VPD and why do I care

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Stumay111

Active Member
@guitarguy10 Thanks for all the info! I think your thoughts about ducting the exhaust outside are good! I'm going to try it. I have the infinity 6 in my shopping cart. With controller of course. My light is a Spider Farmer SF4000 LED.
I've been experimenting with manually adjusting the fan speed to see how well it controls temp and humidity. With a little help from my AC and Humidifiers.
My AC IS outside my tent now. It has a "follow me" feature that controls it by temp from the remote, so the remote is in the tent.
Although today I am getting a temp/hum wifi sensor that works with my phone (and supports multiple sensors). So I can have my AC remote in the living room.

I'm moving to a 4x8 so I think I need the 6.

A Takamine is a guitar. You being guitarguy I assumed... never mind.
 
S

Stumay111

Active Member
Lockedin said:
True - discovered that the hard way:
When I originally hooked up the T-6, I had one 6" duct and one 4" duct for intake. Out of curiosity I cranked the fan to 10:
- The tent incaved HARD - poles creaked & the intakes pinged with the pressure. Had no idea THAT would happen! :shock: :lol:
- Didn't do that again in the 4x4. :bigjoint:

In the 4x8, I'm running three 6" passive intakes (two pulling fresh air, one intake in the room - seems to even out my temps nicely)
No creaking or serious incaving - though the sides do pull in a bit when I turn the fan up over 7; which is never - I go to 5 to cycle the air once in a while, other than that - the fan stays on 2 or 3 and my tent maxes at 83f / 55%rh
Click to expand...
This post was originally about VPD. 83/55 according to the VPD chart I have is way into the stress zone.
 
Lockedin

Lockedin

Well-Known Member
Yeah, still trying to improve my environment.
83f is fine, but I know I need to invest in a humidifier for the days when the desert winds here suck the moisture out of everything.
Fortunately, my rh doesn't stay at 35% for too long at a time.

I'm well aware that the original post was regarding VPD
Also very aware that the question I answered asked about running an AC Infinity in a 5x5 --- why would you be surprised I answered that question with an answer about ---- running an AC Infinity in a 4x4.
vpd-chart.png
 
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Stumay111

Active Member
Lockedin said:
Yeah, still trying to improve my environment.
83f is fine, but I know I need to invest in a humidifier for the days when the desert winds here suck the moisture out of everything.
Fortunately, my rh doesn't stay at 35% for too long at a time.

I'm well aware that the original post was regarding VPD
Also very aware that the question I answered asked about running an AC Infinity in a 5x5 --- why would you be surprised I answered that question with an answer about ---- running an AC Infinity in a 4x4.
View attachment 4883934
Click to expand...
I went and got my own chart maker. These values are wider than the chart I have. Thanks~
 
S

Stumay111

Active Member
OK, thanks for all the information you guys supplied. I'm all off into this now.

I've actually written code to calculate the VPD. It's in C#, it's attached.

The Leaf Temp is what throws me. It APPEARS that my leaf temp difference is about -2 with light and -4 without.

That seems consistent. Does anyone else have that experience?
 

Attachments

BlandMeow

BlandMeow

Well-Known Member
Stumay111 said:
OK, thanks for all the information you guys supplied. I'm all off into this now.

I've actually written code to calculate the VPD. It's in C#, it's attached.
Click to expand...
How are you getting your values for the calculation? I did the calculation via Google sheets for my data set using the escorted values from a hygrometer/thermometer.

VPD Monitoring

I don't have enough dogecoin to drop on a pulse pro or any other advanced monitoring system for my tent. I purchased a hygrometer thermometer (link at the bottom) which provides the feed to their app via blue tooth. It also allows for a result export function which will send a .csv file to your...
www.rollitup.org
 
S

Stumay111

Active Member
BlandMeow said:
How are you getting your values for the calculation? I did the calculation via Google sheets for my data set using the escorted values from a hygrometer/thermometer.

VPD Monitoring

I don't have enough dogecoin to drop on a pulse pro or any other advanced monitoring system for my tent. I purchased a hygrometer thermometer (link at the bottom) which provides the feed to their app via blue tooth. It also allows for a result export function which will send a .csv file to your...
www.rollitup.org
Click to expand...
I am using SensorPush. $200 and you have all you need to read temp and humidity. It reports VPD but it's calculated.
They provide a pretty simple API that you can use to poll the sensors (they read every 60 seconds).

