As the current evaluation methods of gas engine-driven heat pump systems (GEHPs), primary energy ratio (PER) is incapable to evaluate the seasonal performance of gas engine-driven heat pump water heater (GEHPWH), and seasonal primary energy ratio (SPER) is too complex in procedures. An evaluation method for seasonal performance of GEHPWH should be proposed, which is both simple and accurate. This paper presents a new evaluation method named integrated primary energy ratio (IPER) based on PER and SPER. In order to test the validity of the evaluation result, experimental studies about seasonal performance of GEHPWH have been carried under the working condition of summer. Experimental results indicated that the calculation result of IPER is relatively accurate compared with the calculation result of SPER, while the experimental and calculation procedures of IPER are much simpler than that of SPER. The seasonal performance of GEHPWH calculated with SPER is 2.09 in summer, and the IPER value of GEHPWH in the same condition is 2.01, the error compared with SPER is only 3.7%. (C) 2014 Elsevier B.V. All rights reserved.