Survey and evaluation of heating technologies for worldwide agricultural greenhouse applications

This paper reviews and evaluates all the available heating technologies for worldwide agricultural greenhouses and discusses the representative applications of each technology. Available information on the location, ground area, cover materials and performance of the greenhouses coupled with each technology such as water storage (including solar flat plate collectors, ground-source heat pumps and shallow solar ponds), rock bed storage, phase change material storage and earth-to-air heat exchanger system is collected and presented in detail. Using the collected information an attempt has been made to correlate the approximate storage volume or weight of the material required for a given greenhouse area for different storage media under various greenhouse cover materials. These relations can be of great importance to the potential users for the successful development of future applications. Apart from the above-mentioned technologies, a complete review and performance evaluation of other greenhouse heating technologies such as movable insulation, north wall storage, ground air collector and aquifer coupled cavity flow heat exchanger system is also presented. Heating potential (overall performance) of each system under different cover materials along with their advantages, limitations and suitability is also discussed.