At present, most of the air conditioning water systems in my country's super high-rise buildings are cascade heat exchange methods with plate water-water heat exchangers in the middle, including two types of heat exchange methods: primary plate heat exchange and secondary plate heat exchange. The cold water is lifted from the low-rise area to the high-rise area for closed heat exchange, so that the low-rise area and the high-rise area are subjected to the pressure of their respective heights, thereby reducing the problem of excessive pressure in the low-rise area.
The main features of this system are:
(1) The height of each area is generally controlled at about 100m.
(2) The plate heat exchanger is used as the equipment for heat exchange between primary water and secondary water. Because of the high efficiency of this type of heat exchanger, the temperature difference between the primary and secondary water can reach 1℃. The heat exchanger is usually set in the equipment layer.
(3) In order to ensure the dehumidification capacity of the secondary water, its water temperature cannot be too high, generally at 7~8℃, so the primary water temperature is generally 5~6℃. Therefore, it is difficult to meet such requirements for chillers.
(4) When the system is zoned, the height that primary water can reach should be used as much as possible, that is, the load of the building should be borne by primary water as much as possible, which is an important energy-saving measure. Secondary water has a lower energy level than primary water, so its ability to treat air is slightly inferior; excessive use of secondary water will increase the area of the heat exchanger and the circulation volume of secondary water, that is, energy consumption will increase.
(5) Since the height of the primary water system is generally high and the chiller is located in a lower position such as the basement, the chiller is placed on the suction side of the water pump to avoid higher bearing requirements due to the influence of the water pump pressure. As for the relative position of the plate heat exchanger and the water pump in the secondary water system, even if the maximum pressure value of the plate heat exchanger can reach more than 2.0MPa, the principle of reducing its pressure value as much as possible should still be followed.