Solar hot air panels - update

[Dave B]

Well,

  I finally got my panels moved into the shop to work on. The staining is complete and Dave Moller and I just siliconed in the flat steel (22 guage I think he said) absorber plates. These are a single sheet each panel. These look painted already but is just the reflection and they are wiped clean with laquor thinner.

  Now it's time to measure the vent locations and cut those out as well as installing a few baffles before painting the flat black. Dave Moller is fabricating the mounting brackets and I will be measuring out the exact mounting locations on my South wall very soon. It will be interesting to experiment with the fan size and thermostat etc. after all is installed.

  I hope to get these completed and installed to make good use of them for the remainder of the Winter and into Spring, these will be good months to experiment. Thanks to everyone for your comments.  Dave B.  

[jclaudii]

Do you have a schematic of how you hope to plumb it?  This is interesting of what your doing.  Do you plan to to record the temp readings of the air blowing out at certain times?  Also, how much insulation is going to be on the back and sides?  

[Dave B]

There will just be a vent at the top and bottom and I am figuring the location and size of those now. Eventually I'll be logging the temperature out and will probably use a snap disk thermostat to cycle the fans. There is 1" of insulation sides and back and my glass is tempered dual pane. To make things easy and neat these will initially be mounted vertical flat against my Southern wall. Thanks for the reply,  Dave B.

[BobK54]

I made two panels like this years ago when I lived on Long Island.  After two months of use, the heating oil company called and wanted to know if I put in a wood stove!!!  They WORK.  My latest panels haven't made it to the roof yet.  Still in the basement.  Outer case material suggestion:  steel studding channel (the stuff you use on the top and bottom, not the studs themselves.  The studs have holes in them).  That material is roughly 2X4 shaped "C" channel, has no holes AND is already galvanized.  Easy to work with too.  My current panels have corrogated sheet steel as an absorber plate.  I have AMAZED people with the output!!  Selective paint is OK, but not sure it is worth the money.  I used barbeque paint.

[Dave B]

Hey BobK,

  Thank you for the input on your panels. I wondered what your glazing was (is) ? I also wondered if the select paint is worth it ? I have read several places that high temp paint or similar might gass and cause the glazing to fog over. $20.00 a can for the select paint is pretty steep but pulling the glazing (dual pane in my case) will be no treat either if I have to clean it soon because of possible gassing of the regular high temp paint.

  Were your panels convective only or did you have fans, what did you use ? Sorry about all the questions but it is interesting and exciting to hear that you had such good performance. I can't wait to get these completed and mounted. Just like my wind generator capturing energy out there, why not ?  Dave B.

[MattM]

If you can get enough tension on the metal to stretch it those frames will make great drums!  

At 1.75 lbs per foot^2 that thick of steel isn't light.  I feel sorry for the guy that has to carry it. It should work well to carry over some residual heat after the sun goes down. And it shouldn't blow away until the winds are hurricane strength.

[Dave B]

Matt,

  Maybe I got the guage number wrong, the steel sheet for the absorbers is thin stuff. The glass is a different story, dual pane and it's heavy. Dave B.

[mbeland]

Hi,

I have read a few posts about solar hot air panels and I have no doubt about their efficiency.

What I am wondering is how do people using these panels deal with temperature fluctuations in the house caused by a lot of heat during the day and little during the night.

I see two solutions:

1. - don't bother and just accept the extra heat during the day until a maximum is reached then stop the fan
   
2. - increase the heat mass of the house to tamper fluctuations.
   
   

If any other views, I would be interested

Martin

[Dave B]

Storing energy is the name of the game. I'll let the house get as hot as it can in the colder months with the help of solar. I own a Log Home, thermal mass is like a great big battery and it's amazing how long this holds the heat. I could always open a window but that sure would be a waste. Dave B.

[DougT]

Hi Dave

I enjoy your project and look forward to seeing your results but as a semi novice to this subject I have a qustion.

Is the use of Dual Pane glass a mistake? I have and old house with both dual and single pane windows and it seems that I get much more heat gain from the single pane. Isn't one of the reasons for dual pane to keep heat gain/loss at a minimum?

Good luck with your project

Doug

[Airstream]

Just a thought - there are problems reusing some 'newer' (dual pane) windows since they may have selective coatings that are opaque to the IR portion of sunshine, ie: low solar gain low-e glass.

The coatings on glass will be facing the airspace - for rejecting solar heat it is applied to the outside pane to help keep the building cool, for conserving interior heat and allowing sunlight to help heat the building it is placed on the inside pane.

