Variable-Speed Transport Refrigeration for Changing Thermal Loads
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Solution Overview
Problem
Traditional refrigerated cargo trucks have fixed-speed refrigeration systems, limiting their ability to efficiently adjust cooling capacity based on varying cargo compartment conditions, leading to inefficiencies and increased fuel consumption.
Innovation Solution
A variable frequency drive unit connected to the vehicle engine, which delivers electrical power to the compressor and evaporator fan, allowing frequency adjustment based on sensed parameters like temperature differences and door positions to optimize cooling capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed-speed compressor and evaporator fan are used in a transport refrigeration unit, then the system has simpler control mechanisms, but the system cannot adapt to varying thermal loads and operating conditions, resulting in reduced energy efficiency and increased wear on mechanical components
Solution Approach 1:
The patent applies dynamics by transitioning from fixed-speed motors to variable-speed motors that can dynamically adjust their rotational speed based on real-time thermal load conditions. The controller receives feedback from temperature sensors and adjusts motor speed accordingly, enabling the system to adapt to varying cooling demands while maintaining optimal energy efficiency and reducing mechanical wear through controlled start-stop cycles.
2Loss of energy
If variable frequency power is applied to compressor and evaporator fan, then the system achieves better energy efficiency and component protection, but the control system becomes more complex with additional sensors and frequency regulation mechanisms
Solution Approach 1:
The patent implements feedback control by using temperature sensors to continuously monitor thermal conditions in the cargo compartment and on the evaporator. The controller processes this feedback information and adjusts the frequency of power supplied to the compressor and evaporator fan motors accordingly. This closed-loop control optimizes energy efficiency while preventing excessive wear on mechanical components.
Solution Approach 2:
The patent applies parameter changes by varying the frequency of electrical power supplied to the compressor and evaporator fan motors based on thermal load conditions. By changing the frequency parameter, the system can dynamically adjust motor speed and power consumption to match actual cooling requirements, thereby improving energy efficiency and reducing mechanical stress during start-up and operation.
3Reliability
If the evaporator fan runs at high speed continuously, then maximum cooling capacity is maintained, but excessive wear occurs on the fan motor and increased energy consumption
Solution Approach 1:
The patent applies dynamics to the evaporator fan by enabling variable-speed operation controlled by a controller that responds to thermal conditions. The fan operates at high speed only when maximum cooling capacity is required, and reduces speed or stops when cooling demands are lower. This dynamic control maintains reliable cooling performance while significantly reducing energy consumption and mechanical wear during periods of lower thermal load.
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
Enhances cooling efficiency, reduces set point recovery times, improves fuel efficiency, and decreases CO2 emissions by dynamically adjusting power delivery to match cooling demands.
Implementation Method 1
a compressor configured to compress a refrigerant
Implementation Method 2
an evaporator heat exchanger operatively coupled to the compressor
Implementation Method 3
an evaporator fan configured to provide return airflow from a return air intake and flow the return airflow over the evaporator heat exchanger
Data Source
Figure 1~3
Figure 2
Figure 4
AI summary
A transportation refrigeration unit for cooling a cargo compartment includes a compressor configured to compress a refrigerant, a compressor motor configured to drive the compressor, an evaporator heat exchanger operatively coupled to the compressor and an evaporator fan configured to provide return airflow from a return air intake and flow the return airflow over the evaporator heat exchanger. A drive unit is configured to deliver variable frequency electrical power between a minimum frequency and a maximum frequency to the compressor motor and the evaporator fan. A frequency of the electrical power is based on one or more sensed parameters of the transportation refrigeration unit.