Air - Your Grow Room's Atmosphere

Air (or atmosphere) is the gaseous envelope that surrounds this planet.

It's mostly of a mix of gases, but also contains solid and liquid particles. The two main catagories are:

Non Variable components

• Oxygen (21%)
• Nitrogen (78%)

• Other gases like: Argon, Neon, Krypton, Hydrogen, Xenon, Radon in very small amounts

Variable components

• Carbon Dioxide (0.03% variable)
• Water (vapour, liquid) Dust, Smoke, Smells

As you can see, oxygen and Nitrogen make up 99% of air! Well, the laws of physics affect them like they do any other gas or liquid.

There's a direct relationship between temperature, pressure, volume and density. Any change in one means a corresponding change in all the others.

The change is always the same and is always predictable.

By understanding the relationships between each of these factors (and how it affects plants), you can really fine tune your environment.

When air is heated:

• its volume increases (it expands)
• its density decreases (it becomes lighter)

This means that there's a fall in pressure. When this happens, the amount of water vapour it can hold increases.

Conversely, when air is cooled:

• its volume decreases
• its density increases

This means there's an increase in pressure, and the amount of water vapour it can hold decreases.

So, heating air makes it expand, which means it can hold more water.

So far, so good.

but...

If the air you're heating has a set amount of water in it, as it expands, the relative humidity drops.

This sounds complex, but it's not...remember, your RH tells you how full of water your air is, as a percentage (%).

As your air warms, it has the same amount of water, but is less % full of water, simply because it can hold more water.

Of course, when you use high intensity lights, a lot of heat is generated. Make sure you've got a good air exchange system. If this isn't enough to keep your humidity in check, you may need to humidify your air.

It works in reverse, too.

When air is cooled, it contracts - if it has the same amount of moisture, the relative humidity increases.

If you keep cooling, eventually you'll reach the dewpoint temperature. This is the point at which your air is 100% full of water.

When this happens, visible water droplets start to form.

This is why you sometimes you get condensation in your grow room after the lights go off and the room cools.

Again, good air exchange can prevent this from happening. Failing that, there's always dehumidifiers!

Without CO2, photosynthesis can't happen.

Since plants use CO2 you need to exchange air to keep levels high.

Fortunately, CO2 is a variable component - you can increase CO2 levels. Normal atmospheric levels are around 350ppm. Air inside your home can be as high as 800ppm, just from people breathing.

So, that's annother good reason to use input air to your grow room from indoors.

It's been found that plants can cope with CO2 levels of up to 1200ppm! Don't be afraid to add CO2 - MyCO2 Bags are an easy and affordable option.