Integrated environmental control in mushroom tunnels.

Abstract

The main objective of this investigation was to achieve improved control of the micro-climate around the mushroom crop. The work was based on two approaches. One, which required the greater part of the work, was gaining an understanding of the characteristics/physics of the climate control system as a whole within mushroom tunnels and the other was the application of modern control strategies to manipulate more effectively the conditions at the cropping surface. The work showed that the influences of the operation of the air conditioning on the crop micro-climate was far greater than the expected adjustment of, say, temperature and that novel systems and improved measurement of the micro-climate were required in order to optimise the control of air conditions. The operation of the heating system caused a load dependent, i.e. seasonal, variation in the average drying power of the air at the crop. While heating (on/off control) was in operation, air flow effectively ceased at the cropping surface and the effect persisted for the duration of the heating and a recovery period afterwards. Various simple strategies could be implemented to minimise these effects but a novel design for air distribution provided a means of eliminating the effect. Because of the complex relationship between the delivery of conditioned air and the consequent flow at the cropping surface, improved feedback from the crop micro-climate was found to be essential for improved control. A new sensor was developed in conjunction with the Department of Electronic Engineering, NUI Galway that provided a low cost measurement of the very low air speeds used in mushroom growing. The Irish mushroom-growing system (bags and tunnels) offers more potential for accurate control than other, tiered, growing systems. The goal of the second aspect of this project was the provision of an accurate and robust control system for mushroom tunnels. Work focused on the control relationships between inputs and outputs of the system. A Teagasc Walsh Fellowship supported the early work which was carried out in conjunction with the Department of Electronic Engineering at NUI, Galway. Initial work prior to this project, with control specialists in DIT, Kevin Street College of Technology, was extended to provide a mathematical/control model of the main physical processes involved. A second Walsh Fellowship supported a link with the control systems group in the Department of Electronic Engineering, Dublin City University and allowed further control studies in mushroom tunnels.