Trying to do the math on an affordable HPA system

The 4.15LPH nozzle flowrate is unique to your system, the same nozzle in a different system would likely result in a different value. The same applies to accumulators, if you have two identical tanks. same brand and capacity they may not be the same. Testing will provide the answers but they will only be applicable to your system. If the test is geared for 500 cycles a day it may not be accurate for1500 cycles a day, its similar to calibrating a meter for 5000ppm when you plan to measure 500ppm, calibrating to 500ppm will provide better accuracy

That makes sense, and good points!

If I am reading your recommendations for flow rates and on/off times correctly, that 1500 cycles per day number should be at least close to the upper end of what I would need, and the 500 number would be on the lower end for early growth?

There are still lots of variables and unknowns to deal with here. Of course, the only way to know for sure if I got it all close enough will be to see how the roots look.

The testing will be interesting, and Im looking forward to all that. Im sure Im going to be pestering you for more advice and recommendations as I move forward though.

Oh - the new tank arrived and its NOT damaged! Back to building.....

DM-2 TDS meter - mini review.

I ordered this with the new tank, and just got around to playing with it. Not surprisingly, it wasnt calibrated very well out of the box. It was reading a 1413uS test solution as 880 on the IN and 799 on the out. The instructions say its using the .5 scale, so I adjusted both channels to read 706.

After rinsing, and drying the probes, I checked some nute solution I have that reads 1.3 EC / 650 PPM on the .5 scale with my BlueLab meter. The IN read at 820 and the out read 710. Hmmmmmm. The calibration didn't hold, or maybe I did it wrong. The buttons are a little tricky to use with my fat fingers.

So, I re-calibrated both to read 650, using the nute solution as the reference. After several rinse, dry, test, repeat, the meter seems to be holding the calibration reasonably close. The specs say its +-2%, and that seems to be about right. The variations were on the order of +- 10 to 15 PPM or so. Part of that Im sure is the solution not flowing. Even small movements of the probes or stirring of the solution change the readings a good bit.

Then I diluted the nute mix down to the 320 range. The IN now read 300 +- and the out reads 330 +-. Thats more like a 10% total variation - 5% up on one and 5% down on the other.

So, for this particular meter, it looks like its going to be important to calibrate it close to the range you are trying to measure.

Its also going to be important that both probes are in still water, or water that is moving at the same speed more or less. Other wise, one will read higher than the other due to the flow difference. The instructions say you can compensate for still water by calibrating 3% higher than the test solution, but I havent done that yet. I'll see how the meter reads when its plugged into the supply solution, and compare that to the reading I get from the rez with my BlueLab.

I dont think I really need to worry about the absolute value of the IN or OUT readings as long as I can accurately see if there is a significant difference between the two. Its that difference that will tell me how the plants are feeding and if the EC of the nute solution needs to go up or down.

Its not going to be useful for detecting very small differences between the supply PPM and the run-off PPM, and probably not for mixing nutes, but it should be fine for monitoring larger differences in the root chamber.

Dang and darn and shoot and crap! Things were going very well today. I finally got the control panel together, and powered everything up to look for leaks, adjust pressures, flush the system, etc, etc.

BUT - the stupid plastic "adjustable pressure relief valve" I bought is NOT a pressure relief valve at all! It is some sort of stupid bypass, pressure reducing, flow regulator piece of useless stupid junk. The stupid thing lets water flow through no matter what the setting is. 100% useless crap. On top of that, its not covered under Amazons warranty, so I have to get a return authorization, AND pay return shipping!!!

aaaaarrrrggggg!!!

Here is my control center. Its ugly, and I still need to tidy up the wiring, and a few other details, but it will get the job done. I managed to get everything to fit where I can reach it easily, and keep and eye on stuff.Now off to Home Depot for a 150 PSI T&P valve.....

Im all better now -well almost.

One thing I really liked about that crap valve I bought was it was plastic. All the other ones are brass, bronze, or stainless. The stainless versions are $$$$, other than some cheap ones that only go up to 100 PSI. I need well over that for the system to work, so Im stuck with a brass water heater T&P valve. Its at the highest point in the system, and there will be trapped air in the riser, so maybe it wont corrode too badly. Im still going to have to keep an eye on it and hope it doesnt contaminate the nute solution with copper. I may have to replace it yearly though. We will see.

Im plumbing it in so that if it pops, the discharge will go back into the rez.

