**2. Experimental Method**

The experimental set-up of the heat pump system with a high-pressure side chiller is shown in Figure 1. In order to get the heat from the highest temperature condition and give it to the coolant, the developed chiller was installed at the discharge side of the compressor, hence it is called the high-pressure side chiller. The experimental set-up mainly comprised of electric compressor, condenser, evaporator, expansion device, chiller and heater core. The specifications of the primary components of the experimental set-up is presented in Table 1. The experimental set-up had three fluid circulation loops, namely the refrigerant circulation loop, coolant circulation loop and air circulation loop. To control the ambient conditions for the experiments, the experimental set-up was housed inside a psychometric calorimeter which consisted of a cooling coil, heating coil and humidifier and was controlled using a PID controller. Using this facility, the experimental test conditions were set to a temperature of 120 ◦C and pressure of 2500 kPa. The scroll-type electric compressor was driven using a compressor driver at a specific frequency and current. The power input measured by a power meter and current were used to evaluate the compressor work. The refrigerant loop comprised an electric compressor, chiller, condenser, expansion valve and evaporator, while the coolant loop consisted of a chiller, water pump and receiver tank. The chiller was the additional component in the heat pump system and the common component in the refrigerant loop and coolant loop which was located next to the electric compressor. The high-pressure and high-temperature refrigerant discharges from the electric compressor transferred the heat to the coolant in the chiller. The coolant, which carried the heat from the refrigerant, circulated in the coolant loop and transferred the heat to the air in heater core. The heated air in the heater core passed through the cabin of the electric vehicle for the heating purposes. To measure the flow rates of the refrigerant and coolant, a mass flow meter and coolant flow rate meter were installed in the refrigerant loop and coolant loop, respectively. The refrigerant loop consisted of auxiliary components, namely, an accumulator, electronic expansion valve with driver and three-way valve. The temperatures and pressures of the refrigerant and coolant were measured using temperature and pressure sensors which were installed at the inlet and outlet of the electric compressor, chiller, condenser, evaporator, heater core, electronic expansion valve and accumulator. The measured temperature and pressure data were monitored in a data logger and recorded in a computer. The range and accuracy of each instrument is presented in Table 2.

The experiments were performed in two modes, namely, cooling mode and heating mode. In cooling mode, the inlet air conditions to HVAC were set to temperature of 25 ◦C, relative humidity of 60% and flow rate of 450 m<sup>3</sup> /h, the compressor speed was varied from 4000 rpm to 6000 rpm, the coolant inlet temperature was varied from 35 ◦C to 55 ◦C and the coolant volume flow rate was varied from 10 L/min to 20 L/min to evaluate the performance of heat pump system with a high-pressure side chiller. In the heating mode, the ambient air temperature and air temperature were set to −6.7 ◦C, air volume was fixed to 300 m<sup>3</sup> /h, coolant flow rate was set to 10 L/min, air velocity was varied from 3 m/s to 5 m/s, compressor speed was varied from 2000 rpm to 6000 rpm and the coolant temperature was varied from −6.7 ◦C to 50 ◦C to evaluate the performance of the heat pump system with a high-pressure side chiller.

*Symmetry* **2020**, *12*, x FOR PEER REVIEW 5 of 25

**Figure 1.** Experimental set‐up of the heat pump system with a high‐pressure side chiller. **Figure 1.** Experimental set-up of the heat pump system with a high-pressure side chiller.



**Table 2.** Range and accuracy of each instrument.

