Thermal modeling aspects of solar greenhouse microclimate control: A review on heating technologies

•Review on modeling aspects of greenhouse models.•Information on working principles with heat and mass balance equations.•Formulation of the generalized procedure for thermal model development.•Concluding remarks with suggestions for further studies. Modeling of greenhouse microclimate is very important to maintain optimum inside environment during different stages of plant growth. To formulate an accurate thermal model, computation of precise solar radiation input and overall heat transfer coefficient is important as these affect the greenhouse energy and mass balance. Initially, we briefly review the modular studies related to solar radiation capture and overall heat transfer coefficient for greenhouse applications. Numerous thermal models have been developed to describe the microclimate of a greenhouse and validated at various locations, climates and crops. We review all these independent thermal models (static as well as dynamic) and discuss in detail the representative ones. In adverse winter climatic conditions, greenhouse has to be coupled with various active or passive heating systems to maintain the inside microclimate according to crop needs. We also review greenhouse thermal models integrated with heating/heat storage systems such as: rock-bed, phase change materials, earth-tube heat exchanger systems, all types of water heating systems (water thermal mass storage, heat-pipe heating system, shallow solar pond heating systems, geothermal based heating systems viz. ground source heat pump system, solar-assisted ground source heat pump system, aquifer coupled heat exchanger system), ground air collector system, north wall and thermal curtain, and soil heat exchanger system. Important aspects of each representative model such as: type, tool/program used for solution/simulation, input data used to run simulations, interactive components, parameters studied, assumption made, important model characteristics and results obtained are discussed at length. Based on the compiled information, a generalized procedure is devised to formulate greenhouse thermal model. Finally, based on the main characteristics and results of the study, some important conclusions are drawn and suggestions made for further studies.