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 Post subject: Insulation U values
PostPosted: Wed Apr 26, 2017 11:16 am 
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Hi All,

Long time no see !

Just helping someone set up a small area within their greenhouse for orchids so going to build a small insulated area for them.

The question is what materials to use, a single sheet of 10mm twinwall polycarbonate on a wooden frame or using 1" bubble wrap on both sides of the frame so it has at least a 1" air gap.

While we can find a U value for the polycarbonate, have not been able to find anything on a double layer of bubble wrap with an air gap.

Any info / thoughts on which would be best or any better method ?

thanks


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 Post subject: Re: Insulation U values
PostPosted: Wed Apr 26, 2017 4:21 pm 
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The problem with wide air gaps is the U value goes in the wrong direction as you increase the air gap. This is because you get air movement inside the gap which transfers the heat. Far better to have multiiwall polycarbonate. If you want really good insulation I would go for 25mm multi wall polycarbonate.



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 Post subject: Re: Insulation U values
PostPosted: Wed Apr 26, 2017 6:07 pm 
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SilverShaded wrote:
The problem with wide air gaps is the U value goes in the wrong direction as you increase the air gap. This is because you get air movement inside the gap which transfers the heat. Far better to have multiiwall polycarbonate. If you want really good insulation I would go for 25mm multi wall polycarbonate.


Thanks, interesting, would not have thought the air gap would have transfered heat like that.

Have used polycarb myself, but the biggest problem seems to be sealing the ends properly, otherwise they are prone to condensation, well if used as the main greenhouse glazing.


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 Post subject: Re: Insulation U values
PostPosted: Wed Apr 26, 2017 6:42 pm 
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ricky wrote:
SilverShaded wrote:
The problem with wide air gaps is the U value goes in the wrong direction as you increase the air gap. This is because you get air movement inside the gap which transfers the heat. Far better to have multiiwall polycarbonate. If you want really good insulation I would go for 25mm multi wall polycarbonate.


Thanks, interesting, would not have thought the air gap would have transfered heat like that.

Have used polycarb myself, but the biggest problem seems to be sealing the ends properly, otherwise they are prone to condensation, well if used as the main greenhouse glazing.


Yeah, its because it starts to circulate around when the gap is over a certain width.


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 Post subject: Re: Insulation U values
PostPosted: Fri Apr 28, 2017 6:32 pm 
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I have used polycarbonate with no problems in the past.
The only problem is the initial cost!
David


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