Keeping Cool and Comfortable
By Erik Biksa
AIR CONDITIONING
The modern grow room outfitted with high-output air conditioning can produce higher yielding crops consistently in less space. Increased sophistication in climate control can provide working parameters that were not achievable in the conventional grow rooms described in earlier indoor growing guides. High-output gardens requiring sophisticated air controls may not be the best choice for the single light gardener or those with limited resources. The equipment typically consumes considerable amounts of electricity. Some machines also require copious amounts of water for cooling. Installation has become more simplified when equipment is purchased from specialty suppliers.
Conventional air conditioning discharges the hot air removed from the growing area. The process would be self-defeating if the warm air was not discharged to the outdoors, because the heat would remain in the area. Although this method is capable of more precisely controlling the temperature than outside air exchanges (conventional grow rooms), it does still require that large amounts of heat will need to be exhausted from the growing area.
Water-cooled air conditioning, as the name implies, requires a considerable amount of cool running water to operate. While the unit is operating, most models will require approximately 1.5 gal. (~6 L) of flowing water per minute. The principle behind using this type of device for indoor and often subterranean growing environments is that the heat generated from the grow room goes down the drain with the water after flowing through the equipment, compared to ducting hot air to the outdoors to control growing environment temperatures. Ponds, rivers, and other inexpensive sources of water are required to operate such units. When properly installed, the grower simply sets the temperature on his or her thermostat. The equipment is capable of maintaining temperatures within a pre-set differential, typically ~9ºF (5°C). If narrower temperature differentials are maintained, the equipment is cycled more frequently. This is less efficient in water and electrical consumption.
Water-cooled air conditioners tend to be as bulky as they are water and energy intensive. They can weigh into the hundreds of pounds (kg) and may occupy valuable space ranging to refrigerator-sized. However, when properly crated with the aid of a hand truck they can be moved by two people with relative ease.
Water-cooled A/C equipment typically requires 240 V or more for the power supply and a dedicated high-amperage circuit breaker or fuse. A cold water supply will need to be plumbed from the pressurized source to the unit. Industrial-grade hoses may simplify the installation. An added benefit for the grower is the appliance’s ability to remove moisture from the air (humidity) in the cooling process. This moisture collects in the drain pan beneath the condenser and must be drained freely away. This procedure can be simplified with an industrial-grade hose, but the machine must be higher than drain level, as it works by gravitational flow. Some designs integrate air-purification materials such as activated carbon into the air-intake portion of a standard water-cooled air conditioner. Restricting the intake may diminish the cooling efficiency of the machine.
Cooling requirements vary from room to room. Insulation, the air volume relative to the number of lamps, and the number of walls are all factors that play a role in sizing a water-cooled air conditioner. Air conditioning is most efficient when operated in a well-sealed and insulated room. Coupled with multiple HID lamps and propane- or natural gas-burning CO2 generators, cooling demands can make it hard to obtain optimal growing temperatures. Calculate your cooling requirements based on 4500 BTUs (British Thermal Units) per 1000-W lamp. This factor helps provide a margin of buffering. Consult the chart detailing the cooling output of various units relative to the number of lamps per room.
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Relative Cooling Output of WPC Series |
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|
Max Lights |
BTUs |
AMPS |
|
3 |
12,000 |
9 |
|
5 |
18,000 |
12 |
|
6 |
24,000 |
12 |
|
8 |
30,000 |
16 |
|
10 |
36,000 |
18 |
|
12 |
44,000 |
21 |
|
17 |
60,000* |
31.5 |
|
25 |
90,000 |
30 |
|
34 |
120,000 |
38.2 |
|
*60,000+ units usually require a 3-Phase power supply. |
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If a water-cooled air conditioner fails while lamps and the CO2 burner are operating, the room can get excessively hot. Beyond certain temperatures crop loss is inevitable, but there may be worse consequences, including fire. As a precaution it is recommended that a high-amperage relay be wired to the power supplied to the HID lighting system. A line-voltage heating thermostat is installed in the grow room, set to 95°F (35ºC), and wired to the relay to act as a trigger. If the temperature reaches greater than the set point, the lamps will shut off until temperatures are below the set point. In this configuration the heating thermostat thinks the lights are heaters. So, when the temperature rises above the set point the “heater” (lights) shut off. This precaution has saved more than one crop.
