Transport refrigeration system and method of operation
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Solution Overview
Problem
Transport refrigeration systems face inefficiencies due to varying ambient conditions and product loads, requiring high refrigerant mass flow for rapid cooling and then low flow for maintaining steady temperatures, leading to suboptimal compressor operation and energy usage.
Innovation Solution
A refrigeration system with an economizer circuit and a variable speed compressor drive, allowing for selective switching between fixed and variable speed modes to match cooling capacity with demand, using a refrigerant flow control valve and a controller to manage the system's operation across different modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the refrigeration system operates at high refrigerant mass flow during pull down mode, then rapid cooling capacity is improved, but energy efficiency deteriorates during steady-state operation
Solution Approach 1:
The compressor speed is made variable rather than fixed, allowing the system to dynamically adjust refrigerant mass flow based on cooling demand. During pull-down mode, high speed provides maximum cooling capacity, while during steady-state operation, reduced speed maintains temperature with lower energy consumption. This resolves the contradiction by making the system adaptable to different operational phases.
Solution Approach 2:
The system changes the operating parameters of the compressor (speed, refrigerant mass flow rate) based on the thermal load conditions. By modulating these parameters between high (during pull-down) and low (during steady-state), the system achieves both rapid cooling when needed and energy efficiency during maintenance operation.
2Temperature
If the refrigeration unit is designed with capacity for deep frozen products, then low box temperature capability is improved, but cooling capacity mismatch occurs for fresh produce applications
Solution Approach 1:
The variable speed compressor enables the refrigeration unit to dynamically adjust its cooling capacity to match different product requirements. For deep frozen products, the compressor operates at high speed to achieve and maintain low temperatures. For fresh produce, it operates at low speed to maintain higher temperatures, thus adapting to different applications with a single unit design.
Solution Approach 2:
The refrigeration system is designed to serve multiple product types and temperature requirements through variable speed control. The same hardware configuration can handle both deep frozen goods (requiring -18°C or lower) and fresh produce (requiring 2-10°C) by adjusting compressor speed, making the system universally applicable to different cargo types.
3Use of energy by moving object
If variable speed compressor drive is added, then energy efficiency is improved, but system complexity increases
Solution Approach 1:
The variable speed compressor system incorporates feedback control where the controller monitors cargo space temperature and adjusts compressor speed accordingly. This feedback mechanism automates the speed adjustment process, reducing the need for complex manual control systems while maintaining energy efficiency through responsive temperature-based control.
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 solution enables efficient operation across a wide range of cooling capacities, optimizing energy use by matching cooling demand, reducing compressor load, and maintaining precise temperature control in transport refrigeration units.
Implementation Method 1
an economizer heat exchanger through which a portion of the high pressure refrigerant is cooled by a portion of the low pressure refrigerant
Implementation Method 2
a first expansion device disposed downstream with respect to refrigerant flow of the refrigerant heat rejection heat exchanger and upstream with respect to refrigerant flow of the refrigerant heat absorption heat exchanger
Implementation Method 3
a refrigerant heat absorbing heat exchanger, also referred to herein as an evaporator, through which expanded refrigerant having traversed the expansion device passes in heat exchange relationship with air to be cooled
Data Source
Figure 1
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AI summary
A refrigeration system for a transport refrigeration unit and a method of operating the refrigeration system for cooling a temperature controlled cargo space are disclosed. The refrigeration system includes a primary refrigerant circuit including a refrigerant compression device, a motor for driving the compression device; a variable speed drive for varying the speed of operation of the compression device; and a controller operatively associated with the variable speed drive and the compression device. The controller controls the cooling capacity of the refrigeration system by selectively controlling the speed of said compression device in a first continuous run mode of operation and by selectively powering on and powering off said compression device in a first cycling mode of operation.