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Temperature and pressure parameters of central air conditioner chiller
1, evaporation pressure and evaporation temperature In the operation of the chiller, evaporation temperature, evaporation pressure and cold water into the evaporator heat is closely related. When the heat load is large, the return water temperature of the evaporator cold water increases, causing the evaporator temperature to rise, and the corresponding evaporation pressure also increases. On the contrary, when the heat load is reduced, the cold water return temperature is reduced, and its evaporation temperature and evaporation pressure are reduced. In actual operation, when the heat load of air-conditioned room is reduced, the cold water return temperature is reduced, and the evaporation temperature and evaporation pressure are equally reduced.
According to China's JB/ T3355-1998 standard, the rated working condition of the chiller is chilled water outlet temperature 7℃, cooling water return water temperature 30℃. Other relevant parameters are the chilled water return temperature of 12 ° C and the cooling water outlet temperature of 35 ° C.
According to the national standard GB/ T18403.1-2001, the rated working condition of the chiller is the chilled water inlet and outlet water temperature of 12℃/7℃, and the cooling water inlet and outlet water temperature of 30℃/35℃. Therefore, the working condition of the chiller when leaving the factory is 12 ° C /7 ° C, and the water temperature in and out of the chilled water is 30 ° C /35 ° C.
In operation, in the case of meeting the requirements of air conditioning, the cold water outlet temperature should be increased as much as possible. Under normal circumstances, the evaporation temperature is 2℃~4℃ lower than the cold water outlet temperature. The evaporation temperature is usually controlled in the range of 3℃~5℃. Too high evaporation temperature is often difficult to achieve the required air conditioning effect, and too low evaporation temperature not only increases the energy consumption of the unit, but also easily causes the evaporation pipe to freeze and crack.
2, condensing pressure and condensing temperature In the chiller, the pressure indicated by the high pressure meter is called the condensing pressure, and the temperature corresponding to the pressure is called the condensing temperature. The level of condensation temperature, in the case of constant evaporation temperature, has a decisive significance for the unit power consumption. The increase of condensing temperature increases the power consumption, in addition, the increase of condensing pressure of the centrifugal refrigeration unit will cause the host surge. On the contrary, the condensation temperature is reduced, and the power consumption is reduced.
Therefore, in the operation of the chiller, attention should be paid to ensuring that the cooling water temperature, water quantity, water quality and other indicators are in the qualified range. When the air is present in the condenser, the temperature difference between the condensing temperature and the cooling water outlet increases, while the temperature difference between the inlet and outlet of the cooling water decreases. At this time, the heat transfer effect of the condenser is not good, and the outer part of the condenser feels hot. In addition, the scale and silt on the water side of the condenser pipe also play a considerable role in the influence of heat transfer.
3, the pressure and temperature of cold water air conditioning chiller is generally in the standard working conditions of the cold water return temperature of 12℃, water supply temperature of 7℃, temperature difference of 5℃ under the conditions of operation.
The cold water flow of evaporator is inversely proportional to the temperature difference between supply and return water, that is, the greater the cold water flow, the smaller the temperature difference; Conversely, the smaller the flow, the greater the temperature difference. Therefore, the operating condition of the chiller stipulates that the temperature difference between the cold water supply and return water is 5 ° C, which in fact specifies the cold water flow of the unit. This control of cold water flow is shown to control the excessive force drop of cold water through the evaporator.
Under standard working conditions, the water supply and return pressure on the evaporator is reduced to 0.5kgf/cm2. The pressure drop adjustment method is to adjust the opening of the outlet valve of the cold pump and the opening of the water supply and return valve of the evaporator.
4, the pressure and temperature of the cooling water chiller operates under standard working conditions, and the return water temperature of the condenser is 30 ° C and the outlet temperature is 35 ° C. For chillers in operation, the environmental conditions, load and cooling capacity have become fixed values. At this time, the condensing heat load is undoubtedly fixed. The standard stipulates that the temperature difference between inlet and outlet is 5 ° C, and the flow rate of cooling water must also be a certain value. And the flow rate is inversely proportional to the temperature difference between incoming and outgoing water. Therefore, the chiller operates under standard conditions, as long as the temperature difference between the inlet and outlet of the cooling water is specified. This flow rate is usually controlled by the cooling water pressure drop in and out of the condenser.
Under standard working conditions, the condenser discharge water pressure drop is set to about 0.75kgf/cm2. The pressure drop setting method is also to adjust the opening of the cooling pump outlet valve and the condenser inlet and outlet water pipe valve.
In order to reduce the power consumption of the chiller, the condenser temperature should be reduced as much as possible. There are two desirable measures: one is to reduce the return water temperature of the condenser, and the other is to increase the cooling water.
For centrifugal chillers, too high or too low condensing pressure will cause surge. When the centrifugal chiller encounters this situation, it should be noted that the difference between the condensing pressure and the evaporation pressure is not too small, and the requirements for preventing surge should be met, otherwise surge will occur. In the autumn, when the temperature is lower, it is more advantageous to run a reciprocating chiller, because the condensing pressure is lower at this time, and the power consumption is greatly reduced.
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