Controlling environment by VPD

[f-e]

Rules... must be a computer thing.
I think a basic humidity setting that's adjusted as temp changes in a linear fashion should be okay. It should really be log, but we don't expect huge changes in temp, just 18-32 in which range a linear adjustment should be sufficient. At least as a first step.

I bet the code for a fan speed adjuster based on temp or humidity is out there. So integrating the two isn't a huge leap. It's a comparitor of sorts.


I'm still analogue, where it doesn't seem that hard to be honest. I would likely take a humidity hunting fan speed controller. Then modify the sensor side, switching in resistors. This would only move the fan speed up, so it would first need calibrating low. So some of the correction resistors were needed for normal. From there you could add or remove them. Taking a voltage obtained from the temp sensor, perhaps wired as a divider, you would cascade some voltage operated switches to bring in the resistors that fudge with the humidity controllers sense of whats happening. It's really just a handful of bits. China will have it all on a chip soon enough though. If not already..

 

[Horselover Fat]

I'm kind of wondering how big of a difference vpd is going to make. I mean 0% or 100% humidity would be very bad, but how big a difference would there be within reasonable tolerances? I know my humidity has varied quite a bit, but I don't think I've seen a difference in growth related to it.

 

[Switcher56]

It should be simple enough to program since it is an X factor (algorithm) it is simply (I think) applying it to any given temp. That being said, as we know, nothing is linear. OTOH we are not scientist. How close is close enough

 

[exploziv]

It's not rocket science, and I'm not asking technically how to do it, but how to apply it.
I mean there is a perfect point between being too strict with the environment, using too much electricity, having appliances battling the elements at both ends of the spectrum sometimes, and having a good, stable enough environment with best energy efficiency. Example: I make rules strict so that they keep RH within 5% of the optimum. I have the humidifier running now, but then the controller reads the data again and too much humidity has been added and has to run the dehumidifier to compensate. Or speed up the exhaust.
Anyway, hope I finish the updated logging and graphing part of my controller soon so I can see the data in a graph. Now i just have it set to record averages and min/max.

 

[f-e]

I had a dream, and in this dream I used £3 eBay Temp&Humidity boards. Pwm boards, and a shared capacitor with discharge resistor. Who's voltage controlled fan speed. $20


A look at LED use tells a story. To keep transpiration going we had to raise temps and lower RH with an accumulative effect greater than the bands on these graphs. Even then, we have to use more Calcium.

I find the graphs informative, without taking any real notice of the actual numbers. I notice a throttling of water uptake around 70%RH running 28c temps. While below 40% they have problems. In the middle somewhere will do. The stomata work.

 

[Switcher56]

I had a dream, and in this dream I used £3 eBay Temp&Humidity boards. Pwm boards, and a shared capacitor with discharge resistor. Who's voltage controlled fan speed. $20


A look at LED use tells a story. To keep transpiration going we had to raise temps and lower RH with an accumulative effect greater than the bands on these graphs. Even then, we have to use more Calcium.

I find the graphs informative, without taking any real notice of the actual numbers. I notice a throttling of water uptake around 70%RH running 28c temps. While below 40% they have problems. In the middle somewhere will do. The stomata work.

Hence why I run 55%. That is not where I was getting at though. I was talking about programing a unit, that will affect both RH and temp @ canopy (using huey and exh. fan) to maintain that environment IAW with set point, as defined in VDP studies. That X factor has a value.

 

[WaterFarmFan]

This is a good discussion. I have been interested in this subject of late. Most points have been covered, but I think that an important part of maximizing VPD is to master the unique seasonal variables of the outside environment like rain and big temp swings, as these invariably change the dynamics of any room within a room. I think that large spaces would be easier to control with the scale of powerful tools. If you really want to practically implement VPD, then you need the AC, humidity controls and power to crush the outside environment. This can be expensive and not really practical on tent-scale. Also noted, one must pay attention to light schedule and outside temps. While it is cheaper to run lights at the night, the humidity might be higher. If room is not dialed in to high level, then any VPD mods, like adding a humidifier, could have terrible results.

I certainly don't claim to be an expert, but I will say their does seem to be some correlation between negative pressure and hitting the VPD sweet spot. Perhaps, this is because a properly designed (non-sealed) room (which vents to much larger temp controlled space) that removes heat from top and adds cool air to bottom will naturally create a more VPD friendly space, and negative pressure helps to achieve. You need controllers with high accuracy temp/humidity sensors (at canopy level) that run AC and dehumidify inside room and THEN you need to master the outside elements with additional AC, heat and humidity controls. If you are not controlling the temp and humidity of the air coming into your room (within a room), then you have no hope to stay in VPD range. If your incoming air gets hotter and more humid later in 12/12 schedule, and your inside AC and dehuey cant keep up, then you need to add more environmental control.

IMHO, a good digital controller with accurate sensor (like an Autopilot Eclipse) plus overpowered AC and dehumidifier combos in room makes reaching and most importantly MAINTAINING VPD sweet spot possible. You still need to adjust the controller to be within VPD range, but perhaps, if you want to get fancy, that you could put 2 or 3 of these digital controllers in series but that would require multiple ACs and dehueys to pull off. Is the cost worth it to you? Depends on scale, I guess...

