Abstract: Air conditioning cold water system variable flow, the use of primary pump system, and a pump using frequency control, then the use of constant pressure control is not the most energy-efficient control, to achieve the maximum energy-saving effect, the pump variable frequency control should be used variable Pressure control methods, the system pressure changes along the pipeline characteristics curve changes.
Keywords: air conditioning, cold water system, pump, variable frequency control, 1, cold water system, variable flow, primary pump, variable frequency speed control
With the self-control technology and automatic control products mature, the current air-conditioning project, the application of variable flow water system has accounted for the vast majority, especially in large and medium-sized air-conditioning systems, almost 100% utilization. In the performance of chilled water unit variable flow [2], chilled water unit in the partial load of its frozen water can vary within a certain range, and has little effect on the efficiency of chillers, cold water system and the load side of the variable flow can be combined with the design , Which is used in the cold water system, a pump variable flow system, a pump directly by the frequency control is possible to give full play to the variable frequency pump excellent energy-saving effect of frequency conversion, the comprehensive energy-saving effect is significant, but the control method used is different, Its energy-saving effect is also different.
Cold water system variable flow, the end of the electric two-way valve according to the room temperature control switch, causing the system flow changes, resulting in cold water supply and return manifold pressure changes, in order to chilled water pump frequency control to adapt to the system Flow changes, the system still needs to set up a water supply and return water pipe bypass valve as a backup, when the flow to reduce the minimum flow chillers, chilled water pump frequency, no longer continue to reduce the flow rate control, then start Auxiliary by-pass electric 2-way valve bypasses part of excess flow because chillers are usually more than one, as in the case of two units, by stopping a host the flow has been reduced by 50% and the single further reduction to 50% Not much, so auxiliary bypass electric two-way valve will not start and is generally closed.
2 frequency control pump energy saving principle
When the system flow rate changes from QA to QB, the operating point of the system will move from A to B ', the system pressure will increase, the system will have the most surplus pressure head and The most energy-saving; if the frozen water pump frequency control with constant pressure, when the set pressure is HA (HB), the pressure sensor detects the pressure difference (HB'-HB), issued a control command to reduce the inverter output frequency Pump condition curve from n0 change to n1, constant pressure value to maintain HA constant, obviously than the constant speed pump to reduce (HB'-HB) this period of dynamic pressure loss, so than constant speed pump has obvious energy saving effect; However, If the variable frequency variable speed variable pressure pump control, pressure changes along the pipeline characteristics curve changes, then the control device sends a control command to make the pump operating conditions curve from n0 to n2, the actual operating point for the B "point, Than the constant pressure control and reduce (HB-HB ") this period of dynamic pressure loss, so the most significant energy-saving effect.
3 frequency control pump energy saving
In the above analysis, it can be seen that the constant pressure control mode often adopted by the variable frequency speed governing water pump, although the control is relatively simple and easy to implement, only need to set a pressure value and pressure feedback signal, and the system pressure can be maintained by the frequency conversion speed regulation Constant, which is also derived from the feed water pump variable frequency speed constant pressure water supply, at present there are already quite mature styling products in the country, manufacturers are also more, but will be such a constant pressure control directly applied to the control of air conditioning and cold water system Inappropriate, not the most energy-efficient control methods, we can see from the above analysis that the most energy-efficient control is the use of transformers, the control system pressure along the pipeline operating characteristics of the curve changes, the most significant energy-saving effect, so frozen water pump Of the variable frequency speed control device must be programmable control chip can be achieved.
Cold water system is installed, the first measured when debugging system flow changes, changes in the total pressure difference and the frequency of frozen water pump frequency relationship, a single run and parallel operation of the situation, the commissioning of all data measured induction and simulation, Actually, the approximate calculation formula of pipeline working characteristic curve is formed, and then it is stored in programmable control chip as the basis of variable frequency speed regulation of chilled water pump in operation. The principle of minimum pressure difference is preferred in operation. The average frequency, frequency conversion to chiller minimum frequency lock, chilled water pump starting from the low frequency change.
In the current engineering applications, if the project uses building control system, and control of air-conditioning system included, to achieve the above transformation control is not difficult, but if the project did not use building control system, because there is no transformation Variable speed control stereotypes products, to achieve there is a certain degree of difficulty, due to procurement, and ultimately had to use constant pressure control, in fact, the current level of technological development and development, with programmable control chip control device has been very easy To achieve this, also called for the control of manufacturers for the characteristics of air-conditioning system, the development of variable-pressure control of frozen water pump variable frequency speed control of stereotypes products, can make the application of the transformer control more convenient and achieve more energy-saving effect.
4 Conclusion
Air conditioning cold water system variable flow, chilled water pump using a pump frequency control, chilled water pump to achieve the largest energy-saving effect, variable frequency control of chilled water pump variable frequency control should be used, the system pressure changes along the pipeline characteristics curve changes, recommendations Manufacturers develop the appropriate stereotypes.