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.

Cooling Your Pool With Solar

In many climates pools gets too warm just from the direct sun heating them. A common joke we used to hear in the early decades of solar pool heating was that my pool is already solar heated. Its warm all summer just from the direct sun. Its true. The top surface area of the pool sees the same solar energy per square foot as the solar collectors up on the roof. The pool is also losing some of this energy at the same time same as the collectors. If the pool is in the shade it still has the same losses but 100% of pool top surface area in collector area is missing from the energy balance equation. That is why shading on the pool is almost a one to one relationship in terms of how we have to size solar. For every square foot of shading on the pool we need almost one sq ft of solar collector to get that pool back to the same temperature it would be at if it was in the sun. A shaded pool is a cold pool so we get a lot of demand for solar from these homeowners. When we factor in the shading AND size the system to extend the season as we normally would we're sometimes telling people to expect the pool to be 30 degrees F warmer than they are used to. Pools that are in the sun have the opposite problem. They get too hot on their own even with the cover off. Today I had an e-mail from someone in Slidell Louisiana asking about cooling a pool with solar and I thought I'd share my response.

Yes solar is very effective as a pool cooler. Many companies used to include the automatic cooling feature in their automatic controls but over time eliminated that feature because solar turning on automatically in the middle of the night woke everyone up. Air flushing through the pipes makes noise. We had one customer who left the system in cooling mode for 2 years without knowing it. For these reasons we don't automatically keep the pool temperature down. We just turn solar on manually at night on purpose.

Its hard to quantify it because its radiation heat loss as well as convection but it definitely does work as a pool cooler. Its very important in heating pools that we don't run solar when the sun isn't out because it will cool the pool. The more common use is as a house cooler. In this case the solar gain is taken off the house reducing or eliminating air conditioning loads. Now the pool gets too hot so you run solar at night to cool the pool. In other words you run solar all the time manually not automatically (you just switch the auto controller to test mode). Heating beats cooling because the sun is hotter than the night sky so you are still looking for ways to cool the pool but what isn't in question is the value of being able to pump water thru the black thing on the roof.


My best guess is that on a day you might gain 10 degrees from solar you might lose 3 degrees from running solar at night. Once we have these systems monitored we'll be able to look at this kind of thing quantitatively in the real world instead of trying to employ the Stefan-Boltzmann equation based on an equivalent night sky temperature that depends on cloud cover to calculate radiation heat loss and then add that to estimated convective losses. Real life is so much more real. Nobody has proven global warming mathematically. We need to see glaciers melting and extreme hurricanes before anyone pays attention. I use global warming as an example of how complex the heat balance on a swimming pool can be. The variables are too variable for anyone to be able to say with certainty what is happening but we have done a lot of work toward the goal of predicting what will happen to a pool after we solar heat it and a big part of that work is verification. Our charts under sizing have been verified hundreds of times on real situations. Whenever anyone asks us to quantify our claims we point right to the charts for an area close to them and we extrapolate up or down based on the variables. We try hard to not make unsubstantiated claims. You lose credibility really quick when you start playing salesman and telling people what you think they want to hear. Its a very tough habit for any professional salesman to break so if you're a salesman break the habit. Get technical. We have to be diligent about our technical approach to this industry.

In-Floor Cleaning

In-floor cleaning system on pools are common in Arizona. Not too common elsewhere. A distributor head that looks like an octopus distributes flow from one set of nozzles on the pool floor to another moving dirt along and toward the drain where it is sucked up by the pool pump into the filter for removal later. The dirt gets kicked up of course and technology has changed so sometimes the idea is the nozzles just kick the dirt up everywhere and skimmers and bottom drains take the dirty water to the filter. Its a wonderful concept but it requires a lot more pump power than otherwise. Normally we'll see 2HP pumps on these pools. A pool without in-floor cleaning would only need 1/2 or 3/4HP. The power requirement is threefold higher before we even consider the load. The infloor cleaning system requires more pressure. That means the pump works harder. That means it uses more energy so a pool with a 2HP pump and infloor cleaning running the same 8 hours a day might consume 5-10 times the energy as a pool without the feature. That means 5-10 times the electricity bill.

