The CO2 Heat Pump Water Heater as a New Countermeasure Against Global Warming: Drastic Improvement in Energy Efficiency in Three Years Since Its Debut

Yoshiaki Shibata, Chiharu Murakoshi, and Hidetoshi Nakagami, Jyukankyo Research Institute

Keywords

Abstract

The CO2 heat pump water heater (CO2HPWH) for residential use was brought to the Japanese market in 2001. It is composed of a heat pump with CO2 as the working fluid and a hot-water storage tank. The use of natural refrigerant CO2 and an annual total efficiency higher than that of combustion boilers are the main features. It has been widely alleged that the annual total efficiency, including heat loss from the storage tank, achieves 3.0. In order to verify its performance in situ, we carried out field performance tests for the units in 2004-2005. Units manufactured in 2004 and installed in six homes demonstrated that the annual total efficiency exceeded 3.0 and the primary energy efficiency was no less than 1.0, with a fuel-to- electric conversion factor of 0.366. In this paper, the market growth of the CO2HPWH in Japan and its performance improvement is described. Results from the field test which we carried out are also reported in detail. The paper concludes with a discussion about the potential for further improvement.