The next steps are:

1) flush the system
2) adjust the cutoff switch, and pressure reducer to the levels I want. Starting points will be 80 PSI on the reducer, and 85 cut-on for the pressure switch. Cut off will be around 125 or as hi as I can get it.
3) measure the usable volume of nutes that the tank will hold with those pressure differentials. If the math is accurate, it should be around 1 gallon out of the 4.5 gallons the tank is rated for.
4) I need to build a fixture to mount/hold the solenoids and nozzles. The solenoids need to be outside the root chamber, so they stay dry. At the same time, I want as short a distance as possible between the nozzles, and solenoids to reduce lag in the spray. Plus, it would be nice if they were easily serviceable if they get plugged up. Thats going to take a little thought.

Ive decided to just go with 4 nozzles. Im pretty sure its going to take that many to fill the chamber properly. I can always reduce the ON time if needed.

Ok, back to testing, and adjusting - hopefully with no more surprises!

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Some more tank volume math.

This new tank is listed as 4.5 gallons.

I just did a series of tests with the pressure switch set to turn ON at 85 PSI and OFF at 115 PSI. Im able to get .86 gallons or 3.25 liters of water out of the system with that pressure differential. The bladder is pumped up to aprox 82 PSI. That works out to a true volume for the tank of 3.7 gallons. Thats higher than I was expecting, but Im happy with that.

It takes the Ukla solenoid pump right at 7 minutes to replace that water, and get back up to 115 PSI. One unanticipated consequence of that 7 minutes of run time, is that the pump heats up from 72F to 155F. Thats well within the spec for the pump, but I prefer it run cooler than that, so I rigged up a small 12 volt .9 watt CPU cooling fan to blow on the pump. With the CPU fan running, the temp maxes out at 115F. Thats a very comfortable temp. I would prefer a 110 volt fan that was only on when the pump is on, but Im not going to sweat an extra .7 watts.

For now, Im going to leave the cut off pressure set to 115. I'll make adjustments depending on what my final flow rates actually are. Im omk with the pump cycling a little more often to reduce the length of the run time.

After re-reading several of Atomizers old posts, and doing some more math, Ive changed my mind. Im going to start with three nozzles instead of four, and see how it looks.

I happen to have a bunch of left over 3/4" PVC fittings and pipe from various projects, so I made two fixtures to hold the nozzles and solenoids. One will hold either two, or 4 nozzles, and one will hold three. It will be easy to switch between them if necessary.

The construction is simple. I have a heat gun that I use to heat up the PVC pipe. To make the flat, angled mounts for the solenoids, I just heat the ends until they get soft, then squeeze them between two pieces of wood in a vice. Bend the pipe to the angle you want and allow to cool. Same deal for the two angled legs on the three nozzle fixture. Heat until soft, then bend to the angle you want and allow to cool. If you dont have a heat gun, a propane torch will work if you are careful.

You can even do it over your kitchen stove - as long as the wife doesnt catch you!

These are just sitting in the tent to make it easy to take some pics. They will end up sitting on the floor, inside a water heater drain pan. The pan will catch any runoff that drips out of the chamber. The solenoids will be outside the chamber and the nozzles will just stick through the fabric. The root chamber is about 23" deep, and these are tall enough to place the nozzles aprox 12" - 13" down from the top of the chamber. They will be firing up at about 45 deg or so. I can easily adjust the height of the nozzles by adjusting the length of the vertical pipes. I can adjust the angle they point by slight bends in the tubing between the solenoid and the nozzles.

Im still playing with options to catch the runoff for EC monitoring. Im concerned my fabric pots will just soak up the spray and not allow any to get to the probe. I'll know how thats going to work out after I get it hooked up and start spraying.

I finished roughing in the fixture with three nozzles so I could run some tests. Thanks to Atomizers suggestion about how to light the chamber, the mist shows up much better. Im getting a solid 3 to maybe as much as 4 seconds of decent looking hang time. They dont show up in the video, but there are still some small droplets floating around after 5 seconds, when the next shot starts. Im assuming those are the smaller ones. They seem to just kind of float aimlessly rather than dropping.

With three nozzles, the coverage seems to be ok, but not perfect. There is an area all the way around the perimeter of the chamber at the top that barely gets any mist. I can feel it on my hands, but its not much compared to the center area. The 'dead zone' is maybe 3" to 4" wide. Everything inside that radius seems to be getting good coverage.

Tomorrow I'll play around with pointing them more up than they are now to see how that does. They are angled up at roughly a 45 deg angle now, and the nozzles ended up 11" down from the top.

I have lots of little details still to do, but the main work is complete. A few more days and I will be ready to start some clones!

Here is a quick video. This is 1 second ON and 5 seconds OFF @ 80PSI.