We are working with a dealer in Tucson at this moment, Kevin, we'll call him. Kevin's PV (photovoltaic solar electric systems for electricity) company just installed a $90,000 solar electric system for a customer and the new pool is getting solar heated as well. The customer is more comfortable with Kevin than the pool company's recommended solar company who wants to put large coils of polyethylene pipe on the roof. Kevin has demonstrated our flat roof no roof penetration ballasted Powerstrip system (not published on www.h2otsun.com yet) to the customer and he's impressed. The problem is the pool company wants to install a 2HP pool pump with infloor cleaning. We've recommended a variable speed pump to minimize operating cost and to allow fine tune adjustment of the pump after the fact so minimal energy is wasted with the infloor cleaning feature. They finally gave in and agreed to this but not without a lot of resistance based on the premise that in-floor cleaning systems need to operate all the time the pump is on. If that is true then there is little electricity savings to be had. What we believe to be the case is that infloor cleaning does not have to be on all the time. Customers we have talked to have reported that 2 hours a day is plenty. With a variable speed pump we can program infloor cleaning to come on for 2 hours near the end or start of the filtration cycle. During these times the load is high but we can minimize it by setting the pump speed just right. With a Pentair VS 3050 (our preferred vfd pump) for example, we have the choice of 3050 different operating speeds. Not only do we get to set the speed just right but at any one operating point the motor on this variable speed pump will be 92% efficient whereas a regular motor on a regular pump is more like 55%. That's the motor. The pump that is attached to the motor also has an efficiency that must be multiplied by the pump efficiency to get the overall efficiency (we call the whole thing the pump normally). The pump part of the pump will be more efficient on a single speed pump because the impeller and housing are designed for that one speed instead of 3050 speeds but the difference isn't as much as the motor. Overall we typically see efficiency 30% better with a VS3050 pump (pump/motor combo) than we do a single speed pump doing exactly the same thing. I have this data straight from the horse's mouth. My friends at Pentair gave me access to actual test data that was done leading to the Title 20 law in CA (Jan 2008) that stated that anything over 3/4HP was illegal on a residential pool (retrofits and new construction). There's talk that variable speed pumps may become mandatory next round. Its socialism I tell you and its the best kind. The pool industry proved that it is incapable of taking efficiency into consideration in their pool designs so Arnold had to step in and terminate their oversizing habits. Now its not just me and a few top pool design teachers spouting off about 1/2HP vs 2HP. Now the pool builders themselves are all about energy efficiency in CA. Not so much in AZ.

