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Has anybody insulated the greehouse floor?


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#1 manders

 
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Posted 07 July 2011 - 13:16 PM

Seen lots of topics about bubblewrap etc but just wondering if anybody has insulated the floor? That must also be a fairly large heatsink in winter?

#2 petesredtraps

 
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Posted 11 July 2011 - 21:15 PM

Seen lots of topics about bubblewrap etc but just wondering if anybody has insulated the floor? That must also be a fairly large heatsink in winter?


Interesting point. If you wanted to do it, you would use insulation board.What you say has relevance,last winter even though I tried to heat the greenhouse,the cold was so severe,it's looking like 95% of my Cephalotus collection are dead.

#3 mobile

 
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Posted 11 July 2011 - 21:48 PM

...the cold was so severe,it's looking like 95% of my Cephalotus collection are dead.

I'm sorry to hear that.

#4 ada

 
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Posted 12 July 2011 - 06:09 AM

Sorry to hear the cold got to your plants as well Pete.Just takes longer to find out with cephs.
ada

#5 manders

 
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Posted 12 July 2011 - 21:28 PM

Interesting point. If you wanted to do it, you would use insulation board.What you say has relevance,last winter even though I tried to heat the greenhouse,the cold was so severe,it's looking like 95% of my Cephalotus collection are dead.


Sorry about your cephs...

I think once youve insulated the walls and roof the obvious place to lose heat is through the floor, just cant find any rules of thumb for how much you lose that way and a rigorous calculation would be mind-boggling.

I was thinking of 50mm polystyrene insulation with 'something' on top.

#6 mattynatureboy44

 
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Posted 12 July 2011 - 21:58 PM

I have recently thought of putting a couple of layers of old carpet down over the slabs, but don't really know how much it would help or if it would actually make any difference.

#7 petesredtraps

 
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Posted 13 July 2011 - 17:58 PM

Sorry about your cephs...

I think once youve insulated the walls and roof the obvious place to lose heat is through the floor, just cant find any rules of thumb for how much you lose that way and a rigorous calculation would be mind-boggling.

I was thinking of 50mm polystyrene insulation with 'something' on top.


Polystyrene of course,something on top-I would go with 1/4" Ply ,and I'd treat both sides with water seal first. "Old carpets" no,no, they would harbour damp,pests,and stink and rot.

#8 Peter Hewitt

 
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Posted 13 July 2011 - 18:06 PM

Polystyrene of course,something on top-I would go with 1/4" Ply ,and I'd treat both sides with water seal first. "Old carpets" no,no, they would harbour damp,pests,and stink and rot.

I must second that, carpets are the ideal breeding ground for spider mites and the like. A nice thick layer of sawdust would insulate well and could then be swept out in summer, or a layer of pine needles.

#9 manders

 
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Posted 28 September 2011 - 07:36 AM

In the end i went for eva interlocking tiles on top of the polystyrene, waterproof and easy to clean, although bit of a sterile feel for a greenhouse, more like play area lol, but now ive got used to it i kind of like it.

#10 pulsar

 
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Posted 29 September 2011 - 21:36 PM

you shouldnt really need to insulate the floor.heat rises anyway.also depends what you have as floor as concrete and soil will tend to absorb any heat that it gets during the daytime to slowly release it when the air temperature drops

rob

#11 Alexis

 
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Posted 29 September 2011 - 23:37 PM

Yes, stone creates an 'urban heat island' effect.

#12 manders

 
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Posted 30 September 2011 - 13:43 PM

A better option might be to insulate the floor and store the heat in tubs of water, stone has a low heat capacity so you would need a tonne of it (literally) to do any good (1 tonne stone heated to 10 degress above surroundings can only store <2.8kWhr of heat) and it would probably increase the heat loss through the floor (low heat capacity / high thermal conductivity).

Water on the other hand is 5 times more effective at storing heat.

If all your trying to do is prevent a light frost then heat island/storage isn't a bad idea, but if your permanently heating a greenhouse to 10 or 15C, well above average winter ambient, throughout the winter, a heat island/storage probably isn't going to reduce your total heating bill at all surely?

#13 mobile

 
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Posted 30 September 2011 - 14:39 PM

I'll be very interested to see the results from this. Keeping temperatures above 5'C in a greenhouse get prohibitively expensive, especially here in the Scotland.

#14 will9

 
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Posted 01 October 2011 - 07:30 AM

A better option might be to insulate the floor and store the heat in tubs of water, stone has a low heat capacity so you would need a tonne of it (literally) to do any good (1 tonne stone heated to 10 degress above surroundings can only store <2.8kWhr of heat) and it would probably increase the heat loss through the floor (low heat capacity / high thermal conductivity).

Water on the other hand is 5 times more effective at storing heat.

