# A Critical Review of the Status of Current Greenhouse Technology in China and Development Prospects
## 5 Research on Chinese Greenhouse Technology
### Energy Supply and Storage
(2022) conducted energy analyses at eight different sites in dry climates. The results showed that the use of phase change materials in a greenhouse with an area of 142.6 m\({}^{2}\) could save up to 14,577 kWh of electricity per year, up to 1348 kWh of natural gas energy per year, and 6.2 tonnes of carbon dioxide emissions per year, with cost savings of up to 59% [42]. However, PCMs have their drawbacks: the thermal behavior of phase change materials is affected by a variety of factors, such as the local climate, the surrounding environment, the structure of the building, etc., and the optimal thermal behavior of PCMs depends on a series of conditions [43]. The phase change temperature of a single phase change material with high latent heat value is generally 20 to 30 \({}^{\circ}\)C, while the phase change temperature range of composite phase change material is larger, which is unfavorable to phase change under small temperature differences in an environment, and there may be problems such as whether it will dilute the phase change material and whether it is suitable for combination with the wall structure when in use [44]. [PERSON] et al. [45] designed a greenhouse heating system based on a dual-source heat pump consisting of an air source and an ambient air source inside a solar greenhouse, which collects waste heat from the interior of a Chinese solar greenhouse to heat a multi-span greenhouse. The test results show that the dual-source heat pump achieves a COP of 3.4-4.2, which is 6-11% higher than that of the air-source heat pump, depending on its setup for switching the sources during the heating process in winter. [PERSON] et al. [46] constructed a ground-source heat pump (GSHP) heating system capable of seasonal solar thermal storage (SSTES) and diurnal solar thermal storage (DSTES). During the non-heating season, SSTES overcomes the thermal imbalance of the GSHP heating system in agricultural greenhouses, while in the heating season, DSTES can take part of the heating load of the greenhouse, reduce the electric energy consumption of GSHP heating, and improve the annual coefficient of performance (COP) of the heating system. Other heating systems have also been studied. [PERSON] et al. [13] designed a heating system using biomass flue gas as a thermodynamic medium to heat shallow soil in a greenhouse through a buried flue gas-soil heat exchanger. The results showed that the  
Figure 14: A vacuum tube solar collector system (courtesy of Mr. [PERSON], Binzhou Xinrui New Energy Technology Co., Ltd., China). biomass heating system could increase the average air and soil temperatures by 5.1 \({}^{\circ}\)C and 8.2 \({}^{\circ}\)C, respectively. Although considerable research has been carried out (in China and internationally) on the introduction of renewable energy systems in greenhouses in commercial practice, the active heating systems used mainly correspond to conventional systems of hot water circulating in a closed circuit of steel pipes and forced hot air heating systems [47]. Therefore, the north walls of greenhouses remain the most popular passive solar heating system in China.