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Fluid Dynamics.

Its about a 17sq foot opening on each side, i started smaller and each increase created lower temperatures. Mostly because the exhausts dispersion was wide and was able to vent more outwards.

As far as i understand it, higher static pressure fans have no relation to creating negative pressure. This comes from airflow, so i should be looking at increasing the airflow no ?. On top of that adding another fan in series like i have wouldnt help, since series stacking does not increase airflow, only the static pressure limit of the fan.
I had a expensive mixed flow fan that i had installed at the beginning which has great static pressure figures. It only drew power and had no effect on airflow.

How does a shroud work ? Does it help with direction of flow ?
Thanks for all your help dw2, its really helped.
 
Danofdanger,
The shroud, like duct work, can prevent slippage at the tips of the fan blades. Much like the turbulence on the end of an airplane wing, the higher pressure air at the front of the blade tries to 'slip' around the tip of the blade to the lower pressure back side of the blade creating turbulence, friction, and reducing the efficiency of the fan. The closer the fit (smaller the gap) between the blade and shroud or duct, the better the flow. The shroud will tend to keep the stream of air going in the same direction (like a nozzle on a hose).
A higher rated 'static' pressure fan creates the same pressure on the intake (negative pressure) as it creates on the discharge side (positive pressure). Air flow alone does not necessarily create pressure, although, flow does create velocity pressure. A tire has pressure, but does not have any flow.
Keep on a truckin'
 
Yep i'm with ya.
Well i was able to build negative pressure today after applying a cover around the exhausts so theres no leakage. Soon as i turn the fans on i seen the black polyethelene sheets suck in and the toy windmill start to spin. But i can also see air bleeding through the long gap accross the top. Being 6000cfm it may be enough to bring negative pressure from the leaks and from my passive intake. It really all depends how well it mixes and drags. It might end up being i cover up my passive intake and let the top running gap as the intake. Its all trial from here. Il let you know after today how the temps are.
Peace out.
 
It sounds like You are getting a handle on it. Just don't change too many things at once and, I have found that keeping good records of changes and results, help me out with deciding what to do to obtain the results that I wish.
I envy You, having all of that space, I'm growing in a space 71 inches wide by 22 inches deep, and 84 inches tall (a closet!!), but every situation has it's own problems. Like Roseanne Rosanna Danna used to say on Saturday Night Live (in the 70's) "It' all ways something".
 
No Title

Well it was a long one. Its safe to say i was in or at the greenhouse for most of the sun out day. Will be expecting sun burn.

Anyways, i preceded to cover up the exhaust which ended up pretty good (picture supplied). I was still noticing drafts coming from the gap accross the top so i decided to block it up with some insulating batts. This done a good job and i could tell after this that i had a proper negative pressure.
Heres a video of me testing the negative pressure effect.


I went about testing passive intake sizes. I started really big, more than the recommended and calculated. It wasnt until i narrowed it down to about 10 squared feet that i noticed airflow and the windmill spin. This is about the calculated amount when you devide the cfm by 600. I settled on 5 sq feet as this had a more desired air velocity. This video demonstrates how important vent sizing is for pressurization.


The result however was less pleasing. After retrieving the numbers and calculating the difference, i ended up no better if not worse than 50°F. It just means i was getting good airflow with the tunnel design and i think its a tad better. It also has good circulation and mixing which is a added bonus.
I clearly just need more airflow. Even with the combined 6000cfm it wasnt enough. However these haf fans are not built for pressurized enviroments so that probably doesnt help. I even tried adding a 500cfm mixed flow fan to see if it would help with the stress. But it was negligable.

What i think i will do is add another fan in parallel with the last fan near the exhaust. This will increase negative pressure as it throws more air out. I think if i put it at the front by the intake this would barely do anything as the air cannot travel that far. I would need two more to carry the energy all the way through. At least this way i can keep energy costs down and also have a higher negative pressure. This combination may be the ticket.
 

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Danofdanger, It looks like your going in the right direction. The addition of a evaporative cooler might be a way to get the results you wish. First, the type of fan that they use (squirrel cage, or, technically, a centrifugal blower) is capable of producing higher pressures than a vane axel flow (fan type) blower, and, with the addition of the evaporative cooling, could lower your temperatures it better levels. I do not know what the weather is like in your location, but you may need to not use the evaporative cooling during the bloom to keep from having mold problems.
 
Good idea 9fingerleafs. Probably wouldn't want to mist during flowering, but outside temps should come down by then anyway. Probably work well during veg, my plants always smile when I squirt them down. Looks like Danofdanger and DW2 are making progress toward a solution...
 
Yea i wouldnt have to use it during flowering. I am just trying to figure out how much power they use, in my location i only have available to me a portable 10L evap cooler. Its relatively cheap but it all depends how much power it uses. I just discovered too that lean to greenhouses are particularly difficult to cool as they generate more heat because of the extra surface area. You can pretty much consider them to be twice the size of a regular free standing greenhouse. So its no wonder this is requiring so much effort. It just tests my skills is all ;) .
So my options so far are evap cooler or two new fans. Or perhaps both.
Thanks for your help so far, iv learnt a lot.
 
