EFFECT OF SUCTION PRESSURE

The suction or evaporator pressure decreases due to the frictional resistance to the flow of refrigerant. Let the suction pressure p_s decrease to p_s′ as shown in p-h diagram of Fig. 19.16. The effect of decrease in suction pressure are:

1. The refrigerating effect decreases from (h₁ − h₄ ) to (h_1′ − h_4′)
2. The compression work increases from (h₂− h₁) to (h_2′ −h_1′ ) 

Therefore, the COP decreases for the same amount of refrigerant flow. Hence, the refrigerating capacity of the system decreases and the refrigeration cost increases.

Figure 19.16 p-h diagram