Hello,
My first post here. I am 100% amateur, just fan into greenhouses, yet, I did not have any (well I am having first one, but its only 1m2). But I am so excited about this idea, that I am googling hours and days to get more info
Here are my thoughts:
Like every building, also the greenhouse has some heat loss, during day and night. How much of a heat loss is 55F difference, I am not sure. Example: outside 0F, inside 55F, and the main factor is the lambda of the foil/glass or R value.. In different words, how much heat we capture, or let thru/out.
Imagine if our greenhouse would be built only from 2 glasses, between which, there would be vacuum. We would have close to zero heat loss, therefore one tea candle would keep up the heat at desired 55F (ground temp)
But thats impossbile, as there is no glass like that, and even if we use regular glasses, it would be extremely expensive (maybe $15/sq ft , but the Uw=1 or so, so heat loss would be very high still.
Perhaps, as mentioned, a movable insulation (2' of some good wool/EPS), but not sure how to handle sunrise/sunset temp shocks / heat gain=loss shocks.
Regarding radon, I think it behaves like gas - it simply escapes from greenhouse, unless its 100% airtight.. I think it should escape thru regular foil (even two or three or more), but not sure about window.. But any gap in greenhouse = heat loss, hm.
But back to the topic, so we have some heat loss value, so we need to match it with heat gain. There is no battery, which would match it for whole winter, because it is impossible to insulate the battery itself. We could pack/insulate the battery underground or even above ground with 5' wool/EPS, but the heat will be lost after few days, or weeks at most, IN MY opinion. No technology can catch heat forever, nor for month. it would need to be MASSIVE, and the problem is - IS the heat gain during day/summer/sunshine high enough, to store such energy? I have no idea. Just thinking aloud.
The good thing is, there is 40-50F underground, "for free". But still, rain = heat loss, wind = heat loss.. lack of insulation = heat loss.
Thats why I am googling days around, if there is a true and existing greenhouse with data during winter, eg in +-NY area (my place is Slovakia, Europe).
The cost is one thing, but it SHOULD be one time investment, so if it pays off in 10 years, it is quite interesting (its not liquid asset I am afraid, so no house selling in near future?)
I am not able to calculate the loss with much accuracy... Maybe someone is?
For me - amateur, its easier to simply build some 2-10m2 and test it
The more passive, the better, the less on/off mechanical switches the better. I can not believe its not all around us already... "Free" food basically
Also, what about mirrors, mylar ? Few sq ft of extra nondirect sunlight... Or what about rocks as thermal storage?
http://www.engineeringtoolbox.com/sensible-heat-storage-d_1217.html
But I am afraid, none of this alone is able to generate passive 365.25 days greenhouse.And combining them = too complicated, easier and cheaper just to turn on the heater and bear the costs.. (because the time I would need to monitor it is "expensive" but I never calculate this into costs, but imagine one day the system fails, and all veggies will go to compost, that would hurt too...)
Anyway, thanks for great forum, so much new information for me
