Heat Paradox

Wondering Star · May 2, 2010

Got an interesting one...

My cooltube is about 15" above my plant and there a 12" fan blowing air through the gap between them [I also have an extractor venting air outside my tent].

In terms of heat for the plant, I always hear you should check to see if it is uncomfortable for your hand under the light. For me it is fine, very nice breeze and not too hot at all! Feels lovely actually.

Thing is, the temperature reading on my digi thermometer at the same point is like 93 degrees farenheit... so whats the deal here? Is my digi not accouting for that lovely breeze i feel on my hand?

Advice is always appreciated, many thanks in advance...

Tee Five · May 2, 2010

It was recently pointed out to me that if your temperature gauge is under the light you must put it in shade to read the amibent temperature; otherwise you are going to have heat radiation added to your reading.

Luger187 · May 3, 2010

put the thermometer in shade

deprave · May 3, 2010

also - any breeze is going to feel cooler on your skin because of the way humans work a breeze will cool us off but its not the same for plants so if your gunna do the hand check you should just turn your fan off while you do it..personally I can be quite comfortable in a 100F room if I have a bigazz fan blowing on me but the fact is that it is actually still 100F

Wondering Star · May 3, 2010

deprave said:
also - any breeze is going to feel cooler on your skin because of the way humans work a breeze will cool us off but its not the same for plants so if your gunna do the hand check you should just turn your fan off while you do it..personally I can be quite comfortable in a 100F room if I have a bigazz fan blowing on me but the fact is that it is actually still 100F

Sorry to ask but are you basing this on theory or on some type of scientific fact? I considered the same type of thing but couldn't find anything to back it up either way.

I have a 125mm extractor fan pulling hot air through the tube and out of the tent. And most people running cool tubes seem to be at a happy 85 degrees. I can only achieve this with my plants about 2.5 feet away, which for me seems too much.

Murfy · May 3, 2010

yes it is scientific fact that air movement will cool human due to perspiration/evaporation-

Wondering Star · May 3, 2010

Murfy said:
yes it is scientific fact that air movement will cool human due to perspiration/evaporation-

but not plants?

Don't mean to sound rude at all here, but what is the point in having the breeze? just to move hot air away from the plants and to generally move air around? However, I guess the reading I am getting would be hotter without the breeze.

Prot3us1` · May 3, 2010

deprave said:
also - any breeze is going to feel cooler on your skin because of the way humans work a breeze will cool us off but its not the same for plants so if your gunna do the hand check you should just turn your fan off while you do it..personally I can be quite comfortable in a 100F room if I have a bigazz fan blowing on me but the fact is that it is actually still 100F

Plants transpire water, humans sweat...it works the same way. I do have proof

Here you go:

A second function of leaves is to allow water to evaporate through their surface in order to keep a constant flow of water throughout the whole tree. This flow of water allows the distribution of nutrients gathered from the soil by the root system throughout the entire tree.

http://www.bonsai4me.com/AdvTech/ATPhysiology.html

'Transpiration is a process similar to evaporation. It is the loss of water from parts of plants "its like the plant is sweating", especially leaves but also stems, flowers and roots.

Transpiration also cools plants and enables mass flow of mineral nutrients and water from roots to shoots.

http://en.wikipedia.org/wiki/Transpiration

As said earlier, heat is generated 2 ways in a grow box, radiated and generated...generated heat is like from the ballast and the filament of the globe..this is the heat we vent....radiated heat is the heat generated by the light hitting the skin or plant...when the sun comes out from behind the clouds and you feel warmth instantly its radiated (the earth doesnt heat up instantly). When you turn on your oven its generated.

Metal in the sun is a good example...metal in the shade on a warm day is slightly cooler to touch than the air...the same piece of metal in the sun is hot...the light hitting the metal excites the molecules, causing it to feel hotter.

My 400w hps is 8cm from the top of my plant. I also have a cfl within an inch. Had another but i was dumb and knocked it off the stand

. Theres no bleaching or anything...heres a pic of the plant:

Sorry to call you out deprave

*passes J*. Gotta have the right info out there tho man!

