2014 Volume 123 Issue 4 Pages 472-485
Besides the immediate need for alternative sources of energy, it has become increasingly crucial to maximize the use of the limited energy sources that remain after the Great East Japan Earthquake. Tokyo, which consumes an enormous amount of energy, should lead this effort by exploring ways of becoming an advanced energy-saving city in the future. This paper focuses on the thermal energy of water, which is one of the available energy sources in Tokyo. The potential of the thermal energy of water could be harnessed to improve the thermal environment and reduce energy use in Tokyo. One way to use this energy is to harness the heat of evaporation by sprinkling water on a pavement in order to improve the thermal environment in summer in cities where the heat island phenomenon is observed. This technique of sprinkling water is known to the Japanese as Uchimizu, and it is a time-honored custom in Japan. Some studies involving field experiments and numerical simulation have investigated the cooling effect of sprinkling water scientifically by applying systematic sprinkling as a countermeasure for the formation of heat islands. The other way of employing this source of energy is to use a ground-source heat pump system, which is a high-performance cooling and heating system, using subsurface and groundwater thermal energy efficiently. Active use of thermal energy of water is considered to be one strategy that Tokyo can adopt to become an energy-saving and environmentally friendly city in the future.