Understanding the growing room

Write the crop species, strain and stage before selecting a climate programme. Then distinguish room air, supply air, return air, compost or bag temperature, and product temperature. They are different measurement locations. A controller can hold its sensor at the selected value while the rear of the crop remains warmer or a nearby bed receives a drying draught.

Prepare a simple room map with marked front, middle and rear positions and representative upper and lower crop levels. Keep probes away from accidental direct spray and position them according to the instrument's instructions. Compare portable and fixed instruments using a suitable check method; two disagreeing sensors create uncertainty that should be resolved before making a large adjustment.

Collect a time history. A reading immediately after watering, a door opening or an equipment restart may represent a short event. Relate readings to those events and to crop response. Give the next shift a written record of changes so it does not reverse an adjustment before its effect has been assessed.

Water inside the substrate or casing is a crop resource. Humidity describes water vapour in the air. Surface wetness is liquid water on the mushroom or structure. These conditions interact but cannot be substituted for one another. Increasing humidification may not restore water to a dry casing layer, and adding water to a bed may leave unwanted wetness on caps.

Condensation occurs when a surface is cool enough for moisture in surrounding air to condense. Review product or surface temperature, air conditions and recent cooling or door-opening events when droplets appear. Air movement can help evaporation but can also dry exposed crop zones. The useful question is where moisture goes after an adjustment, not whether the room feels damp.

Observe the crop after watering under the selected crop protocol. Record water applied, time, affected zone and surface response. Keep observations comparable between flushes. An operator who can explain those changes has more useful control than one who only repeats a fixed number of watering cans each morning.

Do not automatically raise humidity for the whole room. Compare the path of supply air, crop loading and moisture at the edge and rear. If the distribution differs, a room-wide humidity increase can leave the rear wetter while the edge still dries. Investigate distribution with the crop supervisor before changing the programme.

Begin with the observed problem and the most plausible explanation. Write the relevant reading, its location and the expected effect of the proposed adjustment. Change within the approved crop programme and equipment limits. Monitor the variables that the adjustment may also affect: fresh-air changes influence heat and moisture loads, and humidification can change both air and surface conditions.

Define when to inspect again using the response expected from the system and crop. A slow thermal response inside a bed should not prompt repeated large controller changes. If evidence becomes inconsistent, pause and verify the sensor or operating condition. Keep a record of the outcome even when the adjustment does not help; that result narrows the next investigation.

List which loads are essential for the crop and which can wait during a power interruption. Have an engineer check the electrical supply, starting loads, protection and backup arrangement for the actual equipment. Room volume alone does not determine cooling capacity: outside conditions, building heat gain, fresh air, crop heat and operating schedule also matter.

Practise the reporting and recovery procedure with trained staff. Identify who receives an alarm, who checks the crop and who may work on equipment. After a failure, preserve the event history and inspect the affected crop locations. Restarting the machine does not prove the crop has already recovered.

Room air is what a wall thermometer reads. Bed or compost temperature is what the crop actually lives in. Outdoor design temperature is what your cooling plant has to fight.

ICAR-DMR keeps these separate. For button spawn run it holds the room air at 23 plus or minus 1 C, and states that this corresponds to a bed temperature of 24 to 25 C, one to two degrees higher. For oyster it reports bed temperature generally 2 to 4 C above room temperature.

That gap is not an error. The compost is alive and making heat. If you set the room to the crop number, the crop sits above it.

Using button mushroom as the worked example, the 2011 manual gives a ladder. Spawn run: air 23 plus or minus 1 C. Case run: 24 plus or minus 1 C. Then cropping: the air is brought down to 15 to 17 C.

DMR's other documents give other fruiting figures: 14 to 16 C in one table, 14 to 18 C in the seasonal folder, 16 to 18 C in the Hindi farmer folder. These are all ICAR-DMR.

The lesson is not that one is right. It is that a band published for a controlled room, a seasonal shed and a species table are three different claims.

DMR quantifies it. During the first two flushes a button bed gives off about 10 watts of heat per square metre at 17 C and 88 percent humidity, along with its carbon dioxide.

That is why a room cannot be held at one temperature by one setting. Air warms as it crosses the beds, so the far end of a long room runs warmer than the near end.

