Environmental analysis of geothermal heat pump and LPG greenhouse heating systems

The use of low-impact energy sources for greenhouse cultivations is growing quickly due to environmental demands, constrained by the increased price of fossil energy sources, market demand for low cost greenhouse production, and need for air pollution reduction. This paper demonstrates via environmental analysis the efficiency of a Photovoltaic-Geothermal Heat Pump integrated system (PV-GHP) as a greenhouse heating system, compared to a conventional hot air generator using liquefied petroleum gas (LPG-HG). The tests were carried out in twin experimental greenhouses in the Mediterranean area (Valenzano-Italy). In order to evaluate the environmental performance of a heat pump system with electricity supplied from the national grid, a scenario (GHP Geothermal Heat Pump) was realised. The microclimatic conditions in the two greenhouses, the thermal energy produced, and the electricity consumption were analysed. Furthermore, in order to evaluate the long-term environmental impact, an environmental analysis was conducted using life cycle assessment (LCA) methodology, carried out according to standard UNI EN ISO 14040. The interpretation of the results using method CML2001 (Centre of Environmental Science, Leiden, Netherlands) showed that neither system is more advantageous from an environmental point of view and that the GHP scenario has the higher environmental burdens. Limiting the analysis to the emissions responsible for the greenhouse effect, the plant with the geothermal heat pump and photovoltaic panels reduces carbon emissions by 50%. In order to assess the sustainability of the geothermal heat pump plant, the estimated payback-time for energy and for carbon emissions were 1 year and 2.25 years, respectively.