Thermal Environment of Chinese Solar Greenhouses: Analysis and Simulation

Abstract

<abstract> <bold><sc>Abstract. </sc></bold>Chinese solar greenhouse is the most common protected horticulture facility in China. The design of solar greenhouses has been evolving but few designs were based on solid engineering analyses and extensive field testing. This article analyzed three aspects that contribute to their good thermal performance: high solar transmittance of the South facing roof due to limited structural and equipment shading, interception and heat buffering of solar radiation by opaque walls and ground, and good insulation of the North facing roof, wall, and sidewalls. A mathematical model is presented to predict and evaluate the thermal environment of solar greenhouses. The model is based on the heat balance and the heat exchange between the system components. Simulations and analyses using the solar greenhouse model suggest the following: 1) materials with good heat insulation should be used for the outer layer of walls, and those with high thermal conductivity and volumetric specific heat should be used for the inner layer, 2) the gained benefits in terms of air temperature and heat flows released from walls to the inside air start to become marginal as the wall thickness increases, and3)by lowering indoor ground the thermal environment of solar greenhouses can be greatly improved. An optimal wall thickness can be determined by weighing the improvements of the thermal environment against the increase in cost associated with material selection and construction.