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Climate Control, CO2 and HVAC

One of the most important and often overlooked factors in building a successful grow room is creating a perfectly harmonious growing environment.  Keeping your plants in a finely controlled and optimal environment is essential to pushing your crop to its full genetic potential. 

When Temperature, Humidity & Co2 levels are monitored and controlled properly and in relation to each other, optimal VPD (Vapor Pressure Deficit) levels are achieved and plants will exhibit signs of accelerated growth which will ultimately result in greater output.  Grow rooms that are "dialed in" will perform at a significantly higher level than identical gardens lacking on environmental controls.  It cannot be stressed enough how important it is to size cooling and heating equipment, humidifiers / dehumidifiers & Co2 enrichment instruments properly.  If desired levels cannot be reached, yield & quality will suffer and ripening of your crop will be delayed.  It is critical that a grower learns the specific needs of each individual variety, strain & cutting that they are growing.  Plants of the same species will flourish under wildly different conditions, depending on the origin of the breed.  An equatorial variety that enjoys long, warm days will require a far different environment than a species sourced from cold climates.  In any case, grow room conditions must be kept consistent and within optimal ranges in order for plants to flourish.

When constructing your grow, whether a closet grower or a commercial grow facility, a few things must be considered.  First, air conditioning needs must be calculated.  You'll need to calculate everything producing heat in your grow space including lights, ballasts, lamps, chillers, humidifiers, dehumidifiers etc.  At that point, we recommend adding between 20%-100% more cooling power dependent on your native climate and ambient temperatures.  Generally, any equipment producing heat or cooling will have an output rating measured in BTU (British Thermal Unit).  We use a simple formula to calculate the total heat load (equipment BTU output + ambient temps) and use an air conditioner with adequate BTU ratings to offset the heat load.  Air conditioners come in a variety of shapes, sizes and efficiency and are generally measured in TONS or BTU, 1 ton is equivalent to 12,000 BTU.  Commonly used air conditioners in for indoor grow rooms are water cooled & split systems.  Water cooled air conditioners utilize water to exchange the heat and require either a large reservoir, a chiller or a cooling tower to operate.  Split systems come in two main forms, central & mini split.  Both utilize coolant in an outer compressor which cycles to an inner air handler through a coil while a fan blows cool air generated by the cold coil into the room.  Where these split systems differ is generally mini splits are ductless and use wall mounted head(s) to cool "zones", central split units usually utilize ducting to distribute cooling evenly throughout the room.  All of these types of air conditioners come with varying levels of efficiency rated in Seer, the higher the Seer Rating the higher the efficiency.  The same goes for heaters which will be used in cooler climates during dark hours of the plants photoperiod.

Once cooling and heating needs have been addressed, humidification and de-humidification will need to be looked at.  During propagation and vegetative growth, plants generally prefer a warmer and more humid environment used to simulate spring and summer.  During this period the plant will exhibit vertical and lateral growth and this is the most common stage of a plants life where a humidifier will be used in the grow room.  Once a plant begins to bloom, you'll want to gradually lower the temperature and humidity throughout the bloom cycle.  This is where air conditioning and dehumidifiers will be used to keep the plants from developing issues related to mildew, mold, pests, insects & mites.  As large flowers begin to form on the plants, but rot, botrytis & powdery mildew are common but devastating issues related to poor environmental control.  These issues along with many others can be controlled and prevented by utilizing the correct equipment and keeping the proper VPD.  You'll want to refer to our (*****INSERT VPD CHART LINK*******) VPD Chart for recommendations on optimal levels.  Again, it cannot be stressed enough how important it is to size your equipment properly.  A good rule of thumb is always to size your equipment 20% above projected levels.  We are asked all the time, how do I properly size my dehumidifier?..  And the answer is relatively simple.  Plants transpire roughly 97% of water they're given daily, so you'll need to size your dehumidifier based on how much water you're feeding each day PLUS ambient humidity.  For instance, if you're water 20 plants 1 gallon a day each, you'll need to remove almost 20 gallons of water a day.  Usually, dehumidifiers are measured in Pints Per Day or (PPD) so you'll be looking for a unit equivalent to 20 gallons or 160 pints per day (8 pints per gallon), or perhaps larger if you're based in a climate that has high ambient humidity.  The water extracted from the air by the dehumidifier will be very pure and near neutral in pH and is perfect for reuse to feed your plants or mix your nutrients with.

Finally, once you've completely dialed in your temp and humidity levels and you've mastered the VPD chart, Co2 is like the cherry on top.  With the ability to raise yields by upwards of 30% and increase growth rates and shorten harvest cycles by a significant amount as well,  Co2 should be a must for any grower.  Growers use co2 generators and bottled co2 in tanks of varying sizes (generally 20 lb & 50 lb) to produce carbon dioxide and use controllers to monitor and raise / lower co2 levels in the room.  Many growers will gradually increase the co2 from ambient levels of around 300 ppm up to a max of 1500 ppm, and then slowly taper it back down the last two weeks during the ripening phase.  Plants can sustain and actually thrive in slightly higher temperatures than in rooms that are not utilizing co2.  When temperature and humidity rise the stomata of the plant dilates and allows for more rapid consumption of the co2 which leads to quicker and more robust plant growth.   

 We here at Healthy Harvest can assist you every step of the way in designing and maintaining climate control in your grow.  We understand the needs of our clients and have experience in constructing grows of all sizes.  Please do not hesitate to contact us at 888-259-2074.