Hydroponic Grow Room Ventilation
ventilation in hydroponics
Humidity in hydroponics
Plants absorb water through their roots and allow it to evaporate out through their leaves. This process works by capillary action, where water molecules have a strong attraction to one another and as some are evaporated they draw adjoining molecules with them up the whole plant. Dissolved nutrients are present within the water, too. This complete process is known as transpiration and is influenced by the surrounding humidity.
Relative humidity is “the ratio of actual water vapour content to the saturated water vapour content at a given temperature and pressure expressed as a percentage”. Each species of plant has their own optimal conditions, but relative humidity absolutely affects leaf growth, photosynthesis, disease, pollination, and overall yield. For example, larger leaves grow in increasingly high relatively humid environments as the turgor pressure, the water pressure inside plant cells, is higher from a decrease in transpiration.
When relative humidity is low, plants close their stomata and increase their mesophyll resistance to maintain a suitable concentration of water. This indirectly decreases carbon dioxide absorption and lowers photosynthetic processes.
High relative humidity may negatively influence how well a plant can distribute pollen, which may not be of huge importance to you as a hydroponic grower but it remains relevant. Furthermore, incidents of pathogenesis increases with high relative humidity. For instance, fungal spores germinate favourably on plant leaves in such conditions.
Neither relatively humidity that’s too high nor too low positively affects crop yield and all of the above impacts your plants ability to optimise growth and, ultimately, economic yield. As plants age and mature they begin to prefer less humid conditions, without removing excess vapour this will build up quickly.
Temperature in hydroponics
Temperatures exceeding optimum levels rather than being too cool are more likely to occur in hydroponics.
There are two kinds of reactions during photosynthesis, the light-dependent, and the light-independent reactions. As the name suggests, light-dependent reactions involve photons interacting with the leaf, these reactions aren’t affected by the temperature. Light-independent reactions are unrelated to the intensity of light but they are affected by the temperature of the plant.
Enzymes within the leaf catalyse reactions during the light-independent stages of photosynthesis. If the enzymes and other proteins in the cell become too hot they lose their extremely specific shape and denature, meaning their ability to perform chemical reactions as they should diminishes.
Until the optimal temperature is reached, photosynthesis doubles every 10℃/18℉. Beyond the optimal temperature, the rate of photosynthesis starts to lower again. Plant tissue dies when it reaches approximately 46℃/115℉. High temperatures can result in the products of photosynthesis (sugars) being used up (respiration) faster than they’re made, called photorespiration.
Plants lose heat through transpiration, long-wave radiation, and heat convection to the air which is dependent on wind speed. This ties in with humidity above, and if transpiration is lost through environmental factors, causing stomata to close, or injury to the plant, it can be very difficult for it to cool itself. Heat injury to plants includes scalding and scorching, leaf drop, leaf death and a drop in economic yield.
Carbon Dioxide in hydroponics
Your plants use carbon dioxide during photosynthesis, it’s the carbon source for the anabolism of sugars. Plants need carbon dioxide to continue living and growing and, a as a result, without carbon dioxide plants will die.
Increasing carbon dioxide in a growing environment will speed up the rate of photosynthesis until the biochemistry of the light-independent reactions become the limiting factor. At which point adding more carbon dioxide will make no difference to the process.
Atmospheric carbon dioxide is at 0.041% at the moment, and according to www.co2.earth that’s roughly 409.01 parts per million as of the 5th of May 2017. Compare this with oxygen which makes up just over 20% of atmospheric gases and works out at 200,000 parts per million.
It doesn’t take a genius to understand the depletion of carbon dioxide in a confined space isn’t going to take long. Once the levels drop, photosynthesis is going to halt and economic yield is compromised.
Photorespiration describes the oxidation of the RuBisCO enzyme instead of it binding carbon dioxide, the intended outcome. This happens in approximately one-quarter of all potential reactions because of competition between carbon dioxide and oxygen for the same active site in RuBisCO. Photorespiration is wasting the energy gained through photosynthesis which is, by extension, needed to drive more photosynthesis. If your hydroponics system doesn't account for ventilation and provide suitable carbon dioxide then photorespiration will increase and yield will go down.
