Thoughts on greenhouse.

[Beek]

I've just got an aluminium 6*8' greenhouse on Freecycle and I can't wait to get it back together and glazed again.

Does anyone have any advice/strong opinions/experience of the best way to construct a base that has;
1) a high thermal mass
2) drainage
3) no nooks and cranies where slugs/snails can hide
4) Re. 3) can be pressure jetted or flamed.

First thoughts. Have a shallow (30cm) water store with a perforated floor suspended above it. Keep the temperature stable in the summer. Add old radiater painted black as a solar convection heater. Heat store doubles as rainwater collecting sump. Overflow to soakaway sorts drainage.

Any comments woud be very welcome.

[MKG]

I admire your thinking, Beek, but don't you think it might all be a bit OTT? The temperature in a 6 x 8 greenhouse fluctuates wildly and QUICKLY as the sun comes out or disappears behind a cloud - the effect of the sun through glass is bloody quick, whereas the effect of your heat store/sink would be slow. The usual answer is to leave the door open for a while or watch your plants shrivel before your eyes (or fit shading). Both of those things might reduce the efficiency of your heat store. I fear (don't actually know - just my thoughts) that your pool of water will do more to raise the internal humidity than anything else - something which is not always desirable.

I don't want to sound negative, because I may be speaking from my nether regions.

[Annpan]

If you can use a covered water container that would be better I guess
Water is supposed to be a fantastic thermal store... I have seen radiators being used as shelves in a greenhouse - I think they were plumbed in and heated but I was thinking of painting a few black and using them that way... somehow

I am watching this thread closely as I am looking for ideas myself...

I was planing on heavy black stone for the flooring - but then my proposed greenhouse is pretty big (35x12ft... from freecycle) and it would not all be floored, just paths.

[red]

re 3 - if you slug pick every night.. you do get on top of the slug/snail situation in a controlled area like a greenhouse. I have some beautiful unblemished lettuces in mine at the mo - wouldn't stand a chance outside!

[Beek]

Hi MKG
The point of the thermal store in the greenhouse was to help stabilise the temperaturate fluctuations in such a small greenhouse. My thinking was to make it thermally "soggy", to soak up heat from the warm air when it was too hot, and to release heat too the air when it was too cold. My first plan involved 885 liters storing 3705kJ of heat/ degree Celsius. I take your point about humidity though. It might produce a tropical jungle effect which I don't want. That, plus the fact that we can't afford a butyl liner at the moment, has forced a rethink.
The main purpose of the greenhouse will be to extend the growing season so the purpose of the latest, much smaller, heat-store, will be to keep the temperature inside at a minimum of 10 oC for as long as possible and frost free all year. The store is now a 200litre HDPE barrel which I got for free. 200l gives a store of 838kJ/oC. It wont take heat from the air when it is too hot. I'll open the door as you suggest I have a black painted radiater which will eventually sit outside, in an insulated box, facing south, as a passive solar collecter. I was hoping to double glaze the box, but, you know how it is, you've never got a bit of double glazing the right size So it will be single glazed. The barrel will be higher than the radiater and have a heat exchanger inside. The radiater will have a water/antifreeze mix and I'm relying on thermosiphoning to warm the store inside the greenhouse. I intend to box in the barrel with insulation to enable the temperature inside to climb without warming the greenhouse air during the day/warm periods, and havig air vents which can be opened at night/cold periods.

[Beek]

Hi Annpan,

35 * 12 feet is a decent sized greenhouse. This is me green with envy. Is this the greenhouse that formed the subject of a different thread? Isn't Freecycle a wonderfull concept!

You say "Water is supposed to be a fantastic thermal store... " You betcha!
It has a specific heat of (roughly) 4.19 ie. it holds 4.19kJ of heat for every kilogram/litre per degree Celsius. Compare that with Dry earth(0.3), Brick(0.22), Basalt rock (0.2), Concrete (0.18) and you can see just how effecient it is. Plus, of course you can move it to move the heat to where you want it.

I like the idea of radiaters as shelving in a greenhouse, plumbed to give a trickle of heat to plants. My greenhouse is too small One workbench already takes up a quarter of the floor area, but I amm going to need a propagating bench.... and I have an old radiater in the garage... hmmm.

[pskipper]

The victorians used to have boxes on the outside of the greenhouse with vents leading in and rotted their manure in the boxes to keep the temperature up over the winter, eco-friendly and you have well rotted manure to dig in!

[Annpan]

Hi Annpan,

35 * 12 feet is a decent sized greenhouse. This is me green with envy. Is this the greenhouse that formed the subject of a different thread? Isn't Freecycle a wonderfull concept!

Certainly is - it is still a heap of wood and glass, and 10 miles away but we should be getting it here at the weekend

We don't know how big we will be able to make it here (it is in 4 sections) it sort of fell apart when we were dismantling it... but we reckon we can still get a 12x12 ft greenhouse out of it... We'll just need to wait and see how it can get patched up and put back together.

Great news on the water as a thermal store - wow, it really is great.
I also like the idea of the rotting manure to heat it, I also have a plan to attach a chicken house to it/ it it to keep it above freezing in winter - I want a lemon tree, so I am trying to work out how to do it without any electricity.


By the way if anyone wants to help us put the thing up, PM me