I have an IR thermometer that I use to read leaf temp. I do that at various times and record them in a database.

in my code I have this to calculate VPD. The function GetLPDFactor looks up in the table based on an average difference during that time of day. They seem pretty consistent.

double LPD = GetLPDFactor();

This is just the scientific formula for VPD, written in c#. Temp factor is a number I got by hacking into the PulseLabs spreadsheet they put out.

var expFactA = (610.78 * Math.Exp((tempFactor + LPD) / ((tempFactor + LPD) + 238.3) * 17.2694));
expFactA = expFactA / 1000;
var expFactB = -(610.78 * Math.Exp((tempFactor) / (tempFactor + 238.3) * 17.2694) / 1000 * (double)Humidity / 100);
var retTempFactor = expFactA + expFactB;

This is the matrix for tempFactor.

var TempMatrix = new Dictionary<decimal, int>();
TempMatrix.Add(59M, 15);
TempMatrix.Add(60.8M, 16);
TempMatrix.Add(62.6M, 17);
TempMatrix.Add(64.4M, 18);
TempMatrix.Add(66.2M, 19);
TempMatrix.Add(68M, 20);
TempMatrix.Add(69.8M, 21);
TempMatrix.Add(71.6M, 22);
TempMatrix.Add(73.4M, 23);
TempMatrix.Add(75.2M, 24);
TempMatrix.Add(77M, 25);
TempMatrix.Add(78.8M, 26);
TempMatrix.Add(80.6M, 27);
TempMatrix.Add(82.4M, 28);
TempMatrix.Add(84.2M, 29);
TempMatrix.Add(86M, 30);

So that's how I read the data.

My software, based on that data, then takes actions based on it.

The actions (for now) are simple. They turn Smart Plugs by TP LInk on and off. These plugs have my AC, Humidifer, and dehumidifier plugged into that.

If, for some reason, what I have can't control temp or humidity, it looks up in a table what the opt temp is (for RH that you can't control) and adjusts the target of the other facet accordingly.

I"ve done all this based on the responses I got in this thread I started.

Thanks to all again.
 
Lockedin

Lockedin

Well-Known Member
Green_tourist said:
Thanks for sharing your experiences, I am struggling with high temps in a 4x4 and was considering t8
Click to expand...
I ran a T6 in my 4x4.

Any setting over 5 made the walls suck in severly.
I could have added additional intakes for balance - the trick there is to ensure that you're pulling cooler air in.
 
V256.420

V256.420

Well-Known Member
I keep my exhaust fans on 24/7. I buy 2 sets of extra tent poles for my Gorilla Lite tents. They sell the kits for about $20 each. Great for the negative pressure problems :eyesmoke:
 
S

Stumay111

Active Member
bk78 said:
Well there’s a difference between rapid growth, and regular growth.

Keep vpd in check 24/7 and you’ll experience the rapid part
Click to expand...
@
DoubleAtotheRON said:
This is the first grow (in week 7 of flower) that I have followed VPD to the chart. I can say that the growth has been explosive compared to previous grows.
Click to expand...
Yeah, I'm seeing the same in my 5 week old Gelato. Keeping my VPD in the .9 - 1.1 range with my software (see other post)
 
SNEAKYp

SNEAKYp

Well-Known Member
Another big reason to follow VPD too is that it's very helpful in battling PM especially at the higher temps/RH's. I have my 4x4 with a T6 and am extremely happy with the results thus far. If I were to do it again I'd buy the S6" ac infinity fan and then pick up their controller 67 which is a bit more sophisticated than the one that comes with the S6.
 
G

guitarguy10

Well-Known Member
SNEAKYp said:
Another big reason to follow VPD too is that it's very helpful in battling PM especially at the higher temps/RH's. I have my 4x4 with a T6 and am extremely happy with the results thus far. If I were to do it again I'd buy the S6" ac infinity fan and then pick up their controller 67 which is a bit more sophisticated than the one that comes with the S6.
Click to expand...
I've learned that good airflow is the best way to counter PM but trying to stay within safe vpd us definitely important too
 
Tht_Blk_Guy27

Tht_Blk_Guy27

Well-Known Member
Lordhooha said:
An 8” is too much for a 5x5 alone. For instance, my personal grow at home I have a three tents a 3x3 and 2 5x5’s one cloud line 8” will suck the sides in on all of them At a 1 which is the lowest setting. All of my mommas and clones are sitting outside of those tents and I use one 4” to vent that area. For my big commercial rooms I use one 6” per room Which are 30x15x15 and they’ll vent everything out of those rooms in 30 mins easy. Those fans move a shit ton of air. Choose your cloud line wisely.
Click to expand...
tell me about it lol i run 2 cloudline t4s in my 2x4 and MAN these things beast out. never gone above 3 on them because my tents will implode. get a Bluetooth controller if you haven't, it mechanizes some of its more nuanced controls and settings
 
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