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SolarInterested

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Spam Stomper
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Reply with quote  #21 
Be Careful About Insulation (link)
"The common polystyrene insulation board (this is the "pink", "blue" and "white" stuff) will not hold up to much above 130F, and the batch enclosure temperatures will exceed this, and melt the insulation.
An example: http://www.builditsolar.com/Experimental/pinkfoam.htm
Polyisocyanurate insulation board works well, and comes with an alum reflective surface already installed."

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Both temperature rise and airflow are integral to comparing hot air collectors

TJTurner

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Reply with quote  #22 
Excellent, thank you guys. I figured there was a reason you weren't using it! I did find out that I have a Menards within a reasonable driving distance. They have it in stock...so I'll try that. The HD and Lowes have nothing...

Tj
gbwillson

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Reply with quote  #23 
Menards often has both the polyiso and the twin wall glazing on sale.
TJTurner

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Reply with quote  #24 
Gary...

Since you mentioned the twinwall, I've poked around and found your posts on the glazing comparison. Good stuff. But for the ZP, do you think you need the twinwall? If the airflow is not leaving the screen gap, could it be better to use a higher transmittance material, like the acrylic you used in your transmittance tests? I haven't compared costs, just thinking out loud.

Tj
gbwillson

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Reply with quote  #25 
Tj-

If you are looking for GaryBIS, he hasn't been here for a year so. If you meant me, I think the choice to use twin wall glazing has a few things to consider:

If you live in a cold northern climate, I think it's probably better to use twin wall. Yes, the ZP does a good job of limiting the air movement outside of the screen gap, but there is still the fact that the glazing is cold. So depending on the distance the screen layers are from the glazing, an insulated glazing probably does some good. The frigid glazing will draw heat from the screens due to the close proximity. Twinwall has an R-value of 1.6, whereas a single layer has about half that. And higher insulation value helps keep the heat inside. 

At least here in Minneapolis, the cost for a sheet of 6mm twin wall polycarbonate glazing can be purchased for as little as $30 for a 4x8 sheet when on sale. Whereas a 4x8 sheet of ⅛" clear polycarbonate is 2-3 times as much and never goes on sale.

6mm twin wall allows 82% of the desired light through to the inside of a collector. A single layer of polycarb allows about 92%. So you do gain 10% more light. But this may be more than offset depending on where you live.

And lastly, twinwall is semi opaque, so the view is mostly obscure from view. This can be good if you don't want someone to see the innards of your collector, especially if the quality of workmanship is less than stellar. It's always neighborly to have a nice looking collector.

I suggest you price out and check availability in your area as these factors may help make up your mind for you. 

Greg in MN
TJTurner

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Reply with quote  #26 
Sorry Greg...

You're right, I totally mixed up you and Gary. It's the "G"! Sorry about that.

Good points. I wonder where that break even is in terms of performance (not price). I'm in Ohio, so I'm not so far north as you. And we're pretty moderate in terms of temperature, but the R value is a great point. I'll likely have to depend on price anyway. I really don't care what my neighbors think. They can see some of my property, but we have no real rules out in the country where I live--kind of an advantage, huh!

Thanks! I appreciate the insight. I'm getting closer to building. In fact, my son and I may venture in on some smaller test collectors for a science experiment. Got to get him hooked, too!

Tj
gbwillson

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Reply with quote  #27 
Tj-

I sure wish I lived away from the city where you are not stifled by regulations and laws. My heater is close to the street. It's close enough that I had to clean the glazing last week from all of the salty road spray. It's also on a corner and the first house you see as you enter the neighborhood. So I kinda feel an obligation to have a nice looking house and yard.

Great idea getting your son involved. Kids learn about alternative energy in school, but having first hand experience using it will likely make for a lifetime of interest. Does your son's bedroom have a south window? Might be a great place for an experimental solar heater. 

Greg in MN
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