solar powered heat sink ?

[Magiccat1978]

Hi

I was lucky enough that my other half bought me a new 8 x 6 greenhouse for my birthday I was looking at ways to keep it a little warmer at night as here in Scotland we seem to have a shorter growing season and I was hoping to try and extend my growing time a little. I came across this Solar Greenhouse Heat Sink - Solar and wondered if anyone had / is successfully using such a system. I was hoping it may keep my greenhouse frost free for a little longer during the cool Autumn nights.

Any experiences / comments would be greatfully recieved before I send him out to dig a big hole for something that may or may not work

thanks
Laura

[OllieMartin]

I don't have a greenhouse so can't advise, but I did find the article pretty interesting.
What I don't understand though is how the heat sink material (gravel in this instance) warms up. If you drive air through it during day AND night, surely you'd draw heat out of the greenhouse during the day to heat the gravel up.
I'm probably missing something. Could do with one of the Vine's braniacs explaining it to me,

[Lazgaot]

The gravel heats up because some of the heat at the top of the greenhouse is recycled through it. Not all the heat is pumped into it and absorbed 100%. After a time everything in the GH will get to the same temperature.

It would work better if the heat store (gravel etc) was only drawn on when the internal temp dropped below at certain threshold, 15C say. The internal structures of the GH will absorb heat all day and release their heat once the sun goes down,so there will be a natural decline in temp through the night anyway.

[BFG]

I seem to remember Robert Winston improvised a greenhouse heat sink in "It's Not Easy Being Green", using water to store the heat. Might be worth googling that to see what he did and how it worked.

[Snadger]

Theois quite a few innovative ideas floating around! The Victorians were the masters of using the heat generated from fresh manure composting to heat their grenhouses and frames.
You've just remeinded me I have to take my five gallon jerry can to the allotment. I intend filling it with water and jamming it behind the flue pipe on my woodburning stove hopefully tp act as a heat sink!

[COMPOST CORNER]

It's not easy being green, I seem to remember, used glass chippings in the pit below the GH and a solar powered fan to push the hot air from the roof of the GH down a pipe to the sink, which released the heat at night.

[snohare]

It definitely works, this is considered commonplace technology in some circles in the US.
The extra energy effectively comes from the solar panel. Without it or the fan, there is less energy in the heating/cooling from convection cycle that naturally operates in the greenhouse. Usually, excess heat is radiated/convected away through the glass (in this case, "excess" means whenever the temperature outside drops below the temperature inside) overnight, or even just during a cooler day. This isn't so noticeable because the temperature inside is raised by the heat trapped by the glass. (Yes, the greenhouse effect...!)
With a solar panel and fan, you are taking away some of the excess heat and storing it in the "heat sink", which releases it over a longer period and thus increases/prolongs the minimum temperature inside the greenhouse being reached. (The fan is switched/ switches off at the end of the day Ollie, thus leaving the heatsink to radiate stored heat that rises gradually throughout the night.)
Really, it is exactly the same technology as all these ground source heat pump heating systems using brine in pipes that are being installed in eco-friendly houses nowadays, so there is no fear that it will not work ! The only difference is scale, and that this heatstore is inside an area that usually has a raised temperature - so don't expect it to work well at - 18 C.

[OllieMartin]

It definitely works, this is considered commonplace technology in some circles in the US.
The extra energy effectively comes from the solar panel. Without it or the fan, there is less energy in the heating/cooling from convection cycle that naturally operates in the greenhouse. Usually, excess heat is radiated/convected away through the glass (in this case, "excess" means whenever the temperature outside drops below the temperature inside) overnight, or even just during a cooler day. This isn't so noticeable because the temperature inside is raised by the heat trapped by the glass. (Yes, the greenhouse effect...!)
With a solar panel and fan, you are taking away some of the excess heat and storing it in the "heat sink", which releases it over a longer period and thus increases/prolongs the minimum temperature inside the greenhouse being reached. (The fan is switched/ switches off at the end of the day Ollie, thus leaving the heatsink to radiate stored heat that rises gradually throughout the night.)
Really, it is exactly the same technology as all these ground source heat pump heating systems using brine in pipes that are being installed in eco-friendly houses nowadays, so there is no fear that it will not work ! The only difference is scale, and that this heatstore is inside an area that usually has a raised temperature - so don't expect it to work well at - 18 C.

Thank you

[Pumpy]

Yes, I can confirm it works, haven't done it myself but did donate a couple of fans to someone who was doing it and I heard later that he had positive results.

Pumpy

[Jimmy]

The linked article shows the heak sink under the greenhouse.
However I can't see why it can't be separate. You could build a box out of re-cycled wood, line it with blocks of Polystyrene and fill it with rubble.
Jimmy