Even if the coating is on the inside pane in your collector it may still stagger the collector output since the inner pane will be heating up from IR absorption without a lot of surface area to xfr the heat to the air being heated.

If it is more than an irritation a glass shop will probably have a small handheld test meter that can show if & where the coatings in window assemblies are positioned...

[Dave B]

True to a point but depending on the type of solar collector you may loose heat quickly back out through a single pane of glass before you can move it effectively. In my case I am using a flat plate absorber where the heat is being washed off between the absorber and glass so if this were a single pane I could loose more heat back through the glass than with dual pane. A single pane may be more effective with a design where the heat is being washed off the back side of the absorber and the glass is very close to the absorber thus not relying on the glass to hold the heat as much as in my case. It will be interesting for sure and like anything you can think it to death, the main thing is to DO IT. Thanks for the comment,  Dave B.

[BobK54]

Dave:  the air panels I made years ago were glazed with 1/8" plexiglass.  At that time it was quite affordable, not so sure now.  I didn't have any problem with outgassing of the paint.  I made sure the paint had finished "curing" by setting the panels in the sun for a few days with some 6 mil plastic sheeting as a cover.  If anything outgassed, it probably stuck to the throwaway plastic before I put the plexi on the panels.  Funny thing:  the panels I made were suggested by an article in Popular Science or Popular Mechanics in the late 70's!  I just googled the material and found someone has a patent on the application.  Figures.  Here is the link: http://www.freepatentsonline.com/4154220.html   The "absorber" was a material known as Foamglas.  Typically Foamglas is an insulator.  In this case you put grooves in it to increase surface area and then painted it black.  The "absorber" really never got very hot.  The air in the immediate vicinity of the painted Foamglas got VERY hot however!  I'll try to post a picture.  The only one I have now is one I have carried in my wallet for 30 years!  I'm looking for some better pix.  I'm hoping the ones I found welded together by water damage downstairs aren't the only ones I have......

[Dave B]

Thank you Bob for your information. I looked at the channel you talk about for the frames but couldn't figure out a good way to support this dual pane glass, it is very heavy. Also it seemed a bit awkward to set up a way to support the insualation and or absorber plate besides. I understand pretty much the limitations of wood as a frame with heat fluctuations etc. but for the cost these wooden frames are built like a you know what and now have a superior exterior finish on them besides. Hey, a wooden framed exterior window or sliding door lasts how long if maintained properly ? Again, it will be interesting and I am very much looking forward to getting these completed and installed. Update photos again soon, I installed the baffles and drilled the vent holes earlier today. Thanks again for your information.   Dave B.

[MattM]

If you have access to even an 8' to 10' siding brake then it shouldn't be too hard to make a light gauge sub-frame inside your panels.  The sub-frame could be sealed to the flat plate collector and as long as you leave an air gap between all the steel and wood.  Also leave some holes through the bottom of the frame.  This would allow for the wood frame to breathe.  The goal would be that any water that condensates inside the frame has an exit point.

[MattM]

True, dual pane glass is about 40% better on average as an insulator than a single pane.  (ot -Argon gas fill is not a huge difference as an insulator but it seems to keep the glass cleaner.)  You are better off with either dual or triple pane windows on your house in the winter and summer months above the 35th parallel.  I live in a fairly temperate zone of the 40th parallel and the solar heating is good for only about a quarter of the day during winter months, which means my thermal losses through the window are going to be a greater issue.  ymmv

[Dave B]

Yep,

  You can always do one more thing, it's easy to think a project to death with out even getting started. I make a plan and do it and I sure seem to get things done that way. Then learn from it and improve from it if you do it again. Thanks for the ideas, I like reading and seeing photos from others who have been there and done that. Time to get busy building, updates to follow.  Dave B.

[laskey]

I don't have a good south facing surface on my house, expect on the roof. so for testing purposes, I've built an insulated window port I can connect 6" insulted hoses from the panel on a support in the back yard to the house.  I'm heating my computer room in my basement.  The heat pretty much goes straight up through the floor into the master bed room.  I found both rooms get pretty warm, so what I did in the basement is install a thermostat, and boost blower on the inside wall of the house.  When it gets too hot in the computer room, the fan sucks air from the rest of the unfinished basement, and blows the hot air from the room across the basement floor. That cement has plenty of thermal mass.  Of course if the forced air furnace comes on because it's cold in the living room and kitchen then all that solar heat is rapidly re-distributed to the rest of the house.  When the panel is running the furnace won't run as often, or as long.  In the spring, the furnace hardly runs at all, and my panel is just as test, and has had some aging problems that need to be addressed in version 2.