We have a pretty good idea what’s on your mind when it comes to solar pool heating. And if you don’t see your question below, just fill out our brief contact form and we will get back to you with an answer.
Generally speaking, you can double the number of days of pool use per year up to 290 days in Northeast Florida.
A lot depends upon how you use your pool and your tolerance for colder temperatures. Residents of northern climates are completely comfortable swimming in 78°F water and this is usually the temperature required for competitive swimming events. On the other hand, Florida residents usually like their pool water a bit warmer; at least 80°F or more. And if you are heating your pool for therapeutic reasons, you will want at least 85°F water and possibly as warm as 90°F.
A screened pool in Central and South Florida will typically be at least 80°F or warmer for about three months and may reach 83–85°F from mid August to early September. Open pools are a bit warmer because the pool surface receives more direct solar energy, and may stay comfortable for an extra month or more.
Doctors and physical therapists regard swimming as a very beneficial form of exercise because it works the entire body without impact stresses on the joints. A heated pool can safeguard your health and contribute to your well-being by allowing you to exercise throughout the year.
And while children love to swim and can often tolerate lower temperatures, pediatricians caution that repeated chilling can make young children more susceptible to respiratory infections. This can also be true for elderly swimmers. A heated pool prevents chilling and problems associated with excessive body heat loss.
After subtracting the installed cost of a gas heater and propane storage tank, you will usually recoup the additional cost of a solar pool heater within about one year for propane and less than two years in the case of natural gas.
This assumes keeping a pool at least 80°F or so during the spring and fall and at least 76°F or so during the winter, at current fuel costs. An additional financial benefit of solar is that the leading solar pool heating collector panels have useful lives of 20 years or more. Even the highest quality gas heaters have to be replaced every 10 years or so, and the average is probably closer to seven years.
Completely. All you do is set your pool pump’s time clock or automation system to run during the daylight hours, then set the solar pool heater’s automatic control temperature indicator to your preferred temperature. The control system takes care of the rest. Sensors compare the temperature at the solar collectors with you pool water temperature. Whenever the solar collector temperature is at least four degrees warmer than your pool water, the control system adjusts a motorized valve to divert pool water through the solar collector panels if your pool is not at the desired temperature.
And even if your pool cannot reach your preferred temperature setting during the coldest winter weather, your pool will always be warmer than a neighbor’s similarly situated unheated pool, without you spending a penny on expensive fuel.
Every situation is different and relying upon simple “rules-of-thumb” can lead to unrealistic expectations and unhappy cusotmers. Among the many factors we consider when sizing a pool heater are:
- desired swim season length
- preferred water temperature
- type of pool use (exercise, kids playing, casual dips, etc.)
- therapeutic requirements
- screen enclosures and other direct shading of pool surface
- open space and windbreaks, especially along northwest to northeast exposures
- waterfront location
- distance between pool equipment pad and pool heater
- for solar, availability of sufficient unshaded roof or other installation location
- for solar, direction best available roof area faces
- willingness to use a pool blanket
- ability and willingness to pay increasing energy costs
Your pool’s water volume (gallons) does matter, especially if your system is installed during the winter, because the water temperature of an unheated pool during the winter months can be as much as 20 degrees below the desired temperature. In this case, dividing the estimated average daily Btus of heat input from the heating system by the pounds of water in the pool (water weighs 7.5 pounds per gallon) tells us how fast we can bring the pool up to the desired temperature.
On the other hand, in normal operation we are simply trying to replace the two to four degrees of water temperature lost overnight, and most heat loss occurs through evaporation at the pool’s surface. This is why we size pool heating systems in relation to the pool surface area.
A solar pool heating system will typically collect about half the solar energy of a clear, sunny day on an overcast day. If you have ever had the experience of going to the beach on an overcast day and still getting a sunburn, you understand this phenomenon. Clouds block many of the visible wavelengths of sunlight, but much of the heat energy still gets through.
Solar pool heating collectors typically deliver excellent performance in Florida during cold weather because the sky is very clear during winter high pressure waves. On the other hand, increased evaporation from your swimming pool surface can significantly reduce your pool temperature during cold fronts. A pool blanket can help keep the heat from escaping.
