4.1.4. Pressure Characteristics

The pressure ratio between low and high pressure of refrigeration system affected compressor power consumption. The behaviors of pressure ratio of tested system with high-pressure side chiller for various operating conditions during the cooling mode is presented in Figure 5. The variations of pressure ratio with coolant operating conditions and compressor speed were experimentally recorded for HVAC inlet air conditions of temperature of 25 ◦C, relative humidity of 60%, flow rate of 450 m<sup>3</sup> /h, and air velocity of 3 m/s. At coolant inlet conditions of 35 ◦C and 10 L/min, the compressor speed varied from 3000 rpm to 5000 rpm and pressure ratio was analyzed. With the increase in the compressor speed from 3000 rpm to 5000 rpm, the low pressure decreased; however, the high pressure remained constant in the range of 1100 kPa because the coolant and ambient conditions remained constant. As an effect of this the pressure ratio which is defined as the ratio of high pressure to low pressure, increased with the increase in the compressor speed. Pressure ratio increased by 26.8% from 3.05 to 3.87 with the increase in the compressor speed from 3000 rpm to 5000 rpm, as shown in Figure 5a. This was the reason behind the increase in the compressor power consumption as depicted Figure 2a. In the case when the coolant temperature increased from 35 ◦C to 55 ◦C, the low pressure remained constant, whereas the high pressure increased up to 1500 kPa. Therefore, the pressure ratio increased with the increase in the coolant temperature. The pressure ratio increased by 35.0% from 3.6 to 4.87 with the increase in the coolant temperature from 35 ◦C to 55 ◦C, as shown in Figure 5b. The effect of coolant temperature on the pressure ratio caused an increase in the compressor power consumption with an increase in the coolant temperature as shown in Figure 3a. However, the pressure ratio affected little

with the variation of coolant volume flow rate from 10 L/min to 20 L/min because of the same operating conditions of coolant temperature and compressor speed.

*Symmetry* **2020**, *12*, x FOR PEER REVIEW 13 of 25

(**b**)

**Figure 4.** Effect of coolant volume flow rate on (**a**) cooling capacity, compressor work and coefficient of performance (COP) and (**b**) P‐h diagram of heat pump system with chiller during the cooling mode. **Figure 4.** Effect of coolant volume flow rate on (**a**) cooling capacity, compressor work and coefficient of performance (COP) and (**b**) P-h diagram of heat pump system with chiller during the cooling mode.

4.1.4. Pressure Characteristics

20 L/min because of the same operating conditions of coolant temperature and compressor speed.

The pressure ratio between low and high pressure of refrigeration system affected compressor power consumption. The behaviors of pressure ratio of tested system with high-pressure side chiller for various operating conditions during the cooling mode is presented in Figure 5. The variations of pressure ratio with coolant operating conditions and compressor speed were experimentally recorded for HVAC inlet air conditions of temperature of 25 °C, relative humidity of 60%, flow rate of 450 m3/h, and air velocity of 3 m/s. At coolant inlet conditions of 35 °C and 10 L/min, the compressor speed varied from 3000 rpm to 5000 rpm and pressure ratio was analyzed. With the increase in the compressor speed from 3000 rpm to 5000 rpm, the low pressure decreased; however, the high pressure remained constant in the range of 1100 kPa because the coolant and ambient conditions remained constant. As an effect of this the pressure ratio which is defined as the ratio of high pressure to low pressure, increased with the increase in the compressor speed. Pressure ratio increased by 26.8% from 3.05 to 3.87 with the increase in the compressor speed from 3000 rpm to 5000 rpm, as shown in Figure 5a. This was the reason behind the increase in the compressor power consumption as depicted Figure 2a. In the case when the coolant temperature increased from 35 °C to 55 °C, the low pressure remained constant, whereas the high pressure increased up to 1500 kPa. Therefore, the pressure ratio increased with the increase in the coolant temperature. The pressure ratio increased by 35.0% from 3.6 to 4.87 with the increase in the coolant temperature from 35 °C to 55 °C, as shown in Figure 5b. The effect of coolant temperature on the pressure ratio caused an increase

**Figure 5.** Pressure ratio characteristics with (**a**) compressor speed and (**b**) coolant temperature in cooling mode. **Figure 5.** Pressure ratio characteristics with (**a**) compressor speed and (**b**) coolant temperature in cooling mode.
