Colder inside !!!

I just moved my radio thermometer base into the greenhouse three nights ago, and was surprised that on night one the minimum inside was only 0.5C above the minimum outside. On night two it read exactly the same inside and out at -2.8C. But last night it was -2.8C outside and half a degree colder at -3.3C INSIDE.

My greenhouse is really an 8' x 10' wooden summerhouse, but with a complete southfacing front that is all glass. It has been fully insulated with bubble wrap. Overall it should be a bit warmer than the average greenhouse.

Although my background is in physics, I am still perplexed. When I insulated it I was expecting it to be two or three degrees warmer than outside. But on reflection I was kidding myself. Insulation slows down the rate of heat loss. But eventually, without any form of heating, the inside will reach the same temperature as outside.

That is not to say that insulation in an unheated greenhouse is of no value. It is not just a low temperature that can kill plants - but it also depends on how long it has been at that temperature. If you spent 10 minutes in a butcher's deep freeze, you would come out unharmed, but if you spent 48 hours there you would dead. Insulation reduces the period of low temperature, even if sometimes it does not alter the ultimate low.

My conclusion is that next year I must have some form of frostguard heating.

 

Nowt wrong with the logic there!
This is a pic of my brand new g/house, with an electric fan, you can just about see in the back left corner - a parasene one, frost guard. It's great - strongly recommend it

 

That's a nice size Nixon. But no snow - its snowing hard here now. The time when you most want heat is the time when its too cold to do anything about it. :D

 

the grond was hard frozen at the time of the pic yesterday - the camera decided to go on strike after I'd taken that one - just whirred and beeped a bit, and refused to work until I took it back indoors, poor thing!(we've had snow this morning, by the way, but it's all gone again)

 

Looks super Nixon. Is that a solid concrete floor?

 

Yes - it took a lot of doing! This g/house is 8ftx12 ft with double doors - fantastic! It's really nice in there when it's cold outside! I've even got kettle and teabags!

 

The concrete floor should act a bit like a storage heater and help keep the temp up a bit at night.

 

I think you are right Peter, insulation only works if given additional heat.
After all, if it keeps the warmth in at night, its going to keep the warmth out during the day, you cant win. :D

 

Spider plants would look nice in there (when it warms up).

 

yes, wouldn't they! Ta!
Glad you all approve of my new greenhouse - my husband did a sterling job! (And built a 10x8 one for m-in-law too!

 

Insulation holds up the flow of heat in both directions.
It does depend on which mode it`s using though,ie: conduction,convection or radiation.

All that wood is good compared to metal..notice that not many heatsinks are made of wood

 

Presume the radiation can get through bubble polythene then, so if the sun's out its OK, but if its cloudy then not so good.

 

Ideally you'd have plain glass on a sunny winter day & 6in + of insulation when the sun went below the yardarm. :(

[ 04. March 2006, 12:57 AM: Message edited by: Tortuosa ]

 

A lovely greenhouse and do use bubble wrap I have been using it for years. I left a "window" in my concrete floor for a early peach and grape some plants like their feet outside. Quite a bit of snow here and cold at night the coldest winter for many years. I noticed the buds on one red camellia have almost all rotted.

 

Hi, all, I'm very envious of that greenhouse, nixonf23. Mine is only 6x8.
I have finally discovered what happened to my heating, temp. went down to -7 sporadically with heater set to frost free. It's the wind! If there's a wind from west, draughts are lowering the temperature at one end. My heater is not a fan heater so I think this makes it worse. There are places where I can see gaps up in the eaves.
I left all the floor as earth, I hadn't thought about heat loss from the floor. I didn't put any bubble wrap up either as it was too much of a fiddle trying to get behind all the plants. I was wandering if it would work taping it round the outside next year, it would be so much easier!