The ventilation Setup
As well as your grow room needing fresh air entering and stale air leaving, there must be some level of circulation to mix the air into its appropriate ratios rather than left to separate in a process known as stratification.
Plants benefit from a gentle breeze ruffling their leaves. Aside from makes them feel fabulous, it provides access to all the correct gases and the physical stress will strengthen them structurally, helping them to bear larger fruit if they're that way inclined. Emphasis on gentle, though, if leaves dry out they’ll start to shrivel and curl up, something you want to avoid.
To make these wind currents, oscillating fans are your friend. No need for anything fancy as long as the functionality is there to support your hydroponic growing. For instance, you can now purchase models which attach to poles, the wall or are freestanding.
Some fans can be programmed to move their heads in distinct ways, but make sure you’re able to create a breeze in all areas of your grow room. Test this by gluing feathers to a stick and placing it in all positions. If the feathers move, you’re good. If they don’t, you need more air movement.
Extractor Systems in hydroponics
Inline extractor fan will open up your grow room to the outside world by moving air from the inside to the outside. Inline refers to the fan being located inside the grow tent or grow room or connected via a port. There are several methods for calculating the size of extractor fan you’ll need, we’re just going to keep it simple here. Your grow room has a volume, for ease let’s say you’re calculating this in feet. Measure the width, length, and height of the room to get the volume in cubic feet.
For example: 1ft x 1ft x 10ft = 10ft3
Fans will indicate how much air they can move in a minute, so, if it’s feet it’ll be cubic feet per minute (cfm). You want your air replenished once per minute.
There are two types of air intake into your grow room, passive and active.
Passive intake relies on diffusion and negative pressure. The idea is a fan blows stale air out of the room and nothing forces fresh air in but the pressure difference created will balance the grow room out with fresh air. The intake hole needs to be 3 times the size of the exhaust hole so that the pressure gradient is great enough to allow the fresh air in naturally.
Active intake relies on energy input from both ends. There’s a fan blowing air out in the exhaust hole and blowing air into the intake hole, the size of the holes can be the same.
Carbon filters in hydroponics
Some people grow plants which are particularly potent and even a grow tent can't contain their odours. There are a few different techniques used to remove as much smell as possible but the most popular method is to install a carbon filter. As the name suggests, carbon filters contain carbon, specifically charcoal. What makes charcoal so effective is its large surface area but this can be made even larger by treating it with oxygen, forcing more pores. Once treated with oxygen it's called activated charcoal and its surface area is reported to be as much as 500m2 per gram.
The principal criterion in carbon filter purchasing is ensuring the filter can handle the volume of exhausted air the fan pulls through. If not, the air isn't going to have contact time to percolate through all of the spaces and bind to the charcoal. For example, if your fans are moving 20cfm then you're much better off with a filter which can handle 40cfm to absorb all of those nasty impurities.
Removing molecules from the air with activated carbon is a process termed adsorption. The adsorbate, odour in this case, stick to the outside of the of the charcoal to form a film across the adsorbent, the charcoal.
Have you seen our other Articles on hydroponics?
The Basics Of Hydroponics | The Kratky Method | Types Of Hydroponics | Deep Water Culture | The Drip System | The Wick System | Lighting In Hydroponics | The Ebb And Flow System | Nutrient Film Technique | Nutrients For Plant Growth | Ventilation For Hydroponics | Growing Media Used In Hydroponics | Hydroponics | The Best Way To Cure Root Rot | How To Choose A Grow Tent | The Best LED Grow Lights | Everything You Need To Know About Nutrient Lockout | The Best Air Pumps For Hydroponics | The Best PH Meters For Hydroponics | What Mom Never Told You About The GH Dual Diaphragm Air Pump |