Introduction of large-scale low-temperature logistics cold storage parallel compressor system technology

Introduction of large-scale low-temperature logistics cold storage parallel compressor system technology

In recent years, with the international logistics giants and retail giants investing heavily in the Chinese market, as well as the transformation of domestic civilian cold storage facilities and the rise of domestic retailers, China's low-temperature logistics and retail industries are experiencing traditional refrigeration equipment and systems. The process of transitioning to advanced refrigeration systems and equipment abroad. The following describes the technical application of the cold storage parallel compressor system.

In the entire cold chain, large cold storage, low temperature logistics centers and supermarket refrigeration systems consume almost half of the cold chain system; for low temperature logistics centers and supermarkets themselves, refrigeration systems account for a large proportion of their operating costs. For example, supermarket refrigeration systems account for about 40% of the total investment in supermarket equipment, and consume an average of nearly 50% of total electricity per year. Therefore, the improvement of large-scale cold storage, low-temperature logistics center and supermarket refrigeration system has a profound impact on the improvement of Chinese people's quality of life, the healthy and sustainable development of China's social economy and the building of a harmonious society. Introduction of large-scale low-temperature logistics cold storage parallel compressor system technology

This new trend poses a very pressing and challenging topic for refrigeration technology: how to provide efficient, energy-efficient, stable, and low-cost refrigeration systems for China's rapid development of large commercial refrigeration facilities.

I. Introduction to large direct evaporative refrigeration system

Direct evaporative cooling is considered to be a way to save energy in large refrigeration applications due to the elimination of the heat transfer temperature difference with the brine. In general, large direct evaporative refrigeration systems have the following characteristics:

1. The cooling capacity is relatively large, and it is usually necessary to use 5 to 50 refrigeration compressors of about 20 horsepower.

2. Running all year round, the load peaks and valleys are large, and part of the load is obvious.

3. The frozen and refrigerated objects are perishable and spoiled fresh foods, and the temperature and humidity control requirements are strict.

4. The evaporator needs to be defrosted, and the load on the system after the defrost cycle is large.

In the process of large-scale development of commercial refrigeration systems in China, stand-alone systems have gradually failed to meet the needs of large-scale refrigeration applications, mainly in:

1. The number of units is large, the cost is high, and the land occupation is too large, affecting the aesthetic and commercial planning.

2. The peaking ability is weak. Usually, the compressor is configured according to the large load of zui. Under partial load, the compressor is inefficient due to energy regulation (hot gas bypass, etc.) under partial load conditions. In order to prevent frequent starting under partial load conditions, the delay device is often used, but this often causes the compressor to operate under severe working conditions, and the efficiency is degraded. If the delay device is not installed, the compressor will start and stop frequently to reduce the compressor. life.

3. It is difficult to automatically control the temperature and humidity. Generally, the pressure controller is used, and the suction pressure fluctuates greatly.

4. In order to pull the temperature down quickly after the evaporator is defrosted, the compressor horsepower is usually further amplified, which usually further aggravates the situation of the "large horse-drawn carriage".

Second, parallel compression system for large commercial refrigeration

In large commercial refrigeration systems, traditional single-machine systems are often combined into a large central refrigeration station and a parallel compressor system (commonly known as Rack in foreign industries). Multiple compressors are connected in parallel on a common rack and shared. Components such as suction and exhaust headers, condensers, and accumulators provide refrigerant to the respective evaporation ends of the entire refrigeration system.

The parallel compressor unit better matches the dynamic cooling load of the refrigeration system. By adjusting the opening and closing of the compressor in the whole system, the situation of "large horse-drawn carriage" is avoided, for example, when the demand for cooling capacity is small in winter, the compressor is opened less, and when the demand for cooling capacity is large in summer, the compressor is opened more. The suction pressure of the compressor unit is kept constant, which greatly improves the efficiency of the system. Contrast experiments between single and parallel units have been performed on the same system, and the parallel unit system can save 18%. Introduction of large-scale low-temperature logistics cold storage parallel compressor system technology

All control of the compressor, condenser and evaporator can be concentrated in the system's electrical control box, and the computer controller can be used to optimize the system's efficiency, which can be basically completely unmanned and remotely operated. Since the system has a large margin (a part of the evaporator is defrosted while another part of the evaporator is cooling), the idle compressor after defrosting immediately participates in the cooling, and the temperature of the cold storage or the freezer can be lowered to the specified requirement within 5 minutes. The use of a parallel compressor unit can greatly reduce equipment costs, reduce installation engineering, shorten construction time, and reduce equipment room area. Therefore, for the end user, after adopting this technology, the comprehensive initial investment can be reduced by about 20%.

In developed regions such as the United States and Europe, parallel compression technology has become the main product in the commercial refrigeration market. At present, China's large-scale cold storage, low-temperature logistics distribution center and super shopping center are developing rapidly. The parallel compression system is becoming the mainstream of the market with its unparalleled advantages. In response to this phenomenon, we have conducted an in-depth discussion of this technology, both in theory and in practice to prove its advanced nature. However, many of its energy-saving advantages have not yet been fully explored, and its more advantages will gradually be recognized and applied in our future work.