Because the usage of CFC and HCFC based refrigerants are restricted due to the depletion of ozone layer, the $NH_3$ gas, in the experiment is evaluated to the performance characteristics for the superheat control to improve the energy efficiency. The experiment is carried out about the condensing pressure of refrigeration system from 1,500 kPa to 1,600 kPa through the degree of superheat from 0 to $10^{circ}C$ at each condensing pressure. As a result, in the case of shell and tube type of heat exchanger, the COP is more efficient than other cases at the degree of superheat $1^{circ}C$ at each condensing pressure. In the case of shell and disk type of heat exchanger, the COP is the most efficient at the degree of superheat 0.