In this article, we're going to walk you through managing the air once it's in there, or controlling the airflow within your growroom.
Problems with plants are, more often than not, a consequence of improper conditions within the environment. Many growers see yellowing leaves and make the mistake of assuming it's because of a nutrient deficiency. No amount of added nutrients or magic potions is going to fix the problem though.
Yellowing/deficiencies are usually symptoms of 'unbalanced environmental conditions affecting the plant's ability to physically uptake nutrients. Calcium is a key example of this; not enough transpiration (humidity too high or no air movement) and it won't be mobile through your plant. Adding calcium to your reservoir won't help you, until you sort out the problem at the source.
Temperature and humidity are intrinsically linked, annoyingly, in an inverse manner. Warm air holds more moisture than cold air, so as the temperature of the air rises, growers will typically see the relative humidity decrease at a proportional rate. In practical terms for your growroom, this means any changes you make to your ambient temperature will have an opposite impact on your relative humidity levels (and vice-versa). Fine control of both these variables will involve a few different bits of kit and a fair bit of tinkering.
The goal with a growing space is to achieve consistency and balance between temperature and humidity for your plants. Here, we're going to concentrate on how to actually go about controlling these parameters.
First things first; you're going to need to decide where you're going to place your intake and exhaust equipment. What you're aiming for is as even a draw over as much of the area of your grow room as possible. Use circulating room fans to increase and optimise airflow throughout the room as a whole, ensuring there are no dead spots harbouring stale air. This is a fairly basic principle but needs careful consideration when you're designing a room.
When your lights are blazing, you will no doubt need to adjust your fan speed to cope with the increasing temperatures. There are a variety of fan speed controllers available. Manual fan speed controllers are a starting point, but usually require constant amendments to the speed.
They won't give as consistent a temperature in your grow room because they don't react to a fluctuating environment. Automatic controllers with temperature probes gradually adjust to changes in temperatures with either a step up, or a gradual increase in speed, dependant on make and model.
Other than CAN'S promising new controller, digital fan speed controllers tend to make fans hum slightly as they distort the signal being delivered to the fan. A magnetic controller such as the SMS will create no excess noise from the fan at all, but may not have hysteresis control features to compensate fan speeds and maintain negative pressure in your room. Choose wisely.
Mostly an issue when your lights turn off. Even with fan speed controllers going to their lowest setting you will likely need to heat up the air temperature at 'night'. Oil filled radiators may well lure you with claims of using less electricity, but they don't compare to the effectiveness of a decent fan heater.
A great example is the Bio-Green Tropic Heater, whose heating elements will only turn on when the temperature drops below the set parameters, thereby doubling as a circulatory fan for the day cycle as well.
For lights out, you may well be able to lower your humidity to acceptable levels with simply the use of a decent fan heater. For late flowering periods during your daytime cycle, you may find yourself requiring a de-humidifier. They come in desiccant and compressive versions.
Air compressor based versions may promise larger levels of extraction, but tend to vary their effectiveness with fluctuating temperatures. They also tend to be louder than their desiccant cousins, whose output remains consistent over a wide temperature range. Anything from 16L to 22L per day is usually sufficient for the average growroom.
Choices for increasing humidity currently range from smaller ultra-sonic ceramic disc mist makers to centrifugal based units. The ultra-sonic versions (ideal for relatively small rooms) create a mist with a much finer particle size, which evaporates and raises the relative humidity a lot quicker than the centrifugal versions.
Suitable for larger growing areas, these spin water through a grate at high speed and smash it into a spray; these larger spray particles taking slightly longer to evaporate. High pressure nozzle types may shortly be hitting the scene which promise to be a great bit of kit. Watch this space.
Most de-humidifiers come with inbuilt settings allowing you to change the humidity parameters from the unit itself; humidifiers usually require extra equipment for fine control of your environment. For example, the highly accurate Faran Humidistat HR-DHTC we used in this issue's filter tests.
A good Thermo-Hygrometer will record the extremes of both measurements (Max and Min) usually from two points: the unit itself and an external probe. Your other equipment, like fan speed and humidity controllers, will also come with their own measuring equipment and in turn their own probes as well.
Where you position your measuring equipment and various probes plays a major part in how effectively your equipment will operate, and is often under looked.
You need the measuring probes to work from readings that will reflect the majority of the main section of your growroom that you're concerned about: fairly central in the space as a whole, and just beneath the top of your plant canopy. Ideally, have a few units measuring from multiple areas to get a greater idea of the overall average.
No two setups are the same, so trial and error is the only way you'll achieve a happy medium for your own growroom. Remember; no matter what some brightly labelled packaging might tell you can't force your plants to do anything, all you can do is try to provide them with the best environment in which to work their magic, so don't be too hard on yourself when you don't get there straight away.
If the incoming air is very cold, avoid blowing directly onto plants. Particularly in winter, this chill factor could hamper growth.
Use intake filter or mesh fabric (a pair of tights) over vent to filter unwanted pests from outdoors.
Ensure all ducting is securely connected to avoid any air leaks and un-filtered air entering the exhaust system. Check by running a lit splint along run and near connections and see if any smoke is sucked in.
Don't place your humidifier directly under your filter! Use a warm water supply where possible, this will evaporate quicker from the mist and raise the relative humidity faster.
Use an RO machine for the water supply to your humidifiers. The cleaner the water the better it is for the longevity and performance of all the equipment within your grow space, but particularly reflectors and filters.
Raising your relative humidity will lower the ambient temperature. This can be a saviour when operating on the brink of your extraction fan's limits.
Don't position your measuring equipment in the direct glare of your lights, or somewhere that they might get wet.
Choose a shady spot, level or within the plant canopy. Have a fan blowing over your probes. Stationary air around the probe will give you unrealistic readings of the room as a whole.
If you're using a simple max/min unit, one set of measurement a day is just about enough to cut it. Ideally though you need to build up a map of temperature changes throughout the day, over a number of days. Data logging temp/humidity monitors are becoming very cheap nowadays and can provide a much greater insight than your standard max/min unit ever can.
Once you've uploaded all the stored data, you should have a clear idea of the extent of regular temperature changes throughout the day and night. From there you can really begin to tweak the operating parameters of your other environmental control equipment. Or if your equipment is hooked up to timers, you can then set up a more appropriate routine.