For summertime, hot dry, West Texas GH that's 33' L X 12' W X 10' H, roughly 400 sq ft, 4000 cubic feet, I want to try to delay fresh air ventilation exchange for as long as possible each day for experimenting with sealed system CO2 injection.
I'll have a monster solar heat build up challenge, to say the least, but I want to invite suggestions here for mass cooling setup that might could be used to extend that closed up period by any additional x number of hours on a daily basis.
I'll vent structure (abandoning CO2 for the day) and can even partially or completely shut off any additional solar gain whenever this scheme to cool internal air has been maxed out and internal temps getting overly excessive.
I've no illusions of beating the sun at this game, just postponing and extending into the daylight hours a little longer the maximum time under CO2 closed system before surrendering and abandoning CO2 for the day.
Here's what I have in mind that I'd first be interested in suggestions to maximize its effectiveness, before suggestions for going in a totally different direction, though eager to explore whatever sounds like it'd work better.
I've got ten IBC 260 gallon totes I can fill with water after I position them outside, nearly right up against and all along northern long side of GH wall, all in a tight row, and then airtight box them all in, on bottom & top, too, as a single group with 5" freezer panels (50 cents sq ft salvaged) through which I can pump hot exhaust air from GH into one end of this rectangle 'cooling box' and after that CO2 enriched hot air has wound all around, under and alongside them, hopefully cooled down some, air can next be inline fan pumped through either a swamp cooler or mister before it re-enters bottom of GH interior on opposite side where it'd been exhausted.
BTW, very low humidity there to begin with and GH can usually use some additional anyways. However, I don't have unlimited water to go crazy solely relying on evaporative cooler to do it all non-stop. I also don't have unlimited power for overly aggressive traditional mechanical cooling either. Everything's PV, batteries and inverters powered.
I'm also strongly considering that with all that water mass and the way it'll want to stratify, might be much better off just plumbing & pumping it to circulate through a radiator to where the air goes through it right before it next goes through that evaporative cooler or mister. Might could then get away with saving some water and energy only employing evaporator when this radiator and all other measures had maxed out first and it's needed most then, as a last resort, to better cap rate of internal air temp rising.
Also, to 'recharge' these IBC totes at night, in the 'cooling box', they will all have been spray painted with the best high emissivity paint or coating I can find, still looking for that if any suggestions, and all the insides of this box will have highly reflective mylar and the top will flip open 45 degrees outward, so at night I'd have it opened to maximize radiant cooling of the IBC containers, besides being exposed to the typically 25-30 degrees cooler ambient night air temps. Also, north side of GH above top of this 'cooling box' will also have that same reflective mylar up its outside to better facilitate IBC totes reflecting their heat skyward. From down in the box, all the totes radiant heat 'will see' is reflective mylar to the cold black outer space above.
Additionally, if employing the radiator plumbed to and pumping the cooler water in the totes during the daytime heat to cool the GH exhaust air going through it, then I could also redirect in & out air flow through radiator at night to help cool that same water anytime the ambient air is cooler than the water by directing that cooler ambient air through the radiator then instead.
Anyways, that's the basic plan, appreciate any other considerations I've overlooked or other suggestions to maximize this set up or, if basically too little cooling gain for all this proposed effort above here, another way altogether to explore.
Some of the questions I'm struggling with...
How fast, how many air changes per minute or longer duration, do I need to ideally be aiming to move exhaust air round trip through the IBC and radiator and/or evaporative cooler gauntlet?
Slower, so it gets chance to cool down more in contact with totes/radiator/evaporator longer, or always fast as possible to have higher volume of air/water contact?
What range of size CFM inline exhaust fan and also pusher fan at radiator and/or evaporative cooler might I be needing then, considering air resistance drag along most it's tortuous path?
I'll need some radiator and pump flow and fan size 'rules of thumb' to get a fix on sizing that whole system and suggestions on sources, too.
BTW, Cool tubes in the ground I'm a big fan of, too, but cost of excavation and piping has it not on top of my list... yet.
I'm thinking now for that night sky radiative cooling of the 10 totes combined 2,600 gallons water mass enclosed in the 5" freezer panel 'cool box', it'd be much more efficient and a whole lot easier not to mess with lifting and securing that freezer panel top every night, then mornings closing, and risk then not maintaining a good seal moving it so frequently, but instead just pump the water to the top.
