Many research projects have been conducted to combine waste heat from industrial processes to heat pumps in order to save energy consumption. Among the heat demands of industrial processes, low pressure steam under 150°C occupies a large portion, therefore the demand for steam generating heat pumps is high. For efficiency and reliability, the working fluid in steam heat pumps has a critical point above the steam generation temperature. Among commercial refrigerant satisfying this, R245fa was selected. Under same suction superheat R245fa tends to have smaller discharge superheat than R134a. To secure superheat without increasing temperature difference in evaporator, an internal heat exchanger was applied to a steam heat pump cycle. Sensitivity analysis to suction superheat was performed for R245fa and R134a. The results showed that R245fa had better performance response than R134a. This means R245fa has more advantages in applying internal heat exchanger compared to R134a.