This depends upon what time of your system is installed and will be greatly accelerated if you use a pool blanket to keep the added heat in the pool. For most solar pool heaters and with a pool blanket in place, an unheated pool will usually come up to temperature within three days or so during the spring and fall.
Of course, if your next door neighbor’s pool is unheated and has similar site factors (screen enclosure, windbreaks, etc.), you can simply compare water temperatures.
However, if you don’t happen to have such a convenient comparison point, or if you simply want to better understand your pool’s temperature dynamics, the method described below will provide you with a pretty good approximation of what your pool’s current 24-hour average temperature would be without supplemental heat.
- Go to www.Weather.com and enter your zip code into the Local weather search box at the top of the page.
- When the results page for your local weather appears, look in the left column for the list of links for different types of local weather data (“Yesterday,” “Right Now,” “Today,” “Hourly,” etc.). Select “Monthly.”
- Record the daily high and low temperatures for each of the preceding six days. You should have 12 temperature points.
- Calculate the average for the 12 temperatures. The result will be a good estimate of the current day’s temperature of an unheated pool in your locale.
Remember that on a sunny day, a solar heated pool is usually at least three degrees warmer during the afternoon than during the early morning hours.
Also, keep in mind that www.Weather.com often publishes the same weather data for every zip code within a single county or large metropolitan area. However, actual air temperatures within the same county or metro area will vary: a bit warmer in urban surroundings and a bit cooler in rural surroundings. This is called a microclimate difference. You can get a good estimate of any microclimate difference applicable to your pool by comparing the Weather.com current local air temperature for your zip code with an outdoor thermometer reading. Just make sure the sun isn’t shining directly on the thermometer.
No. This requires two different systems. Home water heating water temperatures of 125°F to 140°F call for solar collectors constructed with metals like copper that conduct heat well, and insulation and glass cover plates to keep the heat from being dissipated into the air. Swimming pool solar collectors typically operate at temperatures of just 76°F to 95°F, so they can be constructed of polypropelene plastic and do not require insulation or cover plates.
Millions of square feet of polypropylene solar pool heating collector panels have been operating in the field since the late 1970s. You can easily expect 20 to 30 years of service from high quality solar pool collectors.
No. The mounting systems for all solar collectors approved for installation within Florida are engineered to withstand hurricane windloads. It is not unusual to see completely intact banks of roof-mounted solar panels on a heavily damaged house following a hurricane.
No. First, polypropylene solar pool heating collectors do indeed expand and contract throughout the day, so our mounting systems are designed to allow the solar collector panels to “float” inside the roof mounting straps, free to expand and contract as needed without putting any strain on the mounting hardware roof penetrations.
Second, conventional sealants can lose elasticity over time. This is not a significant issue for applications like window and bathtub caulking, but the extreme temperatures experienced on a roof surface are a different story. So our roof mounting penetrations are sealed with a special high technology sealant, originally developed for the aerospace industry. This sealant has been proven to maintain its elasticity over several decades.
No. Solar panel expansion and contraction occurs so slowly that it is not apparent to the naked eye. And such a slow rate of movement has no effect on your roof surface.
No. Quite the opposite. Solar pool heating collectors actually protect the portion of roof they cover because the sun’s energy is being absorbed and carried away by the pool water circulating through the panels. Also, because a bank of solar pool heating collector panels typically covers a fairly large area of roof, it can keep your attic a bit cooler whenever the system is operating.
I’ve heard that the U.S. Department of Energy determined that loose tube collectors are best for pool heating when they selected this type of solar pool heater for the Atlanta Olympic Games. Is this true?
No. This particular system was actually selected to cool the Olympic venue pool.1 Here’s what happened. The swimming and diving competitions of the 1996 Summer Olympic Games were held at the Georgia Tech Aquatic Center, which was designed as an outdoor facility in order to increase spectator seating capacity from 2,000 to 15,000. (The Aquatic Center was converted to an indoor facility about five years after the Atlanta Summer Games.)
Pool water temperature for competitive swimming events must be maintained between 25°C and 28°C (77°F and 82.4°F).2 An outdoor pool’s temperature tends to match the 24-hour average air temperature for the preceding week, and Atlanta’s average daily air temperature in late July is 88°F. It isn’t unusual for temperatures to climb into the high 90s.
