A dynamic model and an experimental study for the internal air and soil temperatures in an innovative greenhouse

•Simulation model for internal Greenhouse temperature including soil reflectance.•Greenhouse soil heat exchange affects internal temperature by approximately 12%.•Solar air heaters as greenhouse roof maintain better internal temperature year round. An innovative greenhouse which integrates a conventional greenhouse with roof mounted solar air heaters is used in this investigation. This design reduces the solar radiation incoming to the greenhouse in summer which reduced the load and cost of greenhouse cooling and provides a means of solar heating. Experimental measurements of the internal air and internal soil sub-layer temperatures in the greenhouse, without crops, were performed in Baghdad University, Baghdad, Iraq (33.3 °N, 44.4 °E). Measurements were recorded for clear and partly cloudy winter days. A dynamic model was developed to predict the all internal temperatures of the greenhouse. This model includes soil surface heat exchange with the greenhouse air which was found to give a more accurate prediction of the internal temperatures. Soil surface heat exchange has a positive contribution to the internal environment. The input parameters of the model were the measured meteorological conditions and the thermo-physical properties of the greenhouse components which include the cover, inside air, and soil. Comparisons between the predicted and measured results show good agreement. Also, results show that soil sub-layers inside the greenhouse at 50cm depth are the best place for heat storage elements. The integrated system rendered maximum differences between ambient and internal air temperatures of 16°C in February and 10°C in June without operating any heating or cooling system.