In the forties and fifties of last century, the heat pump industry developed rapidly, but the revolutionary development of heat pump technology really began in the 1990s after the "oil crisis". When the oil crisis broke out and oil prices soared, people realized that oil, as a non-renewable resource, would inevitably become more and more expensive. As a product that can achieve low energy consumption through technical means, heat pump has re-entered the historical stage and attracted people's attention. For example, in the United States, the output of heat pumps soared from 82,000 units/year of197/kloc-0 to 300,000 units/year of 1976, and 1977 jumped to 500,000 units/year again. At this time, Japan came from behind, with an annual output of more than 500,000 units. At present, the heat pump market is growing exponentially every year, and the development momentum is quite rapid. The real combination of the hot water function and cold air function of heat pump technology into the household category should be counted from the German invention of "air conditioning water heater" in the early 1990s. At that time, it was called "hot water reactor pump" or "heat pump boiler" Its biggest advantage is that it can not only heat hot water for users, but also cool the kitchen. This function is very practical, and the product has been greatly welcomed by Europeans in just a few years, and now it has become the first choice for hot water equipment in new residential buildings in Europe. Unfortunately, due to technical barriers and high prices, this product has not been listed in China for a long time. With the deepening of technical exchanges between China and Europe and the improvement of manufacturing level in China, domestic manufacturers have introduced technology and started to manufacture this kind of product in recent years, and many cases have appeared in high-end villas and luxury residential areas (see figure).