Research progress of thermal storage technology in energy-saving solar greenhouse

Abstract: Chinese energy-saving solar greenhouse originated from the southern of Liaoning Province, which had fully independent intellectual property right, and played an important role in protected horticulture. Although Chinese solar greenhouse has rapidly developed more than 30 years, insufficient heat preservation and thermal storage and poor environment control ability caused by unreasonable greenhouse structure still exist in Chinese solar greenhouse. Therefore, to optimize the energy conservation of Chinese solar greenhouse is needed urgently. Soil, wall and skeleton in Chinese solar greenhouse can realize the thermal storage during the day and thermal release during the night. Compared to passive storage, the thermal storage of Chinese energy-saving solar greenhouse can provide more heat energy for greenhouse through the transformation of sunlight by materials, structures and equipment. Based on solar energy source, by means of mechanical power equipment, active heat storage uses indoor soil, wall, frame structure, and phase change materials as heat absorbing medium to accumulate heat, and the opposite is passive heat storage. The heat of active/passive storage all comes from the sunlight, and there are 2 ways to use the heat. One is to maximize the use of the indoor captured solar energy or indoor surplus heat, and the other is to use outdoor solar energy. Currently there are many thermal storage forms, such as active lighting thermal storage, air circulation thermal storage, water circulation thermal storage, phase change material thermal storage, pebble thermal storage, heat pump thermal storage, combined thermal storage. Through the adjustment of the tilting roof angle in active lighting thermal storage greenhouse, more solar energy is gotten indoors, so that the indoor heat accumulates more. Air circulation thermal storage means excess thermal energy is stored into the underground soil or wall, including underground air circulation storage and wall air circulation storage. Water circulation thermal storage uses water as the thermal storage body, and the water accumulates heat during the day, and releases heat during the night, including water curtain heat storage and pipeline water heat storage. Phase change material thermal storage uses phase change material as the thermal storage body, and its strong thermal storage capacity is used to provide indoor heating. Pebble thermal storage uses pebble as the thermal storage body, and its strong thermal storage capacity is used to provide indoor heating. Heat pump thermal storage uses electricity to convert the low-grade heat energy extracted from air, water or soil into high-grade heat energy for indoor heating. The heat pump is divided into 3 types: water source heat pump, air source heat pump and soil source heat pump. Combined thermal storage is the combination of 2 or more thermal storage methods for indoor heating. This paper reviewed the relevant research results of heat storage technology in solar greenhouse, analyzed the main technical problems and research emphasis, prospected the future development direction and the research content from 4 aspects, i.e. traditional solar greenhouse transformation, new structure development, technology integration of the research method in heat storage and application of heat storage greenhouse, and provided reference for the heat storage research of energy-saving solar greenhouse in China..