## 2 Experimental Setup and Configuration  
### System Configuration  
#### 2.1.1 Set-Up  
Figure 1 shows the schematic diagram of the experimental set-up for evaluating the cooling performances of the air-conditioning system with the two parallel refrigeration cycles for a special purpose vehicle. The experiments were performed and analyzed in the psychrometric chambers. The psychometric unit consists of two chambers to control temperature and humidity conditions, respectively, as shown in Figure 1. The psychrometric chambers were controlled by using a proportional integral differential (PID) control, and the two chambers were equipped with temperature and humidity devices which comprised a cooling coil, a heating coil and a humidifier, to control the temperature and humidity settings of the air with an accuracy of \(\pm\)0.2 \({}^{\circ}\)C. The temperature range for the psychometric chamber was \(-\)30 to 60 \({}^{\circ}\)C. The humidity range for psychometric chamber was 30%-95% RH (relative humidity) with humidity accuracy of \(\pm\)5%. The measurements of the psychometric chamber for the indoor compartment and the psychometric chamber for the outdoor compartment were 4000 mm (length) \(\times\) 2300 mm (width) \(\times\) 2300 mm (height) and 7000 mm (length) \(\times\) 2300 mm (width) \(\times\) 2300 mm (height), respectively. The position of indoor chamber and outdoor chamber is highlighted in the schematic as shown. Both compartments were equipped with the PTC (positive temperature coefficient) heater and the refrigeration system for controlling the temperature and humidity conditions during the experiments and for reaching the required cooling capacity. Figure 1: Schematic diagram of the experimental setup. In this study, an air conditioning system with two parallel refrigeration cycles for the special purpose vehicle was designed using R-134a. In the tested air conditioning system with two parallel refrigeration cycles, two reciprocating compressors with a displacement volume of 160.0 cm\({}^{3}\).rev\({}^{-1}\) at 380 V were installed and driven by the electric motor of 8.0 kW, since each reciprocating compressor connected to the electric motor. Two thermostatic expansion valves (TEV) were positioned in front of the evaporator part. In order to ensure adequate sub-cooling and prevent vapor expansion, the two receiver tanks with a height of 320.0 mm and a diameter of 120.0 mm were used and installed at the outlet of the condenser part. Two accumulators with a height of 180.0 mm and a diameter of 120.0 mm were located in front of the two compressors to prevent the liquid refrigerant flows into the compressor inlet. Table 1 shows the specifications of the air-conditioning system with the two parallel refrigeration cycles for a special purpose vehicle. Figure 2 shows the schematic diagrams of the condenser part and evaporator part of the two parallel refrigeration cycles for the air conditioning system of the special purpose vehicle. Figure 2a shows the configuration and air flow mechanism of the evaporator part of the air conditioning system for the special purpose vehicle. The evaporator part with measurements of 1100 mm (length) \(\times\) 920 mm (width) \(\times\) 220 mm (height) located at the indoor compartment had four fans with radial type and two heat exchangers. Size of the heat exchanger with an aluminum plate fin was 850 mm (length) \(\times\) 160 mm (width) \(\times\) 163 mm (height) and fin pitch was 2.0 mm. The fan of the evaporator part was multi-blade type. The fans applied to one section of the evaporator part circulated the air to the inner space through the middle hole of the evaporator part, as shown in Figure 2a. The cold air passing the evaporator is distributed into the outlet ports of the evaporator part. Figure 2b shows the configuration and the air flow mechanism of the condenser part of the air conditioning system for the special purpose vehicle. The condenser part located at the indoor compartment had one fan and one heat exchanger.