Prot

Wondering Star · May 3, 2010

Prot3us1` said:
Plants transpire water, humans sweat...it works the same way. I do have proof Here you go:

http://www.bonsai4me.com/AdvTech/ATPhysiology.html

http://en.wikipedia.org/wiki/Transpiration

As said earlier, heat is generated 2 ways in a grow box, radiated and generated...generated heat is like from the ballast and the filament of the globe..this is the heat we vent....radiated heat is the heat generated by the light hitting the skin or plant...when the sun comes out from behind the clouds and you feel warmth instantly its radiated (the earth doesnt heat up instantly). When you turn on your oven its generated.

Metal in the sun is a good example...metal in the shade on a warm day is slightly cooler to touch than the air...the same piece of metal in the sun is hot...the light hitting the metal excites the molecules, causing it to feel hotter.

My 400w hps is 8cm from the top of my plant. I also have a cfl within an inch. Had another but i was dumb and knocked it off the stand . Theres no bleaching or anything...heres a pic of the plant:

View attachment 915424

Sorry to call you out deprave *passes J*. Gotta have the right info out there tho man!

Prot

Thanks a lot for this. So is it the breeze which helps the leaves to transpire and evaporate water? Or are the two unrelated?

What I need to know is, does the breeze from the fan which cools my hand when I hold it under the light, also cool my plant to the same degree? Because my temperature reads 90 degrees F, which is too hot for me, but with the fan, it feels fine. Like standing outside on a warm summers day in a breeze

which is very pleasant for a human. Is it the same for the plant?

Prot3us1` · May 3, 2010

The rates may be different between human and plant, but the end result is the same...the water uses heat to evaporate...thus there is less heat...as long as you arent stressing the stomata (foliar feeding, smoking in your grow room, shooting light up under the leaves at too high intensity) will regulate water loss just like our pores do.

Mass flow of liquid water from the roots to the leaves is caused by the decrease in hydrostatic (water) pressure in the upper parts of the plants due to the diffusion of water out of stomata into the atmosphere. Water is absorbed at the roots by osmosis, and any dissolved mineral nutrients travel with it through the xylem.
The rate of transpiration is directly related to the degree of stomatal opening, and to the evaporative demand of the atmosphere surrounding the leaf. The amount of water lost by a plant depends on its size, along with surrounding light intensity, temperature, humidity, and wind speed (all of which influence evaporative demand). Soil water supply and soil temperature can influence stomatal opening, and thus transpiration rate.

The plant will be fine, so long as theres enough root mass to keep enough water flowing to cool the plant. The plant has the ability to increase and reduce the flow of water and thus the temperature of its tissues by opening or closing the stomata.

I thought the green text was interesting though. Soil temperature may affect stomatal opening...so warm soil means more water is sucked up, along with more nutrients.

I learned something from helping you!

prot

Prot3us1` · May 3, 2010

Wondering Star said:
Thanks a lot for this.

Thank you for being polite! If you have a spare sec and wish to could you hit the little star pic between "journal this post" and the triangle with the (in the same row as reply, reply with quote and multi quote) . This is adding +reputation to me, for helping

.

*rips bong*

prot

Wondering Star · May 3, 2010

"I learned something from helping you!"

- This is often what happens when you help others

Thank you. I'm not going to move my light further away, i have seen no ill effects either, growth seems normal and no burns or wilting.

desertrat · May 3, 2010

deprave said:
also - any breeze is going to feel cooler on your skin because of the way humans work a breeze will cool us off but its not the same for plants so if your gunna do the hand check you should just turn your fan off while you do it..personally I can be quite comfortable in a 100F room if I have a bigazz fan blowing on me but the fact is that it is actually still 100F

i don't know where to start, this is so wrong.

Wondering Star said:
Thanks a lot for this. So is it the breeze which helps the leaves to transpire and evaporate water? Or are the two unrelated?

