Performance investigation of heat pump–gas fired water heater hybrid system and its economic feasibility study

• Hybrid water heating system is designed for numerical performance analysis.
• The performance of the system is calculated using mathematical models.
• Characteristics of the system performance is investigated.
• Economic benefits of the system are estimated.

Heat pump water heaters have been introduced to improve energy efficiency of water heating in buildings. Although much research has been conducted to make up for weak points of heat pumps which occur when their purpose is converted from air-conditioning into water heating, there remain some points to be improved to perform as stably as conventional water heaters. Recently, the hybrid water heating system, which is the combination of a heat pump and a traditional gas fired water heater, is proposed as an alternative water heater to perform more efficient water heating stably. In this paper, the hybrid system is designed for general residential houses in Korea, which have floor area of 106.47 m2 and its performance characteristics are analyzed numerically. To obtain the performance of a hybrid water heating system, the mathematical models of heat pump components and the correlation, which is derived from experimental data of a gas fired water heater, are applied. Also, using the result of a performance calculation, the economic feasibility study is carried out, with the concept of energy cost savings, to quantify the merits of the system and to establish its operation strategy. The monthly electricity and heat consumption data in a Korean residential house and the price of electricity and gas are applied to reflect an actual situation.