Its cool bro im still pondering how do lower it the cheapest short term and long term
Why would you want to lower it? I read all the posts, you don't have mold?
Lowering your humidity at peak flower setting time is counter productive for you plant and you. Toss Co2 in there and your burning money too. The short of it is something called VPD (Vapor Pressure Deflect). Science lesson attached but the short version is
Your plants have pores on the leafs that are called Stomata, they open and close depending on the VPD or humidity+tempurature = VPD
so the more humidity the wider the stomata open and the more Co2 they can eat to power the plant. It's just plant science, I have 2 25gal auto feed humidifiers in my room that run 24/7 to keep the humidity at 65%, lots of pix in my sig.
Humidity and Vapour Pressure Deficit (VPD)
For years Relative Humidity (RH) has been used as a measure of how much water vapour is present in the air and is probably still the preferred method used by experienced growers. In a greenhouse, the amount of water vapour present has a direct effect on a plants ability to transpire and hence grow.
Another measure called vapour pressure deficit (VPD) is also used to indicate humidity and is felt to be more directly related to a plants wellbeing. VPD combines the effects of both humidity AND temperature into one value and so gives a good indication of plant wellbeing without the need for the grower to do any mental arithmetic. VPD values run in the opposite way to RH values so when RH is high VPD is low.
If humidity is too low (i.e. high VPD), the stomata on the leaves tend to close in order to limit transpiration and prevent wilting. This closing of the stomata will also limit the rate of CO2 uptake and hence limit photosynthesis and consequently plant growth. Low humidity also reduces turgidity (water pressure within the plant cells) and this in turn also restricts growth.
Conversely, if humidity is too high (i.e. low VPD) the stomata will fully open but even so the plants will be unable to evaporate enough water to carry minerals into the plant and so again, growth will be impeded and mineral deficiencies (particularly calcium) may occur. In addition, the plants may exhibit soft growth, fungal problems and mineral deficiency symptoms.
It is frequently stated that VPD more closely matches what the plant "feels" in relation to temperature and humidity and therefore forms a better basis for environment control. Unfortunately, VPD is extremely difficult to determine accurately as it is necessary to know the leaf tissue temperature. Attempts to measure leaf temperature reliably on an ongoing basis have often ended in disaster. One of the problems is that the plants leaves are in differing amounts of sun with some leaves in full sun, some in partial sun and others in full shade. This makes the concept of "leaf tissue temperature" particularly complex.
By measuring the temperature and relative humidity within the crop canopy the calculated VPD is still a useful measure as it combines both temperature and humidity into a single measure in a way that approximates the well-being of the crop. As an example, for many crops it is suggested that RH should be kept between the following limits at the stated temperatures:-
Temperature [SUP]o[/SUP]C
| Min RH (apply fogging)
| Ideal RH
| Max RH (for disease prevention)
|
15
| -
| 50
| 73
|
20
| 46
| 64
| 80
|
25
| 60
| 73
| 86
|
30
| 70
| 80
| 89
|
You can see from the table that the higher the temperature is the more humidity is required by the plants. The above makes it difficult to specify control parameters as different RH settings are required at different temperatures.
Now look how much simpler this is made by using VPD as the whole of the above table is contained in just three VPD values as follows
Maximum VPD (too hot and dry - apply fogging)
| VPD ideal
| VPD too low (too cool and humid -warm/ dehumidify)
|
1.25
| 0.85
| 0.45
|
AutoVent 2 and 3 environment controllers estimate the VPD based on the air temperature and humidity in the crop canopy. It will only be close to the true figure for a healthy transpiring crop. The VPD calculator below allows the VPD to be estimated based on both air and leaf temperatures. This clearly shows the possible error in VPD due to just a 1 deg C difference between air and leaf temperature.
As a general rule, most plants grow well at VPDs of between 0.8 to 0.95 KPa
Fogging or other humidification is usually applied at VPDs above 1.25KPa and heating and dehumidification at VPDs below 0.45KPa
Use the on-line calculator below to calculate the VPD from Air Temperature and Relative Humidity (with and without leaf temperature). You need to be connected to the internet to use this link.
VPD CALCULATOR
http://www.autogrow.com/vpd_calc.php
