How temperature and humidity relate

[Islandgrow]

I'm trying to think of a more intelligent way to put this but... I don't know what the numbers in the main block mean.

Here is something on it from another site has more info so you can google . Essentialy if the plant doesn't transpire it doesn't take up fluids. So no nutes uptaken. The Effect of Relative Humidity on Your Plants.>>>>>>>>>

RH can be easily measured using digital or analogue meters called "hygrometers." They are available for around $15 at your local indoor gardening store. But what do the readings mean for your plants?

Turns out-they mean a great deal! While many novice growers focus solely on keeping temperature in range, many take their eye off the ball as far as RH is concerned-perhaps because they don't fully understand what it is or how to manipulate it to their advantage.

Have you ever been to Florida in July? You'll know that it's not just the heat that's oppressive, it's the humidity! You feel constantly wet with sweat - the whole place feels like a sauna you can't escape from! (Sorry Floridians!)

RH has an ever more direct effect on plants. Plants need to "sweat" too - or rather, they need to transpire (release water vapor through their stomata) in order to grow.

The amount of water plants lose through transpiration is regulated, to a point, by opening and closing their stomata. However, as a general rule, the drier the air, the more plants will transpire.


Under Pressure

All gasses in the air exert a certain "pressure." The more water vapor in the air the greater the vapor pressure. What does this mean? Well, in high RH conditions (think of Florida again) there is a greater vapor pressure being exerted on plants than in low RH conditions. From a plant's perspective, high vapor pressure can be thought of as an unseen force in the air pushing on the plants from all directions. This pressure is exerted onto the leaves by the high concentration of water vapor in the air making it harder for the plant to 'push back' by losing water into the air by transpiration. This is why with high RH plants transpire less. Conversely, in environments with low RH, only a small amount of pressure is exerted on the plants' leaves, making it easy for them to lose water into the air.

"carpe diem"

 

[Graytail]

I also have this chart for VPD - seems a good place to drop it. We get so concerned about mold that we typically keep RH way too low for our temps.

The numbers represent the difference between vapor pressure inside the leaf and vapor pressure of the ambient air outside the leaf - the deficit.

You can calculate vapor pressure from the temp and RH of each, assuming the RH inside the leaf is 100%. Many of a plant's internal processes are dependent on the same sort of concentration/deficit states. Minerals pass into roots because their concentration is lower in the root and higher in the soil, so they will migrate into the lower concentration of the roots. When VPD is low, RH is too high outside the leaf, and the plant has difficulty in transpiration and growth slows. When VPD is too high, the air is too dry and the plant begins to lose the ability to regulate water in its tissues. The stoma shut down and the leaf edges curl. The plant has trouble supplying the growth tissues with the appropriate nutrients, and growth slows.

 

[Weaselcracker]

Well- it's extremely likely that I'm just too stoned see straight but what I meant is-
I understand what RH is, and dew point. I see the temps up and down the left side, and RH along the top. What are the numbers in the main block? This is where my mental state probably becomes painfully evident...

 

[Graytail]

I remember reading the article I got this from, and I was a science major so formulas don't freak me out, but I honestly don't remember and I don' think any of us really want to know specifically anyway.

The two charts have different numbers, so one might be a percentage and the other one a difference, but again, I don' really wanna know. It's the color bands that are important, and the shocking idea that it might be better to run 70+% humidity in our tents.

 

[TheFertilizer]

I don't know, I think this might meet kind of a limit if we're talking about a space with a heavy exchange of air flow because I run my 4x4 with a 400 CFM fan and the thing is pretty much constantly in the 20-30% RH range. My temperatures can vary quite dramatically though, a full 20 point spread on the F scale. However even with temperature swings that dramatic the RH doesn't shift that much.

 

[Graytail]

I don't know, I think this might meet kind of a limit if we're talking about a space with a heavy exchange of air flow because I run my 4x4 with a 400 CFM fan and the thing is pretty much constantly in the 20-30% RH range. My temperatures can vary quite dramatically though, a full 20 point spread on the F scale. However even with temperature swings that dramatic the RH doesn't shift that much.

