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matlocc

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Posts: 66
Reply with quote  #1 
I started with the kids by having them creating models of how the energy got from the sun to the panel and then heating the air.  It went very well and I think I have them hooked.
I do have two 2 x 4 collectors on my porch and have been playing around with them to get a feel for this better.  My first question is, where do you locate the snap switch? I had mine in just below the output vent and it kept cycling on and off.  This happened every minute or so. The switches are on at 120 and off at 80.  It was -6 degres but I was getting 128 out of them. Is there a place or way to mount them where they won't cool as fast, or do I insulate the backside to make it work.
Also What is the trick to attaching the insulated duct work?  I realize the my set up is temporary and I ran the stuff through some 2 inch foam board using just a piece of straight pipe punched through, then into my window.

Thanks in advance.
Chuck

gbwillson

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Reply with quote  #2 
Chuck-

I bet you are glad to finally have something to show for all of your hard work. 

I'd suggest you move the snap switch out of the stream of air as well as out of direct sun. An upper corner out of the main flow is ideal, as the movement of air is much slower. Having the switch directly in the airstream will tend to cause faster cycling. A simple bent piece of metal can be used to shade the switch. 

There are a lot of different duct connectors, of take-offs that can be used to attach the duct to the collector box. It depends on personal preference and the thickness of the material used. I assume you are using 4" ducts? Not nearly as many styles as 6"-8" fittings which are more popular. You may have to use an adapter if you can't find what you need in the 4" size. The fitting I prefer is this one, which has an adhesive foam seal on the back and can be screwed if desired.
https://www.menards.com/main/heating-cooling/ductwork/ductwork-fittings/flowtite-plain-duct-fitting/p-1444432238020-c-14260.htm?tid=-5290109853989658377&ipos=41

Greg in MN
matlocc

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Posts: 66
Reply with quote  #3 
Thanks, Greg.  I am using 4 inch. The duct question was attaching the flexible duct to the outlet. I didn't have any support and the wight of it kept pulling it loose. (used duct tape and cable ties)
As far as the snap switch why do I want it shaded? Don't you want it to get hot?
gbwillson

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Reply with quote  #4 
Use worm clamps to hold the flex ducts to the fittings. As far as the snap switch location, I'm not sure you need one since you will be closely monitoring the conditions at all times. It's not like you are going to leave them unattended for more than a few minutes. So if the sun is out and visible, it makes for a good day for an outdoor class. That being said, you do want them hot, but like a thermometer, you likely will get a false reading. This way, you are reading the temp inside of the box and not the temp of a black piece of metal which can cool off quickly should the sun go behind a cloud. Hopefully, this should minimize short cycles. 

This might also be a great intro for the students as to a few of the issues and limitations with alternative energy, but why we need to continue to explore and improve alternate forms of energy.

Greg in MN
Gordy

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Posts: 137
Reply with quote  #5 
Chuck,

Just wondering why you chose the, on at 120 and off at 80 snap switch's? Mine are on at 90 off at 85. With my PV panels the fans would kick in too early the switch fix's that, With passing clouds or end of day the PV generally lose power just before the switch cuts out. My switch is mounted to the top of the door frame above the outlet and shaded from the sun.

The cycling could be the switch position, but it could also be too much air flow from the fan. Have you tried restricting the intake of the fan to reduce the CFM through the collector?

When you say "or do I insulate the backside to make it work." Are you referring to the switch or the collector?

There are some pictures and info of my 36" x80" door collector at this link.


http://simplysolar.supporttopics.com/post/solar-heaters-in-frigid-temps-9608609?pid=1302771738

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Gordy,
Minnesota
matlocc

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Posts: 66
Reply with quote  #6 
I have the 120 80 snap switches because a company donated them.  I am going to introduce electrical circuits to the kids at a later date.
I meant to cover (insulate) the backside of the switch so it didn't cool as fast.
I will have the kids play with switch positions later. Today we are taking the empty boxes out to get a baseline of temperatures, no fans just convection.  Then the kids can begin to try ideas for materials, baffles, etc... inside.  Then we will introduce fans and start figuring all the math! (they love math!!)  By worm clamp is that a big hose clamp? What are flame ducts?
gbwillson

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Reply with quote  #7 
FLEX ducts! Damn autocorrect! And yes, worm clamps are the same as hose clamps. 

Greg in MN
matlocc

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Posts: 66
Reply with quote  #8 
I  had them out today getting base data. There is a better write up on my facebook page but I don't know how to link it. 20180109_113727.jpg  20180109_113742.jpg  20180109_113747.jpg  20180109_113918.jpg  20180109_113925.jpg
stmbtwle

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Reply with quote  #9 
Great pictures!

You could try copying the address at the top of your facebook page, and posting it here. That usually works. Example:

https://www.facebook.com/Aretha-Project-307885346030194/?ref=ts&fref=ts&__nodl

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

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Posts: 66
Reply with quote  #10 
The link would only go to just facebook but here is the write up:

I FINALLY have my solar hot air heaters up and running for my applied science class. We spent a day making models on paper describing how heat is able to be changed from the suns rays and then somehow changing from light to heat, then warm the air inside them. Quite a few misconceptions were revealed during the process, but we are still learning. I have to thank http://www.maverickhousewares.com/ for donating the wireless thermometers to our project. The students were able to set up boxes and get some baseline data on temperature changes in them today. Most were surprised by the temperature change in an empty box with two vents, but now we move on to experimenting with baffles and airflow vs temperature rise and efficiency. The temp change today was 75 degrees between the bottom and top. Most were 48/50 air going in and in the high 138 to 147 going out! JUST THE SUN! http://senasys.com/ also donated snap switch thermostats for the project so that the airflow can be controlled by computer fans without monitoring. I can't wait to see how all of this plays out, but today was fun and the kids are interested. Thank you, everyone for your support.
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