NFT or HPA? & Root Zone Ventilation

Hey guys, I'm setting up a grow room and I'm trying to net the best possible results. Honestly, I'm more excited about designing a really cool grow room/setup more than the plants I'm actually growing lol.

I can't decide if I want to do Nutrient Film Technique or High Pressure Aero. Either one I do will follow true methods, not sloppy or "sorta" NFT/Aeroponics. I'm using plenty of HID light and I'm building the room to be air tight with CO2 enrichment. I was thinking about doing NFT and using a cooling system (of my own design) to keep the nute tank temp at 65F, with 2 separate tanks for the juvies and the flowering adults. Oh, ya, doing 8 juvies and 8 adults, autoflowers like lowryder 2 or other autoflower strains. My room temp/humidity will be controled as well.

So ya my idea for NFT was to cool the nute solution and also cool the air in the root zones (in the NFT channels) and control the humidity by using a fan ventilation system running through all the nft channels. Air would be brought in from outside, filtered, pass over cooling tubes (heat exchangers) and then a thermostat would regulate the temp, and a humidistat would control the ventilation fan. The air flowing through the root zones would be very gentle, just enough to keep fresh air moving through to control humidity and bring in fresh air. Since I'm doing CO2 in a climate controlled room set at 90-95F ambient, I know that the root zones may get warmer, and also that is a lot of humidity in the evaporating nute solution which will raise the RH in the grow room, which I want to keep at around 50%. I want to keep the root zone at around 70% RH, 65F air temp and 65F nute temp. The gullies will be 3' long and have about a dozen very tiny holes drilled through the bottom to allow an air pump to gently aerate the water as it flows by the roots. I've put a lot of thought and research into the NFT setup, but now I've been questioning it and wondering if I wouldn't achieve a better grow with an HPA system.

Since I'm doing hydroponics and investing all the time/money into building a dedicated room, sealing it off, using CO2 and climate control, I obviously don't want to use the wrong technique here.

The high pressure aero setup would be done pretty much to the book. I'm not sure what I would use for growing spaces though, maybe some fence post PVC (i think that is 6"sq)... Something that is deep and will provide plenty of root space/aeration.

Do you guys think that my NFT setup will yield good results, or would I be better off going with an HPA setup and abandoning my root ventilation/root space climate control idea that I had with the NFT? Or should I do some sort of combination? I guess what I'm also wondering is if my root ventilation idea is any good or not.

I think the benefits of controlling the root space climate is:
1. Constant RH % control which should promote root growth and keep pathogens @ bay.
2. Root temp control, should also help promote health and keep pathogens away
3. Keeps fresh air moving through to clear out toxins and stagnant air accumulation around the root zone when it gets larger.

I've done all sorts of searches to try and find experiments or discussions about root zone ventilation and have come up dry (no pun intended lol). It seems like a good idea on paper (and in my head) but I may be entirely wrong. I know that you want the roots to dry out slightly for a very brief period, so I think if kept the root space at a constant RH and temp that the roots would be pretty damn happy.

Any input is appreciated

From what I've read (I grow DWC) your going to be better off going HPA, that being said you could design a large verticle HPA/NFT combo where the water drains downhill back to the rez after being sprayed. There are many grow journals that use large diameter PVC (forgive my analogy) but they make it look like the original donkey kong level where each is slanted the opposite direction to get the desired flow from gravity.

Also it is recommended you use a timer such as 1 min on, 5 min off for your sprayers which will allow optimal time for root zone aeration.

Its not possible to hold the root space RH at a constant level with HPA. Ventilating the root space will remove the mist and chill the root surfaces in the process, so maintaining a constant root temp will be difficult as you`ll need to account for windchill .
The roots absorb the moisture, if you need forced ventilation to dry them out you are delivering too much mist.

HPA grows the most efficient roots, their surface area is highly absorptive. No other method that I am aware of is as conducive to root hair development, or as efficient as HPA. You do not want to over wet roots. Attempting to feed roots that are already wet does nothing to further nourish the plants, and will prevent them from developing lateral roots and root hairs.

