Greenhouses are a great way to improve conditions for your plants, and are an absolute necessity for any serious gardening in colder climates. When the time came for [gentleworks] to build a new greenhouse, rather than going with a conventional design, they decided to go with a geodesic dome instead.
The greenhouse uses a few techniques that will be unfamiliar to those used to run-of-the-mill carpentry. The individual cedar struts meet at a series of hubs, constructed out of short lengths of Schedule 80 PVC pipe. The struts are attached to the pipe with steel straps, screwed into place. This doesn’t give the strongest of holds, but as most of the loads on the struts are compressive in nature, it works well in practice. Plastic sheeting is used as a covering to help let in plenty of light while keeping the cold out. The greenhouse is also heated, and can maintain a 40 deg F temperature differential with 14,000 BTUs.
It’s a build that has us wanting to throw up a dome or two in our own backyard. We’ve seen other geodesic structures before; if you’re working on one yourself, be sure to drop us a line.
I was really curious how they devised the window shapes….plastic sheeting, man, i just don’t think it lasts. i was thinking cut glass could work, if you can keep the shape consistent and cut well…though you’d have to struggle to avoid ponding at the joints.
It may not last, but it’s very cheap; add in the material, labor and time costs of making all those cuts for glass, you can afford to replace it annually as long as your frame lasts, and come out quite ahead. Plus, as you point out, it alleviates weather-related maintenance issues with the structure.
Unless there is plastic thatvstands uo to thevradiation from the sun, no it would need replacing. But plenty of temporary greenhouses use plastic.
Geodesic domes apparently leak, but because ofbtechnique, not design. A bit of rain here us probably okay.
In the sixties, they scrounged. At Drop City they’d go to the junkyard and chop panels out of cars with axes. Probably used what glass they could find
Greenhouses are meant to have airflow, so a few gaps certainly are not an issue.
However it would be good to have a few sections you could open wider (not that this would be hard, put the plastic on a suitable sized triangle frame and attach with hinges where desired).
I was looking at the covering an wondering would there be any advantage in terms of lower heating costs, but probably not in terms of light of in having two layers of the the plastic sheeting one on the outside and one on the inside.
A bit like double glazing, kind off (well without the vacuum), so that in effect you would have the outside air temperature, the temperature of the air trapped between the outer and inner plastic sheeting and finally the internal air temperature. The radiation losses would probably remain about the same, but the rate of heat transfer through convection would be slowed by having to traverse an extra isolated layer of air.
Commercial greenhouses covered in plastic use two layers like you describe along with a small fan to keep the area between them filled with air. That might be a little more difficult to pull off with this shape rather than a tunnel, but it is helpful.
Double glazing does not enclose any vacuum. It´s at best nitrogen gas at ambient pressure + some clay-like tiny beads caged within the metal frame separating the two glass plates, for absorbing humidity. The metal frame and the glass is then sealed with silicone ta the edge.
On mine it’s Argon gas. But it’s definitively not vacuum.
That’s not true – there are definitely vacuum-insulated windows, unsurprisingly called vacuum-insulated glazing or evacuated glazing units. And it’s definitely not “at best nitrogen” – filling the gap between the two panes with nitrogen gas at ambient pressure would be odd, considering that’s, well… air. There are a few websites (not window manufacturers!) that mention nitrogen but I think they’re just wrong.
Heavy inert gases are used because they’re monatomic and can’t carry energy rotationally, so you can get a boost even without a fantastic seal.
Also because a vacuum will cause stress in the glass and on the joints which will be aggravated by thermal cycling, whereas argon will retain the same atmospheric pressure as either side of the window, removing a stressor from the joint
The whole point of a dome is maximum strength and volume using minimal materials. That structure with 2 x 4s is strong enough to park a car on – I think I’d suck it up and rip the 2 x 4’s the long way (and it would still be overbuilt). Very cool though – was the location given? I’m assuming Canada somewhere.
You can buy 6 mil greenhouse plastic that they claim will last 5 years. I am on year 2 with no issues. I air stapled it onto my studs and air stapled wood strips over that. I went with a more traditional shape. However, I did build a dome like enclosure for my parrots. If you are interested in a dome that has a lot of options, goes up fast, and is relativity inexpensive, search for starplates.
Where’d you get your plastic, if you don’t mind me asking? I’ve been wanting to build something similar.
The worlds marketplace, eBay. Do a search for 6 mll greenhouse plastic. I think that is what I searched for.
