fThis paper introduces a heat pump system with a latent heat storage utilizing seawater installed in an aquarium. Heat from the seawater is collected and used as the heat source for the heat pump system. This maintains the indoor conditions at constant temperature and relative humidity. With regard to the heat pump system using low-temperature unutilized heat source, development is introduced on a heat source load responsive heat pump system, with combines a load variation responsive heat pump utilizing seawater with a latent heat (ice plus water slurry) storage system using nighttime electric power serving for electric power load leveling. The desired outcome would be to show that the costs of generating heat energy with the seawater-source heat pump are significantly less than those with the air-source heat pump and the oil-fired system. Additionally, the CO2 emissions for the seawater-source heat pump compare favourably as they maybe less than those for the other conventional assumed systems described. (c) 2005 Published by Elsevier B.V.