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SIZING a SOLAR POOL HEATER

If you need help please call (858) 683 0800. This sizing form works for typical residential pool situations. If your situation is unusual let us help you by phone.

In order to size and price a solar pool heater we need this information from you as a starting point. If you'd like our help its best if you can gather that information then fill in this basic form .

The following is a web based calculator that will allow you to come up with our sizing recommendation based on achieving the pool temperatiure goals illustrated on our regional performance curves linked at the left under "REGIONAL".

In a typical situation 75% of pool top surface area in collector area on a pool where a cover is used means we're bumping the pool temp about 10 degrees and this is about what you need to enjoy the pool thru an extended season. If you don't use a cover go 100% and expect less. You will see a bump in pool temperature of 18 degrees. That's not an error. Look at the charts for your area to see what this means in terms of season and temperature.

You may want to watch this video on the subject or solar pool heating sizing first

Heat loss and gain to the pool is all based on the top surface area of the pool. There is an enormous amount of energy lost each day from a pool. Evaporation off the top surface is a huge factor. Direct gain to the pool by the sun is a big part of the heat gain. Wind loss, shade, are all proportional to the top surface area of the pool. The depth only affects the temperature fluctuation daily not the amount we "bump" the pool temperature up.

Measure top surface area (average length times average width) and enter it here in square feet.

  
The first chart below shows a typical solar heated pool in San Diego, California with a properly sized system. Note that if you are going to use a cover we're normally recommending 75% of pool area in collector area assuming the collectors can face south and there are no unusual shade or wind issues. Note the "bump" in pool temperature this provides. This kind of sizing will raise the pool temperature 10-15 degrees. As you can see that is enough to provide a fully useable pool for a longer season than you would normally achieve using a gas heater

Similar charts for your area can be found under the "REGIONAL" links found on the navigation bar to your left.

If you'll use a cover on the pool early and late in the season then enter 0.75. If you want to heat the pool without the hassle and expense of a cover then enter 1. It doesn't matter much where you are, the proportion of pool area in collector area that makes sense is usually the same because the "bump" in pool temperature you're after is probably the same. You can adjust this factor up or down proportionately depending on what you want to achieve. For example if you are only looking for a 5 degree bump instead of 10-15 then you can drop this factor from 1 or 0.75 down to 0.5 or 0.33. Power is proportional to the surface area exposed to the sun and the bump in pool temperature is proportional to the power. Note that without a cover our standard base sizing is 100% (enter 1 in the box). Look at the season of pool use you can achieve at no heating cost and without the hassle or esthetics or safety issues of a cover! That shows why solar pool heating is the only way to go for so many pool owners. You wouldn't heat a pool with gas and leave it uncovered in the fringe season months. You would with solar.

Enter starting factor of pool area 0.75 or 1.00.
Don't use percent symbols, please.

Direction of Roof Factor

The direction the collectors face is an important factor too of course. If the collectors are facing north they are facing away from the sun. Face the solar collectors somewhere south of the true east/west line. In the sun and facing the sun are not the same thing.

The best way to determine the roof direction is to look at the property on Google Earth or a map. The orientation is all relative to true south/north not magnetic south. A compass on the other hand shows magnetic directions which are different. The middle of the solar day is when the sun is directly true south.

 
ROOF DIRECTION CORRECTION FACTORS
 
  Shallow pitch
1 to 3 in 12
Normal pitch
4 to 7 in 12
Moderate pitch
8 to 11 in 12
Steep pitch
12 in 12 (45 degrees)
True South Facing 1.00 1.00 1.00 1.00
True SW or SE 1.02 1.06 1.08 1.10
True ESE or WSW 1.07 1.15 1.20 1.25
True E or W 1.10 1.20 1.30 1.40

Using the table to the left enter an appropriate adjustment factor for roof direction here:

 