As a small personal use grower, I have avoided installing an accumulator, but I do use a Aquatec 8800. I have my rez higher than the pump, so the pump and feed lines stay primed to the mist heads during the dry cycles, but am confident that my first second of pressure is not the same as I would get using an accumulator; it lacks the initia push. This being my 4th grow using this technique, and tweaking each time (and with Atomizers expertise) I feel I am more in the ball park than ever.

The most current learning tidbit was discovering how critical early veg wet times are.

Thinking my supposed AF would finish in 2 weeks (that was 5 weeks ago and she's still not finished) I started a grow in my backup system; same pump and heads, but an IGE timer, whose minimum wet cycle is 30 seconds. The roots grew fast and long (see photo), like a baseball bat whereas HPA roots look more like a softball. They hit the bottom of a 15" deep pod in 10 days.

The photo below is the result of 2 weeks of vegging using 30 second wet times. I lifted the roots off the bottom using lava rock and a commercial lighting diffuser, so they do not soak in runoff. Note the majority of lateral roots are on the bottom, consequently, the nutes have a long climb to get to the plant, clearly not efficient. Now that said, the plants are doing well, and will still yield some fine herb.

This new awareness is huge, but as it is already heating up here (yesterday was 89 degrees) and my grow area is anything but climate controlled, I will have to wait until cooler months to use this knowledge.

hth



hth

Atomizer said:

Its not possible to hold the root space RH at a constant level with HPA. Ventilating the root space will remove the mist and chill the root surfaces in the process, so maintaining a constant root temp will be difficult as you`ll need to account for windchill .
The roots absorb the moisture, if you need forced ventilation to dry them out you are delivering too much mist.

Click to expand...

mmm, I disagree Ventilating the air will remove the moisture, true, however if the ventilation is very gentle and it only comes on when the RH rises above 70% (a humidistat) that should keep the RH in check. I should also mention that the air entering the root zone space will all ready be in the mid 60's.

Just to clarify, I mean that I'm not looking to blow crazy air through the root zone but rather just a very gentle current and only when the RH goes above 70%. I know that this may seem trivial, but in the long run it may prove to be a good idea, and not difficult to setup either.

Let me know what your thoughts are on that.

PetFlora: I'm not using "accumulators" either. I'm using 3 "pressure vessels" (undisclosed containers at this time lol). One tank will be filled with flower nutes, the other tank with veg nutes, and the third tank with RO water, for the last week or so of the flowering before harvest. I'll also be growing AF's like you. Each plants spray nozzles will be individual and allow me to give any particular plant whichever nute/water I need to. Each adult will have 2 high pressure misting nozzles. Juvies will have 1 each, spraying directly up, where as the adults will probably get sprayed from the side near the top so that the water can run down the roots and drip to drain out. None of the nutes/water will be recycled. It all goes directly into a sewer drain. Each tank will hold 2gal of nute mix or RO water, the rest will be filled with a 140PSI of compressed air. All the nute mix will be filtered as well. I'm really going for a very controlled environment here, as you can probably see. If all works out, I will upgrade to a much higher PSI later down the road, but I think 140PSI is good for now and it definitely does qualify for TRUE aeroponics.

I don't want to give all the specifics of my setup out just yet... I will show a little more later on when I have proven results to back my theories. I will say that the entire setup is extremely environmentally friendly and most of the watts being used up are for the lights, rather than cooling systems, etc. The cooling system is the secret part

Thanks guys!

Hi
The slightest airflow will vent the mist as it has very little mass to keep it in the chamber. From experience i can tell you the humidistat (even one that has an adjustable differential) will be next to useless as the root chamber is far too dynamic. After the misting pulse ends the RH begins to climb as droplets evaporate into the air. The RH reaches a peak after some minutes and then starts to fall, it could be 10 minutes before it drops back to the starting point. Sometimes it doesn`t drop back all the way as any standing water left behind after the misting evaporates slowly which constantly bolsters the RH.
The humidistat will never call for mist unless you alter the setting.
Roots can`t use moisture in vapour form (RH) as its a gas. If you run airflow into the chamber you will affect the temperature and that in turn affects RH, if you have standing water as well..the RH will increase (evaporation rate increase/temperature drop), its the exact opposite of what you expect to happen from running the air Your roots will dry out long before the standing water evaporates.
Don`t take my word for it though, put a hygrometer probe in a test chamber and record the starting RH, use a spray bottle to fire some very fine mist into it. Start your stopwatch and see what happens to the RH and how long it takes to peak and fall back. Bear in mind a timed misting cycle may be 1 sec on / 2minutes off, the humidity won`t reach the peak inside 2 minutes let alone fall back to start

