Analysis of the technical, environmental and economic potential of phase change materials (PCM) for root zone heating in Mediterranean greenhouses

Root zone heating systems offer increasing crops quality and productivity. However, these systems are based on the use of nonrenewable fuels. This paper reports on a study of different design solutions for a root zone heating system, based on thermal energy storage with PCM. The objective of the study was to define, through multiple experiments, the most efficient PCM melting/freezing temperature and location with respect to the substrate (i.e., under the substrate) for the application under study; as well as, to determine the system's environmental and economic feasibility, with life cycle assessment and life cycle cost methodologies. Results show that the best melting temperature for the application under study is 15 °C. To increase the efficiency of the system, PCMs may be macro encapsulated and wrap the entire perlite bag. Moreover, it seems that PCMs are far to substitute conventional root zone heating systems because it does not provided enough heat during nights. Nevertheless, PCMs can help to reduce the operation time of conventional systems. Based on one night results it seem that PCM could provide annual saving of between 22 and 30 kg of eq. CO2/ha·day. However, it does not seem to be feasible if PCM prices (8€/kg) do not decrease significantly.