One of the major driving forces is the iterative cycles caused by errors.

This paper introduces the patent design optimization of the chamber and grate of combined circulated hot-water boiler developed and designed by Harbin Institute of Technology,and achieving shut-down compensation,dereasing boiler height and saveing cost by appling combined circulation.

The problems existed in operation of the water-fire tube shell hot water boiler of large capacity were analyzed, and the technical principle and structural characteristics of the water-fire tube shell hot water boilers of large capacity with combined circulation ,which are for solving the problems mentioned above, were presented.

In the paper,the design principles for the hot water boiler of large capacity were analyzed and discussed,and the technical principle and the structural characteristics of the water tube hot water boiler of large capacity with combined circulation,which is designed recently according to the design principles mentioned above,were presented.

Some methods were introduced to solve the problem that was encountered when applying ASHP in colds regions, these includes as employing two-stage compression and cascade cycle to decrease pressure ratio, employing variable frequency compressor to increase refrigerant cycle volume, employing Turbo technology, high efficiency compressor and he.

The cascade heat pump unit functions in both single-stage cycle and cascade cycle by optimizing control conditions and maximizing energy-saving.