## 2 Literature Review
### LHTES Systems in Greenhouses
#### 2.1.3 LHTES inside Greenhouses  
In some previous works, the container containing the PCM was used directly and without intermediaries in the greenhouse, which stores the system's excess solar heat by changing the phase. This heat returns to the system at night. The following is a review of previous works in the field of LHTES applications inside greenhouses.  
[PERSON] et al. [37] examined the effectiveness of basic and customized greenhouse dryers of groundnuts. A natural convection greenhouse drier was modified using a latent heat storage unit (LHSU) packed with beeswax as a PCM. Groundnut samples were dried at GJUST (Hisar, India) in June 2019 using a modified greenhouse dryer (MGHD) and a simple greenhouse dryer (SGHD). When a groundnut sample was dried under the MGHD, 23.45% more moisture evaporated than when it was dried under the SGHD. Also, more tremendous greenhouse energy and exergy efficiencies were discovered for the MGHD. Moreover, groundnut-drying-specific energy use was 67.16% lower in the MGHD. Figure 19 presents the suggested system's schematics by [PERSON] et al. [37].  
[PERSON] et al. [38] proposed a transparent envelope with a PCM (PTE) incorporated into usual plastic greenhouses to respond to dynamic variations in temperature and daylight. The PTE can function as a governor to balance light and thermal performance, in contrast to opaque structures combined with a PCM. The performance of the proposed plastic greenhouses incorporating PTEs in terms of photothermal efficiency was experimentally investigated by [PERSON] et al. [38]. The various PCM melting temperatures (three different temperatures) and the seasons (transition, fall, and winter) were compared in a logically built plastic greenhouse with adjustable interior lighting and air temperature. The findings  
Figure 18: The suggested system’s schematics and pictures by [PERSON] et al. [36].  
demonstrate that PTE-equipped plastic greenhouses significantly adjust thermal energy storage and release while reducing inside sunshine. Due to the lower outdoor temperature and sunlight, PTEs with low melting temperatures are beneficial. Understanding built-in PTEs can assist in identifying the optimal states to construct a low-cost, readily replaced passive heating system for plastic greenhouses. The suggested system's schematics and pictures by [PERSON] et al. [38] are demonstrated in Figure 20.  
Root zone heating systems improve crop quality and output. These systems, however, are predicated on the utilization of nonrenewable fuels. [PERSON] et al. [39] described an investigation into several design possibilities for a root zone heating system based on thermal energy storage using a PCM. They determined the most efficient PCM melting/freezing temperature and location concerning the substrate (i.e., under the substrate) for the application under consideration and the system's environmental and economic feasibility, using life cycle assessment and life cycle cost methodologies. The results reveal that the ideal melting temperature for the application is 15 degrees Celsius. The perlite bag should be wrapped in the material to shield the PCM from atmospheric temperatures. Based on preliminary findings from a single night, the PCM appears to be able to lessen the environmental impact of traditional gas and oil root zone heating systems. The schematics of the suggested experimental setup by [PERSON] et al. [39] are presented in Figure 21.  
Figure 19: The suggested system’s schematics by [PERSON] et al. [37].  
Figure 20: The suggested system’s schematics and pictures by [PERSON] et al. [38].