AIR PURIFICATION
Indoor gardens rely on artificial conditions. In nature there are forces at work that help to purify the air around us. Indoors we cannot easily re-create these forces, but we can apply the beneficial principles with specialized equipment. For indoor growing situations good quality air is a critical factor, and if it is not addressed, it will become the limiting factor in production levels. Plant health may also count directly on the quality of air. Many plant diseases are airborne; these diseases enter the growing area and spread by air. Air movement is critical for indoor gardens, so it is very important that the air be free of contaminants. Indoor gardens may also develop strong odours. While often pleasant to the gardener, these odours can be offensive and troublesome to others.
Activated carbon filters are used in hospital recirculating air-purification systems, and the technology has been adapted for indoor growing applications. The principle is simple and requires no additional power (assuming existing running fans).
The design principle is simple and effective. A mesh-type frame holds tightly packed activated carbon within the walls. The profile is usually round (see photos). Air is either drawn or pushed through the filter. In-line fans are best suited to the application. The system is more efficient if the air is pulled through the filter rather than pushed through it. If fan speeds are too high or low, the filter may not be effective. Excessive humidity will also decrease the ability of the activated carbon to trap airborne contaminants. A pre-filter usually surrounds the outer area of the carbon filter. This will help to catch coarse airborne materials such as dust and dirt. This helps to increase the effectiveness and service life of the filter.
Some filters are refillable, although a large vibrator or many taps with a rubber mallet are required to get the filters repacked firmly again. Gaps within the filter walls will have more air flow through them, with less protection. Less air to carbon contact means that the filter will not work as effectively. Filters are refilled or replaced every six months to one year, depending on the quality of the carbon and the filter. With higher levels of airborne contaminants present, filter life will be diminished.
The filters are affixed to exhaust intakes, recirculation fans, or intake fans. In sealed environments (CEA) the filter/fan combination is only required for recirculating applications. Recirculating air through activated carbon filters (“scrubbing”) is the most effective way of improving air quality for the growing environment. An activated carbon filter of appropriate size to room volume and fan output is stood vertically and centrally in the growing area. Consult the charts in this section for correct fan to filter sizing.
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Carbon Filter to Fan CFM Sizing Chart |
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|
Filter Height |
Suggested Fan CFM |
|
50 cm |
420 |
|
75 cm |
600 |
|
100 cm |
840 |
|
125 cm |
1020 |
|
150 cm |
1260 |
If the air must travel through extensive ductwork, a slightly higher fan CFM rating or additional in-line booster fan may be required. Fan speed controls can help to fine-tune activated carbon air-purification systems. Multiple filters and fans may be required for larger installations.
The recirculating application is simple. Just sit an in-line fan on top of the filter opening, ensuring there is a tight seal between the fan housing and the top of the filter. Neoprene gaskets help provide a positive seal. The fan is left running 24 hours per day. Air from the grow room is constantly drawn through the activated carbon and delivered back to the room. The purification process is not instantaneous and requires that the recirculation fan run constantly. For example, if you were to create an odour, such as smoke, it would be noticeable. However, if you come back in five minutes, it should be gone.
For exhaust applications, the filters are used for reducing odours exhausted from the grow room out into the surrounding area. The filter is installed before the fan. Air from the growing area is drawn through the activated carbon before it is discharged outdoors by the exhaust fan.
Activated carbon filters may also be used for air intake applications to help prevent spores and other contaminants from entering the growing area from outside air intakes. In this application, the fan is installed in the ductwork before the filter, preferably at least five feet (~1.5 m) away. Fan output should be enough to pressurize the filter. Too much airflow through the filter will decrease the ability of the carbon material to trap unwanted materials from the air.
Fans, Mechanical Ventilation
Good air circulation is important for conventional grow rooms and CEA rooms. Good-quality air circulation fans are integral to the health of the crop. Circulation fans prevent the air from stratifying. If air movement through the growing area is poor, heat and humidity will rise to the ceiling and carbon dioxide will not be circulated over the plants. Moisture will pool on plant leaves, possibly contributing to plant disease. Insects will infest faster because they have a much easier time moving about with low air movement. Plants will grow soft and weak stems indoors. Good airflow will help stiffen branches to support heavy fruits and flowers. With increased airflow the rate of plant evapotranspiration speeds up, because moisture through the leaves is lost more quickly into the air. On smaller, more tender plants, such as cuttings or seedlings, care must be taken to not apply excessive air movement, which may cause them to wilt and dry out. The more the plant canopy increases in mass, the more air movement will be required.
Oscillating fans are readily available and work well to sweep the air evenly through the growing area. The leaves should gently flutter in the breeze. Wall-mount units are favoured because they don’t take up valuable floor space and can be mounted to the correct height relative to the crop. When it comes to wall-mount fans, many growers have found they got what they paid for.
