Topic: solar greenhouse heat sink

[xlynettex]

hello,

we have just been given a greenhouse and want to heat it at night (especially during the winter ).

has any one built a solar heat sink in their green house ?
how efficient is it ?
how difficult is it to install ( not very technically minded :( ) ?

any advice about this would be gratefull

[GodfreyRob]

I once met someone who was doing work in Finland on this - they have frosts in June/July!  A lot of the solutions involved big volumes of stuff (like water) in black painted oil barrels to absorb heat in the day and gently radiate it at night. Thats ok if it is sunny in the day - not much good on a grey wet day here though.

Here's a link: http://www.hobby-greenhouse.com/FreeSolar.html

[xlynettex]

thankx , looks like i have got a lot more reading to do first ;D

[reddyreddy]

there was a great program on the BBC a while ago called "It's not easy being green" and they made a heat sink in thier greenhouse, maybe a book or DVD available?

[Barnowl]

There have been some threads on this before, but they mainly relate to the 'it's not easy being green' version

http://www.reuk.co.uk/Solar-Greenhouse-Heat-Sink.htm

[GrannieAnnie]

My hubby was just talking with a friend who is working on a design for his dad who is a commercial nurseryman. He is putting in 3 feet of rocks ABOVE ground level (sounds odd to me) as a heat sink and a fan to circulate the air thru the rock layer. For cloudy days he'll have to use oil heat though.

[Eristic]

I've been giving some thought to this idea of heat sinks in greenhouses and polytunnels and think they may well be a waste of time and effort at best and possibly have a negative effect on the temperature at a critical time of year.

My reasoning so far is this: If a heatsink dissipates heat during the night such that the ambient temperature of the greenhouse is prevented from dropping by a significant amount then the heatsink would surely suck heat from the air of the greenhouse during the daytime thereby preventing or hindering any temperature rise. In the event of a succession of cold sunless days, (remember those) the heatsink would get colder and colder until it had the effect of turning the greenhouse into an old fashioned fridge. In other words, the heatsink would actually sink the heat to the point that it prevented or severely hindered  temperature rises.

Just a thought provoking comment for the more scientific brains on the forum. Please feel free to pick holes in the argument.

Anyway, if you cannot afford to heat your greenhouse then it should be treated as the traditional cold greenhouse and accept that there will be frosts from time to time.

[GrannieAnnie]

 Last Fall I wrote  and posted pictures about building a walk-in cold frame and using water as the heat siink.  My modest goal was to grow only lettuce which is as you know  is a cool season crop. It was barely up and running when hard frosts hit and didn't have the storage cans for the full 300 gals of water advised and needed  nor was the insulation all finished. There were significant air leaks and rain dripped in thru a window leak. That actually proved beneficial when we went away for 3 weeks and I didn't worry about it being watered.

The lettuce planted  late was tiny and showed very little growth initially however, it all survived anyway and I could harvest small amounts in the dead of winter.
Growth took off quickly in Feb. with some very sunny days and we've had salads from it continuously.   I'm hoping to get more cans of water in there to line the entire back wall by Fall. It won't ever grow tender plants through the winters here unless I'd be willing to install electricity for a fan and lights for the bitterest nights AND cover the glass with protection at night, all of which are beyond me. But so far I've been pleased (and excited) with the lettuce  crop.

[tonybloke]

in response to eristic's comments, the heat transfer is usually done by a computer fan, solar panel powered, with a thermostat in the circuit. ( It only stores heat when it's sunny enough and there is excess heat)
rgds, Tony ;)

[xlynettex]

thanks everyone for your comments and please keep them coming.

We are going to put a heat sink in our greenhouse and experiment with it and compare results with another cold greenhouse. if we are able to keep just above O i will be pleased. the one thing i will take from peoples comments is to make our greenhouse air tight and insulate it well during winter.

thanks

[JoeCocker]

I built a heat sump myself this year, having problems with a suitable housing for the fan. I've used to plastic milk cartons ,but don't think this is really suitable. Also have tried to use a solar tricke charger but it doesn't give off enough power to keep it running. apparently you need a 5w solar panel, does anyone know where i could get a bargin?

I think its a good idea but my installation still need tinkering before it will provide any heat at night.

[GrannieAnnie]

I'm in process of digging around the perimeter to sink insulation to help prevent cold from coming in. Only got one side done before frost came. I'm hoping that helps in mid-Winter.

[Eristic]

Bear in mind that the biggest killer of plants during winter is damp not cold. Ventilation and airflow is vital.

I'm still in two minds as to whether the theory of the heat sink is flawed or not. You may be simply preventing the temperature from rising.

[tonybloke]

Try MAPLINS http://www.maplin.co.uk/ for your solar panel, and use a 4" or 5" square plant pot (with the bottom cut out)  to connect fan to tumble drier hose
rgds, Tony  ;)

[Rhubarb Thrasher]

or ebay

[jaggythistle]

  This any good.........???

   http://www.reuk.co.uk/Solar-Greenhouse-Heat-Sink.htm