Solar heated greenhouse anyone?

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Solar heated greenhouse anyone?
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OtleyLad

Joined: 13 Jan 2007
Posts: 2737
Location: Otley, West Yorkshire

Posted: Wed Jan 28, 15 7:51 am Post subject: 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

Joined: 13 Aug 2006
Posts: 35935
Location: The Hive of the Uberbee, Quantock Hills, Somerset

Posted: Wed Jan 28, 15 8:29 am Post subject:
Have you looked at the information on the Solva stuff? There's some interesting things on there - although they do use rabbits as well

RichardW

Joined: 24 Aug 2006
Posts: 8443
Location: Llyn Peninsular North Wales

Posted: Wed Jan 28, 15 8:46 am Post subject:
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

Joined: 13 Jan 2007
Posts: 2737
Location: Otley, West Yorkshire

Posted: Wed Jan 28, 15 10:26 am Post subject:

RichardW wrote:

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

Joined: 13 Jan 2007
Posts: 2737
Location: Otley, West Yorkshire

Posted: Wed Jan 28, 15 10:26 am Post subject:

Chez wrote:

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

Yes, I've had a look there.

derbyshiredowser

Joined: 11 Feb 2007
Posts: 980
Location: derbyshire

Posted: Wed Jan 28, 15 10:34 am Post subject:
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

Joined: 19 Apr 2007
Posts: 21301
Location: Bethesda, Gwynedd

Posted: Wed Jan 28, 15 10:43 am Post subject:

OtleyLad wrote:

RichardW wrote:

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.

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

Joined: 23 Jan 2009
Posts: 9279
Location: Ayrshire, Scotland

Posted: Wed Jan 28, 15 11:57 am Post subject:

RichardW wrote:

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)

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

dpack

Joined: 02 Jul 2005
Posts: 44456
Location: yes

Posted: Wed Jan 28, 15 12:12 pm Post subject:
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

Joined: 21 Jul 2011
Posts: 16531

Posted: Thu Jan 29, 15 7:27 am Post subject:
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

Joined: 19 Apr 2007
Posts: 21301
Location: Bethesda, Gwynedd

Posted: Thu Jan 29, 15 9:51 am Post subject:
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

Joined: 14 Jul 2005
Posts: 2191
Location: Leeds

Posted: Thu Jan 29, 15 12:27 pm Post subject:
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

Joined: 02 Jul 2005
Posts: 44456
Location: yes

Posted: Thu Jan 29, 15 11:20 pm Post subject:
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

Joined: 21 Jul 2011
Posts: 16531

Posted: Fri Jan 30, 15 7:54 am Post subject:

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

Joined: 14 Jul 2005
Posts: 2191
Location: Leeds

Posted: Fri Jan 30, 15 9:04 am Post subject:

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)

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