I have to thank the many of you who unknowingly – or knowingly in the case of Viz – have provided so much valuable advice, without which this project would have been much more difficult. What a forum the Talk is, M_C we salute you.
This is my first venture into indoor grows. However, I have many outdoor and greenhouse grows under my belt. After much reading and research I decided that it was feasible to construct a grow cabinet suitable for my purposes and location. The location is the key to why I have gone the way I have with my grow space and not used a grow tent. My grow space is in an outbuilding which gets very hot in the summer and very cold in the winter, so climate control was going to be an issue.
The principle behind the cabinet was to insulate the inner grow space from heat in the summer and cold in winter. Stale air is drawn down through the cavity of the cabinet keeping the inner wall warm to prevent condensation in the grow space during winter. It also has the effect of insulating the grow space from the fierce heat developed in the building in summer - especially radiated heat from the roof. To aid air flow, intake and extractor fans are used.
I know that my approach to this is not in anyway 'conventional’ possibly even controversial as I have not found the need for very large fans and ducting and will probably solicit some negative responses due to the equipment I have used. However, as this has been highly experimental it seemed best to use low end kit so as to minimise any potential money loss if it was not correct. After three months of experiment with some old seed of unknown origin I fine tuned the cabinet to produce my working cabinet that currently houses my first grow with seed of known origin and strain.
In order to help control the temperature and humidity I opted to build a double wall cabinet, drawing air directly from outside. This required thermostatically controlled inline air heater to warm incoming air and secondary heater to maintain a minimum 23C in the grow space, as well as a humidifier controlled by an humidistat to maintain 50%RH. With such a small grow space it was obvious that a heater in it would not be practical. To overcome this I allowed space below the plant tray where a heater could be situated. I built the cabinet out of 3 sheets of 9mm MDF and other plywood I had lying around.
List of equipment
•
• AC 220V Digital Air Humidity Control Controller WH8040
• DROK® AC 220V MCU High Precision Thermostat Switch -15~70 ℃ Adjustable Heating/Cooling Temperature Controller with 1 Meter Temerature Sensor Cable
• Inkbird® All-Purpose Fermentation Hatch Freezer Heating & Cooling Digital Temperature Controller Thermostat Calibration Dual Stage with Sensor 2 Relay
• Pro Breeze Professional Mini 6" Clip Fan for Home, Office and Desk (2-Speed)
• RS Components - 2kw Electric Fan Heater Portable Small Silent Hot Cold Watt 1kw Energy Saving CE
• LUMii 24 Hour Heavy Duty Timer with UK Plug
• Xumarket(Tm) Ptc Ceramic Air Heater 500W/220V Insulated Incubator Electric Heater
• SUNMASTER Dimmable Digital Ballast 250W - 600W
• Various CFL and HID Lamps
• ST100 4" 100mm Inline Bathroom Shower Hydroponics Extractor Fan
• 100mm in line duct booster fan
• Ultrasonic Humidifier Mist Maker - 1x Membrane 20mm
Air intake heater and external vent
The incoming air heater is designed to raise the temperature to 20C before it enters the lower chamber of the cabinet. As inline air heaters are quite expensive I built the intake air heater from a box section ordered online together with the tapered section I made from 0.5mm thick Galvanised steel sheet and used a 500W ceramic heater element, making provision for a second if needed. The heater element is controlled by a thermostatic switch.
Fresh air is drawn through the inlet heater by an inline fan via 100mm ducting and passed to the cabinet via 100mm flexible ducting, wrapped with some home made insulation of bubble wrap and duct tape. Warmed fresh air is then channelled around the base passing over the humidifier before entering the grow space. As the air enters it is forced around the grow space by a 6 inch fan, this keeps a moderate air flow around the plant.
To prevent the humidity from dropping to low an ultrasonic humidifier has been placed in the incoming air flow. It is controlled by a humidistat; this cuts in at 49%RH and cuts out at 50%RH, keeping the RH between 48 and 52%.
To maintain a minimum temperature of 23C in the cabinet I have used a fan heater positioned in the lower chamber, drawing air from the grow chamber and venting it back mixed with fresh incoming air. This is controlled by an independent thermostat; the thermostat on the fan heater is turned full on and set to 1KW output. The power is then switched by the independent thermostat as required.
The base has been divided to prevent fresh air from air being drawn into the secondary heater. Air for this is drawn from the grow space and mixed with the incoming fresh air before re-entering the grow space.
The growing area base is a 60 x 60 black tray, supported by 50mm x 50mm timber attached to side of the unit with upright supports going to the base, into which I cut a hole to fit a shower base waste trap connecting to 40mm waste running to a discharge point outside the unit; this meant raising the unit up so a bucket would fit under the waste pipe. The tray has been raised at the edges to direct water to the drain.
The cabinet is lined with Mylar sheeting. I used a commercial spray adhesive to attach the sheet to the walls. However, when exposed to heat the sheeting bubbled. Not sure why, two possibilities. It does not in effect make much difference.
Lighting cables are run up through the cavity and I have devised my own light support device – nylon whipping thread attached to the reflector hangers, passed through small hooks to act as the supports and slides to a fixing hook .
Stale air is removed from the top of the grow space. When using CFL’s the inlet fan is sufficient to maintain air flow for a small plant. The stale air travels down the cavity and into two 50mm ducts before combining into a 100mm duct. When using a discharge lamp a second extractor fan can be switched on to increase the removal of stale hot air.
Cabinet top removed
For the initial veg stage (three weeks) I have used CFL’s as there is no requirement for the intensity of a HID lamp at this stage and it makes climate control easier. I can switch power supply to the lamp holder from direct mains to dimmable ballast so it’s possible to run HID lamps. Most of the veg stage will be under a metal halide lamp, with flowering under a sodium lamp. The size of the space means a 400W lamp is adequate.
Electrical controls
So there it is my grow closet. Feel free to critique, suggest or ask I’m interested to hear what you have to say. There will be a diary started very soon. I’ll post the link here when it’s up and running.
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