Whether or not to install air conditioning in your hydroponic grow room is a decision many new growers struggle with. After all, you’ve got movers, fan ventilation and besides, you’ve invested so much into this endeavor already, so do you really need to fork out even more on this?
If you’re in the deep south this matter is already settled because without a question you’re going to need air conditioning. When you don’t, both your plants and you will be stifled by excess heat and high humidity.
Conditions that are also perfect, incidentally, for a fungal pathogen to infect your plants. This is something you need to avoid at all cost or risk losing the entire grow.
Excessive heat is one of the age-old problems of grow rooms and greenhouses because of high intensity lighting and friction from the various equipment that is required. All of this heat adds up and can ultimately hurt yields through the stress it places on plants.
The ideal root zone temperature is 65-70◦ F.
This surprises a number of newer growers because the common myth about indoor or greenhouse growing is the warmer the better. This isn’t the case and roots thrive and produce a stronger, healthier growth at a moderate temperature.
Maybe you have a water chiller and are thinking that will compensate the need for an air conditioner. While it may, at what cost? If you’re operating a growing room at 80◦ F that chiller is going to be working overtime just to keep the roots cool enough.
This is not to mention the amount of evaporation and condensation that will accumulate because of a high temperature.
A grow room or greenhouse perform best at a consistent temperature.
A big pitfall of rookie growers is a widely fluctuating growing temperature. It is not healthy for the plants to go from a soaring daytime temperature to cool nighttime conditions. This inconsistency will place a lot of unwanted stress on the plants.
This will have a negative effect on root growth, plant health and yield. Remember, a plant under stress is using so much energy just to survive that yields are inevitably going to drop considerably.
In the north, a consistent temperature isn’t that difficult to maintain during the winter months. You set the thermostat at 75◦ and the furnace maintains that whether it’s day or night.
But what about those summer months?
If you live in Wisconsin or Minnesota, the exterior temperature already fluctuates a great deal during the summer months. These states can easily be 70◦ one day and 90◦ the next and how you going to maintain consistency in the grow room given this?
An air conditioner in the grow room will help manage humidity.
The way an air conditioner works is that it not only cools the air through the use of Freon gas filled copper tubes, it also cools by acting as a mini-dehumidifier. Because of this an air conditioner can help a grower manage the high humidity levels which are typical during summer months.
This only helps the dehumidifier work more efficiently and effectively.
Calculating the BTUs needed to cool your grow room
Natural grow room heat
Let’s work with a simple, easy to work with figure as a BTU starting point.
It takes 4,200 BTUs to cool 100 square feet of floor space without considering heat produced by equipment, CO2 production or lights. Working from here it’s simple to calculate BTUs as size increases.
8,400 per 200 F2, 12,600 per 300 F2 and so forth.
Heat from the grow lights
You will now have to factor in the heat produced by lights. For this use the formula of 1000 watt HPS bulb lights x 4000 BTU Bulb Heat = 24,000 BTU.
But the good news is that you’re not just adding more and more BTUs, there are also factors that will reduce them.
You can reduce the total bulb heat by 40% just through the use of air cooled lights.
When using fluorescent lights, you will also need to consider the heat produced by a ballast. This would be 2,500 BTUs for a digital ballast and 3,500 BTUs if you’re using a magnetic ballast.
Heat from grow room CO2 production
Some growers use CO2 burners that run sporadically throughout the day and they also produce heat. Let’s assume the CO2 burner is running 5 minutes per hour. This would be 1,000 BTUs produced per each 5 minutes of operation.
You may be a bit overwhelmed by looking at all those figures but take another look and you may find none of those factors even apply to your situation. If you’re using LED lights, for example, they produce negligible heat that won’t affect BTUs in any meaningful way.
Final conclusions regarding the use of air conditioning in your grow room
The best bet if you’re growing in a climate where the use of air conditioning is in question take a little time to monitor and record grow room temperatures throughout various outside temperature variations to see where you’re at.
If you’re able to maintain a consistent temperature through the use of movers, fans and venting then you probably won’t even use air conditioning. But if you find yourself with extreme highs and lows you’re going to want to think more seriously about it.