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Here's a 3-cubic meter mushroom grow box with very smooth co2 control system.
Removing the side panel, and looking inside you can see two air ducts and the fresh air pipe. The top pipe is supply air duct with 3mm holes and bottom pipe is the return air with 5mm holes.
Problem!
We improvised to make a proportional fresh air inlet valve by using a $15 RV drain valve linked to a standard electronic damper actuator. A 90 degree rotation of the crank arm pushes or pulls the valve open or closed. The stroke of push/pull cycle is adjusted by changing position of the connecting rod where it connects to the crank arm of the actuator. The 1/4 inch ball joints and crank arm are standard HVAC parts. The 1/4 inch connecting rod and L bracket from Home Depot. The wallplug is 24Vac, 800 mAh, enough to run AS310e and the valve actuator.
We followed Rube's vision and installed the RV waste water drain valve on out grobox and it works great! Now, co2 is continuously maintained at 900 ppm during fruiting.
How it works.
AS310e's analog signal (0-10Vdc or 4-20 ma) controls a 0-90 degree proportional actuator. The actuator moves slowly, taking 90 seconds to move 90 degrees. As the actuator slowly turns, more or less fresh air is introduced. AS310e senses the change in co2 level and adjusts the valve slightly back and forth. We set AS310e's analog control signal (0-10 Vdc) so valve is completely closed (0 Vdc) if co2 is 600 ppm, and valve is completely open (10 Vdc) if co2 is 1200 ppm. In practice, the co2 is contolled at about 900 ppm, about about halfway between high and low set points.
See "Analog Range Adjustment" on pag 7 of AS301e's Operator's Manual, and, look at How to Adjust AS310e's Analog Output Signal to learn more about changing the range.
The amount of co2 generated by mushrooms changes from day to day as they mature; between flushes, very little fresh air is needed, while at the peak of a flush 25-50% fresh air is needed to keep the co2 level stable. With AS310e as a controller, its analog signal continously adjusts the amount of fresh air entering the system.
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Agaricus blazei mushrooms grow inside. AS310e's indication of co2 was used to adjust the amount of fresh air entering the system three or four times during 24 hours.
This grobox has a very accurate temperature and humidity control system, able to maintain a
tropical climate, 28C degrees and 95% relative humidity, 24 hours a day, even in winter. But, co2 level would rise and fall as the duct tape was moved 2-4 times a day, not very accurate.
