Adaptive GPC Structures for Temperature and Relative Humidity Control of a Nonlinear Passive Air Conditioning Unit

The use of climate-controlled greenhouses and growth chambers makes it possible to maintain high crop productivity and quality when outside air conditions are not favourable. Climate control accuracy may help optimize production costs by reducing energy consumption and by better respecting production calendars. Such objectives can be reached by incorporating new technologies for crop growth chambers and reduced greenhouses with an HVAC installation. Various climate control technologies have been used for commercial and experimental greenhouses and growth chambers. Many studies have focused mainly on temperature control, while considering relative humidity to be of secondary importance, a background detail. Generally speaking, air conditioning units used in crop growth chambers are made up of heating and cooling system components with a compression cycle (Hanan, 1997; Arquello & Velez, 1999; Jones & Jones, 1984). In addition to the energy cost and the high maintenance expenses for this type of system, they present an ecological issue due to the pollutant emissions generated by the use of refrigerating gases. The main cooling technologies routinely used in greenhouses are ventilation, evaporative cooling, and composite systems. A simple way to reduce the difference between inside and outside air temperature is to improve ventilation. Natural ventilation uses very little external energy, but whether it is natural or forced, ventilation is of limited efficiency and not satisfactory on sunny days. Evaporative cooling using fan-pads (Kittas et al., 2003) or fog/mist (Montero et al., 1994) inside greenhouse and roof cooling systems (Willits & Peet, 2000) represents an efficient means of greenhouse cooling that can lower the inside air temperature significantly below the ambient air, but the range of relative humidity variation remains limited. Fan-pads work on negative pressure, so that very often outside hot air mixes with the inside cool air through infiltration, which reduces the efficiency of the system quite significantly. Mist or