Yep. I've seen Jorge Cervantes make videos about this. Everyone should check out his channel. A little mist can absorb the heat faster than air. But can be moved around just like air ;) its just what I've seen doin by successful and very wise growers again I recommend those videos. Greenhouses are the most covered topic
 
The wattage of the motor on the cooler can tell you how much power it will consume. Multiply the wattage of the motor times the estimated running time, divide this by 1000 to get the Kw (Kilo watts), then multiply by your Kw/hr. cost. I the motor only lists the amperage and voltage you can get the wattage by multiplying the volts times the amperes.
May be You could tack up some plastic sheeting up on the 'solid' wall to reflect the sun light back towards the plants and to also provide an air gap thermal barrier to help cut down on the radiant heat from the wall? It might help and it does not get much cheaper than plastic sheeting, and NO batteries required!!! LOL !
 
Me a sparky ;) but na theres no power specifications on the website or any information online. I dont think a reflector would work unless it was angled out so the enegy is not placed inside. I dont have room for anything else either unfortunately. All good ideas though.
 
9fingerleafs...I have Cervantes' book "MARIJUANA Horticulture The Indoor/Outdoor MEDICAL Grower’s Bible" and it's my go-to book if I need to figure something out. Stupidly, I never thought to look him up on YouTube (Channel? YouTube? I don't know. I'm not a social media or YouTube guy). Whatever he's got to say on this particular subject (fans, etc.) is golden by me. Somebody should put a statue of him up somewhere. Big Sur maybe. When I get some time tonight I'll check out some of his videos and see what his book has to say about cooling greenhouses. Thanks for the Cervantes YouTube tip 9fingerleafs, no doubt tons of great info there.
 
no worries man, jorge is also the authority for me on this subject, i bought the new book, canabis encyclopedia and it blew my mind you gona have a great time watching him explain everything, also check my grandaddy threat i just updated the second harvest, it was all CFL and a lot of training
 
Hi Danofdanger and DW2...swamp coolers are very inexpensive to run, Only a little pump and the fan. The fan can be run without the pump being on. Don't think it would cost any more to run than one of your big fans, maybe less. Much less than an air conditioner. I don't think a little portable cooler would get the job done Danofdanger I know you're not here in the US, but you need something like this even if you have to go to a larger town to find one:
 
9fingerleafs...I went to an outdoor summertime concert once that was put on by a guy whose father was a rich walnut grower. He talked his dad into fronting him the money for the concert. He rented the Madera, CA 1/4 mile dirt track Speedway, hired Maria Muldaur, New Riders, Dan Hicks and several other bands to play on what turned out to be a very hot day. His dad had 2 giant 8 or 10 feet diameter fans mounted on 30 feet tall hydraulic rams, mounted on trailers. Guess he used them in his orchard if frost threatened. Anyway, they made up a pipe that bolted onto the top of the fans, capped one end, drilled holes, and attached the other end to a fire hose which was then attached to a nearby fire hydrant. Those things squirted water at least a couple of hundred feet and saved the day. Without them several hundred hippies would have died from heatstroke that day. One of the most fun concerts I ever attended.
 
Thats really good to know, thanks sticky fingers. I will be looking into that if my last attempt doesnt work as i do not think two extra fans will cut it still. You really have to double your airflow to reduce temperatures by half.
However i have come up with using my 500cfm mixed flow fan as a intake seen as it does nothing on as exhaust. I figure because i run a wind tunnel which has very little to no negative pressure that using the fan (which shouldnt be done if your trying to pressurize as it destabalizes it) as a intake might do something. It has excellent throw as well.
Well see.
 
Haha I'm sure it was a big help. In hot weather I've seen handheld fans with a little water mister right in the center so when you press the button it squirts. On a hot day under the sun the water is evaporated very quickly by the wind. Taking with it the heat from whatever surface it landed. After long periods of time using the fan your face is freezing cold no matter how hot it is
 
Made some good progress today, the mixed flow intake worked well. Before, the best temperature difference compared to my outdoor thermometer was 48°F. Now im getting 37°F. Not bad. Its a pretty good summers day out and it only gets a little hotter throughout the rest of the summer but the max temp iv been getting is around 95°F. This is acceptable for me, 90 max would be ideal but i feel comfortable enough with this. Maybe with some tweaking i could make a little headroom who knows.

To conclude i feel the intake has helped because theres not enough pressure to bring in new air, so bringing it in does its job for it. I also think the HAF fans must have been bogging down under the static pressure when used as negative pressure. Although i had pressurized the room, id say the airflow rate had decreased so much that it was struggling to cycle fast enough. If i had a 2000cfm high torque exhaust fan it would probably do well and perform close to what i jave now.
I prefer my setup however because i am using less power (250 watts). It doubles as circulation fans and mixes the air well.

The lesson of the day is, if you cant pressurize a room, use a balanced pressure system. Plain and simple.

Thanks dw2, sticky fingers, fingerleaf. Been a great trip. Learnt a lot.
 
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