Newhouse Farm

[Grøntsager]

There doesn't seem to be a special forum for the discussion of passive solar greenhouses for home heating.

I put up a popular 22 feet long x 8 feet deep lean-to aluminium greenhouse with a single layer of 4mm float glass over10 years ago. I used their special joining extrusion to connect two of their greenhouses together end to end. The greenhouse faces due south and has a full area brick floor to help to absorb heat and release it slowly. The house wall is the original painted brick.The original idea was cheap passive solar warming and a pleasant place to sit year round.

The temperatures soar in summer but remain just above outdoor ambient in most winters due to endless grey days. On a sunny day in spring and autumn we can open the windows and doors to the house which are covered by the greenhouse for remarkably refreshing warmth. There is a unique feel to passive solar warmth.

In winter, temperatures can drop well below freezing overnight. The greenhouse does help to shelter the southern façade from the prevailing south westerlies and probably offers a little extra insulation. Any free heat is allowed to rise through the open stairwell. Fly-screen meshed, double doors on each end of the greenhouse ensure the house stays free of buzzing nuisances all year round and allow fine temperature control depending on wind direction.

After several attempts with both off-white cotton (rots quickly ) and white parachute nylon cloth shading (too thin and UV unstable) we now use cheap, white, lightweight tarpaulins as internal ceiling shade. It is very unpleasant to sit in open sunshine under glass. The blinds are drawn back up on tensioned supporting cables during the day.

The upside: Our annual crop of cherry tomatoes are the best we've ever tasted.

Plans to cover the roof externally with DIY wooden louvres to block high sun angles have never happened due to likely high cost and winds requiring very strong construction. The greenhouse is sheltered by a 2 metre high x three meter thick beech hedge running east to west. I have thought of allowing some beech spires from the hedge to grow into shade trees. Obviously the hedge blocks low winter sun angles but we prefer the shelter it gives.

Once the summer sun gets through the glass even the professional grower's, reflective foil blinds are totally useless in controlling inside temperatures despite copious ventilation. The sun has to be blocked from outside before it gets in! Greenhouse whitening "paint" has little effect and is ugly, claustrophobic and spoils the view.

Oh dear. Now I think I know why lean-to greenhouses don't get a special section here!

I wonder if anybody else has had much success with an inexpensive lean-to greenhouse for passive home heating? Perhaps you can suggest ways to improve ours which I haven't tried yet?

[Brigit]

Hello and welcome!

Have you thought of planting a vine? I'm going to move this to the permaculture section because I think you'll get more feedback there.

In the mean time have a look at this link.... http://permaculturetokyo.blogspot.com/2007/01/retrofitting-for-passive-solar.html

or this... http://www.dulley.com/docs/f765.htm
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www.thebiggreenidea.org

[GavinWheeler]

I have no direct experience of this, but you might want to look into something called a "Trombe Wall" - more or less a leanto greenhouse used for passive solar heating.
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"Thorry, thur, but Igorth do not 'tetht the principle'. Thtrap it to the bench and put a good thick bolt of lightning through it, that'th our motto. That'th how you /tetht/ thomething!"
Terry Pratchett

[Grøntsager]

Hi Brigit and Gavin

Thanks for the suggestion on vines. It would take some research to find something suitable for our low temperatures but will definitely be worth a look. We eat a lot of black grapes but they are imported from far away so not very green. Perhaps we can find a really hardy variety.

Interesting that you should move my greenhouse post to permaculture. We have been working hard on boundary wind reduction over the last 10 years. Sadly the house is right on the southern boundary where it cops the most wind despite a wind shelter copse to our West and 10 metre high shrubbery on every other boundary. Only the southern boundary is low near the house to ensure we get sun when it is available. I keep thinking a rotatable vertical louvre fence would allow winter sun in but it's just not worth the hassle for so little gain and the thick hedge is more windproof and bombproof in storms.

Thanks for the Trombe wall idea, Gavin. Research suggests that it works best in sunny climates and still better when insulated. More thermal mass would help our cause but the 1960s oil drum storage idea is just too ugly and bulky for our tastes. I would never build a sloping, glazed roof, conservatory/greenhouse ever again and they really ought to be banned. A lean-to greenhouse needs a solid roof to avoid summer heat gain. It can then be insulated to limit overnight heat loss year round. A deep shading overhang is also critical to limit solar gain to the seasons one actually needs it.

Steel and glass architecture has failed to control solar gain but new façade louvre ideas are now becoming more commonplace. I have been photographing every new louvre design now appearing on large Danish glass buildings in the hope of adapting something to my own more modest lean-to greenhouse. Forget about roof vents in summer. Total waste of time unless they are vast and they always leak anyway.

Thanks again for the great ideas. More food for thought.

[Brigit]

Good luck! I'd be interested to know if you come up with a solution.
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www.thebiggreenidea.org