WFF

 

[WaterFarmFan]

I was doing a little reading and thinking about sealed room with co2 and higher temps/humidity vs vented room within a room with lower temps and humidity. VPD is obviously different in each scenero. Does the following paper not imply that higher VPD leads to lower c02 uptake?

https://advances.sciencemag.org/content/5/8/eaax1396

Increased atmospheric vapor pressure deficit reduces global vegetation growth

Abstract

Atmospheric vapor pressure deficit (VPD) is a critical variable in determining plant photosynthesis. Synthesis of four global climate datasets reveals a sharp increase of VPD after the late 1990s. In response, the vegetation greening trend indicated by a satellite-derived vegetation index (GIMMS3g), which was evident before the late 1990s, was subsequently stalled or reversed. Terrestrial gross primary production derived from two satellite-based models (revised EC-LUE and MODIS) exhibits persistent and widespread decreases after the late 1990s due to increased VPD, which offset the positive CO2 fertilization effect. Six Earth system models have consistently projected continuous increases of VPD throughout the current century. Our results highlight that the impacts of VPD on vegetation growth should be adequately considered to assess ecosystem responses to future climate conditions.

INTRODUCTION

Vapor pressure deficit (VPD), which describes the difference between the water vapor pressure at saturation and the actual water vapor pressure for a given temperature, is an important driver of atmospheric water demand for plants (1). Rising air temperature increases saturated water vapor pressure at a rate of approximately 7%/K according to the Clauius-Clapeyron relationship, which will drive an increase in VPD if the actual atmospheric water vapor content does not increase by exactly the same amount as saturated vapor pressure (SVP). Numerous studies have indicated substantial changes of relative humidity (ratio of actual water vapor pressure to saturated water vapor pressure) not only in continental areas located far from oceanic humidity (2) but also in humid regions (3). Although the long-term trend of globally averaged land surface relative humidity remains insignificant (4, 5), a sharp decrease has been observed since 2000 (6, 7), implying a sharp increase in land surface VPD. However, the causes of changing atmospheric water demand are still unclear (8).

Changes of VPD are important for terrestrial ecosystem structure and function. Leaf and canopy photosynthetic rates decline when atmospheric VPD increases due to stomatal closure (9). A recent study highlighted that increases in VPD rather than changes in precipitation substantially influenced vegetation productivity (10). Increasing VPD notably affects vegetation growth (11–13), forest mortality (14), and maize yields (15). In addition, rising VPD greatly limits land evapotranspiration in many biomes by altering the behavior of plant stomata (9). Given that the global precipitation is projected to remain steady (16), the changing VPD and soil drying would likely constrain plant carbon uptake and water use in terrestrial ecosystems (17). However, the large-scale constraints of VPD changes on vegetation growth have not yet been quantified. In this study, we determined the changes in VPD trends through observation-based global climate datasets, and then quantified the impacts of these VPD changes on vegetation growth and productivity, using satellite-based vegetation index [i.e., normalized difference vegetation index (NDVI)] and leaf area index (LAI), tree-ring width chronologies, and remotely sensed estimates of gross primary production (GPP).

 

[Ebdirtrider]

Hardware:
Esp32s
Relays
Raspberry pi (or other home assistant option)

Software:
Home Assistant

You can have full environmental control for $60
All local.
Add another $160 and have full auto dosing for 3 part and auto ph down.
Add another peristaltic pump for $40 for ph up if you want.

Basically a $3 board and a $4 relay you can control anything.

I get leaf temp for vpd from a noncontact ir sensor for $20, temp, pressure, humidity from a bme280 $6,
Co2 from a $30 sensor all hook to a esp32 board with camera $12
Vpd is a calculation based on temp and humidity. So a free sensor.
And leaf vpd references the actual leaf temp for its free calculation.

Anything else hooked up with a board and relay can be triggered by any parameter from any of the above sensors or any other entity's. Most smart devices setup easily also. This way is just totally local but has full wifi access and control also.

 

[WaterFarmFan]

Hey Ebdirtrider. Cool stuff! Do they make a home thermostat that runs commercial HVAC and is programmable and connectable to pi system? Many people use their home as lung room, and for many this is a manual system that not part of VPD automation.

WFF

 

[exploziv]

Depending on the inputs needed to the hvac system, that shouldn't be too hard to obtain.
I mean you could output anything with an arduino or pi, just need to know what does the hvac needs for comunication.
For a less technical solution you could also just add a wifi or wired sensor to the furnace, and control your lung room based on that, if your furnace can take an extra temp sensor.

 

[WaterFarmFan]

I am talking about the standard wall thermostat wiring. Not an expert but I have wired a few to replace bad units.

 

[exploziv]

I haven't seen it ready made for growing, but there are lots of diy-iers around so maybe someone on the internet did it for a smart home system or something. That's the nice thing about electronical diy, basically everything is possible and also lots of examples and tutorials around.

 

[ButterflyEffect]

I run 4 separate arduinos for my 3 flower rooms and a veg room. One thing to keep in mind is the current draw of whatever device you're controlling. Case in point, my dehueys, heaters and A/Cs are all triggered by the arduino relay board but then route to 20A power relays.

The next step for me would be adding VPD control for humidity and connecting them to the network with SD cards so I can grab the data.

 

[exploziv]

Yeah I want to use sd cards for data logging. I can get my data in real time from the network anyway, I could log it on a pc but I want to be energy efficient and log it on the same low power device.

 

[ButterflyEffect]

I hear ya. My system is as inelegant as could possibly be, so I figured it was high time that I made the updates that would at least allow me to monitor remotely and receive alerts.