We made a replica of the Crystal Maze dome for a party once, using 1×2″ pressure treated timber strips and plastic pond liner sheet (translucent), stapled on. It was temporary so ingress protection didn’t matter. We made the nodes from slightly flexible discs cut from plastic garden “trugs” or those slightly rubbery large buckets. Drilled either 5 or six holes in each node plate and bolted the end of a pre-cut slat to each hole. It went up OK but I was shocked at how wobbly it was right up until the last layer, and then it went amazingly solid. We built the top first and added to the bottom. Not sure if there’s a better way to do it but we were definitely winging it, as it was only a prop for our party. They get surprisingly tall too.
I don’t know what the neighbours think of it, but I think this looks nice.
Interesting project and certanly something different.
Cool project, isn’t the best statement for a greenhouse, but still, very cool project.
For how long? BTU is a unit of energy not power.
Converted to 2019 units in the civilised world:
4,1kW for raising the temperature 22,8 °C (although that makes no sense at all, as we do not know at which ambient temperature).
It does make perfect sense sense. The keyword is differential, which means with 4.1 kWh (not kW) difference of 22.8 °C can be maintained over a period (how long?) of time.
And yes, as you ask, over how long a period – if the outside temperature is -70°C the period is very short – however if it is +10°C it can be quite long.
And if I release 4,1kWh within a millisecond, there should be a fair chance that the dome is spread over a larger area.
So I mean what I said, it makes absolutely no sense.
As far as I understand it, you need to provide P = 4.1kW continuously to keep a temperature difference of 22.8°C. From that, you can deduce the thermal resistivity of the plastic sheet, if you were to know the plastic area (which is not expressed in the article). Typically, R = P / deltaT (with R being the thermal resistivity for the complete surface, in Kelvin per Watt). If you were to buy insulation, you’ll look for resistivity per square meter (that is in our previous example: R / domeArea)
Sorry, R = deltaT / P.
He’s obliquely saying that btu is a unit of energy and for R-value we want power / delta T area. You are missing that point and focusing on everything but the energy vs power mistake. Americans use btu when they mean btu/hour.
If the outside temperature is -70 °C then, according to the article, you need to use 4.1 kWh/time-unit to keep -47.2 °C inside. If it is +10 °C then the same power is sufficient to keep 32.8 °C inside.
No, the time in which energy is released is irrelevant. It doesn’t matter if you use 239 mg of TNT or a 1S 75 mAh LiPo battery and an electric motor, both will lift a 100 kg anvil exactly 1 m high. TNT will make it quicker but not a millimetre higher.
For how long? BTU is a unit of energy not power?
Unfortunately it doesn’t really allow for rainharvesting. For anyone who has owned a greenhouse, you’ll know how important water collection is, because the temperature can rise and really dry-out the soil/plants. The old-fashioned sloped roof would still be best for this.
Speaking of temperature, there doesn’t seem to be any temperature control windows. That why he needed to include the electrical active air circulation.
Looks cool though.
I considered a geo dome, but ended up doing a flat roof with this as a pro on my pro/con list. (It ended up being cheaper too, because I used free materials.) I never did do rain collection on this roof, but an isolated back wall and water helped to keep it passively heated/cooled:
https://youtu.be/IzAz_IBGgK0
Good work. Reasonable cheap and easy build. Consider Stainless chicken/poultry wire. Doesnt help with making prettier tho.
How about using this double walled uv stabilised polycarbonate sheeting? https://en.wikipedia.org/wiki/Twinwall_plastic It’s common enough, easily cut with a sharp blade/scored or cut with a saw. And if sealed with a bead of silicone I bet would give some of the double glazing benefits.
And given that it is relatively easy to cut it would be much easier to custom cut the requited shapes and thus get a good fit. It is UV stabilised so with a good fit would stay leakproof for a long time – an important factor as once the upper segments start to leak the timber starts to rot… It is also about 6mm thick so it would leave much less space for any water pooling if fitted into the “framed”cavity or what I am thinking is just silicone the sheet on top of the frame and seal the end cuts with another bead of silicone giving no space for rainwater to pool at all.
Water collection can be done by attaching and silicone sealing half pipe segments at mid point. Bugger to get the angles right but it can be done if you are determined.
And there is nothing stopping someone adding more parallel triangles from the inside creating in effect quad “glazed” “windows giving great insulation but also sealing the timber struts away from interior moisture if the use is indeed a greenhouse. For personal use say for an office etc this would also cut out voice and noise transmission through the walls.