Capacity modulation of transport refrigeration system
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Solution Overview
Problem
Existing transport refrigeration systems face challenges in reducing capacity at low ambient conditions, leading to inefficient energy use and temperature fluctuations, as they either cycle the compressor on/off or add heat, which can dehydrate perishable cargo.
Innovation Solution
A refrigerant vapor compression system with a multi-stage compression device, heat rejection heat exchangers, and a bypass valve that allows refrigerant flow through a bypass line to bypass one or both compression stages and heat exchangers, reducing capacity without compromising temperature control or energy efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the compressor is cycled on/off to reduce capacity at low ambient conditions, then energy consumption is reduced, but temperature control stability deteriorates with large fluctuations
Solution Approach 1:
The compression device is divided into multiple compression stages (first compression stage, second compression stage) with intermediate heat rejection. This segmentation allows selective operation of compression stages to match varying cooling demands, enabling capacity modulation without complete compressor cycling, thus maintaining temperature stability while reducing energy consumption during part-load conditions.
Solution Approach 2:
The system dynamically adjusts capacity by controlling the bypass valve to redirect refrigerant flow between different compression stages and heat exchangers based on ambient conditions and cooling demand. This dynamic flow control enables continuous capacity modulation rather than binary on/off operation, maintaining stable temperature control while optimizing energy usage.
2Power
If heat is added through electrical resistance heaters to reduce cooling capacity, then capacity is reduced, but energy efficiency deteriorates and cargo dehydration occurs
Solution Approach 1:
The patent extracts and removes the need for electrical resistance heaters by implementing a refrigerant flow bypass system. Instead of adding heat through inefficient electrical heating, the system extracts excess cooling capacity by bypassing refrigerant flow through selected compression stages and heat exchangers, achieving capacity modulation with superior energy efficiency and without cargo dehydration risk.
Solution Approach 2:
The system converts the potential harm of excessive cooling capacity at low ambient conditions into a benefit by using the bypass valve to redirect refrigerant flow. This transforms the problem of over-cooling into an opportunity for efficient capacity modulation, where the bypassed refrigerant flow is redirected to maintain optimal cooling levels without energy waste or cargo damage.
3Use of energy by moving object
If a multi-stage compression system with bypass valves is implemented, then capacity modulation and energy efficiency improve, but device complexity increases
Solution Approach 1:
The bypass valve serves multiple functions: it controls refrigerant flow distribution between compression stages, modulates system capacity, prevents condensate entry into the compressor, and maintains stable operation across varying ambient conditions. This multi-functionality reduces the need for separate control mechanisms, justifying the added complexity through consolidated system performance.
Solution Approach 2:
The intermediate heat rejection heat exchanger is positioned between compression stages to preliminarily cool the refrigerant before it enters the second compression stage. This preliminary action prevents overheating and condensate formation, enabling the bypass valve to operate effectively across a wider range of conditions without risking compressor damage, thus managing complexity through proactive thermal management.
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
The system effectively modulates cooling capacity, maintaining stable temperature control and improving energy efficiency, while preventing condensate from entering the compressor, thus enhancing compressor reliability and cargo preservation.
Implementation Method 1
a first refrigerant heat rejection heat exchanger disposed intermediate the first compression stage and the second compression stage for passing the refrigerant passing from the first compression stage to the second compression stage; a second refrigerant heat rejection heat exchanger disposed downstream with respect to refrigerant flow of the second compression stage
Implementation Method 2
a bypass valve disposed in the bypass line, the bypass valve allowing or preventing refrigerant flow through the bypass line; wherein when the bypass valve allows refrigerant flow through the bypass line, at least one of the first compression stage and the second compression stage is bypassed and at least one of the first refrigerant heat rejection heat exchanger and the second refrigerant heat rejection heat exchanger is bypassed
Data Source
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AI summary
A refrigerant vapor compression system includes a compression device having at least a first compression stage (30a) and a second compression stage (30b) arranged in series refrigerant flow relationship; a first refrigerant heat rejection heat exchanger (80) disposed intermediate the first compression stage and the second compression stage for passing the refrigerant passing from the first compression stage to the second compression stage; a second refrigerant heat rejection heat exchanger (40) disposed downstream with respect to refrigerant flow of the second compression stage; a bypass line (90,130) positioned at least one of a discharge outlet port of the first compression stage and a discharge outlet port of the second compression stage; a bypass valve (92,132) disposed in the bypass line, at least one of the first compression stage and second compression stage bypassed and at least one of the first refrigerant heat rejection heat exchanger and the second refrigerant heat rejection heat exchanger bypassed.