Insulation Test

[manders]

Having just re-insulated the greenhouse and done a heat test on it and being rather dissapointed with the result, I wondered if anybody fancied taking part in a little experiment?

Its really rather simple to do, you just have to put the greenhouse heater on at night on a relatively still day when its not raining for a an hour or so. (You have to stop any autovents opening). So what you do is put the heater on a low setting say 1kW, wait for the temeparture to stop rising and then take the temperature inside the greenhouse and outside. From that you can work out how much heat the greenhouse loses and how well insulated it is.

So for mine ambient temp was ~16.7C with the heater on 1Kw the temp in the greenhouse stopped climbing at ~28C. I just have a moderate sized 8ft * 10ft so knowing the surface area you can calcuate the average heat transfer coefficient.

For comparison:

glass is ~6 W/m2/C

6mm Polycarbonate is 3.6 W/m2/C

lower is better.

Mine turned out to be 2.7 W/m2/C which is higher than I hoped because its now theoretically triple glazed, anyway I think i'm losing a lot of heat through exposed aluminium framework but thats by the by.

So is anybody up for doing a comparison? It might be interesting to see how Bubble wrapped greenhouses perform for example. Maybe we can figure out whats practically the best way to insulate a small greenhouse?

All you have to do is measure the inside and outside temperatures with the heater switched fully on low setting but no thermostat. Just divide the heater power (say 1Kw) by the temp difference and the surface area of the greenhouse (including floor area).

So e.g. in my case 1000W / 11C / 33.3 m2 = 2.7 W/m2/Deg C

If your not sure of the suface area of the greenhouse i can set up a simple spreadhseet for you to download or you could send me the dimensions and i'll work it out.

At the end hopefully we could compile a list showing the values (anonymously if you prefer), it should at least be interesting and maybe we can learn how to insulate our greenhouses a bit better... (and save some money)

Anyone fancy trying?

[Alexis]

The best insulator is air, so bubble wrap would be the way to go. Good quality wrap will make a difference as it's designed not to allow the air in the pockets escape over time.

[will9]

It s also very important how high the greenhousse is,a greenhousse from only 3 m high lost match more heat then a greenhousse from 5 m high .Thats the reasson why big growers like in the Netherlands have suchs high greenhousses.

A greenhousse insulate is very difficult ,for good insulation you must tape it al,it s allmost impossible to do how match insulation you used,your plants need fresh air also,you can not closed all .the only you can do is the heatcosts a bit down and hope we got not a bad winter again.

The best greenhouses are make from a woden frame and polycarbonaat plates,this you must never insulate ,if i must make another greenhousse its for sure some like that,ideal for little greenhousses,cost meaby more then aluminium and glass but you must match lesser heat and spare yourself match money,

Cheers Will

Edited September 27, 2011 by will9

[manders]

The best insulator is air, so bubble wrap would be the way to go. Good quality wrap will make a difference as it's designed not to allow the air in the pockets escape over time.

Bubblewrap may well be the way to go and at least its cheap but why not test it and find out for sure? There could be a number of reasons why it's no as effective as you might think.

[manders]

It s also very important how high the greenhousse is,a greenhousse from only 3 m high lost match more heat then a greenhousse from 5 m high .Thats the reasson why big growers like in the Netherlands have suchs high greenhousses.

A greenhousse insulate is very difficult ,for good insulation you must tape it al,it s allmost impossible to do how match insulation you used,your plants need fresh air also,you can not closed all .the only you can do is the heatcosts a bit down and hope we got not a bad winter again.

The best greenhouses are make from a woden frame and polycarbonaat plates,this you must never insulate ,if i must make another greenhousse its for sure some like that,ideal for little greenhousses,cost meaby more then aluminium and glass but you must match lesser heat and spare yourself match money,

Cheers Will

Think you mean lower greenhouses lose less heat surely?

Agreed wooden frame and nice thick polycarbonate would be excellent, anybody got one that they want to test?

[will9]

Think you mean lower greenhouses lose less heat surely?

Yes how higher how better,it s better in summer to ,not so hot ,never have burning plants,but this you can do only whit big greenhousse ,5 m high is not evident for a litttle greenhousse,it s go not work anyway because to small ,but like i say ,you can better make it that you not must insulated,spare money on heat and insulation,and a lot of work every autum and spring.

