Solar hot air panels update - moving to diary

[Dave B]

 I'll be moving this project to my diaries for future updates and testing. Here shows the absorbers as well as the baffles and vent holes. The location of the holes was pretty much determined by the interior walls and then the baffles are located by guess as to what seems like could help with efficiency.

 These panels were originally going to be convective only with no fans but as they advanced and especially the vent locations helped determined the active design.

 There are so many variables discussed with solar panel design that I am sure any one change could possibly be better or worse than another. I look forward to tweaking these to get some good heat from them, it's half the fun to the building process.

  Thanks to all for the comments and look for future updates in my diaries so I don't appear to hog the front page of "solar".  Dave B.    

[sk windpirate]

Hi Dave

I'm not sure if you are installing then vertical or horizontal?

I made one for my small craft shop. Most of one wall. About a 6' x 6' collector.

My cold air goes in on the bottom left, Warm air out the top right. i use a small computer fan and solar to move the air. Its all flat black inside. my partitions are black sewer pipe filled with sand, this seems to retain the heat better. we can get -40 weather (winter)so it needs to be insulated very well. It works real good in temps from about zerro deg F. and up. "when the sun shines of course"

It can produce enough heat to keep it around 60 to 80 degree on a good day.  

 

[Dave B]

Hi Ron,

  Thank you for your reply. These will be mounted vertical so the cold in is lower right and hot air out will be upper right as looking at the panel from outside when mounted. They are both the same which makes things a bit easier and the vent locations are dependent on the location of "stuff" on the inside wall. Maybe not ideal but with the baffles and fan I am sure I will get heat from these.

  You mention a small computer fan and solar to move the air. Are you using any type of thermostat or just that the solar will power the fan and at the same time the air will be warm enough not to circulate cool or cold ? At present my vents are 4" diameter. I assume you are then using a DC fan direct no batteries ? What size fan, voltage and solar panel as well ? Thank you for your help.  Dave B.

[sk windpirate]

Hi Dave

Just a low voltage fan, direct to the solar power. I had two old walkway lights that worked on 2 AA bats. "3 volts each" total 6 v. They turn the fan quite well when the sun shines. On a cloudy day the fan sits ideal. No thermostat. If it gets to hot i close the bottom vent some to regulate the amount of air going in. I may get a bit fancy this year (summer). and put a controll of some kind.

I found the longer and slower the air moves in the collector the warmer you can get. The more pasive material in the collector the longer it will give heat in the evening.

 

[MattM]

What are you going to use to block back flow of the cold air once the sun goes down?

If you are going to force air into the frame then take advantage of thermodynamics to prevent back flow; suck cold air from the floor of your room then channel said flow of cold air through the same hole through the wall as the outflow.  When you force cold up the wall and back down the backside of the frame to its inflow hole you create a natural trap for the cold air when the fan is not running.  The advantage is you can regulate the hole affair with a thermo-sensor to run at whatever desired temperature you want and when it shuts off the fan you have minimal back draft.  If you are not going to force air into the frame then you might consider a simple louver opposite the bottom hole on the inside of your room.  If you don't prevent back draft in the lower hole you will bleed warm air into your panels and lose heat at night.

The slats look like L-brackets of sheet metal.  Simple.  Reproducible.  And most important of all, they work.  Keep in mind if they had been U-brackets or Z-girts then it would add support for the glass.  I assume you are still going to paint the interior matte black, too?

It's a nice clean design.  Looks great so far.

[Dave B]

Ron,

  Thanks for the information. I figure it will take some adjusting of air flow and temp etc. and I look forward to it. I'll probably set up a variable speed on the fan and a thermostat to get things dialed in to start. Not much sun around here lately but we sure have had wind, snow and cold temps. Maybe I can get the mounting brackets installed tomorrow but it is going to be very cold. Dave B.  

[Dave B]

Matt,

  I haven't figured the back draft arrangement yet but I'll post what I end up with. Yes, the whole inside will be black, not sue yet of the paint or coating I'll use either. No need for added support of the dual pane glass that's why the simple pop riveted sheet metal baffles. Thanks for the reply,  Dave B.

[ghurd]

I thought about a dryer vent.  They open wide so the fan flow would not be restricted, if air flow was not expected to hold it open.

Maybe a small gear head motor and a rod or cable with a couple limit switches to hold it open or closed (without using power).  Home brew linear actuator idea.

G-

[Dave B]

Thanks Ghurd,

  I've been thinking about the back draft too. A simple deal like a dryer vent would be great (I like simple) but I think maybe it would have to be a bit more sensitive with a smaller fan like this and then it might be tough to get a decent seal.

 I'm still not sure if I'm going to blow air into the bottom or suck it from the top either, I suppose there are advantages to both. Anyone with thoughts on this and what have you done about the back draft arrangement ?

 I am getting anxious to get these finished and installed. I have to shovel about 2' of snow first just to get back there. I might do that today cause I see it's warming up, it's 17 F now.  Dave B.  

[sk windpirate]

Hi Dave

Keep us posted on your results.

What are you using for Glass?

I'm using 1/4" - 6mm plate. (I tried Lexin, "that sucked")

I'm going to try one with thermopane this year to find the better one.

Our bay window faces the winter sun. It is only thermopane (2 sealed panes "no" Agron gas). I paced a 6x6x1/4" 150x150x6mm plate of steel painted

flate black in the sunny window. I attached a thermo senser to the plate. house temp was 25c 75f the black plate reached a temp of 121 F / 40+c. out side temp

-20c "0" f... still lots of room to improvements. Solar has lots of protential, if the clouds stay away.

Also see, build it solar.com

Garry has lot of of test results and experments that have proven good

 

[MattM]

The simple route for forced air is to run an air channel up the wall and back down to the inflow hole; this creates an air trap.  As cold air settles in the trap it stalls the air exchange.  If your fan isn't blowing you aren't moving a significant amount of air.  You want to google the properties of air and make sure you are not pushing air with too much restriction or you won't move air when the fan runs, too.  Your air could potentially expand about 30% within the heating process during the winter months, so try to keep the outgoing air the lesser restricted.