DMR gives the engineering answer for its own rooms: to obtain 17 C and 85 percent humidity at the bed, air leaves the air handling unit at 14 C and 100 percent humidity. The supply air is deliberately colder than the target.

Some numbers are not preferences. False truffle appears above 23 C, and NHB, reproducing ICAR guidance, says avoid temperatures above 26 to 27 C during spawn run and after casing, and keep cropping below 18 C.

Blotch needs 20 C or above with water on the cap. DMR ties olive green mould to pasteurisation above 60 C. At the end of a crop, a cook out at 70 C held for 12 hours kills pathogens in the compost.

So when you write a set point, write beside it whether it is a preference or a limit. Only one of those two can be traded for electricity savings.

Relative humidity says how full the air is compared with how much it could hold at that temperature. Warm the same air and the reading falls without a drop of water leaving the room.

So a humidity figure means nothing on its own. Always write the dry bulb temperature next to it.

ICAR-DMR sets 95 percent during button spawn run and case run in a controlled room, then reduces it to 85 percent for cropping. A naturally ventilated seasonal shed cannot hold 95 percent, which is why the Hindi folder gives 80 to 90 percent for the same stage.

DMR measures the loss: about 31 grams of water evaporates from one square metre of bed every hour at 17 C and 85 percent humidity.

That water has to be replaced or the casing dries and pinning stops. The manual gives a simple rule for watering after picking: for every kilogram of mushroom harvested, add one litre of water.

Casing moisture at pinning should sit near 50 percent, which DMR states as 50 plus or minus 2 percent. Water lightly and often rather than heavily once, and water the casing surface rather than the mushrooms themselves.

When moist air touches a surface colder than its dew point, water forms on that surface. In a mushroom room those surfaces are the ceiling, the cold panel near the air handler, and the mushroom cap itself.

This matters because of one threshold. DMR records that bacterial blotch spreads when a free water film stays on the cap for more than three hours, and at 20 C or above.

NHB adds the operational rule: avoid humidity above 85 percent together with temperature above 20 C, and give extra ventilation and air movement after watering so that caps dry quickly.

Air humidity and substrate moisture are separate numbers and separate instruments. Mixing them is a common error.

DMR gives finished synthetic compost at 68 to 72 percent moisture at spawning and 64 to 66 percent after Phase II. Above 72 percent the compost cannot breathe and plaster moulds appear. Below 64 percent, with a wet casing over it, NHB reports weeper mushrooms.

Other crops carry their own figures: milky substrate at 65 to 70 percent, shiitake blocks at 60 to 65 percent. Learn to test moisture by squeezing a handful, and record what your hand felt each time.

A button bed gives off about 10 grams of carbon dioxide per square metre every hour during the first two flushes, when the mycelium is most active.

During spawn run that gas is wanted. ICAR-DMR keeps 10,000 to 15,000 parts per million with the whole air recirculated and no fresh air entering, because high carbon dioxide speeds the spawn through the compost. Case run continues above 7,500 parts per million with no fresh air introduced.

So a closed room is correct for two weeks and wrong on the day after. This is the single largest stage error in small units.

Fruiting starts with a deliberate change. DMR brings the room down to 800 to 1,000 parts per million, which is what pinhead formation needs, and holds 1,000 to 1,500 parts per million once pinheads become buttons.

Get it wrong and the crop tells you. High carbon dioxide at pinning gives onion shaped mushrooms with a bulbous base and small cap; later it gives long stalks with small open caps.

Other species sit far lower. For oyster, the 2011 manual asks for less than 600 parts per million during cropping, while the Hindi folder sets the limit at 800. Both are ICAR-DMR.

DMR converts this into air changes. From venting to the end of the second flush, about six air changes per hour are recommended. From the third flush, four per hour hold oxygen near 16 percent.

The damper position follows: 30 percent fresh air and 70 percent recirculation for the first two flushes, then 20 percent fresh and 80 percent recirculated. A milky crop needs a minimum of three to four air changes per hour.

Fresh air is also a doorway. DMR asks for two micrometre filters on fresh air entry points, and NHB asks for nylon net of 35 mesh or finer on doors and ventilators against flies.

