What does ventilation for oyster mushrooms consist of?
There are quite a few ways to distribute the air flow in oyster mushroom chambers, since there is no generally accepted standard.
The main directions are air exchange with and without air ducts (Tornado system).
I prefer the proven air movement pattern that is used in champignon cultivation and adapted for oyster mushroom cultivation:
- air goes through the air ducts located on top, with recirculation.
- The hood is also on top, on the opposite wall or diagonally from the supply fan.
Consider how to make air supply and exhaust in the growth chamber.
Why is ventilation necessary when growing mushrooms?
We need to create such flows of air movement in the entire volume of the room, which will take away the waste products from the growing druse (CO2 and moisture evaporated from the surface of the mushroom cap).
The flow moving through the ventilation system must have certain parameters (specific values depends on mushroom strain):
- humidity 87-92%,
- temperature 14-16 degrees,
- amount of CO2 — from 800 to 1000 ppm.
Mushroom grow room air exchange.
Air exchange for growing mushrooms is not calculated in air volumes per hour, but is calculated by the amount of substrate loaded into the chamber.
The amount of air required is calculated in cubic meters per ton of mushroom blocks.
Components of mushroom fruiting chamber ventilation:
1. Medium pressure blower
The fan must be centrifugal.
In growing chambers up to 15 tons of substrate, both a duct centrifugal fan and a snail fan can be installed.
In rooms with 20-50 tons of substrate, a snail fan is required.
2. How to choose a blower
With intensive loading of chambers (from 160 to 200 kg per square meter) and simultaneous fruiting (with a single-zone method), the throughput of the fan is calculated based on an air flow of 300 cubic meters. per 1 ton of substrate. If there are blocks of different ages in the room, and simultaneous fruiting of all batches does not occur, 180-220 cubic meters / ton are taken for calculation.
3. Duct diameter
The diameter of the central and side air ducts is calculated according to the formulas, based on the fact that the speed of air movement in them should be 4-5 m/s.
Those air ducts are made of tin, which are located before the blowing fan and suck in outside and recirculated air.
They must be the same diameter as the central distribution duct.
The central air duct has the largest diameter, and the distribution (side) duct has a smaller diameter.
The formula takes into account the capacity of the fan and the number of side air ducts.
For chambers no longer than 16 meters, I made a ventilation calculator in Excel.
There are also ready-made ventilation calculations for chambers filled with up to 8 tons of substrate, the maximum area of the growing chamber is approximately 120 square meters.
4. Holes in polyethylene ducts
Why not just make holes in air ducts, but put nozzles?
This is done to create directed jets of air and increase their speed.
Disposable plastic cone cups do a great job of this function.
The distance between the nozzles-cups is from 0.45 cm to 80 cm.
First, according to the formula, the total number of cups is calculated and their diameter is determined – a certain amount of air per hour must pass through the total cross section of all holes.
And then, knowing the total length of the side air ducts, the distance between the nozzles is calculated.
The speed of the jet from the nozzle is 8-9 m/s. With intensive loading of chambers (especially with a single-zone method), the air flow per hour increases, and the speed can be up to 12 m/s.
5. Recycling in mushroom growing
This is a system for supplying air from a room.
The recirculation pipe is located before the heat exchanger and fan. It supplies air from the chamber, which is mixed with fresh air.
Thus, microclimate jumps are smoothed out – after all, the air from the growing chamber is already heated and humidified to the required parameters. Recycling significantly reduces the cost of mushroom production in winter.
After all, oyster mushroom does not need a large amount of fresh air as much as well-organized high-speed streams. The percentage of opening of the recirculation damper depends on the number of mushrooms that are fruiting at the same time in the growing room.
A filter is installed on the recirculation pipe to clean the flow that enters the system from fungal spores. Otherwise, the fan blades and heat exchanger lamellas will clog and work worse.
6. Plate-fin Heat Exchanger
Air heating takes place only in the ventilation system.
In the growing chamber, the air cannot be heated with radiators, heat guns, buleryan!
The heat exchanger is built into the ventilation tin pipes in the area after mixing the recirculation and street air, always before the fan.
Learn more about space heating.
The hood must remove all the outside air that has entered the room. If the hood is weak, the blower fan will not supply the calculated amount of air, but less. The flow rate will drop, which may adversely affect the shape and condition of the oyster mushroom fruiting bodies.
The power of the exhaust fan is about 90% of the blower.
At maximum air exchange, when the fresh air damper is 100% open, the exhaust fan should run at full capacity.
When using recirculation, the speed of the exhaust fan must be controlled by a frequency converter or damper so that it draws as much air as the fresh air damper is open.
The hood must be placed at the top! Carbon dioxide does not accumulate at the bottom near the floor.
It is a myth. In a room where ventilation works, this is impossible – carbon dioxide is not a brick that has fallen and lies on the floor. It mixes with the air flow.
The exhaust fan should be placed 15-20 centimeters lower than the supply fan. See picture for option 2.
When the flow from the duct goes down, it partially captures the secretions from fungal drusen. If the exhaust pipe is at the bottom (option 1), the air immediately goes into this hole.
If the hood is located at the top, the air, hitting the floor, goes under the ceiling, between the downdraft and the blocks, and removes the vapors from the oyster mushroom.
Since mushrooms need air fully prepared, moisture should enter the air only in air ducts.
That is, humidifiers must be built into the ventilation system.
How long does ventilation need to run?
If there are mushrooms in the chamber – all the time!
You can not turn on ventilation and humidification on a timer, two hours after two or other intervals – this should not be.
Otherwise, you will not get a stable microclimate, increase humidity and temperature fluctuations.
The exhaust fan, as well as all ventilation, must always be running in the grow room if the fresh air damper is open. If the system is in 100% recirculation mode, then the exhaust fan is turned off.
Air mixing in a chamber without air ducts
This option is possible if the camera loading per 1 sq.m. is 100-130 kg, and the room has high ceilings.
Or if you have blocks only on the floor, in one or more tiers.
See here for placement without shelving.
Calculating this type of ventilation is quite difficult, you have to experiment.
Such a system is called Tornado – axial fans are placed under the ceiling in the premises, which accelerate and mix the flows, perfectly removing CO2.
One or more axial fans are placed below to provide exhaust.
Ventilation in the growing chamber should ALWAYS work, creating a certain, stable microclimate.
The energy savings associated with periodically turning off the fans and humidification system do not justify the loss in yield. Due to jumps in microclimatic parameters (temperature, humidity, CO2), the fruiting bodies of oyster mushrooms are deformed, and yield losses can reach 5-10% in two waves.