May 24, 2019


Blog on relative humidity measurement

Jul 25, 2018

Climate in the growing room
All growers recognise the importance of climate in the growing room. How the climate feels when you enter the growing room is a good indicator. Sometimes what your instinct says goes against what the data from the climate control computer suggests. Experience can help you finetune that “instinct” if you go into the growing rooms daily. In this blog I will be give you some simple tips of things to check in relation to RH measurements every time you inspect the growing rooms. This can help avoid errors in measurements and climate control.

Clean the water reservoir
The growing room is cleaned after it has been emptied. Cleaning the RH measuring box should be part of this routine. Ensure the water reservoir of the RH measuring box is emptied and cleaned. It wouldn't be the first time a slimy bacteria forms in the reservoir, so that even the new sock or wick feels slimy. This reduces evaporation, resulting in a higher RH measurement than in reality.

Replace the sock
When you clean the growing room remove the sock from the wet bulb sensor. Do not replace it immediately but wait until the room is filled. While there is no sock in the wet bulb, the wet bulb and the dry bulb should both give the same temperature reading. This is a routine action that can prevent a lot of headaches. On many farms, this is only done sporadically - or not at all - so a long time passes before anyone notices any deviations. And problems can occur fast, as just 0.1OC deviation is already a 1% difference in RH!

The fan
There is a fan in the RH measuring box in the majority of climate control systems. This ensures a constant flow of air over the sensors. The fan can sometimes malfunction. This is not reflected at once in the RH measurement, so checking whether the fan is still running by listening when you look at the RH measuring box is a small, but very worthwhile, task.

Replace the sock later on?
During mycelium growth the RH is not that important as water is still sprayed onto the casing soil. If drier air causes the casing to dry out faster, it is easy to add more water into the casing.
So you could think: “Let's just replace the sock later”. Completely wrong. Why? The Mollier diagram of course! By also measuring the wet bulb temperature, the computer can determine the energy level in the air. This enables the computer to decide whether to use outside air for cooling. If there is no sock, the computer will always measure a higher energy level because it “thinks” the RH is always 100%. The result will be extra costs for cooling because the computer decides too quickly to use outside air which has a higher energy level than the actual air in the growing room. You will use more energy and risk burnt compost due to an insufficient cooling capacity.

Mark den Ouden
Mushroom Office

Next Masterclass Compost and Mushroom course are:
22 to 27 October 2018
18-23 February 2019

Last modified on Friday, 27 July 2018 07:19