The refrigeration host is referred to as a chiller, which is an important part of the data center air-conditioning system. The refrigerant is generally water, referred to as a chiller. The cooling of the condenser is realized by heat exchange and cooling of normal temperature water, so it is also called a water-cooled unit. . The data center has a large demand for cooling capacity, and better energy efficiency can be obtained by choosing a centrifugal unit. The chiller in this article refers specifically to the centrifugal unit.
The centrifugal refrigeration compressor is a rotary speed type compressor. The suction pipe introduces the gas to be compressed into the impeller inlet. The gas rotates at a high speed with the impeller under the action of the impeller blades. The gas does work, the speed of the gas is increased, and then it is drawn out of the outlet of the impeller, and then introduced into the diffuser chamber; since the gas flows out of the impeller, it has a high flow velocity, in order to convert this part of the velocity into pressure energy, a A diffuser with a gradually enlarged flow section is installed to convert energy to increase the pressure of the gas; after the diffused gas is collected in the volute, it enters the condenser of the unit for condensation. The above process is the centrifuge The principle of compression, as shown in Figure 1; In addition, in order to condense and take away the cold, the air conditioning system includes a cooling water system and a chilled water system.
01
Centrifugal unit composition
The composition of the centrifugal unit is as follows: including centrifugal compressor, evaporator, condenser, throttling orifice, oil supply device, control cabinet, etc., as shown in Figure 2 and Figure 3. The compressor is mainly composed of a suction chamber, an impeller, a diffuser, a bend and a reflux device, and a volute.
Features of the centrifugal unit
The characteristics of the large centrifuge unit are as follows:
1. Large cooling capacity. Since the suction capacity of the centrifugal compressor cannot be too small, the single-unit cooling capacity of the centrifugal compressor is relatively large. Compact structure, light weight and small size, so it occupies a small area. Under the same cooling capacity, the weight of the centrifugal compressor is only 1/5 to 1/8 of that of the piston compressor, and the greater the cooling capacity, the more obvious it is.
2. Less wearing parts and high reliability. Centrifugal compressors have almost no wear during operation, so they are durable and have low maintenance and operating costs.
3. The compression part in the centrifugal compressor is a rotary motion, and the radial force is balanced, so the operation is stable, the vibration is small, and no special vibration reduction device is needed.
4. The cooling capacity can be adjusted economically. Centrifugal compressors can use methods such as guide vane adjustment to adjust the energy within a certain range.
5. It is easy to implement multi-stage compression and throttling, and can realize the operation and operation of the same refrigerator with multiple evaporation temperatures.
Common Faults of Chillers
The cold machine will encounter some problems during construction and commissioning, and failures will also occur during operation. The handling of these problems and faults is related to the safety of data center operation and maintenance. The following are some cases that occurred during the construction and operation of cold machines. Relevant processing methods and experiences are for reference only.
01
No load debugging
【Problem phenomenon】
A data center needs to debug and test run the chiller, but the installation of the terminal air-conditioning equipment has not been completed, and the site also lacks the necessary dummy load, so the commissioning work cannot be carried out.
【problem analysis】
After the installation of the centrifuge unit in the data center is completed, the terminal equipment in the computer room is not installed, the freezing water channel at the terminal is blocked, and the chiller cannot be debugged. The load is too small to reach the lower limit load of the chiller, and the debugging work cannot be carried out. On the other hand, because the cold machine has not been debugged, the server equipment in the main computer room cannot be powered on and run, forming an endless loop with each other; in addition, during the debugging process, the required dummy load power is huge, and the operation process will consume a lot of power; the above factors lead to cold machine debugging. become a problem.
【problem solved】
Use the no-load debugging method for debugging. This process is to make full use of the heat exchange capacity of the plate exchange, exchange the cold generated by the evaporator of the refrigerator to the condenser side of the refrigerator through the plate exchange, and exchange the heat released by the condenser of the refrigerator back to the evaporator side through the plate exchange , so as to achieve a complete match between the cooling capacity of the refrigerator and the heat load, and the cooling tower only takes away the shaft power of the compressor. Using this method, it is easy to achieve the comprehensive performance test under different loads. The water circuit circulation of the cold plate replacement and debugging is shown in Figure 4.
The system debugging steps are basically as follows:
1. Open the bypass valve in the sub-collector, and ensure that the waterway is unblocked to form a circulation when the terminal air conditioner is not installed;
2. Fully open the chiller on the chilled water side and the plate exchange valve to ensure that the water passage of the chiller and plate exchange is smooth, and the cold water drawn by the chiller and the heat returned by the plate exchange can be mixed smoothly; normally open the chilled water pump and manually adjust the frequency to 45Hz or more , and ensure that the water circulation is normal;
3. Fully open the cooling water valve of the chiller, partially open the valve on the cooling water side of the panel replacement, and turn on the cooling water pump to ensure normal water circulation. Adjust the pump frequency to 41-45Hz; do not turn on the cooling tower fan first;
4. Under normal conditions of chilled water and cooling water, turn on the chiller and conduct stand-alone trial operation;
5. The cooling water temperature of the chiller starts to rise, and the chilled water starts to cool down;
6. Adjust the heat transfer capacity of the plate exchange according to the opening of the cooling water valve of the plate exchange, and adjust the opening of the valve between 1/4 and fully open;
7. Partially turn on the fan of the cooling tower according to the temperature of the cooling water, whichever can take away the shaft power of the compressor.
【Experience】
In order to reduce energy efficiency and consider natural cooling, data centers are generally designed with cooling tower + plate replacement cooling technology. During commissioning, the heat exchange capacity of the plate exchange can be used to obtain enough heat from the condenser of the chiller as the heat load for chiller commissioning, that is, the cold generated by the chiller is taken away by the plate exchange.
The principle of no-load debugging is to make full use of the heat exchange capacity of the plate exchange, exchange the cold generated by the evaporator of the refrigerator to the condenser side of the refrigerator through the plate exchange, and exchange the heat released by the condenser of the refrigerator back to the evaporator through the plate exchange Side, so as to achieve the matching of cooling capacity and heat load of the refrigerator, this method is simple to operate and easy to implement.
Post time: Feb-15-2023
