CFD modelling of transparent bubble cavity envelopes for energy efficient greenhouses

Traditional greenhouses with single glazing have very poor thermal performance and the energy use for providing a productive internal environment is high. A cavity envelope formed by two transparent membranes and filled with transparent liquid bubbles can provide the greenhouse with super thermal performance. The liquid bubbles in the cavity transmit daylight while providing a thick blanket of insulation, thus reducing heat losses in winter and solar gains in summer. A computer model has been developed to simulate the thermal performance of a transparent bubble cavity envelope and the internal environment of the greenhouse. It has been found that the cavity convective heat transfer coefficient, equivalent thermal conductivity and thermal transmittance of a transparent bubble cavity envelope increase with bubble diameter and porosity as well as the internal–external temperature difference when bubbles are not compact in the cavity. The equivalent thermal conductivity and thermal resistance also increase with cavity width but the cavity convective heat transfer coefficient and thermal transmittance decrease with the increase in cavity width. A greenhouse with the transparent bubble cavity envelope has a better thermal environment with a significantly less energy requirement than does a traditional greenhouse.