Insulation not working!!!

[Garden Manager]

Can anyone give me some idea of the effect temperature wise that bubble wrap insulation has?

I ask this because at present it seems to be making  little difference at all! I was getting very small temperature differences at night before fitting the insulation (sometiems no difference at all) and now with insulation fited I am STILL recording only minor differences between inside and outside temperatures. I did wonder if my electronic max/min, in/out thermometer was on the blink but it seems not. Something is wrong with the greenhouse it seems.

Please help

[jennym]

I may be wrong here, but I think that using bubblewrap will only reduce the rate at which temperature drops, not the end temperature.
So, if you had 2 glasshouses, one with bubblewrap and one without, and measured the temperature in each every couple of hours, you'd find that the one with bubble wrap cooled down more slowly, but probably by the end of the time period, all the heat would have been lost from both anyway. The thickness of the bubblewrap would affect this too, as would the specific heat capacity of any materials within the building.

[Delilah]

Double or triple layer the bubble wrap

[MikeB]

 I placed a min/max thermometer in the bubblewraped GH and one outside, the difference in the min temp at the end of 24 hours was the the GH stayed 3 degrees warmer i.e. outside temp -1 deg C, inside temp +2 deg C.
I was using small bubblewrap, large bubble wrap will give better insulation.

[Garden Manager]

I am not sur what is not working - the insulation or the thermometer. It only shows 0.5c diference  between inside and outside, so if the temperature falls to even -1c outside it will still fall below zero inside.  Doesnt sem to have done any harm to the plants inside, though with the cannas i am not too sure as I have never overwintered them before.

I am using small bubble wrap and as yet have not used my heater in conjunction with the insulation (i  was hoping not to have to use the heater so much with the insulation!).

Quite frankly i am at a bit of a loss as to what make of it all.

[Mrs Ava]

I think you will find Richard, Jenny has explained it perfectly.  The greenhouse will still freeze, even with bubble wrap, when the temperatures are low enough for long enough.  Even with my bubble wrapping and fleece and polystyrene chunks, I use a thermostically controlled electric heater on a frost free setting.  Nothing is wrong with your greenhouse, just look at them, gaps galore, thin glass, metal frames.  Is it any wonder they get so cold!  All I can suggest is either getting a heater or start using fleece as I think with the very cold winter that is forecast, we are all going to be desperately trying to keep our greenhouses warm!

[myrtle]

I've got my tubular heating thermostat set to 30 by day and 15 by night and I 'm lucky if it gets to 10 day or night in this frosty weather, I've had to resort to a fan heater (alright today though).  I'm going to add yet another tube and another layer of bubbles and see if that works.

[Derekthefox]

Emma and jennym have explained it perfectly. You will also find you have various 'leaks', where draughts can get in, and these will rapidly pull out any retained heat.

Derekthefox

[Garden Manager]

I understand now. Insulation only slows the heat loss, it doesnt prevent it. With the temperatures i have recorded since installing it i dread to think what the internal tmperature would have got down to !

Thanks for the help.

[MagpieDi]

No wish to worry you Richard      but the thermometer registered  -5C  the other night, in my unheated greenhouse !  I move my Cannas into the heated conservatory, as have lost them in previous years, even wrapped well with fleece!

[Garden Manager]

What really annoys me is that if i could have an electricaly powered, thermostaticaly controled heater in the GH then i wouldnt have to worry. I did plan to have one in the GH, and have got one (I now use it in the conservatory) but in the end couldnt get electricity to the GH so am having to rely on insulation and a little parafin heater.

Not ideal but there we go

[MagpieDi]

I tried using a paraffin heater one winter, but found it so frustrating and tiresome to keep an eye on, but that's just me in winter hibernation mode!! 
Do hope it works for you this winter Richard.

[Garden Manager]

I tried the parafin heater first time with the insulation last night. It was a cold night and made about 7 degrees difference, which i was pleased about. thatsaid i will only put it on when there is a cold night forecast, otherwise i will be running out to get more parrafin every  five minutes!

[john_miller]

Can anyone give me some idea of the effect temperature wise that bubble wrap insulation has?

I ask this because at present it seems to be making  little difference at all! I was getting very small temperature differences at night before fitting the insulation (sometiems no difference at all) and now with insulation fited I am STILL recording only minor differences between inside and outside temperatures. I did wonder if my electronic max/min, in/out thermometer was on the blink but it seems not. Something is wrong with the greenhouse it seems.

An issue you may be confronting is the phenomenon that was unexpectedly found by early users of poly tunnels (showing my age here as I was around to be told of it!). On any night soil will radiate it's accumulated heat from the day in the form of long wave radiation (radiational cooling). When there is cloud cover overnight, or simply moisture held in the atomsphere, this radiation will be reflected back to the ground as shortwave radiation. On a night where temperatures are approaching freezing this reflected radiation can make the difference between a frost or none. As these temperatures approach 0C however the presence or absence of wind can in turn make all the difference too. What can happen in a plastic greenhouse/tunnel with few places for wind to enter is that the greenhouse can end up colder than the outside air. This is due to plastic being relatively impervious to short wave radiation (but it does allow long wave radiation to escape) and there not being any exchange of air with the outside resulting in excess cooling of the atomsphere inside. Glass will allow the short wave radiation to pass through more or less unimpeded so, all other conditions being equal, glasshouses will remain warmer overnight than plastic ones.

[Derekthefox]

That is genuinely fascinating ...

[MikeB]

Monitored from 2pm yesterday until 2pm today

[Derekthefox]

There is no arguing with data like that ... they are the results I would have expected ...

Derekthefox

[Garden Manager]

There is some fascinating info coming out here. Thanks to all who have contributed.

Its strange i didnt seem to have any problems keeping the greenhouse warm last winter, and that was without insulation (but WITH a heater i might add). It does not bode well for this winter when one cold snap in November has caused worries.

[Mrs Ava]

Just out of curiousity Richard, what are you over wintering in your greenhouse this year??

[Garden Manager]

Just out of curiousity Richard, what are you over wintering in your greenhouse this year??

I usualy overwinter things like stock plants of pelargonium and half hardy fuschias, plus a nice but tender salvia i have. This year i also have cannas which i grew for the first time this year. I grew them in pots otherwise i would have tried leaving them in the ground with a protective mulch to save space in the greenhouse.

I think the cannas are the only thing in there which wont stand it geting too cold in the greenhouse, since the other things have survived lower temperatures in there before.

I am considering setting up one of my old mini greenhouses as an 'inner chamber' to keep at least one part of the greenhouse a little warmer than the rest, and put some of the more sensitive things (like the cannas) in there.