installer, dealer, distributor, manufacturer and consultant spending far more time than I even intended every single day fighting with pool builders over pump sizing. Over my career I saw pool pumps go from 1/2 or 3/4HP to 1.5 or 2 HP on the exact same size pools. The older pools have no trouble staying clear. Its all in the chemistry. Keeping the pump on all day means controlling the chemistry, the scum lines, all day instead of just for the 3-6 hours you end up running a pump if it is oversized. Oversized pumps are noisy because they are oversized. Oversized pumps are expensive because they are oversized. They cost even more to operate than they should usually because they are forcing water through piping not sized large enough for the high power. They fail sooner because of the extra stress from the extra pressure and of course from the solar person's point of view, the pressure is the absolute worst thing you can introduce into a solar heater.

A solar pool heater is a large thin plastic heat exchanger with the sun. When the pool is up to temperature (think hottest time of the year mid summer) the collectors bake in the Hot Sun and the pressure doesn't disappear in every case just because water is diverted away from solar. www.h2otsun.com/pools is a valuable lesson in pressure and solar design to get around pressure. Stagnation temperatures can reach 185 degrees F in the desert. Even in Canada we've seen collectors hit 180F in stagnation. These temperatures are too hot for the pvc pipe the systems are plumbed in and when I say systems I don't mean the solar systems, I mean the existing pool systems. C'mon everyone, let's be real. If you blast a solar pool heater with 30 psi you're asking it to do the job of metals and you can't change the pool plumbing to all copper and you wouldn't want to anyway. We are the only solar company on the face of the planet...except our competitors at Sunbather in Australia that I know of, that accept that we need to avoid collector pressure when solar heating swimming pools. Oh, the big competitors doing millions of dollars a year in sales know it but they are smarter than me. They know that introducing this into the equation requires a lot of extra work and extra training on the part of their dealers. They may have tried but in the end its just not worth the bother. The name of the game is sales not physics lessons. Leave the problems for the pool service industry and keep life simple for the salesmen who boldly install solar and pools faster than they can say, "Will that be cash or charge?" Just sell the damn stuff damn it. I'm being fecicious. I truly believe that there is room in the world for a technology approach to a technology like solar pool heating and I will spend the next half of my life proving it. This blog is the beginning of how we will educate the world on this subject.