Plastic bottles as a heat sink

[davee52uk]

I am going to use old plastic milk containers, filled with water, as a heat sink in my frames and greenhouse. The idea is that the water in the bottles is heated by the sun during the day and then radiates the heat out to warm the 'house or frame, at night.

Has anybody tried this?

[davee52uk]

[cambourne7]

very 'not easy being green' this is somehing i want to try myself next year :)

[caroline7758]

Would you use this method throught the winter as well? How many bottles do you think you'd need (per square metre, for example)?

[cambourne7]

From the not easy being green site

How does the greenhouse heat sink work?
Some details are in the book, but half the adventure is working out for yourself and thereby customising you solution. All you need is:
The heat sink is imploded glass - we used bottles from various parties and the local pub - imploded courtesy of Krysteline www.krysteline.net
Big hole - we lined it with polystyrene that came as packaging
Pipes were standard waste pipes for under sinks etc
Fan was a small 12V computer fan from a market £1.20 - in a box made of scrap wood
A 12V deep cycle leisure battery
Small 11w solar panel and charge controller
Old chimney cowl for the air to be pushed out the glass

Air sucked down from the apex heats the broken glass under the floor. Fan runs 24 hours a day. As the greenhouse cools the cooler air is still pumped through the glass, but when it comes out through the cowl, at floor level, the glass has warmed it so a constant supply of warm air is now being pumped through.

[carolinej]

I'd love to be that clever/organised but I think I will have to make do with the milk bottle version. Much better suited to my 'chuck it up quick' mentality ;D

cj :)

[davee52uk]

I was thinking of stacking up the bottles to cover the back walls of my small greenhouse and also in the cold frame.  These are plastic, not glass bottles. I will paint them a matt dark colour as this best for heat absorbtion/radiation. As no light will be able to get inot the bottles, this should stop algal growth. The idea is that they will keep the greenhouse and frames a extra bit warmer during teh cold months. In summer there should not be so much need but I may try it in a frame to try growing melons.

I have seen stuff about this in American books but have not seen this done in U.K.

Has anybody got any experience of this?

Questions

1. Does the liquid in bottles matter? Would it be better to use old engine oil or salty water?

2. Is it better to have air spaces round each bottle or can they all be lashed together?

3. What's better - lots of small bottles or a few large ones?

4. Could this be used in some way to construct a drier for drying fruit and herbs?

[keef]

mmm - I'm reckon the water will cool down too quickly to make much difference.  Also if its really cold - and the water freezes then you'll have the opposite effect of keeping the frame cold as the ice will take a lot longer to melt back to water..

You really need to use somthing that will hold the heat better - bricks or somthing - but they'd probably never heat up enough.

[silverbirch]

I have to say I'm with Keef on this one.  I tend to leave buckets of water in the gh, mainly so it gets to roughly the same temperature as the soil so watering isn't a shock, but I can't say it makes a difference to the air temperature.

The time you would really need it would be spring-ish or autumn-ish when the sun isn't that strong any more.  I think bubble wrap is probably just as good.

BTW, I did find out it takes 36,000 calories to melt then boil 50ml of water.

[cambourne7]

My plan before i put the greenhouse in to make a box 3ftlong by 2ftwide and 4ftdeep and sink this into the floor of the greenhouse with a large pipe that will go out under the floor away from anywhere i will be planting. (There will be a path down the centre of my greenhouse which will be boxed in the middle will have this heat sump. I am going to either side of that to a dept of 2ft and again 2ft wide fill it will wood chips which will also help insulate the box)

Not 100% certain what i am going to do with this box but i have lots of polystirene to edge it and make a floor. Also going to anti vermin the box and pipe. Have seen a little solar panel on maplin and there on special offer for £10 at the moment (http://www.maplin.co.uk/module.aspx?ModuleNo=98358&doy=28m10#overview) and i have a fan from an old computer.  Keeping my eye out on freecycle for a 12V deep cycle leisure battery if i cant find one i am going to ask my local garage :)

I was given a kettle that is powered by the charger attachement in my car the only problem being that it takes about 10 min so i also need to work out how to power this off the battery :)

I am then going to go to a local place that sells glass blocks and see what i can scavange :) to fill the space maybe glass beads or lumps of glass??.

I beleive that the solar pannel charges the battery during the day the glass soaks up the heat the fan moves during the day and the glass disapates the heat at night into the greenhouse to keep the temp right.

I have an advantage in that i have not yet put my greenhouse up so i can put this in before i put the greenhouse into place and that my lotty neightbour has a phd in physics and a new greenhouse to put up as well :) so i am going to find doubles of everything so that he can help me with my system and replicate the system in his green house.

Information on how to calculate your solar power requirements etc
http://www.tayna.co.uk/Solar-Power-C37.html

Fan - http://www.maplin.co.uk/Module.aspx?ModuleNo=105031&&source=14&doy=28m10

I am wondering if i need a Solar voltage regulator as the following look like things i might need to protect myself with:

Battery reverse feed protection
Overload protection
Battery open circuit protection
Solar panel reverse polarity protection
Lightning surge protection
Deep discharge protection
http://www.tayna.co.uk/catalog/336/0/Solar-Power-Voltage-Regulators-page1.html

But maplin do a bigger panel (4.8w for £25) that has some protection built in which is also tempting
http://www.maplin.co.uk/Module.aspx?ModuleNo=115194&doy=28m10&criteria=clearance&c=Maplin&u=BasketFillers

Cambourne7

(ps - when i put the greenhouse frame in i plan on hammering in some posts to support plants before the glass goes back in, i also plan on putting up a bit of wood with blackboard paint on so i can make notes this will have the solar pannel mounted on the back and means its slightly hidden and less nickable)

[keef]

I wonder how well it will work in winter ?

Pebbles whould probably work as well as glass.

Have you tried ebay for the sola panel and battery etc.. i avoid going to maplins if i can help it, the staff are always completely usless

[Eristic]

why don't you just store your manure in the greenhouse?

[carolinej]

why don't you just store your manure in the greenhouse?

You have to take in to consideration the cost of the specialist equipment needed for doing that, ie a peg. :-X ;D

cj :)

[cambourne7]

cheapest simular solar panel is going for £20 with postage so getting something new for £25 is still a bargin :)

[theothermarg]

I,v got a headach coming on fink i,ll just dig out the bubbles and fan heater as usual
:-[ :-[
marg

[cambourne7]

hehehe, yes its giving me a headache as well :)

[cambourne7]

hehehe, yes its giving me a headache as well :)

Looking at the fan i need Amp Hours of storage required  = 560Ah at 12V
so now i just need to work on the batter and the solar panel

[Eristic]

Amp Hours of storage required  = 560Ah at 12V

That seems a bit big.

[davee52uk]

I went up today and the water got quite warm in the bottles.

I have kept a water butt in the greenhouse before. This works, in much the same way as the bottles. There was never any frost on the butt. When I moved the water butt outside, as it took up too much space, then it did freeze over.

Also thinking of putting aluminium foil on the back wall of the greenhouse and frames to reflect back light and heat.

[cambourne7]

Amp Hours of storage required  = 560Ah at 12V

That seems a bit big.

maths are not my stong point go i am going to get neighbour to help

[northener]

I use the big water bottles that they use in offices makes a difference i reckon, the water certainly gets warm.[and green]