The SJSW series of modular water-source heat pump units provide chilled water for the centralized air handling equipment or terminal devices in central air-conditioning projects. The units are designed in a modular manner and there are two modules, namely SJSW20 and SJSW30. Among them, the SJSW20 has two-stage energy regulation, and the SJSW30 has three-stage energy regulation. Each module can operate and be installed separately, and multiple modules can also be assembled and operated together. The modules can be the same or different. Each module includes a scroll compressor, a shell-and-tube condenser, a shell-and-tube evaporator, and a microcomputer control center, etc. It can be widely used in high-end villas, hotels, hospitals, office buildings, entertainment venues, restaurants, scho