IOW's, atop the insulated panel cover on the top, which all of its segments together total approximately 5' wide by 33' long, I'd pump water from totes below and through a couple hundred feet of hose or piping laying on top there that'd drain back into totes though manifold that connected to them all at their tops under the insulated cover. (With all totes also common plumbed together at their bottoms, they'd be self leveling among themselves.)
The hose/pipe and the aluminum top of freezer panel it sat upon would then all be coated or painted in best emissivity product rated for that night sky atmospheric window between 8–13 μm.
That hose or pipe would also need to be highly thermally conductive, too.
This top insulating panel, that this coated hose/pipe would sit atop, would still have mylar all along around its outer edge all angled up, too, like a solar cooker. And, hose/pipe would have IR translucent thin plastic covering to minimize ambient air temperature eroding night cooling gains via convection interaction with warmer air. Easier to keep emissive top clean then, too, just shake out or replace cheap plastic as needed.
My questions for this portion of the project then are...
#1 - What's best, commercially available, thermally conductive high emissivity paint or coating, ideally targeted for that 8–13 μm window?
#2 - What's best hose or piping that'll readily conduct heat of water passing through it? I know copper would be great, but need to also look at anything cheaper, too.
#3 - What's 'sweet spot' size of hose and pump combo I need to be shooting for to get the maximum tote water mass exposed to that radiative cooling effect up top?
Pump might also do double duty if it works out, with valve at its output, to be the pump for the radiator inside that's only being used during the day cooling internal air there.
Appreciate any thoughts, 'rules of thumb', or suggestions.
Farmers used to use aluminum irrigation pipes to connect from the pump to the sprinklers. These would be highly heat conductive to use as a radiator and may be for sale used in your area.
In the shade they should be able to radiate heat even in the daytime before the water returns to the tanks. I can envision a system where your whole north wall would have a space separated from the GH lined with these pipes and the water being pumped up through them wold cool the air which would fall drawing the air from the top of the greenhouse. Then the warmed water would return to the tank tops through the same kind of pipes exposed for radiant cooling. The system could run constantly on the same pump because at night cold air setteling to the bottom of the GH wold be drawn in and warmed and rise to the top of the GH.
Hans Quistorff wrote:Farmers used to use aluminum irrigation pipes to connect from the pump to the sprinklers. These would be highly heat conductive to use as a radiator and may be for sale used in your area.
Got a lot of the Al irrigation piping out this way.
Tons cheaper than anything copper, that's for sure!
Thanks for that, might need to go visit local scrap yard,,, again.
Sorta related, can anybody tell me how to figure how much heat is lost through a thin horizontal layer of poly film on top of
greenhouse when inside air temp at that ceiling top is 100F and light breeze of 70, 80 or 90F outside wind is brushing by it?
IOW's, what cooling of that 100F air temp might be expected if system isolated where no more heat being added or any other
factors involved, just the relatively cooler breeze outside against that poly that's containing 100F air under plastic there?
Joy, Yes, adding CO2 can be a big plus, faster growth and many plants then thrive at hotter temps than normal, too. It's essentially a gaseous fertilizer.
However, only really shines if everything else is already dialed in first and you only use it during daylight hours, not night.
Many commercial horticulturists (especially marijuana growrooms) will run it about 4X's higher, around 1.200 ppm, some even 1.500 ppm or more, where normal air is typically in 350-425 ppm neighborhood, except for greenhouses without good daytime ventilation, plants eat it up fast during photosynthesis and when it gets down under 200 ppm, they start shutting down in a big way.
CO2 is heavier than air, so in closed greenhouse or growroom that it's being put in, they do it above plants or hose it in at their fans aimed at plants and keep greenhouse sealed up good so it won't leak out too quickly.
Google it, lots of interesting stuff about it out there, also clean burning propane greenhouse heaters in winter can do double duty adding CO2 there, too. And, there's a lot of cleaner ways to add it, too, like getting tanks of it with regulator or fermenting brews inside greenhouse, etc. CO2 ppm meter to check and track air content are inexpensive.