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Simulating Solar Heating System Performance by Computer
To get a recommended sizing and quote for your particular case you can go directly to an on-line form from here or back to the sizing page and learn how to do it yourself....almost.
We've compiled verifiable predictions of what a properly sized solar pool heater will do for your pool based on typical weather for your region. This monumental task has been the result of 15 years of hard work on the part of many people in Canadian government, universities, independant consultants and industry experts like myself. I finally got around to publishing some of this capability. I had to learn how to extract numerical data from the computer simulations and plot it onto a graph that would make sense to a pool owner. I enthusiastically invite further contributions and suggestions from any scientists, engineers, government people and even competitors. We all need to work together to let the public know the truth. Credibility sells and credibility comes from a concerted and honest effort to get at the truth.
I've spent my entire career with nothing much to show for it other than expertise in solar pool heating. In the 1980's and most of the '90's I was the president of one of only 3 manufacturers of this type of technology in Canada. The market for solar in Canada is weak so I had a lot of time to exercise my engineering degree and investigate new applications for the technologies and better ways to bring it all into the mainstream. The Canadian government was very co-operative. In 1989 I met Doug McClenahan, the director of the Active Solar Energy division for NRC Canada (equivalent of the US Dept of Energy). Doug was about to do free testing on all the unglazed solar collectors sold in Canada at the time in Canada's indoor solar simulation laboratory, then Ortech International at Queens University in Waterloo Ontario. We got our collector, the Powermat, included in that testing and a long attempt at collaboration with government began. I learned that the needs and wants of a small solar company trying to exist in the free market are quite different that the needs of politicians and the government officials assigned the task of spending large sums of taxpayer's money to stimulate an industry, however, this story was very positive. Leading up to this time, a group of engineering masters students at Waterloo University had created a DOS based program that would simulate the energy balance on a swimming pool and what a solar heater would do for it in direct comparison to a gas heater. This computer program called "Watsun" needed the results of Doug's performance testing. At the time I barely knew how to use a computer but I jumped on board eager to learn how to give people a reasonable prediction of what a solar heater would do for their pool. 14 years later I'm reasonably certain we've arrived at that goal.
The Canadian testing capability, now operated by Bodycote Materials testing Canada Inc., in Mississauga Ontario uses an indoor solar simulator and the testing includes the effect of wind. The collectors are actually moved through the room to simulate air movement. The only other accredited solar testing agency in North America is the Florida Solar Energy Center. That test facility is outdoors and has no way to include the effect of wind. The Canadians are way ahead of the Americans in solar pool heater testing. Here are recent test results showing the Powermat collector's performance curves and the effect of wind.
On the y-axis we have efficiency. That means the fraction of the solar radiation exposed to the collector that ends up as heat energy delivered to the water leaving the collector.
On the x axis we have the difference between air temp and pool temp divided by the solar intensity on the collectors. Note that pool temp is the temp of the water entering the collector. It is the collector temperature. Depending on flow rate the average collector temp is actually a little higher but that is taken into account in these tests and the computer simulation that uses them.
The Canadian tests show our Powermat collector if anything is more efficient than most. Below are the efficiency curves at low wind speed (1 m/s) for three of the collector brands that were sold in Canada in 1990. Powermat is the one marked AO370. This is my defense against a poor FSEC rating given Powermat back in 1980 when the FSEC didn't even try to limit the wind effect. There is no question about this flaw in the FSEC tests.
At the time SG358 (now extinct) had the highest FSEC rating. As you can see solar collector performance isn't a number like 1000 BTU/sq ft/day. It is a curve that depends on several factors. In fact there are no technical differences between any of these collectors that would cause one to be more efficient than another except en363. That one is a rubber tubing product with a significant gap between flow tubes. That gap heats up and you can feel the inefficiency. If it's black and cold it gains solar as efficiently as possible. That's all there is to the physics of this technology. The challenges are in the longevity, and compatibility with the pool system and the roof they attach to. These are the things consumers need to pay attention to, not the FSEC performance rating.
Enormous effort has gone into that original software then called Watsun and now called Enerpool Pro available freely to the public at the NRC web site but it aint simple. It helps to be an engineer. For those of you who insist I do provide a full guide on what to input and why here so you can make use of this powerful software if you're so inclined.
In 1997 the Canadian government made a further effort to help the solar swimming pool industry in Canada by putting high level monitoring on three pools in Canada with solar heaters and comparing the results to what the Enerpool simulations told us. We participated in this study, providing one of the solar heated pools. We provided help hooking up monitoring equipment and with co-ordination. Bruce Sibbitt MASc PEng ,partner in Caneta Research of Mississauga Ontario was contracted to carry out the monitoring and analyze the results and co-ordinate changes to the Enerpool Pro software to reflect what was learned and make the software more accurate. Bruce did a great job.
The above photos show the Powermat system undergoing this high level monitoring. You can see an anemometer measuring wind speed at pool level. There was also one on the roof. There's a pulse width modulating flow meter and a main computer hooked up to a modem making a call every night. There are expensive pyranometers on the roof measuring solar radiation horizontally and on the roof plane. Temperature sensors and much more, even a flow meter and temperature sensor on the hose that refilled the pool. Data was collected for a whole season and used to validate the computer simulations. This was at least a $30,000 endeavor and it was repeated with two other systems in different parts of Canada. This was the best money the Canadian taxpayers ever invested in Solar Energy. Cudos to NRC CanMet Alternative Energy Division for spearheading it and Bruce Sibbitt for doing the work.
Bruce Sibbitt through his work was able to tell us the values we should input into the Enerpool program for things like the emissitivity of the pool cover, the wind speed correction factor for the roof and the pool etc. As a result of Bruce's good work and the efforts of NRC, the Enerpool software that we've used to create the predictions found on the links in this section is thought to be quite accurate for outdoor residential pools. We've verified many simulations with real systems and every indication is a close correlation with reality. Now that we're publishing it in a form that the general pool owning public can understand easily we expose this to thousands of pools and we invite our existing customer base to compare what they are finding on their own solar heaters to what our predictions are telling us here. So far as I write this in 2007 the correlation has been amazingly close.
Back to Sizing Go here definitely if you didn't come from it in the first place. You gotta see the graphs.