What I need to know is, does the breeze from the fan which cools my hand when I hold it under the light, also cool my plant to the same degree? Because my temperature reads 90 degrees F, which is too hot for me, but with the fan, it feels fine. Like standing outside on a warm summers day in a breeze which is very pleasant for a human. Is it the same for the plant?

YES! animals shed heat by sweating - the very act of sweating reduces the temp of the body with no wind whatsoever. cooling via air flow is a completely separate mechanism than cooling through perspiration.

Prot3us1` · May 3, 2010

desertrat said:
i don't know where to start, this is so wrong.

YES! animals shed heat by sweating - the very act of sweating reduces the temp of the body with no wind whatsoever. cooling via air flow is a completely separate mechanism than cooling through perspiration.

did you even read my post lol? plants sweat too

..

EDIT: Wow that sounded assholish...Im stoned and thought i was being efficient i didnt mean to snap!

What i mean is, animals sweat. Glands open and push out liquid. Air then hits this liquid..evaporating it and carrying away heat.

Plants also sweat. Its called transpiration and it does the same thing as sweat in animals.

Once again, sorry if i sounded rude!

prot

aficionado · May 3, 2010

I run 2x 1000w in a cool tube, less than 8" from the top of the plants with no noticeable ill effect. The tube has fans on both ends pulling air through to cool the bulb.

As to your question, air circulation in general serves multiple purposes, the least of which include assisting in the gas exchange at the stomata within the leaves (which includes moisture exchange). Photosynthesis is an endothermic reaction where energy (radiant), Co2, and water is consumed to form the glucose (sugar) the plant needs. To facilitate this process, the plant use stomata located on the underside of the leaves to intake Co2 and expel O2. This opens the plant up for moisture loss in the form of water vapor. Plants also lose moisture through osmosis when the surrounding humidity is much lower and water is leeched from the cellular walls. Ironically, trichomes are cannabis' natural defense against losing too much water at the end of its lifecycle (end of summer).

When a plant "sweats" through this exchange, the loss of water evaporating has the same affect to the plant as it does us - specifically heat is absorbed locally as the water forms as vapor. Although, what feels "fine" to us, is not necessarily ideal to the plant. Think of the foliage in hot, humid rainforests - not ideal to humans, but many different plants thrive there. My advice would be to study your plant itself and see how it is reacting to your specific setup and do not lend too much credibility to one temp fits all. If it is being heat stressed, it will clearly show. In my opinion, temp probes are best used as indicators of fluctuations in temperature and environmental conditions - where the change in readings is more important than the reading itself.

Hope this helps!

Wondering Star · May 3, 2010

Prot3us1` said:
did you even read my post lol? plants sweat too ..

EDIT: Wow that sounded assholish...Im stoned and thought i was being efficient i didnt mean to snap!

What i mean is, animals sweat. Glands open and push out liquid. Air then hits this liquid..evaporating it and carrying away heat.

Plants also sweat. Its called transpiration and it does the same thing as sweat in animals.

Once again, sorry if i sounded rude!

prot

I am not sure but I think he was agreeing with you?

desertrat · May 3, 2010

did you read my post? where did i say plants did not sweat? the point is when you say "the way humans work a breeze will cool us off but its not the same for plants so if your gunna do the hand check you should just turn your fan off while you do it" is dead wrong advice - the breeze (which in wondering star's case is less than skin temp) will cool off plants and human skin the exact same amount. the breeze is carrying away radiant heat that has impacted the plant.

when you say "heat is generated 2 ways in a grow box, radiated and generated...generated heat is like from the ballast and the filament of the globe..this is the heat we vent....radiated heat is the heat generated by the light hitting the skin or plant." you are wrong. both the ballast and the filament give off radiant heat, which is just energy in the infrared light range. your invented concept of "generated heat" is not a scientific term and is just another way of saying radiant heat. the other type of heat you deal with is ambient air temp which you do measure with a thermometer shaded from direct light.

it's noble to want to help people, but how about learning first?

edit - my bad, first quote was from deprave, but just as wrong

Wondering Star · May 3, 2010

aficionado said:
I run 2x 1000w in a cool tube, less than 8" from the top of the plants with no noticeable ill effect. The tube has fans on both ends pulling air through to cool the bulb.

