Dan Miano wrote:Mike,
Thanks for the detail review. I am going 55 degrees from horizontal. I'm not sure what the standard reference is, horizontal or vertical. This angle maximized solar radiation in the winter months. I added a pic below of the solar radiation info I got from NREL at my location
Dan Miano wrote:Glycerin sounds like a good option and the phase change temp seems perfect. Cost is one issue though, from what I found it would be about $2700 to fill one tank. I can always add it in the future as long as I make access tubes to the tank fill caps!
Dan Miano wrote:I planned to add vertical timbers because the soil is mostly clay and things move quite a bit. I wasn't sure if the total weight of the greenhouse could be properly supported by the raised bed timbers.
Dan Miano wrote:
I'm excited about designing and building an auto thermal curtain for the glazing with that Reflectix material. After doing the math to see how much heat is lost out of the glazing vs. the insulated walls I will lose about 4-5x more heat through the glazing! Even if the Reflectix only gives me an R value of 1, it will reduce the heat loss through the glass by 4x.
Charli Wilson wrote:Looking good.
Any plans on how you're making (or what you're using) for your air/water heat exchanger?
I'm planning something similar, only I've got half the greenhouse running on a 'standard SHCS' with air tubes under the earth, and the other half with an old radiator painted black- heating up water and taking it to an insulated buried ibc container.
Dan Miano wrote:
Do you add anything to the water to inhibit microbial growth, or is it not an issue?
Chris Southall wrote:Nice! this our attempt at a similar project seems to add about 4 degrees at night on a sunny day. http://www.ecodiy.info/solar-greenhouse/
kw hatten wrote:Dan,
This may be my first post ever! Saw this thread and thought I'd forward an interesting video link (have you seen this already?). The concept of annualized geo-solar intriques me; perhaps you can do something on a smaller scale. Kind regards. https://vimeo.com/168761278
ronie dee wrote:Are you heating water in the summer to use for winter? Have you ever heated up a 300 gallon tank of water before?
Mike Jay wrote:Ooof, that is a bit pricey. I checked Bulk Apothecary and they're only $1800 and it comes in the tank already. Still quite expensive. If you know any biodiesel makers I believe glycerin is a byproduct they have to dispose of.
Hans Quistorff wrote:It seems like you could get automotive radiators from junkyards that have electric fans built into them. Hanging from the north celing they would circulate the air in the greenhouse cooling it during the day and warming it at night. They would not have to be run at night during the summer so the tanks will start off hot. You could probably use a separate radiator for each tank only drawing heat from one tank on mild nights conserving heat for cloudy days or very cold nights.
As for the planters, wicking beds work very good in my greenhouse. I layed down a water tight fabric with the sides and ends folded up to the height of the bed. The bottom was sloped 2" to one side and I placed a 3" slotted drain pipe on the deep side with an elbow on one end coming to the surface. I keep a plastic bottle in that as a float level. When I water from the surface any excess drains into the slotted pipe. but once it is uniformly damp keeping the drain pipe full wicks water back into the soil keeping it uniformly damp. I only do this on the south edge of the greenhouse. the rest of the greenhouse has 3' tall barrels with the drain tube circled in the bottom. They work the same and I can put them on a hand truck and move them around and outside for the summer.
David Maxwell wrote:I have some experience here. I built a similar size solar greenhouse about 5 years ago, with Twinwall polycarbonate glazing on south wall and east wall. (This last was probably a bad idea.) Initial heat storage was in 1 gal plastic water jugs stacked along north wall. Not very efficient at capturing heat basically by radiation alone. And the jugs broke down after a year or two. Now have 2 tanks of 450 Litres, (total of about 230 US gallons), with water circulated through 2 car radiators in the peak of the greenhouse by mini 12 V. submersible pumps On sunny days, return from radiator is about 3 degrees C above water going to the radiators. But there is no way that I can maintain a temp of 50 degrees F through the night - it generally falls to just above freezing, despite my running the pumps and fans through the night, (essentially drawing the heat back out of the water in the tanks) (I am in zone 5b in Nova Scotia, Canada, with outside temps dropping at times as low as minus 10 F, (-22 C). My next direction is going to be at reducing heat loss, rather than trying to increase heat storage. (The water gets up to + 20 C after 5 days of accumulated sunshine, dropping gradually to about 4 C after 5 days of heavy overcast, snow, and generally unpleasant weather.)
