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ra

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Posts: 2
Reply with quote  #1 


I figured why not start at the beginning. I took this man's idea, and changed it up a bit. Instead of using styrofoam, I used rubber roofing fiberboard. The board isn't known for any sort of great r value, but I had a piece of it already. I cut it to size for the target window, I cut my in and out holes, I wrapped it in tin foil, and I painted the out-faced side with grill paint. I haven't put it in the window yet. I'll do that in the morning. SO... some thoughts came to mind regarding safety. I have a good many fire extinguishers around the house, but I hope to never have to use any of them! If a paint with a high resistance to heat is needed, why is it ok to use things like styrofoam, wood, cardboard, etc when building these various solar heaters. I used clear packing tape on the backside to keep the tinfoil in place. Now I'm questioning the tape, the plexiglass window, the caulk used around the window, etc. I realize the output is going to be very minimal, but I want to start a downspout based project next. First thought I had when watching the various youtube vids on the downspout air heaters is: downspouts come in black. If we need high resistance paint, what about all the other materials? I see they make heat resistance tape and caulk. Should everything be dipped in heat resistance? How much heat does it take to melt plexiglass? Normal Caulk? Then I started wondering about rubber roofing. Certainly the sun heats a rubber roof up quite a bit, and the glue used to attach the rubber to the fiberboard is quite flammable. Perhaps I'll throw together a rubber based system, or, at the very least, incorporate it in there somehow. Basically, my question is--does heat resistant paint get hotter? Or are we concerned with safety?

solardan1959

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Reply with quote  #2 
Ra,
   Welcome and thanks for the post,  Not sure where to start on your post so I'll focus on the paint first and go downhill from there. 
Quote:
Basically, my question is--does heat resistant paint get hotter? Or are we concerned with safety?
  Not sure why you kept saying high temp paint but I only half focused on the video.  No heat resistant paint will not get hotter but may hold up better to the heat.  Any paint, even latex will work, black is best but depending on what you want it to look like any dark color will work.  High temp paint may be better but any dollar can of black, preferably flat black, spray paint will do.  Plexiglas will work but polycarbonate is better, an used piece of glass will work good also.  Don't know what the rubber roofing fiberboard is, the fiberboard sound okay, the rubber makes me nervous.  As you said it holds up to the heat on a roof but a closed collector can get hotter than a roof exposed to cooling air flow.  Cardboard should probably be avoided unless you experimenting and going to hang around and watch it when it's working.  Clear packing tape, probably another bad idea.  Aluminum duct tape is best.

Are you trying to seal in an existing window as there have been my discussion on the lack of benefits from that or are you building a stand alone collector?  I applaud you trying to use what you have but you may want to surf around some of the hot air collector section for some building tips.

Yes safety is always a concern and the materials used and you need to take many things in to consideration.  Will the materials hold up to heat and not melt or ignite, will they expose you to bad smelling fumes or dangerous gasses when they get hot,  will it hold up to the elements such as rain, wind, etc.

Some better materials may cost a little more but may cause you less problems later.

Good luck!, Dan
netttech

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Posts: 720
Reply with quote  #3 
Welcome RA! It's good to see you are using this forum to your advantage....Asking Questions! [smile]

I too am concerned about the rubber aspect, in regards to smell. Whether it produces a toxic gas...don't know, but it could really stink, when it gets hot.

Have you placed the panel in the sun on the ground for a 'burn-in'? A burn in is nothing more than placing the panel in the sun, to let it heat up, burn-off (so-to-speak) the paint smell etc.

Everything has a heat limit, polycarbonate (mentioned previously) foam (different types), etc., but I'm not aware of anybodies project that caught fire from the sun. All of my panels (3 hot air, 1 hot water) is made entirely of foam panels, with some wood strip supports. This is my 6th year in my solar heat hobby, no problems or concerns of fire.

The polyiso foam handles heat the best & it usually has a foil backing on it already. Polystyrene foam doesn't handle heat very well.

Duct tape will survive the winter better than packing tape, if you are sealing the glazing to the panel. Silicone caulk does a great job of sealing.

I've used plexiglass for 5 years (still going), with no problems, but there are different grades of plexiglass. The polycarbonate is the better choice, howevr you all have to live within money constraints.

I have passive panels using aluminum screen for the collector. In the video, the vents for hot & cold, isn't large enough. They are too small to allow a good airflow. In my opinion, they should be twice the width. Passive heaters work from natural 'airflow', don't restrict it by the vent size.

Keep asking question RA, someone here will have the answers & willing to share.

Jeff
Central IL

 
netttech

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Posts: 720
Reply with quote  #4 
You mentioned thinking about a making a downspout panel. They make good solar panels.

In regards to the video. If a person has double-hung windows, with (or without) a screen, you could make a quick easy 2 layer screen panel.

Build a wood frame (2-3"D) that can be mounted to the outer window frame. Attach 2 layers of black aluminum screen (width & height of window) to that frame so it hangs down if front of, but on the outside of the glass. Mount the frame to the outer window frame, then the glazing to that framework.

On sunny days, open the bottom & top of the window 2" & you have a passive solar hot air panel. It would work a lot better than what is in the video.

[smile]
Jeff
Central IL
ra

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Posts: 2
Reply with quote  #5 
Wow! I'll catch up with these later today. I put my board in the window. There is a slight amount of heat coming from the top hole. I didn't want to caulk the window up till I was certain of heat resistance safety concerns. I suppose it takes something like 450 degrees of heat to cause damage. Or is it 450ish to boil water? I forget hahaha. Thanks for the responses.

Note--I should probably use the east side, because it gets the most sun. I've seen a lot of the vids on various solar heat projects, and they often say use the south side. They are often made by people who live in rural areas. In the city, the house next to you can be a shadow hindrance. Common sense dictates to look for the sunniest spot though! And I do plan on using the south side in the future. The east has it's limits too.
solardan1959

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Reply with quote  #6 
Ra,
   Look at what an oven set to 400 degrees can do to a turkey.  We are not, hopefully, generating anywhere near those types of temps an yes serious damage can occur long before you get to anything like that.  I think most building codes do not want wood exposed to temps above 150 when it comes to venting through walls.  I have seen collectors up to 220 and at that point it starts damaging normal foam and  Plexiglas. 

East does has some serious limits like it won't work after about noon. "Rural" people not only point it south because they can but because that is the place that gets the most sun all day long.  If all you have is east then I guess that's all you can do if mounted to a wall but east for morning, west for late afternoon and evening sun, but as southernly as possible is the best approach.

Quote:
Common sense dictates to look for the sunniest spot though!
probably true, and better to have four hours of good eastern sun than 2 hours of southern sun.
Dan
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