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Comparison Of Screw Chillers And Centrifugal Chillers

Aug 02, 2017

Comparison of screw chillers and centrifugal chillers


1.two models of the profile:

Screw machine: screw compressor in the two yin and yang of the intermeshing, in the case of rotation to complete the suction, compression and exhaust process. Its components are screw compressors, condensers, evaporators, thermal expansion valves and other control components, less than the centrifuge. It has the characteristics of compact structure, reliable operation balance, less wearing parts, high partial load efficiency and long service life.


Centrifugal machine is to rely on centrifugal compressor in the high-speed rotation of the impeller generated by the centrifugal force to produce power for refrigeration, and its components are mainly centrifugal compressor, evaporator, condenser, throttle, suction recovery device, lubrication system And electrical control cabinet and so on. It has a single machine cooling capacity of the large, but there is "surge" and other shortcomings.


2.the structural characteristics of the two models

Screw machine: a single screw compressor refrigeration is smaller than the centrifuge, generally from 30RT - 500RT, so now the large cooling of the screw dryer are used multi - head way, unified control by the microcomputer, adjust, and each compression The machine has a separate cooling system.


Centrifuge: a single centrifugal compressor cooling capacity is large, from 150-3000RT, so the general centrifugal refrigerator are only designed a centrifugal compressor can meet the needs of cooling.


3.two kinds of compressor rotation and transmission part of the structural characteristics:

Centrifuge: the motor through a pair of speed gears and then drive the impeller for high-speed rotation.


Screw machine: the motor directly with the main rotor and vice rotor for each other for low-speed rotation.


Comparison: It can be seen from the above, the screw compressor structure is more simple, and the centrifuge impeller speed than the screw rotor to be much higher, while high-pressure gas on the leaves, impeller has a greater impact pressure, so the failure rate Significantly higher than the screw machine. At the same time, centrifugal compressor due to the complexity of the compressor structure, maintenance and repair is very troublesome, and screw unit structure is simple, maintenance is very convenient.


4.the two models of capacity adjustment problem:

Centrifuge: In general, the centrifugal unit energy adjustment range of 40 to 100%, in less than 40% load operation, the centrifugal unit is more prone to "surge" phenomenon, "surge" serious, you can make the whole unit The core part - the impeller is damaged, so that the centrifugal compressor is scrapped. At present, many centrifuge manufacturers through the "qi" means the unit "surge" critical point to "20%" or "10%", and "qi" is the need to consume a lot of energy, so that the unit below 50% efficiency Lower.


Screw machine: screw machine is the use of hydraulic push valve switch control capacity, part of the load, no unbalanced impact phenomenon. For multi-head screw unit, the energy adjustment range is generally between 7.5 ~ 100%, and can be continuous energy regulation. Especially civil places and commercial places, such as hotels, shopping malls, conference centers, the air conditioning load changes with the seasons and changes in the larger changes in the requirements of the refrigeration unit has a wide range of energy adjustment.


5.two models of maintenance issues

Centrifuge: In general, the centrifuge is a single compressor in the form of maintenance, maintenance, the whole machine needs to shut down to stop the cooling operation. Complex structure, parts and more wearing parts, maintenance costs are higher.


Screw machine: screw machine for the multi-compressor form, and has a separate cooling system, so that maintenance, maintenance, the screw machine only a single compressor off, the other work as usual to meet the building load needs. Unit structure is simple, parts less wearing parts, maintenance costs are lower.


6.the impact of two models on the power grid

Comparison: the two models of large power consumption, but because of the same cooling capacity, the screw machine with multiple compressors in the form of step by step start, the required starting current is much smaller than the centrifuge, The impact on the grid.


7.two models of noise problems:

Comparison: centrifuge speed is high, generally 9000 ~ 40000 r / min, and the use of leaves, impeller suction, exhaust, so the noise value is higher than the screw machine, and sharp. Screw machine is by yin, yang rotor meshing rotation to complete the suction, exhaust, its speed is low, usually 2950 r / min, the noise value is generally about 75dB (A), and not sharp, and centrifugal units generally 80 DB (A) above.


8.two models running costs comparison case

Centrifuge and screw machine power consumption is large, but in the same cooling capacity, the screw part of the load when the energy efficiency is higher than the part of the centrifugal load energy efficiency.


With a total cooling capacity of 5632Kw (1600 tons), if the use of three units, each cooling capacity of about 650 tons of cold.


The following 650 cold tons of chillers, for example, comparative analysis of the two units of power consumption. According to the statistics, the total running time of the chiller is 100%, the running time is 2.3%, 75%, 50% and 25% respectively, and the running time is 41.5%, 46.1% and 10.1% respectively. The project is calculated according to the annual air-conditioning time of 4 months, the overall operating time of 4 × 30 × 10 = 1200 hours. Then the unit 100%, 75%, 50%, 25%. Running time were 27.6,498,553,121 hours.


Centrifuge unit

Manufacturers of the 1000-19XR7070555EKS unit, for example, the unit full load COP 5.58.

The COPs were 5.97, 574 and 3.87 respectively at 75%, 50% and 25% load respectively. (650 × 3.517 × 100% ÷ 5.58 = 410); 276kW (650 × 3.517 × 75% ÷ 5.97 = 276), and the energy consumption of the unit is 100k, 75%, 50% and 25% (650 x 3.517 x 50% ÷ 5.74 = 199); 148 Kw (650 x 3.517 x 25% ÷ 3.87 = 148).

Unit 4 months total power consumption of 410 × 27.6 + 276 × 498 + 199 × 553 + 148 × 121 = 276719 degrees


Screw unit

Manufacturers of RSW-1000-4 unit, for example, the unit full load COP 5.24.

Unit under the 75%, 50%, 25% load under the COP were 6.63,7.23,6.03. (650 × 3.517 × 100% ÷ 5.24 = 436); 259kW (650 × 3.517 × 75% ÷ 6.63 = 259), respectively, under the load of 100%, 75%, 50% and 25% ;

158 kW (650 x 3.517 x 50% ÷ 7.23 = 158); 95 kW (650 x 3.517 x 25% 6.03 = 95).

Unit 4 months total power consumption of 436 × 27.6 +259 × 498 + 158 × 553 +95 × 121 = 239884 degrees.


650 cold tons unit in the four months of operation, the screw unit total power consumption of 239884.6 degrees, centrifugal unit total power consumption of 276719 degrees. That is to say, the screw unit saves 36834.4 degrees than the centrifugal unit, which saves nearly 15% of the operating cost.

Note: ① 1 US cold tons = 3024 kcal / h (kcal / h) = 3.517 kw (KW)