Custom Environmental Controller

[koosjr]

Interesting. I see this part of the forum is not very active. I thought that controls would be of considerable interest.

I am an industry expert in controls and I also design my own, but I also do like it when systems can me made to run on more natural means.

 

I would however like to investigate designing a monitoring and control system for the room I plan.

With a custom designed controller, one can often get great value for money if you have a nice big integrated controller with a single processor and the I/O's on the board are well thought out for the application. This means minimal circuitry is needed and you end up with a board that can be very repairable compared to commercial controllers.

An integrated board also makes data logging considerably easier - especially in terms of event recording.

I have already designed and implemented a large controller for a Micro-Greens cabinet. It can do pretty much everything. It has 4 circuits of lights with independent timers, 5 spray circuits with independent timers, it switch circulation fans and the aircon units in duty/standby fashion, it can also do humidification, control a dual axis solar tracker, 3 storage tanks with level control and it has generator control where one can automate the startup of cheap chinese generators.

It has a touch screen that gives you clear and precise feedback of every I/O under control.

That is probably not a bad platform to start from for a comprehensive cannabis controller.

 

Lets say you are a serious breeder and can dream wild, what would you have liked to have in such a system?

 

My first reaction:

1. Obviously temperature control, duty standby.

2. Humidity control in a case like this is also a must. Small addition if one want to go the full monty.

3. Backup water tank level control, with pressure pump control.

4. Automatic watering cycle with soil moisture sensor

5. Then I would like to have multiple temperature sensors.

6. Lux sensors could perhaps be considered, although I have not found the perfect ones yet.

7. Generator control is certainly on the list for a serious room. Then it can start a dumb generator automatically.

8. Probably CO2 control, but CO2 sensors are unfortunately maintenance items and does not last forever.

 

Right, what one needs to consider though is how Temperature control, humidity control and CO2 control effects each other.

 

As far as I can see, CO2 should be above a minimum level and upper limits can be quite high - high enough that it would not be a limiting factor to cator for. To raise minimum levels, add fresh air or dose it from a bottle if you have the money.

Humidity can obviously be a problem if it goes too high or too low. An air conditioner will always lower humidity when it runs, but it cannot be the primary means of reducing humidity as at some point the room temperature can become too low.

Humidification in itself is something I would avoid like the plague as humidification devices are notoriously unreliable. The question is then: Is LOW humidity often a problem in a cannabis room, or only high humidity. The latter can at least be catered for by either the AC unit or adding some fresh air.

[Ill_Evan]

In the pursuit of obtaining the perfect environment, the optimum vapor pressure deficit (VPD) is used in order to program your perimeters. 

I wouldn't worry too much about CO2 unless you're going to push your umol past 700 and do CO2 injection. 

You'll probably forget about the lux once it's dialed in during setup and after a few runs. 

1 hour ago, koosjr said:

The question is then: Is LOW humidity often a problem in a cannabis room, or only high humidity. The latter can at least be catered for by either the AC unit or adding some fresh air.

I would rather have a grow room in low humidity during the entire run than I would want a room with high humidity. They say you want a humidity of 60% during veg and below 40% for flower. I have grown a full cycle with a room below 40%. I have only ever experienced bud rot and fungus issues if the environment goes above 60%. This can also happen very quickly so even if you experience a high humidity for an hour or two like during loadshedding it could cause issues. You don't want to give any latent spores in the air any reason to bloom. 

[koosjr]

Quote

I would rather have a grow room in low humidity during the entire run than I would want a room with high humidity. They say you want a humidity of 60% during veg and below 40% for flower. I have grown a full cycle with a room below 40%. I have only ever experienced bud rot and fungus issues if the environment goes above 60%. This can also happen very quickly so even if you experience a high humidity for an hour or two like during loadshedding it could cause issues. You don't want to give any latent spores in the air any reason to bloom. 

 

Being an HVAC designer, Psychrometrics is my forté and I had at one stage a commercial biltong drier on the market that worked on the refrigeration principle. So at least I can follow this discussion.

To get down to 40% is very rare in natural conditions so I highly doubt your figures.

What I suspect is that you used one of these electronics Temperature/humidity meters to give an indication.

However, electronic humidity sensors - even the good ones - are far less accurate than what the data sheets claim. Even very expensive sensors gave me erroneous readings on high and low values.

Usually below 50% they start to runaway to the low side, and above 90% they start to run away on the high side. I have seen this over and over especially in laboratories where I had to do full humidity control.

At least though the runway is fairly accurate, but all it is then is a figure that you can use as reference for the meter you have.

The most accurate way for me is still the old dry bulb / wet bulb thermometer. Nothing can fool that. It is perfectly reliable anywhere in the range.

 

I have to agree that high humidity will cause you trouble within the hour. We also had that in the biltong rooms. If the system goes down you need to take immediate action. 

 

[Ill_Evan]

3 hours ago, koosjr said:

To get down to 40% is very rare in natural conditions so I highly doubt your figures.

What I suspect is that you used one of these electronics Temperature/humidity meters to give an indication.

Definitely true. In that case disregard all my measurements. 

The dehumidifier and tent plus ventilation might be a factor as well. 

[koosjr]

Look, it is not a matter of simply disregarding your figures. A "wrong" value is not bad if it is at least accurately wrong all the time. You het my drift?

We often have to work with what we have.

The actual driving force as you have mentioned, is indeed vapour pressure. Most people - engineers included - have no idea that this is the fact.

However, difference in vapour pressure is not something one can measure easily - most of that eventually is determined empirically.

[Ill_Evan]

For science! 

[Chris Jay]

Quote

I wouldn't worry too much about CO2 unless you're going to push your umol past 700 and do CO2 injection. 

One of the pioneers in the cannabis automation industry recently launched a C02 censor to attach to their unit as an addon. Being in the heart of legal cannabis growing and having a commercial product being sold I would think this is a very important part of the concept, however I am not to sure how many people would use CO2 in South Africa.