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Green house with no glass  RSS feed

 
Len Ovens
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Location: Vancouver Island
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This is just a thought off the top of my head... no try out experimentation or anything like that.

I was not too long ago reading in one of the forums about using waste glass as roof tile. Much of the comment that followed said that glass is energy intensive to make or even remelt/form. Certainly using glass for a greenhouse is an appropriate use of technology, particularly in colder climates. Also, I would not suggest a glass replacement such as plastic.

However, I am thinking about a mix of technology in the winter green house and micro-climate that would allow much earlier planting than a micro-climate setup if not as good as a glass house.

I general, it seems to me most micro climate setups are roofless, but use walls (mostly high mass) to change local temperature. Cold area green houses on the other hand, extend an insulated north wall into part or all of the roof, leaving only the east, south and west walls with glass.

What if a structure was made with the insulated north wall and roof, but with no glazing in the south and east/west walls? Siting would be important so as to avoid pooling of cold air for example. The east/west walls could be partly closed or angled in such as way to limit the early spring or late fall open aperture to parts of the day when sun was actually above the horizon. The roof would be heat reflective while blocking the radiation path to deep space which causes frost so easily.

What other technologies could be used to make this workable and how much could this extend the growing season. What kinds of plants would this be suitable for? Could this allow some plants to over winter that would normally not? (think small trees like citrus)

Just Len's brain belch this morning...
 
Cristo Balete
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Location: In the woods, West Coast USA
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Not sure where you are, Len, but most greenhouses, if they don't have a heating system, are about holding the heat in, from whatever source, and that means blocking the wind and not letting heat, that rises, escape. I haven't heard of roofless greenhouses because that defeats the purpose of capturing heat, unless you mean in the hot summer roof vents allow excess heat out.

The other crucial part of light on plants is allowing ultraviolet, so if you only focus on heat, you might exclude ultraviolet, and that doesn't work for plants. Some of those corrugated plastic panels block out too much of the UV rays. A reflective north wall can be helpful, but I haven't found it to make enough difference to add that expense and maintenance to the greenhouse.

if you are talking about a solid, dark roof, you'd end up with a carport, and that's not enough light, nor enough heat. If the ends are open,, that lets cold and and wind in. Unless I'm misunderstanding what you've described.

Are you just not wanting to use glass? Because there are a lot of greenhouse plastics that work as well.
 
Len Ovens
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Cristo Balete wrote:Not sure where you are, Len, but most greenhouses, if they don't have a heating system, are about holding the heat in, from whatever source, and that means blocking the wind and not letting heat, that rises, escape. I haven't heard of roofless greenhouses because that defeats the purpose of capturing heat, unless you mean in the hot summer roof vents allow excess heat out.


Not roofless, but more of a micro climate with an insulated, heat reflective roof.


The other crucial part of light on plants is allowing ultraviolet, so if you only focus on heat, you might exclude ultraviolet, and that doesn't work for plants. Some of those corrugated plastic panels block out too much of the UV rays. A reflective north wall can be helpful, but I haven't found it to make enough difference to add that expense and maintenance to the greenhouse.


I am not sure if reflective or absorptive/radiating would be best. I would not expect to use a polished mirror finish, but just light coloured would make some difference. Cold climate green houses are designed to allow maximum UV radiation in. The roof is not expected to help keep the air temperature up so much as reduce radiation loss which is the main cause of frost. This would also help prevent the loss of some ground heat. One of the trite sayings I have heard (supposed to be based on science) is the doubling roof insulation is the same as closing a 6 foot hole in the wall. My experience has shown that holes in the wall are less of a loss than I could have imagined. (a crude hut of logs on a windy seashore, where the slots between logs was 6inch or so, was still a good shelter from the wind and "felt" warm)


if you are talking about a solid, dark roof, you'd end up with a carport, and that's not enough light, nor enough heat. If the ends are open,, that lets cold and and wind in. Unless I'm misunderstanding what you've described.


Siting, to reduce wind. Design, figuring out how much the ends should be open... or how much wider they have to be than the grow area to allow seasonal sun aperture. How high would the roof need to be to let all the UV in? Floor level, can a sunken floor reduce the winds effect on the soil/floor heat loss? Even choice of type of plant placement may make some difference. It may well be worth planting extra plants on the ends to make make some sort of wind break that still allows some light through in winter. Would a PAHS style "umbrella" around the green house keep the soil warmer? Could the walls be designed in such a way as to reflect heat down rather back out the sun aperture?

People in my area used the Pit house to stay warm in the winter. This house had a 6foot hole in the roof... yet was effective even in some places with no fire (Delta area BC Canada ... 49degees north) Glass (or glazing) is magic... or maybe not so much as we think.


Really it is not a matter of where I am, but would it make sense _somewhere_. And hopefully lots of somewheres
 
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