## 2 Literature Review
### SHTES Systems in Greenhouses
#### 2.2.3 Rock Bed as SHTES System
[49] are demonstrated in Figure 29.  
Figure 28: The schematics of the proposed system by [PERSON] et al. [48]. Figure 29: The schematics of the proposed system by [PERSON] et al. [49]: (**a**) front view and (**b**) side view. To investigate the usage of a greenhouse with packed beds of thermal storage for crop drying, [PERSON] [50] proposed a transient analytical model. The effectiveness of an even-shaped greenhouse with a packed bed and crop drier was assessed for drying onions. The model was solved to determine the air temperatures and other drying system functioning components for a day in May for Delhi's (India) meteorological conditions. The parametric study examined the relationship between the greenhouse length, width, air mass flow rate, and crop temperature. The drying rate and hourly decrease in moisture content in the crop trays were studied using the thin-layer drying equation. It was noted that as the day wore on, the crop's moisture content and drying rate decreased, which was an obvious result. They illustrated that in a 24 h drying time, a greenhouse with dimensions of 6 m long, 4 m wide, 0.278 kg\(\cdot\)s\({}^{-1}\) air mass flow rate, and 0.25 m height of packed bed could dry 2280 kg of onions with a moisture content ratio of 6.14-0.21 kg water to kg of dry matter. The schematics of the proposed system by [PERSON] [50] are demonstrated in Figure 30.  
[PERSON] et al. [51] examined and discussed the effectiveness of a rock bed heating system (or SHTES system) in a traditional Moroccan Canarian greenhouse. To improve the quality and quantity of agricultural produce while addressing the issue of conventional greenhouses overheating during the day and excessive cold at night, experimental comparison research was carried out in two east-west-orientated greenhouses. They considered two greenhouses with the same geometrical and operational factors; the only difference between them is the presence of the rock beds, as in the SHTES system. The schematics of these greenhouses are illustrated in Figure 31a. The greenhouse with the rock beds is demonstrated as the experimental greenhouse, and the other one (conventional type without any SHTES) is presented as the control greenhouse. The details of the proposed experimental setup are shown in Figure 31b. Moreover, the performance of the proposed rock beds in two modes, charging (day) and discharging (night), is demonstrated schematically in Figure 31c. According to the results, the nighttime temperature in the greenhouse with the rock bed is 2.6 \({}^{\circ}\)C higher than in the control greenhouse. Also, the outcomes revealed that in the heated greenhouse (with rock beds), the relative humidity was 10% lower at night. Moreover, the fruit quality was much enhanced, and the yield rose by over 29% due to this nighttime microclimate adjustment. In a modified greenhouse dryer with an insulated north wall, [PERSON] and [PERSON] [21] presented an experimental examination of various floor conditions, including a ground floor, concrete floor, gravel floor, and black-painted gravel floor. For different floor conditions, terms such as the heat utilization factor, heat loss factor, total heat transfer coefficient, and coefficient of diffusivity were determined. The experimental outcomes depicted that the painted gravel floor was found to have the most significant temperature differential between the room and outside air at 13 o'clock, followed by the gravel floor, concrete floor, and ground floor with differences of 27, 14,1, and 11.5 \({}^{\circ}\)C, respectively. Moreover, for the  
Figure 30: The schematics of the proposed system by [PERSON] [50]. black-painted gravel floor, gravel floor, concrete floor, and ground floor, the growth in the percentage of the maximum room temperature compared to the maximum ambient temperature was observed to be 50.31, 46.15, 30.1, and 26.6%, respectively, at 13 o'clock. In conclusion, the black-painted gravel bed absorbed the maximum temperature. [PERSON] et al.