Hot Sun Industries Inc., San Diego, California
Hot Sun Industries Inc., San Diego, California
You can fill in the form so that I'll be able to discuss sizing with you. What is an appropriately sized solar heater and what can you expect it to really do in terms of pool temperature and season? That's been the toughest question to answer this industry has ever faced. We've made enormous efforts over the last 2 decades in collaboration with many gov't and research groups to be able to give you an accurate answer. We've achieved that goal and we urge you to read this page and study the graphs. We urge all those we've worked with especially the government of Canada who financed a lot of this work (we didn't get any money) to take notice of where we've taken this body of work since the funding dried up and put some more money into it. There are still a lot of uncertainies. This graph shows a typical properly sized system solar heated pool in San Diego CA.
The above curves are for a 16x32 pool with 25% shade and 8) 4x12 collectors or 75% of pool area in collector area. That's normal sizing for a covered pool. Notice the "bump" in pool temperature a cover alone gives you compared to a cover and solar. The numbers here are little better than what I've been predicting for many years. Without a cover we would normally scale the size of the system up quite a bit. Note even with a solar heater sized moderately as if you had a cover, without a cover solar does more for the pool than just a cover and gives a typical pool season. With the help of a cover in the fringe months solar is certainly all the heater you'd ever need.
Note that we've compiled plots for many major cities. The plots for San Diego on this page are shown to demonstrate the effects of the various factors used in sizing your solar heater. The relative weight of each of these factors is not too regionally specific. Regionally specific data is linked below showing you what to expect in your neighborhood.
Look at a sample system at a major city near you for a better idea of what to expect out of a properly sized solar heater for your pool.
Shading on the pool is a big factor in sizing
Notice above that 75% shade on the pool dramatically reduces the pool temperature. In order to make up the difference of 75% pool shade to 25% pool shade we have to make up for shade on the pool with an equal extra collector area. In our sample case that means 14) 4x12 solar panels instead of 8. Here are the results below. This demonstrates the enormous effect of shade on the pool and why that shady pool is always so cold and why our sizing recommnendation is so high on shady pools.
Above,we've assumed a relatively wind protected pool and roof where solar panels are, an aged bubble type cover and we're trying to show you the effect of a cover and shading on the pool. These are the two biggest factors in the cost of heating a pool. The plots are for a San Diego pool, 16x32 with 25% shading, normal wind levels, 8) 4x12 collectors facing south. That's a typical sizing of 75% of the pool's top surface area in collector area. Let's look at a windy neighborhood where the pool and the collectors will be subject to significant heat losses from wind. If the wind comes from the north the wind effect is minimal. If the wind comes from the side the collectors are hidden in the boundary layer and don't see cooling effect from wind. Note if the roof is flat with no pitch the wind will never directly cool the collectors.
Note above that wind doesn't seem to make a whole heck of a lot of difference. We believe this effect is not reflected adequately on these curves. The Enerpool program was verified and wind effects studied but never in enough detail to really be able to evaluate this effect in more extreme cases. If the collectors are wind protected your solar heater will perform noticeable better if the air temp is colder than pool temp significantly.
The direction the roof faces is also a factor as seen here. This effect varies regionally. We can make up for this effect with more collector area. Covered pool.
Above what we confirmed with multiple other simulations was that to make up for east facing 20 degree pitch roof we'd add 4 collectors to our 8 collector system. To correct for east facing and 45 degree pitch (12 in 12) we'd have to double the size of the system.
Sizing a solar pool heating system is not as simple as sizing a conventional fuel fired heater. Many factors are at play. A pool is a large body of water that gains heat directly from the sun and loses heat by evaporation, convection and radiation to the night sky. These factors are related mostly to the top surface area of the pool so it's a good idea to estimate this as accurately as you can. The depth of the pool only affects the daily temperature swing. It doesn't appreciably affect the amount of energy that needs to go into the pool daily to maintain a set temperature. The most important factors in sizing are the amount of shade on the pool surface especially over the middle 6 hours of the solar day and the use of a cover. The use of a cover when the pool isn't in use and a solar pool heater will eliminate the need for any back-up heating in most cases and provide a comfortable temperature over an extended season.
If you increase the sizing because you have the space and the budget what happens? Is there any point? Absolutely yes as the plots below demonstrate. 8 collectors is the "right" sizing for the pool but extra collectors aren't a waste of money. Results are for a covered pool open 4 hours a day for pool use.
The above graphs are created using data from computer simulations but not just any computer simulation. We've been involved in extensive development of this capability with the help of universities and government groups for almost 2 decades. The simulation has been verified with high level monitoring of real systems. Click here to learn about the software and the extensive effort behind creating these curves.
The biggest draw to solar is that it completely changes the way you use your pool. With solar you start the pool very early in the year and even in early spring months when good weather strikes, your pool can be useable months before the neighbors with gas heaters or heat pumps have dared fire up the beasts. The use of a cover in the early and late months will give the ultimate pool heating experience. If you only need the cover for the fringe season months when pool use is lowest, you really don't have to fuss much with that cover. Just leave it on all week and off all weekend if you use the pool. Solar with the occasional help of a cover on the pool negates the need to ever turn on a gas heater. The only time you'd want to run a gas heater would be a time when weather was unusually poor or you were so far off season the pool use wouldn't justify the gas use. At these times the cost to heat with gas will be highest. That's why solar and a cover used occasionally is the ultimate pool heating solution for your home if you have enough space for a full sized solar heater.
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