| 摘要 |
PURPOSE:To reduce the operating cost of heating by selecting the heating operation either by a heat pump system or by electrical heating using low cost nighttime power upon comparing them to each other within the preset low cost operation zone. CONSTITUTION:A low cost operation zone where the heating by a heat pump system 4 is less expensive than by an electrical heater 10 is determined in advance, and is stored in a memory section 24. Until the hot water temperature becomes the switching temperature, the heating operation by the heat pump system 4 is continued. If the time is within the nighttime supply hours, the heating operation is switched to the heating by the electrical heater 10, which is continued until the set hot water temperature is reached. To heat water in the reservoir tank 1 from the feed water temperature to the set temperature, the heating by the heat pump system is first performed, and, if the time is within the nighttime power supply hours when the hot water temperature rises beyond the low cost operation zone, the heating operation is automatically switched to the heating by the electrical heater 10. |
