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Greenhouse Modeling Trials and Theoreticals  RSS feed

 
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Hey everyone! In reading through a lot of the posts on here I've seen quite a few of yall are more engineering and technologically inclined than I am so I was hoping to pick your brains.

I'm in the planning process for a theoretical future walipini. There are various design options and tweaks people have posted on here but short of building it and then tweaking the structure over the years there isn't a way to know for sure what will work in my specific situations. I would like to build several different models and compare their internal temps under various conditions.

My question is, is there a way to do this accurately? Building to scale isn't going to be too much of a problem (I don't think, although I"m probably simplifying things quite a bit) but accurately mimicing the sun's intensity and output for a 1/10 or 1/100 size model has me hitting a wall right now. I"d like it to be small enough I could stick it in the deep freezer or cooler for testing. Not aiming for super scientific MIT level accuracy, its more to get an idea of doing X will increase/decrease temperature or light by Y degrees. Any ideas on how to mathematically scale down the sun considering sun angle at winter solstice for X latitude and the resulting footcandles? Quick perusal of the internet has everything either geared for elementary school or they have several degrees that I do not possess in mathematics or physics, possibly both.

Or if someone has already done this that's awesome, let me know! Thanks
 
pioneer
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Great question Karlie! 

If it wasn't a walipini I think you'd have a better chance.  Mimicking the earth contribution to the model would probably only work in the actual earth, not in a freezer.  Plus thermal mass of the model would come into play in ways I don't understand.  For instance, a 1' model greenhouse with a cup of water as thermal mass would still freeze solid after 10 hours in the freezer (I think).  Where as a full sized greenhouse with proportionally more water in the same temperatures probably wouldn't freeze nearly as hard.

Are you in any hurry to do this?  Could you build some models outside and see how they work through your winter in the ground?

Building really tiny (1/100th scale) may be more tricky than it sounds.  Getting good sealing and vents that operate (maybe) might be tricky. 

Alternately, could you build the full size walipini with the plan being to redo the above ground part after a season of data collection?  You'd still be just trying one arrangement and then tweaking it from there but at least the cost would be lower.  ie, building a perfectly detailed walipini and then changing it costs more than building a crude walipini and then changing it.
 
pollinator
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I second the recommendation to experiment in the ground. A walipini is just a very large hotbed. That is  where you dig a pit put compost or manure in it for heat and put soil on top then build a frame around it to put a window over the top.  So you can build a series of such structures with small amounts of materials and differing depths and sun angles and use them this winter to see what works best in your climate. You can observe what plants actually do in your models and record the temperatures with a high low registering thermometer. Plus you may get something to eat out of your experiment

You can try different thicknesses of foam panels and heat absorbing materials on the back wall to see which produce the best results.
 
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