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OtleyLad

Solar heated greenhouse anyone?

My new but growing Practically Green group is investigating building a solar heating system to warm our greenhouses.
At the moment we are looking at using thermal collectors (water in pipes) linked to a heat store to then release the heat when the sun goes down.
Anyone any experience of these?
Chez

Have you looked at the information on the Solva stuff? There's some interesting things on there - although they do use rabbits as well Smile
RichardW

Try going even lower tech.

Plenty of thermal mass directly warmed up by the sun.

Add a second skin or layer to the green houses.
OtleyLad

Try going even lower tech.

Plenty of thermal mass directly warmed up by the sun.

Add a second skin or layer to the green houses.


The thermal mass thing is tricky in that a lot of such systems take up a lot of volume in the greenhouse.
We are hoping to come up with something that can be easily fitted into an existing greenhouse without the need to rebuild and ideally occupying only a small area/volume (oh and at minimum cost - just to make it challenging).
OtleyLad

Have you looked at the information on the Solva stuff? There's some interesting things on there - although they do use rabbits as well Smile


Yes, I've had a look there.
derbyshiredowser

With our old greenhouse a wooden Alton we filled the space under the staging with water filled plastic bottles and they kept it a steady heat most of the year. vegplot

Try going even lower tech.

Plenty of thermal mass directly warmed up by the sun.

Add a second skin or layer to the green houses.

The thermal mass thing is tricky in that a lot of such systems take up a lot of volume in the greenhouse.
We are hoping to come up with something that can be easily fitted into an existing greenhouse without the need to rebuild and ideally occupying only a small area/volume (oh and at minimum cost - just to make it challenging).

Wishful thinking.

Thermal mass is the easiest. Like Richard says it's low tech and requires virtually no maintenance.

Dig the flow floor out, insulate it, then top with brick or pavers. Build your shelving on brick piers and add thermal insulation in the walls.

All the materials are cheap and easily available. Throwing technology at it may look attractive and clever but its only really effective when there isn't a viable alternative. It isn't cheap to build or run either.
gz

Try going even lower tech.

Plenty of thermal mass directly warmed up by the sun.

Add a second skin or layer to the green houses.

Look at the sorts of techniques they use at Squash Blossom farm near Rochestter in USA.. Includes a double skinned polytunnel with air blown between the two.
They get power from panels on the barn all year (so long as they can keep the snow off)

http://squashblossomfarm.blogspot.co.uk/2011/06/solar-summer.html
dpack

thermal mass,solar pv to run pooter fan

hot air blown onto thermal mass in day ,heat driven flow in dark .thermal mass was glass in a pit under the floor

iirc dick strawbridge on telly

very low tech but requires a bit of digging
Mistress Rose

I was going to suggest the method Dick Strawbridge used. It is low tech and although you need to do some digging, getting the heat into a pit full of glass, sand or similar will at least allow slow release during the night. vegplot

Did the Strawbridge method prove effective? Is there any data to suggest it's better than simply adding thermal mass to the inside of the greenhouse?

Or is it something people see as a good idea 'cos an eccentric bloke with a shorts and a big moustache did it on the telly and therefore must be good?
mark

If you have the resources I'd do both.

Adding thermal mass (water or bricks) is simpler and means your other system has less work to do and is more likely to succeed.

And of course the gardeners of old did wonders with growing using "hot beds" over heat producing piles of rotting matter.
dpack

i have used raw manure as "fuel"(dug in under the growing soil)for cloches and in cold frames to good effect for early beans and winter salads and have seen it used at greenhouse scale perhaps to less effect.

i recon it only adds a few degrees but that can be enough.
Mistress Rose

I don't think you are going to get more than a few degrees in general. The way of making hot beds used to be to make a pile of rotting manure and then putting soil and a cold frame on top rather than digging the manure in. Pineapples were grown in the UK using rotting 'tan' which would be oak bark; possibly the stuff fished out of tan pits used to dye leather, but in conjunction with heating using water pipes heated by a coal boiler.

I don't know whether the method Dick Strawbridge used has any data. He used a fan (solar powered I think) to drive hot air into the thermal mass during the day for slow release during the night. He claimed he could keep salads growing all year, but he was in Cornwall, so wouldn't expect that to work in the north east of Scotland quite so well, although there might be enough heat just to keep the frost off.
mark

My point is that the couple of degrees again from rotting manure can be vital, but that added to the use of heat store (bricks water bottles) - and the use pumped solar heart from a collector outside the combined effect may well be more significant than one method alone.

Usually in the UK in winter when it is cloudy it is a bit warmer
and the really cold spells come with clear skys - that is good for solar heating strategies of all types...

BUT occasionally we get days with cloudy skies and /or snow covering on collectors combined with an icy blast from the North or East. Having the fermenting heat source can make all the difference in getting your through those days (or you could always use a paraffin heater for a couple of days)
dpack

when i have done the cloche thing i dug a double spit trench half filled it with raw manure ,topped it with soil ,plant into soil ,cover with cloche

i recon that gives a few degrees extra to soil and air temp above just a cloche ,it works well for salad and beans in a chilly place like west yorks
Mistress Rose

Mark I would agree that several different methods will be more likely to produce consistent results. Dpack, that is pretty well the way they used to do it I think, but usually for a long period they used a heap rather than putting it at the bottom of a trench.

I think you have a good few ideas to help you heat your green house Otley Lad. Very Happy
OtleyLad

Mark I would agree that several different methods will be more likely to produce consistent results. Dpack, that is pretty well the way they used to do it I think, but usually for a long period they used a heap rather than putting it at the bottom of a trench.

I think you have a good few ideas to help you heat your green house Otley Lad. Very Happy

I can see it now - a greenhouse up to the eaves in manure (sat over a 2 metre deep thermal store. Half the roof has a PV panel (driving a fan to circulate the air from the below ground thermal store) and the other half a Thermal panel - with just a crack in between so the light can get into the 3 lettuce plants (I know 3 sounds a lot but I'm an optimist you see).

Maybe I should be working for the government...
Mistress Rose

Think you could reduce the dimensions of the manure heap etc. slightly so you could get 4 lettuces in. Laughing alison

I asked Brigit, on FB and this was her answer about the sink hole.

Brigit Strawbridge Hi Alison, it helped a little, but the size of the sink was not large enough for it to be hugely effective. For it t make a big difference you would need the sink to be as large and as deep as possible. Hope this helps x
Mutton

And for my third recommendation of this website for this evening....

www.builditsolar.com

In particular

http://www.builditsolar.com./Projects/Sunspace/sunspaces.htm
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