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Posts: 3
Reply with quote  #1 

Hi All,

Excited about my first post and picking everyone's brains.

We have a house with passive solar air heater built-in. The unit faces South East and is upstate New York. There is a thermistor and a control box that will take air from the first floor floor, then exhaust it in the first floor ceiling. We can control the temperature. In its current state it only blows cold air in Winter, effectively. See below why.

What I don't have pictures of is the interior, so let me explain the setup beyond what might be obvious on the outside:

The interior is built as a box in the attic using duct tape (now falling apart) and insulating foam panels with reflective material - maybe 3/4".  The cool air inlet is on the bottom and the warm vents out the side near the top of the unit.

I plan to re-seal the interior box with aluminum tape and add some of my own sensors. I will probably leave the existing air system for now, but my eventual plan is to track the current "efficiency" before I fix it, then see how it works with iterative upgrades. If everything is looking good I would probably replace the existing control box with my own system using arduino or similar.

However, from the pictures you can see where my questions begin. The exterior face are the vacuum tubes. A couple cracked from bird strikes and I sealed them with tape (for now). Behind that is a clear membrane and behind that is what appears to be attic insulation, but dark in gray color, hanging in curtains as the solar adsorption material. 

I am looking to replace this material with the same material as it has deteriorated, or replace it with something else. 

So, hive mind, I am looking for any comments and suggestions you might have in replacing the material.

While I understand that aluminum cans are an option, I am also looking for something that's very efficient and has some science behind it. I've looked for similar materials, but don't seem to see anything other than home-made experiments. Also, I'm a little concerned about VOCs offgassing from paint, etc.

Thanks in advance!
main pic.jpg  closeup.jpg 


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Posts: 2,461
Reply with quote  #2 
Welcome Solarn00b!

It's really hard to tell exactly what the material is you are trying to replace. Any chance you could gain access for a closer look? But from what I can guess, it looks like a light gray fiberglas mat. Or is it light in color because of years of dust? Also, does the air actually pass through this absorber material, or next to it? 

There are many materials that can be used as an absorber. Most are inexpensive and easy to come by. The fact is that there are very few commercial solar air heater designs, and most of them use a simple metal plate that the air passes behind. Some have thousands of tiny holes in a dark plate for the air to pass though, but this is more of an HVAC pre heat design for commercial buildings. While they work, there are more effective designs. The most efficient designs built today are DIY. The commercial application of solar air heat lags far behind solar PV. But DIY solar heat is also very easy, fun to build, and cost effective. The ROI(Return on Investment) can be as little as a single heating season. Air heater designs such as can, downspout, and the various configurations using window screen or mesh are in most cases, more effective than a commercial unit. These designs are not hard to build, although the can heater usually takes the most build time. But you already have a solar heater in place and are simply looking to change or replace the absorber.

Since the 80's when your collector was built there are now low or non VOC paints available. So when you open up your collector box to change the absorber you can safely retouch the interior paint if needed. I would imagine any 30+ year old heater might need a bit of TLC. And the thought of 30 year old duct tape...

Again, if you can get us a better look at the old absorber material, and how the air passes either through the absorber material or next to it, we should be able to steer you towards a proper replacement. 

Greg in Minneapolis 


Posts: 3
Reply with quote  #3 
Thanks, Greg! Very useful.

I will be back up there at the end of September and be pulling it apart to CAD the whole thing up. I'll report back with the material.

I did read through this and a lot of it makes sense: http://www.iedu.com/Solar/Panels/

While it might not be the most efficient, I think I might do aluminum screen while I'm there, maybe a couple layers of it, because it's relatively cost effective and easy...and I need a baseline for information, anyway.

I'm also working on my sensors,  which are based off of particle.io stuff. Here's what I think I will add:

  • In/Out temp sensor (at both ends of each so I see a temp rise/drop)
  • A few more temp sensors sprinkled throughout the array
  • An ambient light sensor (maybe an array so I can get a sense of light intensity over the entire unit)

I'm also going to add a basic weather kit with anemometer, etc, just to see if I can correlate weather to temp, etc.



Posts: 3
Reply with quote  #4 
Just a quick update for anyone that cares:

Seems like I have to do something else, like replace a toilet, before getting to fix this thing up.

In the meantime, I ran it manually in its current condition on Oct 12/13. I mention the date so I can get a sense of where the Sun is in the sky.

Both days were decent sun, although patchy clouds. Also, at this time of year I only have about a 45 arc of sky.

From about 10-2 PM I get about 90 deg air coming out of the system, with about 70 deg going in. This remains pretty consistent throughout the time frame. Interesting.

Also, here are some pictures of the controller. Anyone ever seen this?


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