The electric water heater must not be taken out of the water during operation. The temperature coefficient of resistance after heating refers to the slope of the secant through tp and tb. The heating method of the system cannot meet the special requirements of the commodity era. Real estate or heating companies in northern cities were forced to heat or stop heating because they were unable to collect heating fees, and users conflicted with heating. In addition, the traditional high-temperature fan central heating system will cause huge energy waste and heat loss. More importantly, once the price of the international energy market changes, domestic coal, oil, and natural gas prices also rise, not only for heat loss, but users also cannot enjoy legal heating.
There is also a centralized heating method, that is, the central air-conditioning system .. The units used in central air-conditioning are: air-cooled pipe machines, air-cooled multi-connections, air-cooled hot water units, evaporative condensation chiller units, and small gas absorption chiller units. According to the different transportation media, it can be divided into three forms: air cooling system, refrigeration system and water system. Due to superior living conditions, the central air-conditioning system in the United States mainly uses air duct systems and electric boilers and gas stoves. The central air-conditioning units provide cooling during the cooling season, and electric boilers and gas stoves provide heating during the heating season, which also meets the needs of domestic hot water. . Japan has a small and large population, energy shortages, and compact housing structures, most of which are mainly refrigerant systems. In China, due to technical, price, and national conditions, air-cooled hot water units and Evaporative chiller has a large market share.