If i was 20 years younger i sell my greenhousse and set a new one ,i have allways trouble when winter came ,insulated and hope it s not freezing to hard for more then 20 years now ,i have try everything but it stay a greenhousse ,very difficult .

Buble plastic cheap?Not here ,i believe 125 Euro for a rol 25m x2 m ,+ the pins for add this, i can not call this cheap,after a few years it s not good anymore ,

Cheers Will

[manders]

Think you mean lower greenhouses lose less heat surely?

Yes how higher how better,it s better in summer to ,not so hot ,never have burning plants,but this you can do only whit big greenhousse ,5 m high is not evident for a litttle greenhousse,it s go not work anyway because to small ,but like i say ,you can better make it that you not must insulated,spare money on heat and insulation,and a lot of work every autum and spring.

If i was 20 years younger i sell my greenhousse and set a new one ,i have allways trouble when winter came ,insulated and hope it s not freezing to hard for more then 20 years now ,i have try everything but it stay a greenhousse ,very difficult .

Buble plastic cheap?Not here ,i believe 125 Euro for a rol 25m x2 m ,+ the pins for add this, i can not call this cheap,after a few years it s not good anymore ,

Cheers Will

Yeah I agree its not cheap at all if you have to replace it every few years, the other thing i dont like about it is it just doesnt look nice. The other problem is unless you buy the 10mm thick stuff or use more than one layer its probably not doing a great deal.

I just think it would be really interesting to see what actual values for heat transfer people would come with from their greenhouses by measuring it.

[Gareth Davies]

Finally got round to doing this for my Nep greenhouse- wondering how practical it might be to raise the daytime temperature a bit for happier highlanders-

Got a value of 2.5. How bad is this? What might it be possible to achieve?

This is a 10 x 12 greenhouse, glass and aluminium, with bubblewrap throughout.

More and more, I'm thinking the only practical way to grow Neps well is with a custom-built wood-and-polycarbonate greenhouse... now if only I could find a few spare weeks....

[manders]

Hi Gareth,

Thats in interesting, we got a simlar result (yours is a bit better), i lined my glass greenhouse with 6mm polycarbonate which gave a similar result as (10mm?) bulbblewrap. I should go and test mine again as i've since also partially used another layer of bubblewrap n the inside and i still havent test the conservatory yet, been too lazy...

35mm polycarbonate should give a value of 1.5, so about 40% less fuel consumption, so far this year it would have only saved me about 20£... and its not cheap to buy.

On the other hand its far easier for me to convince the mrs to buy more insulation than to spend money on heating the greenhouse, lol...

I've i ever get bored of the parrots im thinking their nice wooden framed aviary with some added polycarbonate would make a great nep house...

[Gareth Davies]

Surely the parrots come from a hotter climate and therefore they require a polycarbonate enclosure and more heating to be happy?

I was thinking about the 35mm polycarbonate myself for the future... either that or double glazing the structure with 16mm polycarbonate and a 25mm gap between the panes.

I don't see any other way of growing my lowlanders to a decent size without bankrupting myself.

Is there any way of calculating the theoretical value?

One thing I did this week was add a 2nd layer of bubble wrap to the greenhouse entrance, so now after I've opened the doors, I have to wrestle my way through a bubblewrap curtain to get in, and that has made a surprising amount of difference... it's covered up all the gaps around the door where the major leaks have been.

I've been hoping to turn the heat up a little on the highlanders in the days now, trying to get better results from them than I did last year, when the days were just too cool to get good growth.

[manders]

Unfortunately we chose to keep parrots that live in a cold climate, breeding at -10C was no problem at all for them, anyhow they would strip a nep to its roots in minutes. My ovata is still recovering from a canary attack a few years ago.

In theory its quite easy to calculate the U-value, U total = 1 /(1/u1 + 1/u2 etc ) bit more complicated for the air gap and if the air gap gets too big it actually doesnt help much. I have a spreadsheet somewhere which i can send.

I had similar thought about raising the temperature during daytime and used to do it in my conservatory, it really helps more intermediate ones get through the winter ( like lowland truncatas), didnt do it this year though. Like you im wondering how to insulate the greenhouse much better first.