Transportation refrigeration unit with multiple compressors
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Solution Overview
Problem
Refrigeration systems face inefficiencies due to the phase-out of high global warming potential refrigerants like R404A, leading to lower cooling capacity at frozen goods temperatures and increased compressor discharge temperatures, which are addressed by using smaller, unequally-sized compressors and DC power storage units to optimize refrigeration performance.
Innovation Solution
The system employs two compressors with different displacements, one powered by AC and the other by DC from a storage unit, with an economizer heat exchanger and liquid to suction line heat exchanger configuration to enhance cooling capacity and efficiency, allowing for flexible operation modes and reduced fuel consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If replacement refrigerants (R407F or R448A) are used instead of R404A, then environmental compliance is improved, but cooling capacity at frozen goods temperatures decreases by 10-15%
Solution Approach 1:
The single compressor is divided into two separate compressors with different displacements. The first compressor (larger displacement) handles frozen goods refrigeration at lower temperatures, while the second compressor (smaller displacement) handles high and medium temperature refrigeration. This segmentation allows each compressor to be optimized for its specific temperature range, maintaining cooling capacity with the new refrigerants while improving overall system efficiency.
2Quantity of substance
If a single larger compressor or higher compressor speeds are used to overcome cooling capacity shortfall, then cooling capacity is improved, but system efficiency decreases
Solution Approach 1:
The refrigeration load is segmented between two compressors operating at different capacities. The larger first compressor operates efficiently at lower speeds for frozen goods cooling, while the smaller second compressor operates efficiently at higher speeds for high and medium temperature cooling. This avoids the efficiency loss that would occur with a single large compressor operating at reduced capacity or a single compressor running at high speeds continuously.
Solution Approach 2:
The system dynamically selects which compressor(s) to operate based on the refrigeration temperature requirements. The control system can switch between different compressor configurations (first compressor only, second compressor only, or both together) to match the actual cooling load, optimizing energy efficiency across varying operating conditions.
3Quantity of substance
If a single larger compressor is used to compensate for lower refrigerant capacity, then cooling capacity is improved, but compressor discharge temperature increases
Solution Approach 1:
The compression process is segmented between two compressors. The first compressor with larger displacement is designed to handle the lower temperature frozen goods refrigeration where it can operate with appropriate discharge temperatures. The second compressor with smaller displacement handles high and medium temperature applications, preventing excessive discharge temperatures that would occur with a single large compressor running at high capacity.
4Temperature
If larger compressors are throttled to maintain high and medium refrigeration temperatures, then temperature control is improved, but compressor performance worsens
Solution Approach 1:
The system segments the temperature control function between two compressors. The second compressor (smaller displacement) is specifically assigned to handle high and medium temperature refrigeration, allowing it to operate at or near its optimal performance point without requiring throttling. The first compressor handles the frozen goods temperature range where larger displacement is appropriate. This eliminates the performance degradation that would result from throttling a large compressor for high and medium temperature applications.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration improves refrigeration unit efficiency by optimizing compressor performance, reducing fuel consumption, and maintaining high and medium temperature refrigeration while addressing the cooling capacity shortfall at frozen temperatures.
Implementation Method 1
an economizer heat exchanger and liquid to suction line heat exchanger configuration to enhance cooling capacity
Implementation Method 2
an economizer heat exchanger and liquid to suction line heat exchanger configuration to enhance cooling capacity
Data Source
Figure 1
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Figure 3
AI summary
A transportation refrigeration unit includes an evaporator 32 circulating a flow of refrigerant therethrough to cool a flow of supply air flowing over the evaporator. Two compressors 36,38 are in fluid communication with the evaporator to compress the flow of refrigerant and are configured and connected to operate in parallel with one another. A condenser 44 is in fluid communication with the evaporator and the two compressors. An economizer heat exchanger 56 and a suction line heat exchanger 68 are provided.