## 1 Introduction
### Earth-to-Air Heat Exchanger (EAHE) Test Studies  
The application of the EAHE system in GHs is widespread. However, the COP values and energy consumption differ depending on the conditions related to the design of the EAHE system, soil type, the structure of the GH, and the climate zone, among others. In Delhi-India, the annual maximum heating/cooling potential of EAHE, in the 8.58 \(\times\) 4 \(\times\) 2.5 m\({}^{3}\) microclimate of GH, the maximum value of heating potential was 11.55 MJ and the cooling potential was 18.87 MJ. These values are reached on typical days in January and June [14]. Regarding the performance of the integrated system in Tehran-Iran, the results show that the integrated evaporation system with an EAHE system reduces water consumption by 17% to 49%, with the reduced percentage depending on environmental conditions from climate 1 (with cold or very cold winters and hot and dry or mild summers) to climate 4 (with cool or mild winters and very hot and humid summers) [24]. In another study on a 24 m\({}^{2}\)\(\times\) 3 m GH located in Iran, [PERSON] et al. [25] explain that the energy and exergy efficiency depends on the length of the EAHE pipes, using 39 m for their system. The pipes are installed at a depth of 1 m, with temperature variations at this depth ranging from 22 to 28 \({}^{\circ}\)C. The system used is a horizontal serpentine EAHE, which has a larger foot print. In Bologna-Italy, the soil temperature at shallow depth is 16 \({}^{\circ}\)C. [PERSON] et al. [26] installed 12 EAHE systems in a vertical spiral shape (total length 60 m, installation depth 2 m), which serve as backup for the main GH heating system (24 \(\times\) 8 \(\times\) 12.7 m\({}^{3}\)) during the winter season. The vertical spiral form occupies a smaller area. They state that the EAHE helps reduce energy consumption by 10 to 30%. They also believe their system can reduce gas emissions by 8 to 28% [26]. However, they explain that there is little literature on the energy consumption of GHs. There are many studies in the literature on the application of the EAHE system in GHs for different regions and conditions. However, few studies have been conducted to give an idea of the dependence on climate, EAHE design, and GH design. An experimental study was conducted in In Izmir, Turkey, in the summer of 2009-2011 on the use of a horizontal EAHE system in a cooling greenhouse. The experimental study showed that the total cooling demand was between 0 and 10 kWh. The total thermal energy consumption was 5.84 kWh/day, and the total energy consumption for electricity was 584 kWh, with a COP of 6.3 [27]. For the same system, after seven years of data acquisition, [PERSON] et al. [28] declare that the maximum heat output was set at 12 kW. In different regions of Iran, from climate 1 (with cold or very cold winters and hot and dry or mild summers) to climate 4 (with cool or mild winters and very hot and humid summers), an integrated system with an evaporative cooling system and an EAHE was used in a GH with a size of more than 1600 m\({}^{3}\), where the EAHE system was installed at a depth of 2 m. The average soil temperature was 21 \({}^{\circ}\)C. In the month of February, the amount of heat generated by the heating system in the absence of plants was more than 33.3 kWh/m\({}^{2}\) per month [24]. [PERSON] et al. [29] installed a thick insulated foam layer around the soil of the EAHE to reduce heat loss. They used this system in heating/cooling a 142.87 m\({}^{3}\) greenhouse, in Loughborough, UK. Measurements show that COP\({}_{\text{heating}}\) ranged between 1.48 and 2.97 and COP\({}_{\text{cooling}}\) ranged between 1.20 and 3.45. The 150 m\({}^{3}\) GH studied by [PERSON] [30] was realized in Elazig, Turkey. Vertical and horizontal EAHEs were used in this greenhouse. In the experiments, the operational performances of the different system designs and the soil temperature field in the heating mode were evaluated.