Low Cost Structures For Mushroom Growing Cultivation

•, ip * m nt figure 394. A Texas Reishi production fac it> By modifying hoop-framed greennouses and covering them Kith an open-sided, metal roofec' super-structure growing rooms can be constructed at low cost figure 394. A Texas Reishi production fac it> By modifying hoop-framed greennouses and covering them Kith an open-sided, metal roofec' super-structure growing rooms can be constructed at low cost

Spaceship Model Hulls
Figure 395. A Japanese mushroom grow ' ig house.

mesh to prevent clogging. Th:- basket should be easily removed for daily cleaning. Once every several days, a cup of bleach is washed into the drain to discourage flies from breeding.

Many cultivators install a foot bath prior to each growing room to disinfect footwear. (Shoes are a major vector of contamination of soil-borne diseases into the growing rooms ) These foot baths are built into the cement slab before pouring so that a drain can be installed. A 2 ft. x 3 ft. x 2 in. recessed foot bath is ideal. The drain is capped and filled water. Bleach (chlorine) is added as a disinfectant Placing a plastic, metal, or sponge like grate helps re move debris from the feet and enhances the effectiveness of the foot bath.

7) Rate of air exchange Air exchanges control the availability of fresh oxygen and the purging of carbon dioxide from the respiring mushroom mycelium. High air exchange rates may adversely affect humidity, especially prior to and at primor-dia formation when there aerial mycelium abounds. Should aerial mycelial die back, or "pan", potential yields are substantially depressed. On the other hand, to prevent malformation of the fruitbody, bacterial blotch, and mold infestation, the movement of air—turbidity—is a substantial factor in preventing disease vectors.

The need for adequate air exchange is a direct reflection of the species being grown, its rate of metabolism (as measured by C02 generation), and the "density of fill". Fast-growing, tropical strains generate more C02 than cold weather strains due to their higher rate of metabolism. The density of fill is the fraction of space occupied by substrate vs. the total volume of the growing room Button mushrooms growers often fill up to 1/4 of the growing room space with substrate. This high rate of fill is impractical with most gourmet mushrooms. I recommend filling the growing rooms to no more than l/6th, and preferably l/8th of capacity.

At 1000 c ubic feet per minute (cfm) of free air delivery, an empty 10,000 cubic foot room, will be exchanged every 10 minutes, equivalent to 6 air exchanges per hour. This rate of air exchange is near to the minimum required for gourmet mushroom cultivation. At 2000 cfm, this same room will be exchanged every 5 minutes, or 12 air exchanges per hour. I recommend designing growing rooms which can operate within this rate of air exchange, i. e. between 6-12 air exchanges per nour. The actual rate of air exchange will be affected by the rate of fill and limited by the avenues of exhaust. The growing rooms should always remain positive-pressurized to limit contamination vectors from the outside. A strip of cloth or plastic above the door jam works well as a simple, visual indicator of positive pressurization.

A 400-600 cfm thermal exhaust fan is recommended for a growing room of the above-described dimensions. This fan is typically located at the apex of the growing room, opposite the incoming air. A thermostat, preset by the cultivator to skim off excess heat, activates this fan. Another fan, which I call a "vortex fan" having a 200-400 cfm capacity, is located below the thermal exhaust fan, usually at head level, above the exit door. The vortex fan helps enhance the cyclonic en-trainment of the air as it moves down the growing room. Both fans should be covered, from the inside, with a bug-proof, non-mildewing cloth. This cloth will prevent the entry of insects when the fans are not in operation. Furthermore, the thermal exhaust and vortex fan should have louvered shutters that close when not in use.

This is but one configuration of a growing room. Ideally, the growing room environment acts as a giant wind tunnel, providing a homogeneously mixed atmosphere. Simplicity of design makes operation easy. Each growing room should be independently controlled so fhat crops can be cycled and managed according to their stage of development.

8) Filtration of fresh air supply Fresh air is brought in from the outside and passed through a series of filters. The growing rooms do not require the degree of filtration that is necessary for the laboratory. Since the growing room will, at times, have ftill air exchanges of 4-10 times per hour, the filters must have sufficient carrying ca parity. Air is first filtered through a standard Class 2 pre-filter. These filters are relatively coarse, filtering particles down to 10 microns with 30% efficiency. Pre-filters are disposable and should be replaced regularly, in most cases every one to three months. The next filter is usually electrostatic. Electrostatic filters varv substantially in their operating capacities and airflow parameters Typically, particulates are filtered down to 1 micron with 95% efficiency. Electrostatic filters can be removed, periodically, for cleaning with a soapy solution. Their performance declines as dust load increases. For most growing rooms of 10,000 to 20,000 cubic* feet, a 25 x 20 x 6 in. electrostatic filter suffices when combined with a fan sending 1000-2000 cubic feet per minute airstream into each growing room. See Figure 390 for the location of these filters.

9) Filtration of recirculated air Recirculated air from a growing room is relatively free of airborne particulates during the colonization phase. When the cropping cycle begins, the air becomes thick with mushroom spores. (This is especially the case with Oyster mushrooms and much less so with Button mushroom culti vation.) I have seen the spore load of Oyster mushrooms become so dense as to literally stop the rotation of high volume cfm fans!

