Controlled Mechanical Ventilation to Reduce Primary Energy Consumption in Air Conditioning of Greenhouses

Air conditioning is one of the major cost in greenhouses production. One of the most interesting energy efficiency strategies is the reduction of the energy use itself. Mechanical ventilation with heat recovery could allow for a reduction in energy use for heating and cooling air inside greenhouses. After a preliminary study carried out in laboratory, a mechanical ventilation prototype was tested in a real case. The unit was installed at service of a mini-tunnel greenhouse located in Termoli (Campobasso)–Italy. The ventilation system consists of a high efficiency heat exchanger, able to recover thermal energy from the exhaust air, and a heat pump to adjust the supply air temperature before entering in greenhouse. A perforated duct was installed for the air distribution and a single grid was used to suck the indoor air. To evaluate the energy performance of the unit a supervision system allowed measuring and collecting all the thermo-physical parameters, in each side of the machine, and in the heat pump circuit. Four NTC probes were used to assess the temperature uniformity inside greenhouse. First tests were carried out on temperature control during winter season. They show that the indoor air temperature (set at 27 °C) is suitably adjusted by driving the unit with the reference probe installed on the machine recovery side. Only an offset of few Celsius degrees is observed due to duct heat loss and the recovery grid placed on one side. Furthermore, the mechanical ventilation system had also shown notable energy performance: COPs (mean value) of 5.4 and 5.7 at outdoor air temperature of 18.0 °C and 15.7 °C respectively.