I re-ran the flow tests now that the nozzles are in place, and I have the entire system up and running. I did runs of 100 cycles at .5 seconds, 1 second, and 1.5 seconds.

At .5 seconds, the flow rate for all three works out to 3.92 ml/second.

At 1 second its 3.69 ml/sec

At 1.5 seconds its 3.60 ml/sec.


Not surprisingly, it looks like the extra drips have a larger influence the shorter the ON time is, with a significant increase as it gets under 1 second.

It looks like these final flow rates are slightly higher than the original test. The individual nozzle flow rates went from around 4.3 l/hr to an average of 4.4 l/hr. There may still be some air in the system, so maybe that will decrease a bit over time.

Three nozzles looks, to my uneducated eye, like it is just barely good enough to provide good coverage in the chamber. Things improved a lot as far as the dead zone around the edges just by pointing the nozzles slight more UP than before. Now, most of the chamber walls get fairly even misting from top to bottom all the way around. There are a still spots that get more or less mist, and a few small spots that get almost none, but it looks ok to me for a starting point.

Timing wise, it looks like I need at least .5 seconds, with three nozzles, to fully fill the chamber. The center, upper portion gets the most as that’s where the nozzles are pointed.

Given all of that, I did some more math based on Atomizers recommendations.

.02 - .04 liters/gallon of chamber for each mist cycle for early growth, up to .06 liters/gallon for later growth.

For daily through put, the targets are 1.3 liters /day early on and 2.65 liters/day in later growth.

A .5 second On cycle gives me .043 liters/gallon in my 45 gallon chamber. That’s a little hi, but I don’t think I can go much below .5 seconds and still fill the chamber. I also doubt two nozzles will give decent coverage, so I think Im stuck with that as a minimum.

An on time of 1.0 seconds gives me .082 liters/sec. So it looks like Im going to need an on time of around .7 seconds to hit the later growth target of .06 liter/gallon.

So to hot the 1.3 liters/day target for daily through put in early growth, that works out to an on time of .5 seconds, and a pause time of 136 seconds. Later growth is .7 seconds on and 89 seconds off to get to 2.65 liters/day.

So, if I did all that correctly, I now have starting and ending cycle times to work from. I’ll have to let the roots, and plants tell me if Im close or not.

The target daily throughputs are based on full coverage of 5-80 mist which hangs for the entire pause duration and then some so the roots are never without mist. If you dont have it, the best approach is to make the pulse as short as practical to maximise the number of mistings and adjust the pause based on root wetness and structure. In a lot of cases you`ll find the target daily throughput numbers are reasonably close even though the pulse and pause timing will be different. If the ideal total nozzle flowrate for a chamber is 4.5LPH, and you need 3 x 4.5LPH to get the coverage, you are forced to use 3x the pause to achieve the same daily flowrate.

Thanks for the help - BUT - now it feels like Im totally screwed, and this has all been a complete waste of time, and money.

Basically, what you are saying is that your earlier comment about my hang time didnt mean what I thought. Three or four seconds isnt even in the ball park. It actually sucks big time. My hang time is too short by more than an order of magnitude. In order for this to work, I need minutes instead of seconds of hang time.

Well fuck me.

Are my Hypro's defective? Did I screw something up big time in the setup? Or, (this is what I think you are saying) is it impossible to get that kind of hang time with ANY HPA nozzles? It sounds like your saying its use AA or go home.

Part of my confusion is, it looks like I have not understood anything you said about flow rates, because that 4.5 LPH number has me completely confused. Thats 108 liters/day down the drain? How do we get from 2.65 liters/day to 4.5 LPH?

I know you dont like answering specific questions, and Im in too bad a mood to think clearly enough to ask good ones, so Im just going away for a while so I can sulk in private.

Sorry for the rant. Its more than a little disappointing to find out you have wasted a lot of time, and money you didnt really have, on a project that was hopeless to begin with.

lol, not at all. i`m saying if you adhere to a "set in stone timing" schedule thats based on flowrate, coverage and 5-80 micron mist ,you must have all three or it wont be the right schedule. If AA was the only way to go, i wouldnt have any hpa setups, they`d all be AA Having a throw in the towel mindset even before running the system with plants isnt ideal for any type of aero because they can all be challenging at times. The best way to learn how to run any system is to run it,

Having several grows using HPA light (I did not use a solenoid/tank etc, and my timer was not accurate below 2 seconds) , however, in the cool months it worked great (seeing cotton candy roots is addictive), BUT where I live, high humidity and ambient temps exist 8+ months/year requiring air conditioning 24/7. The added cost for a small grower would likely offset any possible gains in yield. IMHO, Climate Control is a major key to success

I found the cotton candy would quickly go away without fairly tight controls of air temps, humidity, rez temps, and attention to detail like making sure both the in-lin filter AND th mist head filters were kept clean. One such issue was the heat generated by my then 8 bulb hot 5 overly warmed the root chamber, turning it into a steam bath. This issue was somewhat mitigated by covering the lid with HD aluminum foil, but...