Absolutely. There's no way to control RH when we're pumping air through the space. That makes it really tough to hit the right humidity in our small spaces. But in my experience, it becomes a limit to growth really fast. We need to spend more time and money working it out before we use more light. Buying more light is simple - controlling RH isn't.

 

[Arctic Bowl]

I don't know, I think this might meet kind of a limit if we're talking about a space with a heavy exchange of air flow because I run my 4x4 with a 400 CFM fan and the thing is pretty much constantly in the 20-30% RH range. My temperatures can vary quite dramatically though, a full 20 point spread on the F scale. However even with temperature swings that dramatic the RH doesn't shift that much.

Well, I'd be very interested in what the temp/humidity is in the space that your air is coming from to replace the air inside your tent. I'm going to guess your tent is 8 feet tall ( may not be) and its cubic volume would be in the neighborhood of 128 cf. if your fan is truely removing 400 CFM then your removing the equivalent of 187.5 air changes per hour. ( 400 CFM X 60 min / 128cf) which is a lot of air changes to try to keep temp and humidity close with. GT is correct, humidity control is much more difficult to accomplish and will require some planing when your moving that much air thru your space.

I'll venture a guess that your humidity in the space that replaces your air in your tent tracks very very close to the humidity level inside your tent. With that many air changes per hour your fighting a pretty big battle as far as humidity "control" goes. May want to think about slowing that fan way down so you won't have to invest in some commercial grade HVAC equipment that would give you at least a chance to get it under control.

Just to put things into prospective operating rooms typically run in the neighborhood of 25-30 Air Changes per Hour and that's a lot of air and requires some high tech equipment to control the humidity to around 50%. The idea is to run a "slight" negative pressure in your grow space to replace the air bringing in fresh CO2 and to control Oders.

Blessed Buds our friends and be well

Sorry for our laps, iPad has a mental block and won't let me type here often times but, Santa said a new ones coming

 

[TheFertilizer]

Well, I'd be very interested in what the temp/humidity is in the space that your air is coming from to replace the air inside your tent. I'm going to guess your tent is 8 feet tall ( may not be) and its cubic volume would be in the neighborhood of 128 cf. if your fan is truely removing 400 CFM then your removing the equivalent of 187.5 air changes per hour. ( 400 CFM X 60 min / 128cf) which is a lot of air changes to try to keep temp and humidity close with. GT is correct, humidity control is much more difficult to accomplish and will require some planing when your moving that much air thru your space.

I'll venture a guess that your humidity in the space that replaces your air in your tent tracks very very close to the humidity level inside your tent. With that many air changes per hour your fighting a pretty big battle as far as humidity "control" goes. May want to think about slowing that fan way down so you won't have to invest in some commercial grade HVAC equipment that would give you at least a chance to get it under control.

Just to put things into prospective operating rooms typically run in the neighborhood of 25-30 Air Changes per Hour and that's a lot of air and requires some high tech equipment to control the humidity to around 50%. The idea is to run a "slight" negative pressure in your grow space to replace the air bringing in fresh CO2 and to control Oders.

Blessed Buds our friends and be well

Sorry for our laps, iPad has a mental block and won't let me type here often times but, Santa said a new ones coming

Yeah it's generally the same humidity in the room that it's in, though it's a few degrees higher than the ambient room temperature. The one thing I can't understand though is that, the air outside my home isn't even close to the indoor humidity. It's like 90% humidity and snowing outside, but in my room it's 20%.

I have been meaning to get a fan speed controller. Even at half the speed it hardly ever climbs over 50%.

 

[Arctic Bowl]

Yeah it's generally the same humidity in the room that it's in, though it's a few degrees higher than the ambient room temperature. The one thing I can't understand though is that, the air outside my home isn't even close to the indoor humidity. It's like 90% humidity and snowing outside, but in my room it's 20%.

I have been meaning to get a fan speed controller. Even at half the speed it hardly ever climbs over 50%.

Ok, outside temperature is lower than your grow area temp. So, our little molecule is contracted and the water vapor is at a higher %. Once that little molecule jumps from outside into your grow area its warming up and expanding and lower its water vapor %. At this point we haven't added or removed any humidity, we just changed the size of our molecule by changing its temperature.

If you look at the Psyc chart our point we picked at 70 deg and 50% RH, when we raised the temperature to 75 deg our RH dropped to around 42%. Same thing happends when our air comes from a colder outside temperature to a warmer indoor temperature, humidity ( water vapor %) goes lower.

Hope this helps

Blessed Buds our friend and be well

 

[Weaselcracker]

The Psych chart is why I wandered in. Unfortunately I can't read the numbers on it. The reason I was interested in the first place is- most of my bud is stored in one room in large jars with the little digital thermometer/hygrometers in the jars. I'm trying to keep the RH in the jars around 60, give or take a little, presumably around room temp- 20° Celsius.

However the temperature in that room fluctuates a bit and often the temps are lower like down to about 15°, or up to 25°. Or higher/lower, lol.

So at one point I was googling around trying to find a simple scale to relate a given temp/RH to another temp/RH, if you know what I mean. I just wanted to know if the RH in the jar was in the correct range, without having to find a way to bring it to 20°. I assumed this would be a straight linear relationship, shown by a graph or a simple math equation. If my hygrometer is saying it's 52 RH at 14°- what RH would it be at 20°?

But after lots of googling I couldn't find anything that wasn't confusing.

 

[Arctic Bowl]

The Psych chart is why I wandered in. Unfortunately I can't read the numbers on it. The reason I was interested in the first place is- most of my bud is stored in one room in large jars with the little digital thermometer/hygrometers in the jars. I'm trying to keep the RH in the jars around 60, give or take a little, presumably around room temp- 20°

However the temperature in that room fluctuates a bit and often the temps are lower like down to about 15°, or up to 25°. Or higher/lower, lol.

So at one point I was googling around trying to find a simple scale to relate a given temp/RH to another temp/RH, if you know what I mean. I just wanted to know if the RH in the jar was in the correct range, without having to find a way to bring it to 20°. I assumed this would be a straight linear relationship, shown by a graph or a simple math equation. If my hygrometer is saying it's 52 RH at 14°- what RH woukd that project to at 20°?

But after lots of googling I couldn't find anything that wasn't confusing.

If you google a Psyc chart print one off, they do have low temperature charts that will cover your temperature ranges. As soon as we get our new iPad ( better camera than this old one) we will try and post better quality pictures. Frustrating this one has such poor quality, I'll look for a lower temperature chart and try an post closer pictures of the temp/ humidity your looking for. I've got them, just have to find them lol.

Blessed Buds our friend and be well

 

[Weaselcracker]

Thanks. I had never heard of a Psych chart before this- was probably just typing gibberish into Google- that term puts me on the right track.

 

[Arctic Bowl]

Here is a link to a low temp chart that you will be able to see clearly. Hope this helps and any questions we will do our best to help out.

Here is a link to both a normal temp and low temp psyc chart

Blessed Buds our friend and be well

 

[Graytail]

From your moniker, I would assume you're as familiar with subzero climates as I am, Arctic. It's sometimes hard to grasp what a climate with essentially no free water vapor is like. You can warm that stuff up, but there's no moisture in it! For months on end.

Our weather people use "dew point" for our daily humidity levels, which is much more intuitive. In Weaselcracker's case, dew point in the container wouldn't change with temperature. And that's what we want, isn't it? A uniform amount of moisture, regardless of temp, since it's sealed? What do you think?

 

[Arctic Bowl]

From your moniker, I would assume you're as familiar with subzero climates as I am, Arctic. It's sometimes hard to grasp what a climate with essentially no free water vapor is like. You can warm that stuff up, but there's no moisture in it! For months on end.

Our weather people use "dew point" for our daily humidity levels, which is much more intuitive. In Weaselcracker's case, dew point in the container wouldn't change with temperature. And that's what we want, isn't it? A uniform amount of moisture, regardless of temp, since it's sealed? What do you think?