Air changes describe volume. They say nothing about whether air reaches the third rack in the corner.

DMR gives the distribution target: air speed over the crop beds of about 15 centimetres per second. Fast enough to carry heat and gas away, slow enough not to dry the caps.

The site engineering guides make the same point in a harder way: a fan rating is not delivered airflow, and an air change rate is not distribution. Two rooms with identical fans can crop differently because one has a dead corner. Walk the room with a smoke source or a ribbon and watch where the air does not go.

A sensor beside the door reads the door. A sensor in the return air duct reads the average of everything the room has already done to the air.

Neither is the crop. The site engineering guides ask for readings mapped at crop level and at return air, with the measurement method, the placement and the calibration status recorded alongside every value.

That is why DMR can say room air 23 plus or minus 1 C and bed 24 to 25 C in one sentence. Two numbers, two places, one stage. A logbook that does not say where a reading came from cannot be used to fix anything later.

Instruments drift. Humidity sensors age in exactly the wet, warm conditions a mushroom room provides, and low cost carbon dioxide sensors need a fresh air reference to stay honest.

The cheap discipline is a second instrument. Keep one thermometer that never leaves the office as your reference, and compare the room instruments against it every month.

If two instruments disagree by more than their stated accuracy, you do not have a number yet. Note the disagreement in the log rather than picking the reading you prefer, and take the sensor out of service until it has been checked.

Then the target bands mean something. Spawn run air at 23 plus or minus 1 C, fruiting at 15 to 17 C, humidity 85 percent at cropping, carbon dioxide 800 to 1,500 parts per million. There is also a measurement DMR warns about: the nose cannot detect ammonia below about 10 parts per million, which is the spawning limit itself.

Control is a sequence, not a switch. DMR's own airing schedules show it. A severe airing brings carbon dioxide below 1,000 parts per million within 12 hours and the air to 15 C as fast as possible, to force one heavy first flush.

A soft airing takes the same room to 4,000 parts per million at 48 hours, then 2,000, then 1,000 by 72 hours, and gives smaller, better spaced flushes.

Same room, same crop, different result. So change one parameter, write the time, wait for the room to settle, and read again before touching anything else.

The MIDH 2025-26 cost norms show the equipment plainly. A production unit of Rs 30 lakh is itemised in Telangana as two insulated panel growing rooms with a corridor at about Rs 14,00,000, plus an environmental control system at about Rs 16,00,000.

Even the low cost unit of Rs 2 lakh contains a steaming tank or straw boiler, a chaff cutter, racks, a humidifier and exhaust fans.

So the list is: a refrigeration circuit under pressure, a steam or hot water source, three phase motors, a control panel, and water on the floor all day. Each of those has its own rules, and they overlap in one small room.

A refrigeration circuit is a sealed pressure system. Charging, brazing, pressure testing, recovering refrigerant and responding to a leak are trained trades, not maintenance you improvise.

Refrigerant choice itself is a regulated decision. The site engineering guides describe it as balancing safety, current regulation, environmental impact, equipment compatibility and the service ecosystem available near you. Ammonia systems in particular carry statutory requirements for handling and for emergency response.

The farmer's job here is different and still real: keep the plant room locked and dry, keep condensers clear, report noises and oil marks, and never open a sealed circuit.

Motors, a wet floor and long hours are a combination that kills people. Supply, distribution, protection, earthing, motor starting current and backup power are engineering decisions with Indian standards behind them.

The site engineering guides state the rule the whole of this course sits on: do not select from an unverified numeric rule, and final safety and engineering decisions require qualified project review.

What you own is the daily discipline. Earth leakage protection tested, panels closed, no temporary wiring into a humid room, one person who knows how to isolate power, and a plan for what happens to a crop when power fails.

Pasteurisation means hot water at 80 to 90 C and open steam. Autoclaves run at 15 to 22 pounds per square inch and are pressure vessels: trained operator, working gauge, never opened under pressure.

A sealed spawn run room holds 10,000 to 15,000 parts per million of carbon dioxide, so vent it before anyone walks in. An end of crop cook out at 70 C means the room is not a workplace at all until it cools.

Spores are a health issue too. DMR tells oyster growers to open doors and windows two hours before entering the cropping room and to wear a mask.