As to your question, air circulation in general serves multiple purposes, the least of which include assisting in the gas exchange at the stomata within the leaves (which includes moisture exchange). Photosynthesis is an endothermic reaction where energy (radiant), Co2, and water is consumed to form the glucose (sugar) the plant needs. To facilitate this process, the plant use stomata located on the underside of the leaves to intake Co2 and expel O2. This opens the plant up for moisture loss in the form of water vapor. Plants also lose moisture through osmosis when the surrounding humidity is much lower and water is leeched from the cellular walls. Ironically, trichomes are cannabis' natural defense against losing too much water at the end of its lifecycle (end of summer).

When a plant "sweats" through this exchange, the loss of water evaporating has the same affect to the plant as it does us - specifically heat is absorbed locally as the water forms as vapor. Although, what feels "fine" to us, is not necessarily ideal to the plant. Think of the foliage in hot, humid rainforests - not ideal to humans, but many different plants thrive there. My advice would be to study your plant itself and see how it is reacting to your specific setup and do not lend too much credibility to one temp fits all. If it is being heat stressed, it will clearly show. In my opinion, temp probes are best used as indicators of fluctuations in temperature and environmental conditions - where the change in readings is more important than the reading itself.

Hope this helps!

Yes it does help. Thanks. I figuired the breeze would help the plant transpire, or something like that.

As I just said to someone else, at the end of the day, if the plant looks fine and is growing fine then things are probably exactly that, just fine.

Prot3us1` · May 3, 2010

desertrat said:
did you read my post? where did i say plants did not sweat? the point is when you say "the way humans work a breeze will cool us off but its not the same for plants so if your gunna do the hand check you should just turn your fan off while you do it" is dead wrong advice - the breeze (which in wondering star's case is less than skin temp) will cool off plants and human skin the exact same amount. the breeze is carrying away radiant heat that has impacted the plant.

when you say "heat is generated 2 ways in a grow box, radiated and generated...generated heat is like from the ballast and the filament of the globe..this is the heat we vent....radiated heat is the heat generated by the light hitting the skin or plant." you are wrong. both the ballast and the filament give off radiant heat, which is just energy in the infrared light range. your invented concept of "generated heat" is not a scientific term and is just another way of saying radiant heat. the other type of heat you deal with is ambient air temp which you do measure with a thermometer shaded from direct light.

it's noble to want to help people, but how about learning first?

Excuse me, you sit your thermometer in the light and you are reading the temperature of the metal heating up from the light, not the air temperature. Thanks. Generated heat, if i rub my hands together im generating heat by energy conversion. Converting the movement energy into heat and sound...
When you take mains power, and shove it through a transformer you are converting electrical energy to heat, and different ratios of voltage and current. (wash off some voltage, create more current and heat), This is clearly nothing to do with infrared light...

You said that airflow will cool skin at the same rate as plants? wrong...if my skin is dry and i blow hot air on my skin it feels hot because theres nothing taking the energy from the heat before it hits skin. If i sweat that air will feel cold, as the water takes the heat energy and uses it to evaporate the water..this makes my skin feel cold. Plants also do the same thing...the amount of water is DIRECTLY proportionate to the cooling effect. its got nothing to do with simple air moving across a leaf, and everything to do with the fact that the plant sweats like we do. It can regulate the sweat to allow more or less water to pass depending on the temperature. You said and i quote:

YES! animals shed heat by sweating - the very act of sweating reduces the temp of the body with no wind whatsoever. cooling via air flow is a completely separate mechanism than cooling through perspiration.

When im all hot and sweaty i find sitting in a hot room i feel HOT. Add a small oscillating fan and i feel COOL. Im not saying perspiration REQUIRES airflow...but airflow keeps things moving at a good pace, whereas natural evaporation without airflow would take much longer for the same amount of cooling.

And just because you were a total fucking dickwit, it wasnt me that said to turn the fan off. Go back and READ.

aficionado · May 3, 2010

hehe... popcorn anyone?

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