If all your trying to do is prevent a light frost then heat island/storage isn't a bad idea, but if your permanently heating a greenhouse to 10 or 15C, well above average winter ambient, throughout the winter, a heat island/storage probably isn't going to reduce your total heating bill at all surely?


10 a 15° ?? You are a very rich guy i supoose,i think you must first think very hard how you go do this ,the choice of the heater can spare you match money.But this go cost you allways a lot of money.
You can heat a greenhousse on that degrees if it s not freezing match,but if temp drop to - 10 then you have allways trouble ,if go lower then you may be happy if you can hold the greenhousse frostfree.
I wish you very match luck whit this ,i think you go needed,
Cheers Will

#15 manders

 
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Posted 01 October 2011 - 10:03 AM

Hi will9, unfortunately not rich at all which is why paying attention to insulation is of interest to me just now. Most of my plants are normally kept in a conservatory which i heat to 10 or 15C minimum, its very well insulated (twin wall brick, double glazed and thick polycarbonate roof) and partially heated by gas central heating so it's relatively cheap to do.

If a had to build a new greenhouse it would be wood framed, brick walled with thick polycarbonate glazing, but im stuck with a rubbish aluminium framed one. Been talking to my orchid growing friends recently about how best to insulate an aluminium greenhouse, i think it can be done well enough to keep heating bills quite low but really have to pay attention to the details.

Average winter temperature here is around 3 or 4C, so on average, we are only talking about a 6deg rise in temperature, ok the heater needs to be big enough to cope with -10C but its the average that determines the cost over the whole winter.

Heat loss from the bottom half of the greenhouse can be cut to allmost zero as no light comes in their anyway and many people i know have insulated with building insulation to about 4ft off the ground, i'm trying polystyrene myself, but whats really missing are some actual measured heat losses so we can compare methods and get a good solution, i guess people just cant be bothered.

One example is some people have used insulation designed to reflect radiative heat transfer, (the silvery stuff you stick behind radiators) but im not convinced that will do anything, some measured comparisons of different methods would go a long way.

#16 will9

 
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Posted 01 October 2011 - 23:18 PM

Hi Manders,it s never freezing where you live ?Why insulate then so heavenly?I think heating 6 or 7 ° higher is not a problem.Your greenhousse go not cool down very quick ,i wish we have that kind of temps.
I have allways thinking it s freezing where you live,here it s freezing sometimes till -20 ,then it s become a problem.
You must not insulate your floor,insulate only the sides ,50 cm deep in the ground whit isomo plates ,the floor take no heat away.
Whit the temps you have in winter i supoose it s a greenhousse only for very tropic plants that need 10 a 15° ?
Cheers Will

Edited by will9, 01 October 2011 - 23:18 PM.


#17 manders

 
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Posted 02 October 2011 - 03:59 AM

it does freeze here will, but average heating bills you need to estimate on average conditions, it could be -10 for a day and +6 for several days afterwards, but winter average here is a very predictable 2-4 DegC.

i mostly grow highland neps at the moment and a few other things and 10c is a good minimum, i would prefer warmer but as you say it then gets expensive.

#18 manders

 
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Posted 02 October 2011 - 04:00 AM

why do ypu think there is no heat loss through the floor?

#19 will9

 
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Posted 02 October 2011 - 06:21 AM

you shouldnt really need to insulate the floor.heat rises anyway.also depends what you have as floor as concrete and soil will tend to absorb any heat that it gets during the daytime to slowly release it when the air temperature drops

I am agree whit this,you must only see the floor lost not heat ,so insulate only the sides is better then insulate the whole floor els you go create an oven in summer and greenhousse cool not down.the best is make some river ,like you say water hold warmt even longer and it s very good for humidity,i believe there are a few growers that post things like this on the forum in the past.
Highland neps can stand lower temps for short periodes if you make the plants hardy,it s amazing how match tropical plants you can hold on lower temps then books say,but then plants not growing and go in rest,
cheers Will

Edited by will9, 02 October 2011 - 06:26 AM.


#20 manders

 
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Posted 03 October 2011 - 07:16 AM

I agree that you dont lose a lot of heat through the floor, compared to an uninsulated window, but you do lose some, typical building estimates are 2W/m2/K. Although heat rises, in winter i have a heater fan circulating air so there wont really be much temp variation between floor and roof and in any case its the temp at the plant level i need to control.

Yes some highland neps can take 0.5 C, but many others struggle below 10C and look rubbish the rest of the year.

I agree an insulated floor would not absorb much heat in summer and the greenhouse temp could increase faster, I'll have to think about that one. There was some popularity in the uk for the last few years of digging out a heatsink under the greenhouse floor and circulating air through it to absorb the heat in day and release it at night. At the moment i prefer the idea of having tubs of water under the staging and perhaps pumping the hot air through that instead, it would also humidify quite well.

Ok maybe time to go and do some more maths and see how much water would be needed to be of any real use, what would be really usefull is a mathematical model of a greenhouse! :crazy_pilot: