区域供冷系统中冷冻水输送管线的优化设计

Optimized Design of the Chilled Water-conveying Pipeline in the District Cooling System

建立了确定区域供冷系统冷冻水输送管线最优水流速度和保温层最优厚度的优化模型 ,其目标函数为系统的年度费用 ,由冷冻水二级泵的年运行费用、冷冻水输送管线冷量损失费用、二级泵功耗导致的冷水温升所产生的费用、冷冻水二级泵的折旧和维修费用以及冷冻水输送管线折旧和维修费用 5个部分组成 .考虑全年变负荷运行的特点 ,在部分负荷时假设冷冻水的供回水温差不变 ,采用变频泵调节流量 .通过实例计算 ,得到以下结论 :对于区域供冷系统 ,存在最优的水流速度和保温层厚度 ;冷水输送距离对最优水流速度和保温层最优厚度没有影响 ;最优水流速度随电价升高而降低 ,随设计冷负荷增大而升高 ;保温层最优厚度随电价升高而增加 。

An optimized model to determine the optimal velocity of the chilled water and the optimal insulation thickness of the chilled water-conveying pipeline in the district cooling system was proposed, with the objective function of annual system cost which consists of: (1) the annual operating cost of the secondary pump for conveying the chilled water; (2) the cost due to the refrigeration loss of the chilled water-conveying pipeline; (3) the cost due to the temperature increase of the chilled water caused by the power consumption of the secondary pump; (4) the depreciation and maintenance cost of the secondary pump; and (5) the depreciation and maintenance cost of the chilled water-conveying pipeline. In the optimization, the character of the yearly-varied load was taken into account; the temperature difference between the feed water and the return water was assumed constant and the water flowrate was adjusted by the variable-frequency pump. By the calculation of a practical case, it is concluded that there is an optimal velocity of the chilled water and an optimal insulation thickness of the chilled water-conveying pipeline in the district cooling system, which are not affected by the conveying distance of the chilled water. It is also concluded that the optimal velocity of the chilled water decreases with the increase of the electric cost and the decrease of the designed cooling load, while the optimal insulation thickness of the pipeline increases with the increase of the electric cost and appreciably increases with the designed cooling load.