In the end I went back to flood and drain, using lessons/techniques I learned from HPA

and have lived happily evr after

PetFlora said:

Having several grows using HPA light (I did not use a solenoid/tank etc, and my timer was not accurate below 2 seconds) , however, in the cool months it worked great (seeing cotton candy roots is addictive), BUT where I live, high humidity and ambient temps exist 8+ months/year requiring air conditioning 24/7. The added cost for a small grower would likely offset any possible gains in yield. IMHO, Climate Control is a major key to success

I found the cotton candy would quickly go away without fairly tight controls of air temps, humidity, rez temps, and attention to detail like making sure both the in-lin filter AND th mist head filters were kept clean. One such issue was the heat generated by my then 8 bulb hot 5 overly warmed the root chamber, turning it into a steam bath. This issue was somewhat mitigated by covering the lid with HD aluminum foil, but...

In the end I went back to flood and drain, using lessons/techniques I learned from HPA

and have lived happily evr after

Click to expand...

You were able to get super fuzzy/cotton candy root hairs with that equipment? I thought I read all the recent threads on HPA, but at the moment I dont recall seeing one of yours. Have any pics of those roots?

Larry3215 said:

You were able to get super fuzzy/cotton candy root hairs with that equipment? I thought I read all the recent threads on HPA, but at the moment I dont recall seeing one of yours. Have any pics of those roots?

Click to expand...

I did HPA about 5-6 years ago. I did a thread, but not sure you can find it, but,

yes I had very nice basketball size cotton candy, I just couldn't repeat it once the temps changed

PetFlora said:

I did HPA about 5-6 years ago. I did a thread, but not sure you can find it, but,

yes I had very nice basketball size cotton candy, I just couldn't repeat it once the temps changed

Click to expand...

Thanks. I'll look for it when Im feeling bette.r

Atomizer said:

lol, not at all. i`m saying if you adhere to a "set in stone timing" schedule thats based on flowrate, coverage and 5-80 micron mist ,you must have all three or it wont be the right schedule. If AA was the only way to go, i wouldnt have any hpa setups, they`d all be AA Having a throw in the towel mindset even before running the system with plants isnt ideal for any type of aero because they can all be challenging at times. The best way to learn how to run any system is to run it,

Click to expand...

I had a long complex eply all typed up and lost it. Too stoned and too much pain to re-do it now.

Short version is Im not throwing in towel, but I am upset and 100%confused by your last two replys. I ma unable to get the numbers to add up and of course, you didnt answer any of my questions, so that doesnt help much. This is probably coming across poorly - fucking kidney stones sorry

Atomizer said:

The target daily throughputs are based on full coverage of 5-80 mist which hangs for the entire pause duration and then some so the roots are never without mist. If you dont have it, the best approach is to make the pulse as short as practical to maximise the number of mistings and adjust the pause based on root wetness and structure. In a lot of cases you`ll find the target daily throughput numbers are reasonably close even though the pulse and pause timing will be different. If the ideal total nozzle flowrate for a chamber is 4.5LPH, and you need 3 x 4.5LPH to get the coverage, you are forced to use 3x the pause to achieve the same daily flowrate.

Click to expand...

It occurs to me that, even if you are willing to answer them, there is no point in asking you any more questions or trying t clarify any of this stuff until I find out if my nozzles are defective, ripoff clones or ar working as well as can be expected.

I already know they open at 1/2 the pressure than yours do - 30p si vrs 58 psi. The key question is - is my hang time of 3 or 4 seconds the same as your Hypro nozzles? If you are getting minutes of hang time, and Im only getting seconds, then that means my droplet size is way too big.

If this is as good as it gets with the Hypro, is there a different option, that will work in my system, that does have the required hang time? If so, are you willing to share that information with me?

PetFlora said:

I did HPA about 5-6 years ago. I did a thread, but not sure you can find it, but,

yes I had very nice basketball size cotton candy, I just couldn't repeat it once the temps changed

Click to expand...

Would you like me to post some of your epic roots? I’m sure I can find some for you .

Budley Doright said:

Would you like me to post some of your epic roots? I’m sure I can find some for you .

Click to expand...

sure, if you post the ones when I had the environment under control