Incidentally, the cheapest and easiest way to provide exhaust fans during the summer is with a hot-air furnace blower, (available from furnace repair places when they replace somebody's old furnace)
Tom Robertson wrote:Pool blankets make cheap insulators
Or take a page from the double poly green house .
Though a sheet of poly over and use a fan to inflate it.
BTW. Glycerin is a by product of biodiesel.
One question. How did you get from 43,315 BTU's to 86,630 BTU's?
So if you can gather the heat and move it to the tank (say with a radiator) and then distribute the heat AS NEEDED to where the plants need it (low to the ground or underground) it may be the best thing ever...
David Maxwell wrote:I am getting way beyond my competence here, but perhaps my data will be useful, and somebody who knows what they are talking about can check my reasoning. The question was posed as to whether a car radiator, with air blown through it by a fan is an efficient heat exchanger. (I am in Canada, so tend to use metric measures.) I have a temperature monitor which records at 20 minute intervals the temperature of the water in my storage tank, (going to the radiator), and the temperature of the return from the radiator. On Feb. 3, 2017, (a sunny day), the temperature of the return flow first stated to rise above the flow to the radiator at 0945, and this differential persisted until 18:45, (coasting on the heated air in the peak of the greenhouse evn after the sun had set). Thus we had a total of 9 hours of heat collection., or 28 time intervals.. Now we get into alligators. I subtracted temp To from temp FROM at each interval to get the increase in temp during that interval. (Was this legitimate?)(The gain ranged from 0.2 degrees C up to 11.35 degrees C in the 20 minute block) I then treated this as 27 trapezoidal blocks of heat gain and calculated the area of each block using the formula 1/2(T1 +T2), where T1 and T2 are the height of the two sides of the trapezoid, and multiplied each block by 1/27 to get the amount of heat gain in that block. (I believe this corresponds to something called Simpson's Rule (?)) Finally I added the area of each block, to get a total of 6.414 degrees C rise, essentially integrated over the 9 hour period.
The flow of the pump is 3.15126 L/min., giving a total volume of 1701.68 Litres of water flowing through the system during the 9 hour period. 1 kilocalorie heats 1 litre of water 1 degree C, so I captured 6.41435 X 1701.6804 = 10915.17 Kilocalories , or 43, 314.88 BTUs. And, with two tanks, (of 450 Lites each), the total energy capture for the day was 86,629.76 BTUs.
Now, what does all this mean? Assuming that my methodolgy sounds reasonable, (and I am distinctly uncertain about the legitimacy of, for example, my summing the areas of 27 trapezoidal blocks to get a total area under the curve, is appropriate), and comparing my total to the elegant heat loss calculations above, I am not capturing enough heat to last more than a day or two of cloud. But the efficiency of heat transfer from air to water, across the radiators is not bad, (a gain of up to 11 degrees C during the passage through the radiator, at a flow rate of 3.15 L/min, (0.83 US gallon/minute).)
Have at me!
Does anybody have experience installing frameless double paned glass on a greenhouse?
Jeffrey Sullivan wrote:I have an aquaponics greenhouse with 1 300 gallon IBC above ground for fish and and another 200 gallon in the ground in a similar setup as yours for a sump. Even with the 2" foam board around the sump heat does leave it to the ground water around it. I just found this guy on YouTube last night and thought I would share it with you. Might help. https://www.youtube.com/watch?v=6SD5HpXZc1w
This year I plan to build a rocket mass heater and use the mass as a bed for 2-3 IBC fish tanks to heat my fish water and greenhouse. Water is a really good thermal mass. I thought about geothermal but I think this will work much better. Putting your tanks in the ground I think you're already creating a disadvantage since the ground will suck out a lot of the heat even with insulation.
Jeffrey Sullivan wrote:I have an extremely high water table and when there is a good rain the sump will actually start to float if it's not filled above the water table level. I only noticed that the water temp outside the tank is pretty close to the temp inside the tank. No way of knowing how far the dissipated heat goes out underground. Question there is does this give you a larger heat storage area or are you having to generate more heat to compensate the loss.