Investigation of the Energetic Performance of an Attached Solar Greenhouse through Monitoring and Simulation

Abstract

In Canada, energy costs represent a significant portion of the overall operating cost of greenhouses. This energy is mostly consumed in winter to satisfy the heating requirement of greenhouses. Therefore, it is essential to investigate energy efficient systems to reduce the heating requirements in greenhouses, and as a result, improve the overall performance. Solar greenhouses are designed to maximize the heat gain in order to reduce the heating loads in winter. This research work was conducted to investigate the energetic performance of an attached solar greenhouse connected to a rock-bed thermal storage and located in Joliette near Montreal through monitoring and simulation. A TRNSYS model was developed to analyze the energetic performance of the attached greenhouse and rock-bed thermal storage. The TRNSYS model was validated by comparing the measured greenhouse indoor temperatures and rock-bed outlet temperatures to the predicted ones for three periods. The validation results of the three periods showed a good agreement between the measured and predicted temperatures. The optimal design of a solar greenhouse is essential to have high performance in terms of productivity and energy costs. Therefore, a parametric study using the TRNSYS validated model was conducted to investigate the effects of the heating and cooling set point temperatures, rock-bed air flow rate, cover materials, mechanical outside air ventilation, and rock-bed thermal storage size in order to improve the overall design. The parametric study results showed that the rock-bed air flow rate and the U-value of the greenhouse cover material have a significant effect on the greenhouse indoor temperatures. While changing the cooling (rock-bed charging) set-point temperature from 12°C-22°C while keeping the heating (rock-bed discharging) set-point temperature fixed at 10°C did not have a significant effect on the greenhouse indoor temperatures. As the rock-bed size increased, the amount of heat discharged from the rock-bed thermal storage increased. As a result, the greenhouse indoor temperatures increased in winter nights. Moreover, in order to avoid the undesirable high indoor temperatures especially in summer, the installation of the mechanical outside air ventilation is necessary.