Cheaper imported fans will usually have a short service life, often as little as three months. They are likely not intended to run 24/7. Better-quality fans stand up to running constantly for much longer. Pedestal fans can be adjusted for height but often get in the way. They are also harder to place in the grow room without having to run the power cord along the ground. This may pose a danger in wet environments. Tabletop or desk-type fans can be used, but a shelf must usually be constructed to keep the fan at the right height for the crop.
The most efficient fan to use for indoor growing applications tends to be the in-line centrifugal fan. These fans help maintain CFM output against static pressure from closed areas and ductwork. They may be used effectively for pulling or pushing air-movement applications and can be installed with relative ease in various positions. They are lightweight, run quietly, and consume little power, and they are usually rated for variable speed. Ductwork is easily mounted directly to the fan because of flanges made to fit standard duct sizing. Refer to the fan size to CFM chart for more detail.
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In-Line Fan Size to Output |
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Model |
CFM |
|
4 in. (~10 cm) |
165 |
|
6 in. (~15 cm) |
420 |
|
8 in. (~20 cm) |
715 |
|
10 in. (~25 cm) |
760 |
|
12 in. (~30 cm) |
1100 |
Shaded pole blower (squirrel cage) fans are available in a range of sizes and CFM output ratings. For indoor gardening applications the size range is large, from 265–3200 CFM. Blower fans also work well against the static pressure from venting closed areas and extensive ductwork. They can be a little trickier to install because they tend to be larger and heavier than in-line centrifugal fans with similar CFM output ratings. The motors they use require more power to operate and are usually not rated for variable speed control.
To simplify installation, blower fans may be mounted in specially made “blower boxes.” This allows the grower to more quickly install the fan unit to ductwork. The galvanized metal box also provides a measure of safety from the internal blower wheel and helps to reduce noise. While these fans may not be rated for variable speed, they often have three speed capabilities (high, medium, and low). Speed selection is usually done by connecting the black wire from the power supply to one of the three input wires to the fan. The remaining two are capped off securely with marettes. A toggle switch with the appropriate amperage rating may be wired to two of the three fan-speed lines, allowing you to switch from medium to high speed as required. A two-stage cooling thermostat may also be used to control the speed at which the fan is running.
If not using a specialty blower box to house the blower fan, it is recommended that the fan be suspended from the ceiling with eyebolts and bungee cords. Make sure there is adequate support, because the units can be quite heavy. A transition will be required so that the blower discharge (rectangular) can be securely fitted to grow room ductwork. Blower boxes are supplied with flanges for mounting ductwork. Multiple flanges of smaller diameters may be integrated to blower boxes. This is ideal for air-cooled lighting applications because runs of flexible ducting can be made from the air-cooled lighting reflectors directly to the box. Otherwise, ductwork must become extensive in order to keep air moving fast through the protective enclosures. As a precautionary note, most blower-type fans, particularly with higher horsepower motor ratings, may not be run with free air. If ductwork or resistance is not encountered by the fan while it is operational, it may burn the motor out. Models are usually available as direct or belt driven (motor to fan wheel). Belt drives tend to be a little quieter but can also be larger in size. Blower boxes are usually fabricated to fit direct-drive units.
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Blower Fan Sizing to CFM chart |
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|
Blower Wheel Diameter |
CFM (Free Air) |
Motor HP* |
|
9 in. (~23 cm) |
2200 |
1/3 |
|
10 in. (~25 cm) |
2800 |
1/2 |
|
12 in. (~30 cm) |
3200 |
1/2 |
|
12 in. (~30 cm) |
3600 |
3/4 |
|
* 1 HP (horsepower) equals 746 W |
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When purchasing a blower fan remember that larger horsepower motors on the same-sized fan wheel will not increase CFM output drastically. The speed (RPM motor rating) of rotation of the blower wheel relative to wheel diameter largely determines the volume of air that can be moved. Higher horsepower ratings will allow the fan to maintain rated CFM at increased workloads, which may be required for venting through extensive (greater than 25-ft (~8-m)) ductwork.
Axial fans may be sufficient for intake and exhaust applications in closet gardens and small growth chambers. They do not work well against static pressure but can be effective in moving air over shorter distances. They run fairly quietly and power consumption is minimal. Larger-diameter axial fans (6–10 in. (~15–25 cm)) also work well when installed for air movement within the grow room, or for spot cooling of lamps. When fans are mounted stationary for air circulation applications (similar to oscillating fans), the application is referred to as HAF (horizontal air flow). This method is popular among commercial greenhouse growers, where the number of oscillating fans required simply is not practical. Large-diameter 12-in. (~30-cm) HAF fans can circulate up to 2600 CFM and are usually rated for variable speed control. MY