The design of an air system should allow partial to foil recirculation of the air within the growing room. Usually, a recirculation duct is centrally located directly below the incoming air. A damper door controls the degree of recirculation. If the recirculated air is passed through filters, these filters will quickly clog with mushroom spores, and airflow will radically decline If electing to use filters, they should be changed every day during the cropping cycle. A simple way of cleaning the recirculated air is to posi tion mist nozzles in the recirculation duct-work.

Mist Nozzles

Mist Nozzles

Figure 396. Close-up of air supply system for growing rooms featured in Figure 393. Air enters from below, passing through a coarse and an electrostatic air filter. A large squirrel cage blower pushes air into main duct system where two "rain trees" allow the introduction of cold or hot water into the airstream. In-house thermostats coupled to solenoid valves reguiate the cold or hot (steam) water supply. Recirculation shutes enter the plenum from the side. The degree of recirculation can controlled within the growing rooms. Pre-conditioning the air quality to 70-80% of desired levels is recommended before entry into the growing rooms. Provisions for excess condensation must be engineered into system.

Figure 396. Close-up of air supply system for growing rooms featured in Figure 393. Air enters from below, passing through a coarse and an electrostatic air filter. A large squirrel cage blower pushes air into main duct system where two "rain trees" allow the introduction of cold or hot water into the airstream. In-house thermostats coupled to solenoid valves reguiate the cold or hot (steam) water supply. Recirculation shutes enter the plenum from the side. The degree of recirculation can controlled within the growing rooms. Pre-conditioning the air quality to 70-80% of desired levels is recommended before entry into the growing rooms. Provisions for excess condensation must be engineered into system.

The air will be largely rinsed clean of their spore load from the spray of water Ideally, these downward-flowing nozzles are located directly above a drain. Having spray nozzles located below the inside roof line and misting downwards will also facilitate the downward flow of spores to the floor. This concept can have many permutations

10) Hrmidification With the 6-12 an ex changes per hour required during the primordia formation period, full humidification within the growing room is < lifflsult if drav ing in dry outside air. This problem is solved through the conditioning of outside air in an intermediate chamber called a preconditioning plenum. The precond;t!oning plenum is usually located outside of the growing room. Its purpose i$ to elevate humidity and alter temperature to levels adjustable by the in-room env'-onmental systems. One preconditioning plenum can supply several growing rooms, if properly designed.

In cold climates or during the cold winter months, the preconditioning plenum can be largely hun 'd'fied using steam. Steam provides both moisture and heat Thermostats located in the preconditioning plenum and/or grow.ug room actuate solenoid valves on live steam lines coming from an on-duty boiler. Steam is sent downstream to a square-shaped grid of interconnected pipes. Holes have been drilled to orient the flow of steam towards the center. The main air system blower pushes the steam from the precondi'iuning box into the growing rooms. Each growing room has its own high volume axial fan which inflates the ducting and distributes the humidified, and heated air. Since moisture will collect in the polyethylene ducting, provisions must be made for removing this condensate. The simplest solution is to slant the duct at a slight angle. The condensation can then drip directly into the channel drain running lengthwise down the center of the room. (See Figure 393.)

When temperature in the growing room exceeds prescribed levels, the thermostat will close the in-line solenoid valve. Humidity \ 'ill fall. A humidistat sensing the humidity in the preconditioning plenum takes control, opening a separate solenoid valve, sending cold water down-line, activaimg the mist nozzles. The cold water lines should be positioned in a fashion so that they are not damaged when the steam lines are in operation The goal here is to elevate humidity to 75-80% rH. Independent humidifiers or mist nozzles located high in the growing rooms control the remaining 25% of the humidity required for primordia formation. Some companies offer systems which utilize compressed air (100-400 psi) misting systems that emanate a fog-like cloud of humidity. With proper filtration and maintenance these systems work equally as well although typically are much more expensive to install.

Swamp coolers generate humidity and lower temperature of the incoming air. They work especially well when the outside air temperature is high and the humidity is low. These types of evaporative coolers can also be incorporated into the design of a preconditioning box. Heat exchangers must be carefully engineered for maximum effect. The cultivator is encouraged to consult a reputable HVAC (Heating, Ventilation & Air Conditioning) specialist before installation of any of the above-mentioned systems. Often times, independent systems with manual-control over-rides perform better, in the long run, than all-in-one packages. The cultivator must have alternates forhunr dity should equipment fail for any reason. The value of one saved crop can easily offset the expense of a simple back-up system.

11) Insect control Flies are the bane of the mushroom cultivator. Once introduced, a single, pregnant fly can give rise to hundreds of voracious offspring in a few weeks. (For a complete description of the flies and their life cycles, please consult The Mushroom Cultiva tor (1983) by Stamets & Chilton.) Many models of insect traps are available. "Bug zappers" electrocute flies when they come in between two oppositely charged metal screens. Many of the flies endemic to mushroom culture are minute and pass, unaffected, between the electrified panels. I prefer circular bug lights which use an interior fan. A cone shaped vortex is formed well beyond the light. The bugs are thrown into aplastic bag which allows for easy counting by the growing room manager. By attaching yellow sticky pads to the lights, the number of flies that can be caught greatly increases. (See Figure 384). Astute managers rely on the increasing numbers of flies as an indication of impending disaster. These lights should be positioned on or beside every door witnin the growing room, and especially in the rooms prior to the growing rooms. Many of the fly problems can be circumvented through some of the good practices described below.

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