## 2 Literature Review
### SHTES Systems in Greenhouses
#### 2.2.3 Rock Bed as SHTES System
This numerical model adequately duplicated the thermal, dynamic, and hygric fields. The widely used commercial CFD code Fluent module from ANSYS was utilized to model the microclimate in the greenhouse, which was equipped with a rock bed heating system. According to the CFD results, the maximum humidity values were recorded in the bottom portion of the greenhouse. In contrast, the lowest values were reported in the top section of the greenhouse. From the top to the bottom of the greenhouse, these values ranged between 20% and 36%. The schematic of the proposed computational domain and temperature contour as one of their outcomes are presented in Figure 27:4  
A summary of previous works using rock beds as a thermal battery, a SHTES system, and a preconditioning system (both temperature and humidity regulator) is given in Figure 27:5 It should be noted that the references in this table are listed in chronological order. Because the suggested system in this PhD thesis proposal is a system of injection and sucking of greenhouse moist air into the rock bed to store and release the sun's thermal energy as storable energy in the rock bed, a column in this table is considered that shows whether or not the proposed injection/sucking system is used in the reference. Future chapters will offer a more detailed description of how this strategy is used in the proposed system. Table 2 illustrates that according to the best knowledge of the authors, [PERSON] et al. [48], in 1996, was the first work in which the idea of coupling a rock bed-greenhouse system with an injection/sucking system was presented. Furthermore, it can be seen that, generally, the porosity of the employed rock bed in the greenhouse is about 0.4, and the range of the average diameter of the rocks is 25-100 mm. Based on the details described in Table 2, it can be observed that the majority of the work was conducted experimentally, except for one paper ([PERSON] et al. [56]), which was conducted numerically (CFD). It makes sense that a new system's effectiveness and performance in a particular application should be assessed in a lab to ascertain the difficulties and challenges that may arise during operation. However, even though [PERSON] et al. [48] introduced the suggested system around 27 years ago, numerical approaches have not been employed in the proposed rock bed-greenhouse system with a humid air injection/suction mechanism. In contrast, numerical methods are effective techniques for optimising thermal systems to increase performance. According to the literature review presented in Section 2.2 and the details listed in Table 2, it can be concluded that employing a rock bed as a thermal battery, an SHTES, a humidifier/dehummidifier, or even a pre-conditioner could be a very effective and promising method to improve the efficiency of greenhouses during cold seasons, particularly in regions with harsh winters. Figure 27:6 (**a**) The schematics of the proposed system by [PERSON] et al. [56], and (**b**) the slice temperature contour inside the proposed computational domain. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Author**} & \multirow{2}{*}{**Year**} & \multirow{2}{*}{**Method**} & \multicolumn{4}{c}{**Factors**} & \multicolumn{2}{c}{**Suction/Injection Method for Coupling Rock Beds and Cerehouses**} & \multicolumn{1}{c}{**O Outcomes**} \\  & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & \\ \hline \multirow{3}{*}{[PERSON] et al. [48]} & \multirow{3}{*}{1996} & \multirow{3}{*}{Experimental} & \multirow{3}{*}{-} & \multirow{3}{*}{Spherical gravel of 50 to 100 mm diameter} & \multirow{3}{*}{NA -1\({}^{\text{\tiny{1}}}\)} & \multirow{3}{*}{\(\surd^{\text{\tiny{2}}}\)} & This work was the first study in the literature to use injection/solution methods for coupling rock beds with greenhouses.} & This work was the first study in the literature to use injection/solution methods for coupling rock beds with greenhouses.