The correct droplet size range qualifies it as true aero, high pressure provides a means to generate those droplet sizes.. true aero can use negative water pressure

Thanks, Atomizer. I'm glad you challenged my thoughts bc I wasn't aware that the climate in the root zone is so fragile. I'd imagine then that the humidity in the misting process adds significantly to the grow space RH, right? If so, would it still be possible to have a vent system on the grow channels but not use any type of artificial air flow, rather letting the air/humidity move as it wants to? The reason I want to do this is because I don't want to add a lot of humidity from the watering process to the grow room, and I don't want to add heat from the grow room (being kept 85-95F) to the root chamber. (That is why I'd like to isolate the 2 spaces, because of the difference in temp/rh between them) But maybe that isn't such a bad thing because it allows the root zone to shed the excess humidity to the grow space before they get sprayed again. Let me know what your thoughts are on that.



One other thing, I hope you don't mind me picking your brain , I've read that using copper for the nute lines is a bad idea, and if a metal is used to only use stainless. Is food grade stainless steel line OK to use? I don't need to use much, only about 2 or so inches for each plant. It's just easier and much cheaper (and much more reliable if you ask me) to attach the spray nozzles to stainless steel pipe, rather than PVC. I can TIG weld 10/24 stainless nuts on the end of some 1/8" stainless tube and then thread my spray nozzles into the nuts. It'd be cheap and easy for me to do that.

I'd use higher pressure but the solenoid valves I'm using on the nute tanks are only rated up to a 140PSI. High pressure solenoid valves are costly. Maybe in the near future I will upgrade though and then run a higher PSI. The spray nozzles I'm using now have a .012" hole in the center, supposedly for >50 micron. They are the mist nozzles you see around pools, etc. I want to use .008 or smaller but those are only recommended for 250<psi. I'd be interested in knowing how to do this with negative pressure... I do have a refrigeration vacuum pump that I used for servicing/building HVAC systems. You can also make a sweet pressure pump/vacuum pump by using an old refrigeration/air conditioner compressor. You can build seriously high pressures/vacuum with those things, and they are cheap to obtain second hand.

The amount of liquid in each misting should be very small, if any escapes it won`t add much if anything to the room. The plants on the other hand will increase room humidity directly through transpiration. Insulating the chamber will protect the interior from most external heat sources, as long as you don`t forget to add a radiant barrier.

Plastic tubing and john guest fittings are the best option for easy maintenance, stainless is overkill for a few hundred psi but if you have it on hand then why not A small amount of copper/brass doesnt seem to hurt anything but i`d only use it if there was no other alternative.

Thanks, Atomizer. It's going to be a closet grow and it will be completely sealed up (because of the CO2 enrichment) and I'll be using geothermal cooling to cool and dehumidify the room. I know that vegetation will transpire quite a bit of moisture. I'll keep it simple (stupid) and scrap my root vent idea... for now lol. After I get everything setup, I will monitor the humidity in the root zones and then I'll have a much better idea of what's going on and can consider testing my thoughts when I have that data.

Is it safe to use aluminum tanks for my nute solution, or should I keep those s/s as well? I have stainless materials on hand and I can do stainless welds or aluminum welds. I'd like to keep all the metals the same through the system to minimize any chance for electrolysis.
Never mind, I think I'm just going to keep this stainless through out, it's much easier to work with.

** I'm also planning on doing 2 mist heads per adult plant, one on each side of the roots. Seems like a good idea to me, what do you guys think? Also, is there any particular distance or mounting position in relation to the roots that would be optimal?

You didn`t say how big the root chambers will be so its not easy to say. Assuming you have 125psi average pressure and the timer can manage a 1 second mist pulse.. ideally you want to be looking at 20gal of chamber per nozzle (assuming they are 0.65gph each @ 125psi). If you can manage a 0.5second pulse you can use 2 nozzles per 20gal which would help with the coverage.