Abstract
The authors carried out questionnaires and field measurements about the hot water usage and the performance for the CO_2 heat pump water heater in 14 houses for over a year. Based on the results of questionnaires and measurements through four seasons, the characteristics of hot water usage are analyzed in details. The behavior of taking bath has big influence on hot water consumption in houses. Therefore, the dweller's behavior at bathroom and the loads of hot water which are consumed by reheating the bathtub's water are studied And, we suggest the calculation models for the loads of hot water consumption in houses.