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Simulating Solar Heating System Performance by Computer
Download the Enerpool software from the NRC Canada web site. It's free for all to abuse but I'll tell you how to get meaningful results and how we created the charts on the pages that led you here . Click toget the software.
Once you've extracted all the zip files you'll see you have several .tmy files - one for every major city we have typical weather data for. The program needs to assume a weather pattern because this is solar energy we're talking about. The weather data is a carefully constructed hour by hour typical weather profile based on 10 years of measured data from the local weather station (usually the airport so note the airport weather can be quite different).
Once you set up the program you'll find two executable files: nrppro.exe is Enerpool Pro. The other one is Enerpool. Enerpool Pro is useful, Enerpool is not. Enerpool was a weak attempt to mimic the simulation provided by RSPEC called Energy Smart Pools. Both these useless programs are completely focussed on the energy numbers and the payback period. We know the payback period is attractive (less than 3 years in most cases) but what will the system do for my pool? That is the question that we've painstakingly answered using data from the program. Besides we're actively plotting all the relevant results under every major city we have weather data for. I'm telling you how to run this program so you can use it to verify that my graphs on this web site are fair and not fudged at all and so the engineers amongst you can have this capability yourself. You can't trust data like this at face value from anyone. In all my years working with other solar companies on these simulations I've never met anyone in the solar business that didn't think it was OK to fudge the numbers to make the results look as good as possible. That negated the need to make the simulations better. Why worry about accuracy if you're going to fudge the numbers anyway? I think additional efforts should go into this work. When I was given beta versions of this program to test over the years I'd come up with entire new projects that were needed to improve the capability. My suggestions wouldn't be heard too well because putting it out for industry review meant the work was done. That's what "in collaboration" with industry means.
I'll show you how to use the program. Hang on. This ain't user friendly and it's all metric.
Start by making a new file.
Under the system menu you have to fill in the fields under every single selection. You have to go back and forth to the system menu because the programmer never figured out how to make one field come up after the other. Most of that work involved butchering the original program, Watsun, reducing its capability in an effort to make it windows compatible. I pointed this one thing and many others out to NRC officials dozens of times over a decade and nothing ever happened. Now that I've gone ahead and published results the way I have in this web site I'm hopeful they will take notice and finally understand what I was talking about and see where the effort and resources need to go.
Fire up the Enerpool (not Enerpoool Pro) software and off the opening menu choices pick out the pool blanket database and write down all the variables for all the different blanket types. Close this program and never open it again. Get back into Enerpool Pro and enter the data for an aged pool blanket under the blanket data field. We figure every pool blanket is an aged blanket after a week or two. These specs are measured from a normal used pool blanket and there is a significant difference between a new solar cover and an aged one as you'll be able to see if you do comparative runs.
Here's a detailed printout of every piece of data we input into our standard profiles that we used to produce the graphs you've seen so far. It's a PDF file of the actual simulation we did for the base San Diego 16x32 pool with a cover and 25% shade. View the simulation in PDF format.
A few notes. Its all in metric. Sorry about that. Canada is on the metric system and so are all engineers, even American ones, because nobody understands what mass is in US units. Have you ever heard any border guard say he discovered a "slug" of drugs in someone's suitcase? We've all heard the term kilogram though haven't we? A pound is not mass, it is weight. There is a difference. If the neighborhood is windy and the roof exposed to that wind in the direction of that wind then use 0.54 for the wind speed correction factor for the roof. That's what Bruce tells us matches up with real life systems that were monitored and I know the system I provided saw a lot of direct wind. You could see for miles from that rooftop. Similarly, if the pool is exposed use 0.28 there instead of the 0.14 we've used assuming the pool is somewhat wind protected.
You get an output in .hly and .mly values. They are all averages so the monthly numbers are crap. Open the .hly files in a spreadsheet and get them into a column. Then filter out every piece of data except the data for 4PM each day. Now you can plot 365 pieces of data like we did and it actually tells you something. This is the peak daily pool temp. The average doesn't mean anything. Who cares how cold the pool gets in the middle of the night. The average pool temp duting the hours of use of the pool would be a good number but I'm not crafty enough with a spreadsheet to pull that off. What we did was cut and paste the curve into our template of a graph we made in photoshop and adjust it so it matched the temperature scale. We had to convert Celcius to Farenheit. Multiply by 9/5 and add 32. The type of presentation we're showing gives real meaning to the numbers and brings out the value of the data. See, guys? This is what I have been telling you the program needed to do. Not everyone is an engineer and even I am studying each of the curves I produce now in amazement and awe. Mostly amazement that the things I've been saying to people for years are consistent with what I'm seeing. Actually I'm now able to be less conservative in my predictions. It pays to work towards a real truth and it would not be difficult to get the program to output meaningful curves as seen on my web site.
You're welcome. Note: We're not in the business of doing computer simulations. Do not ask us to help you work through a simulation. Contact the people that you downloaded the software from. That'll encourage them to invest more effort into it, not that they need to now that we've finished the job off by publishing what we have but it would be good if the program delivered more pertinent information.
Back to Sizing Go here definitely if you didn't come from it in the first place. You gotta see the graphs.