heat sink

bazil · Post: # 25107Post **bazil** » Fri Jun 30, 2006 2:03 am

hey....i read this article http://www.off-grid.net/index.php?p=570#more-570

i was wondering if anyone knows how on would construct a heat sink as such made out of broken glass as they have

thanx

Luath · Post: # 25115Post **Luath** » Fri Jun 30, 2006 7:57 am

They showed some of the construction of the heat sink on the It's Not Easy Being Green series, including the machine they hired to crush the glass. Very interesting, and by all accounts, seems to work well. Don't know of anyone else who has actually tried it, but there has been discussion on the INEBG froum about altrnatives to the actual crushed glass, if you didn't have access to the glass/machine.

Martin · Post: # 25119Post **Martin** » Fri Jun 30, 2006 8:05 am

I've wondered if the bricks out of an old night storage heater would be useful - they are designed as heat stores - and skips everywhere are full of the things!

Luath · Post: # 25123Post **Luath** » Fri Jun 30, 2006 8:09 am

I think that was one of the alternatives suggested on the Forum, and by all accounts was thought suitable for the job; almost anything that will accumulate and release heat would do. I'm not too technically minded, but it seems there are a lot of things that would do this as well as the glass.

Muddypause · Fri Jun 30, 2006 10:02 am

I didn't see the whole of that episode, but from what I saw, it seems that the heat sink was under the floor of the greenhouse, and had a small fan that drew warm air from the top of the greenhouse, through some ducting, down into the sink. The fan was powered by a small solar panel, and apparently it kept a fairly constant temperature, day and night, in the greenhuse. I guess the fact that the glass was crushed meant that the air could circulate through it, making it fairly effective at taking the heat out of the air, and storing it.

But actually, plain water has a much higher heat capacity, and I have heard of people simply filling barrels of water and storing them under the trestles in the greenhouse, warmed by direct sunlight, and ambient air temperature. This would be a much simpler heat store to install.

Actually, I've been doing a bit of calculation on this. Glass is about 2.6 times as dense as water, but has a heat capacity of less than one sixth, which means that, overall, water will store nearly 2.3 times as much heat as the same volume of glass.

The same calculation for concrete (or storage heater bricks), water will store slightly less than twice as much heat as the same volume of concrete.

Luath · Post: # 25135Post **Luath** » Fri Jun 30, 2006 11:02 am

On the fairly rare occasions it does get very cold down here, I fill black builder's buckets with hot water and leave them in the greenhouse overnight, just enough heat given out to ward off any frost threatening. My other method is to overwinter the pet rabbits in the greenhouses, very successful. I've done it with chickens as well.

hedgewizard · Fri Jun 30, 2006 11:48 am

I'm thinking of doing that with my chickens, but it's going to have to wait until I make the tractor up. A couple of buckets of hot chickens will keep the frost away nicely. Since it's a polytunnel they won't make much of a difference in there, so I'll screen a section off with bubble wrap to make a frost-free area.

Shirley · Post: # 25173Post **Shirley** » Fri Jun 30, 2006 1:03 pm

a couple of buckets of hot chickens... ?? KFC??

hedgewizard · Fri Jun 30, 2006 4:13 pm

Actually when it's hot my chickens usually lie in a heap on top of their scratching hole. It's pathetic.

Stonehead · Post: # 25206Post **Stonehead** » Fri Jun 30, 2006 5:20 pm

You can take this a step further by putting a water filled heat sink under your greenhouse, then linking it to pipes that run through your compost/muck heaps. This also has the advantage that by using careful design you can use thermo-siphoning and avoid using a pump.

Or paint a couple of old radiators black, stick them under glass and use them to keep your water-filled heat sink up to temperature.

bazil · Post: # 25238Post **bazil** » Fri Jun 30, 2006 8:02 pm

thanx again guys ....like the radiator idea stonehead....i wonder how hot it would get?....could you use it for a hot water tank?

Stonehead · Post: # 25251Post **Stonehead** » Fri Jun 30, 2006 9:08 pm

bazil wrote:thanx again guys ....like the radiator idea stonehead....i wonder how hot it would get?....could you use it for a hot water tank?

A good compost heap should range from 40-60C at its peak (called the thermophilic stage), depending on the progress of decompositio, the level of aeration, the carbon/nitrogen ratio, the moisture level and the external heat. You don't want temperatures over 65C as this kills beneficial bacteria.

If it gets too hot, turning it will cool it for a short time but once it starts to cool, turning it can actually increase the heat as it introduces a new oxygen suppy to any matter that has not yet decayed. Once all the material has decayed, then the temperature will steadily decline.

A big 4x4 heap like ours takes about 12 months to full break down, with peak heat for about six to nine months (cold spring and autumns slow it down).

The tumbler composter that we have (one of those green plastic things) only takes six months because it's much easier (and more practical) to aerate it weekly. However, it cools quickly once the weather turns and is completely dormant through winter.

And that's why we have to get our three new 4x4 bins built next week - to get the contents of the old ones shifted and turned so we can get another four months composting done and have the compost ready for October.

Anyone care to join us? We're talking about 192 cubic feet of compressed compost - including pig and chicken manure. As a cubic foot of moist excavated earth weighs around 90lb (the closest I can get to our compost), we're talking about 17,280 pounds (7.7 tons or 7,800kg) of muck. Lovely!

bazil · Post: # 25262Post **bazil** » Fri Jun 30, 2006 10:09 pm

soz buddy......i was meaning could you use the radiator painted black for hot water supply?

and would it only work in british summertime?

i once saw a program on tv that talked about using compost to heat a very large greenhouse...they had melons and exotic stuff growin in there sometime last century it was some sort of big posh country house.

Wombat · Post: # 25271Post **Wombat** » Fri Jun 30, 2006 11:25 pm

I tried the water drums in my small (4m x 3m) plastic house but it didn't seem to make much difference.

I have seen people who use gravel instead of the crushed glass......

Nev

Muddypause · Sat Jul 01, 2006 12:13 am

bazil wrote:could you use the radiator painted black for hot water supply?

That is, in esscence how a solar heating panel works, though it usually works best if the plumbing includes a tank to store the hot water in.

and would it only work in british summertime?

Sunshine is a prerequisite.

i once saw a program on tv that talked about using compost to heat a very large greenhouse...they had melons and exotic stuff growin in there sometime last century it was some sort of big posh country house.

I've got some old gardening books that talk about it, too. There was an era when horse manure was available in great abundance, and these things were easy to do.