Ironically its easier to tie solar into a pool with an oversized pump than it is after we've successfully solved the pressure problem by changing out the customer's pool pump for something sized more reasonably (or gone variable speed). If the pool is simply a pool with infloor cleaning its definitely a pressure situation so we employ a pressure design. Something like case 7 at http://www.h2otsun.com/pk is appropriate. Note that with a high pressure design what we are doing is regulating the pressure. Its easy. We just limit the flow we allow to go to solar. We don't divert flow to solar. The pressure wants to send the water up to solar. The pressure is higher than the roof height. What we are doing is limiting the amount of flow we allow to go to solar and dropping the pressure to the solar collectors. It sounds so easy but its just the beginning because we need to get this low pressure water from the solar panels back to the pool still. We need another pipe that isn't under pressure. Water won't flow from the low pressure solar panels to the high pressure pool plumbing unless we pump it and that would be crazy. We're not adding another pump to force the water from solar back into the pressured plumbing. The best analogy I have ever come up with for this is the kitchen sink. If you open the tap on the kitchen sink you are just opening a valve teed off the pressure line. You aren't diverting anything. The pressure drives the flow from high pressure to low pressure. Once the water leaves the tap its at zero pressure (zero gage pressure equals atmospheric pressure which is 14 psi- zero is atmospheric on any gage). Water flows because it has a place to flow to that is not under pressure. The drain pipe from the sink to the sewer is open so its under no pressure so water flows there. If we tried to force the water back into the pressured pipe it came from it wouldn't flow and the whole kitchen tap line would go under that full system pressure. Note that with no flow the whole thing is under full pressure. You can't regulate pressure without having a low pressure place to return the low pressure water to the pool through. Its a great analogy and occasionally a pool builder stops arguing all-knowingly when this analogy is made and many times we've opened the door of doubt just enough that we start to see an opportunity to win another one over to our side. Our side, by the way, is the side that says we all have a lot to learn from each other and if we are protective and defensive we aren't open to learning anything from anyone. That's old school. New school is the public is smart and has access to this kind of information so you better get with the program if you don't want to get embarrassed by someone like Kevin who admits right up front he has no pool mechanical experience yet there he is making a pool builder with 30 years experience look foolish and costing the pool builder and his gravy train of kickbacks for recommending a truly bad solar company and product, one customer at least. Its unfortunate that the solar guys have to argue with the pool guys in the first place. We are the mechanical design experts and we are the ones who have to take responsibility for a very long time for this large array of thin black plastic expanding and contracting on the roof top freezing in winter to boiling in summer not to mention the rest of the pool mechanical system. Pool builders don't take responsibility if the filter explodes. The solar guys gets blamed and so he should if he is guilty of ignorance. Pool builders need to learn to respect the territory of the solar installer. These days a solar installer has to be responsible for what he installs so he has to follow manufacturer's recommendations. Solar pool heaters need to be designed. In this industry the big players have no standards. They have specs and those specs are surely called on in the event of a major warranty hassle but those specs are not understood by their people in the field. We're writing the book on this. If the pool has infloor cleaning we need somewhere else to deliver the solar heated water. We need a separate pipe to the pool or if its a pool/ spa combo a separate pipe to the spa. Usually there are other inlets to the pool that we can utilize but sometimes not. Think about what makes sense here.



My own personal pool mechanical design premise is that all pool design should start from the idea that the pump needs to be sized right. What has happened historically is that pumps have always been oversized just to be sure. Filtering, solar, salt water, ozone, and vacuuming all require minimal power. 3/4HP is plenty on any residential pool. In floor cleaning, spa jets, waterfalls all require much higher power and should all be on a separate higher power pump that only runs when one of these features is activated. Infloor cleaning would need to have its own filter to accomodate my pool mechanical design philosophy. That adds cost and takes up space so that is no good but I truly believe that if a pool builder simply took 5 minutes to sit down with the customer and give him some choices he'd not only upsell to the better arrangement he'd also eliminate the chance that any of his competitors would win the customer's confidence. In the two pump scenario the job of the solar designer is easy. We just tie in after the filter and divert the flow to solar and return the water before the gas heater. Its Figure 1a in the installation manual you can download at www.h2otsun.com off the navigation bar at the left. The two pump idea never flew well so most pool spa combo pools we run into are single pump systems and that pump is oversized and now that electricity cost (and global warming) is an issue people aren't happy about what the pool company did to them. The retrofit solution is the variable speed pump. In solar /filtering mode the speed is low and electricity cost is low and the pump runs all day quietly. When a higher speed function is called for solar is off and isolated from the pressure by the seals in the 3 way valve as well as the return line check valve and the higher speed kicks in along with higher pressure and everyone is happy..... until the check valve or the 3 way valve leak...We need a failsafe so what we use is a spring loaded check valve. If pressure ever goes too high it'll exhaust water and let you know there is a problem. This is a perfect lead in to my next article which I promise will be a lot more interesting and contemporary. Understanding pressure and flow as it relates to solar design in these first two blogs is absolutely critical. Once you understand what causes pressure and how to solve pressure issues you can tackle any pool mechanical design issue you come across and its really smart to do that before you start adding solar heaters with hundreds of extra feet of plumbing and thin black tubing all over the customers roof. Somebody has to look at the big picture and the pool builders haven't done it in the past so we have to. The situation is entirely different when dealing with commercial pools. There we have design employed. Not so in residential.

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.