Wind Effect

If you're right on the ocean you will have a higher heating requirement because the pool gets cooled so much by the wind. Solar collectors also have a wind cooling effect so look at where they are being located. Normally wind is not a factor we have to consider (enter 1) so just beware of unusually windy situations. Flat roofs protect the solar collectors from wind loss. Use 1 for no wind factor and 1.2 if you think the collectors will see cool wind during the early and late season when you really need the power. Enter 1.5 if you're right on the ocean worst case.The Enerpool program that we used to come up with all of our sizing quantifications and charts for your region was verified and wind effects studied but never in enough detail to be able to evaluate this effect in more extreme cases. If the collectors are wind protected, your solar heater will perform noticeably better if the air temperature is significantly colder than the pool temperature. Its mostly a big deal when there is direct ocean exposure

The design of this type of fin tube style collector affords some natural wind protection as depicted in these examples. There are other reasons to use different profiles but for best performance next to the ocean we swear by the fin tube design. On tile roofs where Powerstrip follows the wave of the tile, we also benefit from the fact the collector surface is hidden from the wind cooling effect.

Factor for wind:

Diffuse Radiation

If the solar collector space is down in a canyon or surrounded by lush forest you aren't getting as much reflected or "diffuse" solar radiation on the pool or the collectors. The diffuse component of solar radiation can be 30% of the total. If you have to squint on sunny days then this factor is just 1 but if its dark you should factor up by as much as 1.3 to make up for it.

Factor for diffuse radiation: 

Shade

Shade on the pool is a huge factor. For every square foot of shade on the pool you need 75% of that area in solar collector area to make up for it. If the pool is half shaded for half the day then it is 25% shaded. The factor to input here is 75% of 25% which is 19% so use a factor of 1.19. Only consider shade in the middle 6 hours of the solar day.

Shade factor:

POOL SHADING CORRECTION FACTORS
10% shaded 20% shaded 30% shaded 40% shaded 50% shaded 70% shaded 85% shaded 100% shaded
one out of six
hours per day
1.01 1.03 1.04 1.05 1.06 1.09 1.11 1.13
two out of six
hours per day
1.02 1.06 1.08 1.10 1.12 1.18 1.22 1.26
three out of six
hours per day
1.04 1.08 1.11 1.15 1.19 1.26 1.32 1.38
four out of six
hours per day
1.04 1.12 1.16 1.20 1.24 1.36 1.44 1.52
five out of six
hours per day
1.06 1.13 1.19 1.25 1.31 1.44 1.53 1.63
six out of six
hours per day
1.08 1.15 1.23 1.30 1.38 1.53 1.64 1.75

Calculate: Pressing "Calculate" will multiply all the above factors together and multiply by the top surface area of the pool. This is your desired total solar collector surface area.

sq. ft.

Now that you know how many sq ft of solar collector you want ideally, measure your roof space. You may have to scale down your expectations or consider a different space.

SOLAR COLLECTOR SITING

The next step is to consider the space for the collectors. In other words what will fit and where. We've broken this up based on the type of roof or mounting location. You might have to go back and forth between siting and sizing to come up with a final choice. Often we can help with sizing and siting if you fill in this form.

Buyer's Guide for Shingle Roof Installations

Buyer's Guide for Tile Roof Installations

Buyer's Guide for Flat Roof Installations

Buyer's Guide for Ground or Rack Mount Installations

Tar and gravel roofs are covered under flat roofs even though they are pitched. Shallow pitch roofs qualify as flat roofs as well. Wood shake roofs are like shingle roofs but you can't use the glue down techniques. You have to make roof penetrations but we have good ways to flash the roof connections.

If your roof type isn't listed or you want us to do it for you just give us this information

Always feel free to just call us. 858 683 0800 in San Diego or 778 300 1803 in Vancouver BC. E-mail h2otsun@gmail.com

If you increase the sizing because you have the space and the budget, what happens? Is there any point? As the plot below demonstrates, absolutely! 8 collectors is the "right" sizing for this partricular example 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 to 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.

Go thru the buying guides listed above or call us and we'll walk you through it.

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