At present, the design of variable volume chilled water system generally adopts primary and secondary double loop. However, this double-loop configuration will produce: the use of two pumps to increase equipment investment; The mixing of chilled water supply and return water affects the efficiency of chiller under partial load. When the actual demand conditions of high-load air conditioning do not coincide with the maximum design conditions, the full load capacity of the chiller cannot be fully utilized. The design of single ring air conditioning chilled water system can avoid the above problems.
As shown in the figure 1, the traditional variable flow chilled water system consists of primary and secondary loops with independent pumps. Usually, the low-pressure head primary pump corresponding to the refrigerator in the primary loop keeps a constant chilled water flow, while one or more high-pressure head variable flow secondary pumps adjust the cold water flow in the secondary loop to meet the actual refrigeration needs. The flow imbalance between the primary and secondary loops causes chilled water flow in the bypass pipe. Although this system achieves the goal of maintaining a constant amount of chilled water flowing through the chiller, it does not achieve the highest chiller efficiency at partial load and limits the chiller’s capacity due to unequal flow rates between the two loops under most operating conditions.
It is necessary to reconsider the actual configuration of the variable flow chilled water system in order to realize the full potential of the integrated HVAC system between air and cooled chiller operating under a high-performance control strategy. Recent studies have shown that an integrated control strategy can be used to directly regulate pump speed without pressure control to meet load requirements, thus achieving greater efficiency in a variable flow chilled water distribution system.
In figure 2, the cooler itself may be a variable speed unit. In any case it shows a high regulation ratio and an increased performance factor when cooling load is reduced. The flow rate required by the water chiller is determined by the size of the refrigeration load being delivered. This is a proper single loop variable flow frozen drainage statistics. Because the load end is connected with a two-way valve, the load side flow also changes with the load. Frozen water flow and chiller capacity can be effectively matched with various load conditions. The cooling capacity limit is defined as the value below which the system cannot operate, as in current chiller systems.