You are 100% correct, dew point would remain the same until we either add more moisture to our air or we remove some moisture from our air. Keeping our RH% at a constant level regardless of temperature is the harder part. I'd be interested to see if those little humidity packets that can add a slight amount of moisture or remove a small amount of moisture at or around the 62% RH would be enough to make our RH inside our sealed jars remain some what constant over a wide temperature shift. Lol I'm feeling an experiment coming to find out. Maybe two jars with temp/humidity sensors in them, both with new humidity packets, one empty and one with a few buds in it. See if they both track close to the same when exposed to different temperatures. I don't think I know a way to hold RH% inside a sealed jar any other way than those small packets and I'm not sure they will work either but I'd be interested in those results. I've read that those packets can work but have no 1st hand knowledge of this, don't see why they wouldn't at least to a certain extent.

GT any idea if those packets have a volume they are ment to control like pint size, quart size? I'd want the test to be done on a volume they are meant to control so the results are correct.

Blessed Buds our friend and be well

 

[Graytail]

You are 100% correct, dew point would remain the same until we either add more moisture to our air or we remove some moisture from our air. Keeping our RH% at a constant level regardless of temperature is the harder part. I'd be interested to see if those little humidity packets that can add a slight amount of moisture or remove a small amount of moisture at or around the 62% RH would be enough to make our RH inside our sealed jars remain some what constant over a wide temperature shift. Lol I'm feeling an experiment coming to find out. Maybe two jars with temp/humidity sensors in them, both with new humidity packets, one empty and one with a few buds in it. See if they both track close to the same when exposed to different temperatures. I don't think I know a way to hold RH% inside a sealed jar any other way than those small packets and I'm not sure they will work either but I'd be interested in those results. I've read that those packets can work but have no 1st hand knowledge of this, don't see why they wouldn't at least to a certain extent.

GT any idea if those packets have a volume they are ment to control like pint size, quart size? I'd want the test to be done on a volume they are meant to control so the results are correct.

Blessed Buds our friend and be well

Heheh, you may have asked the guy on the forum who's most impressed with Bovedas. I have a few dozen quart jars with herb as old as three years, and while the color and terp profile has changed, the cannabinols have not. Typically, it's as strong or stronger, the feel is pliable and soft, and it smokes much smoother. The character of the high changes, sometimes for the worse, often for the good. Ideally, I think 60% would be better but I've no problems with mold, etc. I never thought about changing temps, but I suppose the granules dynamically release and absorb moisture. It's very interesting to weigh various packets. I forget exactly, but it's something like 12-18 grams difference between a dry one and a plump one. Like 5-7 grams - 1/4 ounce.

Here are some pics I took of several well-cured nugs:


Graytail's 3rd - 4x4 - Doc Bud's HiBrix - Latest LED Tech - Lots of Light!

 

[Arctic Bowl]

Those are some amazing looking nugs!!!! Well that's fantastic you have the Bovedas, lol I couldn't think of the name of them but have seen them. Have you watched temp/humidity over veried temps to see if they hold humity close to the same? We're babies at this whole grow and curing so not much knowledge here but, we love hearing how others are doing things for sure. I was curious what the ideal RH% was for long term storage would be an seems like you have that nailed down by the looks of those buds we will have to do some checking around on these, not sure if they have different size packets or only one size. I think I remember seeing them in a few different humidity levels but that may not be the case. Lol the old memory isn't as good as it use to be. We did order a packet of them and have them in with some of our Jared up buds, want to say they were 62%??

Be interesting to see if they do hold the humidity constant at different temps. Never thought about weighing the packets, for sure that could make a difference in its ability to maintain RH% in our jars. One more variable to apply to the testing

Blessed Buds our friend and be well

 

[Weaselcracker]

Reps for the chart Mr Bowl, and for the apparent realization that I've lost the ability to study/comprehend things like this. Will keep at it though.

 

[Graytail]

Boveda Humidipak

 

[Arctic Bowl]

Reps for the chart Mr Bowl, and for the apparent realization that I've lost the ability to study/comprehend things like this. Will keep at it though.

WC if you have any questions fire away we will find the answer you seek. Some pretty sharp folks on this site and we enjoy how great everyone is sharing tips and tricks and not killing us newbies for asking tons of questions.

Blessed Buds our friend and be well