4.1.3. Cooling Capacity, Compressor Work and COP at Various Coolant Volume Flow Rates

The behaviors of cooling capacity, compressor work and coefficient of performance of heat pump system with a high-pressure side chiller for various coolant volume flow rates during the cooling mode is presented in Figure 4a. The variations of cooling capacity, compressor work and coefficient of performance with coolant volume flow rate were experimentally recorded for HVAC inlet air conditions of a temperature of 25 ◦C, relative humidity of 60%, flow rate of 450 m<sup>3</sup> /h, air velocity of 3 m/s, coolant inlet conditions of 35 ◦C and compressor speed of 5000 rpm. The coolant volume flow rate had no significant effect on the cooling capacity as shown in Figure 4a. With increase in the coolant volume flow rate from 10 L/min to 15 L/min, the cooling capacity reduced by 1.47% from 4.09 W to 4.03 W, whereas the cooling capacity remained constant at 4.03 W when the coolant volume flow rate increased from 15 L/min to 20 L/min. The compressor work decreased with the increase in the coolant volume flow rate due to the fall in the high-pressure side of the compressor. However, the decrease in the compressor work with coolant volume flow rate was not significant as shown in Figure 4a. The compressor work decreased from 1.33 kW to 1.3 kW with a reduction of 2.26% for the increase in coolant volume flow rate from 10 L/min to 15 L/min. With the increase in the coolant volume flow rate from 15 L/min to 20 L/min, the compressor work decreased by 1.54% from 1.3 kW to 1.28 kW. Due to variations in the cooling capacity and compressor work with coolant volume flow rate, the coefficient of performance also showed variation with coolant volume flow rate. As shown in Figure 4a, the effect of coolant volume flow rate on coefficient of performance was less because of less effect of coolant volume flow rate on cooling capacity and compressor work. Due to characteristic behaviors of cooling capacity and compressor work with coolant volume flow rate, as presented in Figure 4a, the coefficient of performance increased from 3.08 to 3.1 with an enhancement of 0.65% for the increase in the coolant volume flow rate from 10 L/min to 15 L/min, whereas, when coolant volume flow rate increased from 15 L/min to 20 L/min, the coefficient of performance increased by 1.29% from 3.1 to 3.14. Figure 4b presents the P-h diagram for the refrigeration cycle of the heat pump system with a high-pressure side chiller with various coolant volume flow rates. The working of this refrigeration cycle on the P-h diagram for various coolant volume flow rates was similar to that explained for the refrigeration cycle on the P-h diagram for various compressor speeds.
