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stmbtwle

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Reply with quote  #31 
"Maybe in a perfect world you could have a temperature controlled vfd fan where you could set the outlet temp at a temperature of your choosing then when the collector reached the setpoint, it would start the fan on its lowest possible speed. If after a certain period of time went by and the collector outlet temp was still above setpoint, it would incrementally increase fan speed til collector output cooled down to setpoint and continue doing this as the sunny day progressed thru it's peak. Then as collector outlet temp began to fall, it would slowly lower fan speed to maintain a set outlet temp. Once the fan reached minimum speed and collector outlet temp stayed a few degrees below outlet temp for a set period of time, the fan would shut off. Maybe such a controller already exists."

Right here: https://simplysolar.supporttopics.com/post/show_single_post?pid=1303238615&postcount=25&forum=268066

That's the prototype, and yes it works but I haven't built a collector to put it in. Latest iteration has a knob control and a display showing set temp, actual temp, and fan speed.

So far no-one has shown any interest, so further development has slowed to a crawl.


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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay

gbwillson

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Reply with quote  #32 
Willie-

I've been watching and waiting for further development. I'll admit it's a bit over my head, but that doesn't mean I could figure it out once someone else has figured it out. So please continue and I'll be watching with great interest.


Greg in MN
TJTurner

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Reply with quote  #33 
So way back in my original post, I was really looking for rules of thumb to start with. I really wanted to ensure I was matching the fan size with my collector size and type. I think I have that now. But the last few posts have brought up some good points. I think a good controller could be made to help "optimize" the collector within some limits. I do a bunch of things in the real world, among them programming and some controls for the experiments I conduct. I'm fairly certain I could get a rudimentary response curve for a collector and use machine learning to find a functional form, which I could then set up with a script and a computer to run...maybe controlling fan speed on the fly with the input, output, and collector temps. We'll see...the first step is building the collector! And in fact, I think I'm going to build some small collectors first to do as a project with my boy and to test a few construction techniques...then build the big one in the fall!
gbwillson

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Reply with quote  #34 
Willie-

Any reason you couldn't post it out in YouTube? If you need to post a video, simply record a brief clip explaining what you are attempting to do and what you have so far, and paste your 100+ lines info in the READ ME section. Then people can comment as needed. 

Greg in MN


JC77

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Reply with quote  #35 
Willie,
If it were mine, I'd make it so it compared inlet temp to outlet temp kind of like a differential controller does so the fan ran as long as there was heat available. I'd make the fan speed increase or decrease to keep the outlet temp at say ten degrees above inlet temp or at least make the inlet/outlet temp difference a controlling parameter if the user wanted that mode instead of trying to maintain a set outlet temp.  It would need some time buffers to prevent cycling or have it so the fan ran back to minimum for a few minutes before shutting down to reduce stops and starts on a partially cloudy day. I'm not sure a ten degree temp rise would be the best, I just threw that out there. I could see where setting the outlet temp to stay a certain temperature above inlet temp could cause trouble. Later in the day, as the room heated up and inlet temp rose, the fan would adjust accordingly allowing outlet temp to rise and sacrifice collector efficiency. This would not be a problem at my house but it could be if the collector was large and the space it was heating was small. That's why i mentioned two modes of control. If the fan were connected to a lengthy duct system, minimum speed might not be enough to move air so maybe minimum speed would need to be an adjustable parameter as well. Lots of variables! I wonder if a similar setup would be effective on a solar water heating pump?  
stmbtwle

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Reply with quote  #36 
Greg, see the speed control thread... Yes I'll look at YouTube. Thanks. TJ, from what I've done so far it looks like only one sensor should be required to get a pretty constant output temperature, and the control is really pretty simple. Input temperature IMO is only required if you're trying to determine heat gain. Good for research but not necessary for control.
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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
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