CULTIVATION TIPS ADVISIE Wet bulb control preferrable
Dry bulb inlet air temperature (white line) during pasteurisation is 56°C and wet bulb temperature (red line) is only 54°C.
By Con Hermans AdVisie ‘the mushroom growing consultants’, Heythuysen
hermans@mushroomconsulting.nl Picture: AdVisie
Everyone is familiar with the RH sensor unit with two temperature sensors. One is a dry air temperature sensor (the dry bulb) and the other is a sensor wrapped in a cotton wick soaked in water (the wet bulb). The basic principle is that water evaporating from the wet bulb uses energy which is extracted from the sensor. The temperature difference between these two sensors indicates the RH. In the growing room, each 1°Celsius difference is approximately -10% RH. So if the dry bulb indicates 19°C and the wet bulb indicates 18°C, the RH is 90%. This is explained by the fact that dry air has a lower energy content in kilojoules than wet air and can absorb more heat. This is also called enthalpy. The wet and dry bulb sensors principle can also be used in pasteurisation and phase III tunnels. In this case, the device measures the energy content instead of the RH. The aim is to create a constant and optimal compost temperature for the mycelium. A high volume of outside air in m3 is blown into the tunnel to provide cooling and oxygen. However, the moisture content of the outside air varies greatly from day to night but also shows seasonal variations. This has an immense impact on the energy content. Depending on which phase - pasteurisation, conditioning or spawn run - air with a 10% higher RH may contain 10% more energy. If you applied a constant dry bulb inlet air temperature in mycelium growth tunnels, this would result in an oscillating effect in the compost temperature during the day to night transitions. However, if you apply a constant wet bulb sensor temperature, the result is a more tightly regulated compost temperature. However, what I think is far riskier is using a dry bulb temperature instead of a wet bulb temperature in the pasteurisation phase. You might think you are taking the right approach by, for example, pasteurising at an air temperature of 56°C, but in reality this may only be 54°C wet bulb temperature (see photo), resulting in a significantly less effective pasteurisation. And during conditioning, you assume you are working with inlet air of 42°C, but this could be 38°C, so what you are doing is actually encouraging undesirable moulds. So preferably use wet bulb control in your tunnels. This results in better control of mycelium growth and a safer and more reliable pasteurisation process.
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