# Numerical Analysis on the Performance of a Heat Pump Powered by Surface Water Freezing
## 1 Introduction  
As environmental problems are exacerbated and the deadlines for the \"double carbon\" goals approach [1], clean heating based on heat pumps has been popularized, but in cold regions, they have performance shortcomings. The air source heat pump system has limited use in regions with low outdoor temperatures due to the contradiction between heat supply and demand and frosting problems. References [2, 3] showed the frost effect on the performance of the air source heat pump in different areas of China. The performance decreases year by year with a shallow ground source heat pump system, and the huge investment it requires limits people's desire to install one in cold areas. Because of the potential impact on groundwater resources, the groundwater source heat pump system is not the first choice for clean heating. Papers [4, 5] analyze the blocking problem affecting the heat exchanger in a sewage source heat pump system. Utilizing rivers and lakes, the traditional surface water source heat pump system has been widely used in areas with mild temperatures due to its low cost and relatively stable performance; its _COP_ is usually 3.0-3.5 and its positive effect on the environment is significant. But, in cold areas, its application is limited because the surface water temperature is usually lower than 5 \({}^{\circ}\)C and the water is often frozen in some periods [6]. Although there may be nearby rivers or lakes, the heating solutions in these cold areas usually depend on fossil fuels, such ascoal and natural gas. If the evaporator of the heat pump can adopt a lower evaporation temperature and directly extract the solidification latent heat, of about 336 kJ/kg, from the surface water, the heating demand in cold areas with rivers or lakes could be met. The practical significance of this development is great. The heating feasibility of the surface water solidification heat source heat pump system in cold areas is addressed by existing research and real-world projects. Reference [7] showed that the solidification heat source heat pump system can be used in China's water source environment. Reference [8] put forward a theoretical relationship between the cold water temperature and the heating load to support the design and operation of the surface water solidification heat source heat pump system. Reference [9] provided a project case of the solidification heat source heat pump system in Qingdao City and quantitatively compared its energy consumption, initial investment, and operating cost with the traditional water source heat pump. Usually, the heat exchanger is used to supply the intermediate (often liquid alcohol), heated by low-temperature water to the heat pump evaporator, in which the surface water from rivers or lakes flows in a tube and freezes, while the intermediate flows outside the tube [10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20]. The deicing methods for the heat exchanger include built-in mechanical scraper deicing [7], impact deicing [16], mechanical spiral deicing [21; 22], and ring deicing [23]. Reference [11] designed a kind of external ice brush rotary scraping deicing device. Reference [17] used the condenser heat to deice the heat exchanger by hot melting. Reference [24] used the elastic structure of regular micro-deformation to break the thin ice on the wall regularly. It is clear that heat pump systems and their deicing methods mentioned above are complex, have low efficiency, and easily fail. So, a solidification heat source heat pump with simpler and more efficient characteristics is needed. In addition, Simulink software has been widely used in the design and research into refrigeration systems, because it can accurately show complex energy-exchange processes [25; 26]. In view of the above considerations, this paper innovatively proposes a heat pump system that can directly collect the solidification heat of water using its shell-tube evaporator, in which water flows outside a tube and freezes, while refrigerant flows in the tube.