This meant the Aquatic Center pool water would be at least 10 degrees too warm for competition. So the primary goal of the architects and engineers was to come up with an effective method of cooling the pool.
Most non-metal solar pool heating collectors, including loose tube designs, radiate energy to a clear night sky at roughly the same rate. However, loose tube collectors have much greater convective heat transfer rates than flat plate designs because air is able to flow freely around and between the fluid passageways.
This is a really bad thing when you’re trying to heat a pool and the surrounding air is cooler than the water circulating through the collector’s fluid passageways. And even worse when the wind picks up.
On the other hand, a higher rate of convective heat transfer is great if your primary goal is to cool a pool at night. Thus, a loose tube heat exchanger design was a perfect choice to cool the Atlanta Olympic pool during the hot Georgia summer.
The manufacturer and dealers of this particular loose tube collector system promote the Georgia Tech Aquatic Center project as their flagship large-scale “solar heating” installation, and often point to the Department of Energy selection process for this project as evidence of the product’s solar heating superiority. Nevertheless, the fact remains that the loose tube collector array installed at the Georgia Tech Aquatic Center was specifically designed for cooling. The pool has a steam heat exchange system for primary heating.
No. The argument is that a two-inch solar collector panel header improves efficiency by allowing more water per minute to flow into the fluid passages of the heating surface. While it is true that two-inch pipe has a higher saturation (maximum) flow rate than 1-1/2 inch pipe, a single bank of solar panels is never installed with more than about 480 square feet of total solar collector panel area. (Larger solar systems are broken into multiple panel banks.) Solar panels designed for swimming pool heating temperatures function best at a water flow rate of about 1/10 gallon per square foot of solar panel surface area per minute. So for the best thermal performance, we would never want to flow more than about 48 gallons per minute (1/10 gpm per square foot x 480 square feet) through a single panel bank, regardless of the pipe size. 48 gallons per minute is well below the saturation flow rate of 1-1/2 inch pipe.
Some solar collector panels require larger headers to partially offset the increased back pressure created by a plenum chamber design (see below). Unfortunately, some of the companies that sell plenum chamber collectors teach their salespeople to compare the costs of 1-1/2 inch and two-inch Schedule 40 PVC pipe at building supply outlets like Home Depot and Lowes, to justify higher prices for their solar pool heaters. But this is a meaningless comparison because headers comprise only a fraction of the material in a solar collector panel.
No. The idea is that flow-balancing plenums—secondary water chambers between a solar collector’s headers and the flow passageways of its heating surface—provide more balanced water flow throughout a bank of solar collector panels, and thus more efficient heat transfer.
But this is a solution to a non-existent problem. A basic rule of fluid hydraulics is that flow rates will vary in parallel pipes so that the head losses are equalized through each flow path. In plain English, if the diameters and lengths of the individual parallel flow passages in a solar collector are identical, the flow rates through these passages will be identical. This is always the case in a correctly installed solar pool heating system.
The only practical effect of additional flow restriction in a properly installed solar pool heating system is increased workload for the pump.
Here’s how this idea got started. During the 1970s, a solar collector manufacturer developed a process for heat-welding the heating surface of a polypropylene solar collector to the collector’s header pipes. The patented3 process involved fusing strips of plastic—called flanges in the patent application—along the length of each header pipe, encasing the the ends of the heating surface. The flange design cut manufacturing costs by reducing the number of steps needed to attach the heating surface—and its many individual fluid passageways—to the headers. Unfortunately, the new process created a secondary water chamber along the length of each header, which significantly increased flow restriction through the collector.
An old saying holds that you should find ways to turn your weaknesses into strengths. At some point, someone came up with the idea that the additional flow restriction would ensure that water spread out more evenly among all of the fluid passageways in the solar collector’s heating surface. And so it was that the drawback of substantially increased flow restriction was magically transformed into “flow metering” and “flow balancing.”
Two major solar pool heater manufacturers use the plenum chamber design in their solar collector panels today. Their dealer salespeople sometimes use the example of house central air conditioning ducts to illustrate the need for a flow-balancing plenum chamber. But this is a poor analogy because there is usually great variation in the length and size of air conditioning ducts branching to the different rooms within a house, so there is indeed a need to balance the air flow between the rooms. This variation does not exist within a bank of solar collector panels.