Experimental study of a mechanical ventilation system in a greenhouse

Greenhouse cultivation is one of the most energy intensive activities in agriculture. This is especially true in cold climate zone. Generally heating systems involves boilers fed with fossil fuels. This means low yields of the heat generator and high pollutant emissions. Moreover, the increase of annual crop yield in greenhouses is possible only through a very close control of the internal conditions. Ventilation systems could allow proper control of temperature, relative humidity and CO2rate. For this purpose a prototype of a mechanical ventilation unit was installed at service of a mini-tunnel greenhouse. The recovery unit is equipped with a heat pump and is able to increase the thermal energy recovered, by the flow of exhaust air, through a high efficiency heat exchanger. A first study was carried out to evaluate the thermophysical and energy performances of the system during the heating season. The experimental apparatus consists of mechanical ventilation system, a perforated duct for air distribution, a fog system to adjust humidity and a supervision system to acquire the field data. Another dedicated supervision system allows to measure and collect all the parameters of the prototype, such as thermophysical parameter of the air flow, thermophysical parameter of the refrigerant circuit of the heat pump, status and alarms of the unit. To characterize the whole system under investigation the main data measured are temperature, relative humidity and carbon dioxide inside the greenhouse and temperature in all section of the prototype. Other two mini-tunnel greenhouses are monitored as references. One is heated with radiant tubes placed on the bench and humidified with a fog system, the other is completely passively heated (without heating system) and humidified with the same fog system. A First test was performed to evaluate the ability of the system to regulate the indoor temperature of the greenhouse with a set point of 27 °C. By using a temperature probe installed on the return side of the machine, the results shown an appropriate temperature regulation