System and method of temperature control for a transport refrigeration system
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Solution Overview
Problem
Existing transport refrigeration systems (TRS) lack precise temperature control, leading to temperature and pressure fluctuations, as they rely solely on thermal expansion devices to manage refrigerant flow and hot gas distribution.
Innovation Solution
The implementation of a TRS with liquid line and hot gas solenoid valves that adjust their duty cycles based on measured return air temperatures, allowing for precise control of refrigerant and hot gas flow through time-based controls, using high pulse count solenoid valves to ensure reliable operation and maintain stable temperatures and pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermal expansion devices are used to manage refrigerant flow, then the system structure is simple, but temperature and pressure control precision is poor
Solution Approach 1:
The patent applies dynamics by replacing static thermal expansion devices with dynamic solenoid valve systems that can adjust refrigerant flow in real-time based on temperature feedback. The solenoid valves can rapidly open and close (high pulse count operation) to dynamically control refrigerant distribution to evaporators, enabling precise temperature control while maintaining system adaptability to changing conditions.
Solution Approach 2:
The patent implements feedback control by using temperature sensors to monitor return air temperature and using this information to control solenoid valve operation. The system continuously measures temperature and adjusts solenoid valve duty cycles based on the difference between measured and desired temperatures, creating a closed-loop control system that achieves high precision temperature control.
2Measurement precision
If solenoid valves pulse frequently for precise control, then temperature control precision improves, but valve reliability decreases
Solution Approach 1:
The patent applies periodic action by using solenoid valves that operate in controlled pulse cycles rather than continuous operation. The valves can be pulsed at high frequencies when precision control is needed, but the duty cycle can be adjusted to allow rest periods. This periodic operation mode enables precise temperature control through frequent pulsing while maintaining valve reliability by avoiding continuous high-stress operation.
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 approach provides more accurate and stable temperature control within refrigerated transport units, maintaining temperatures with over five times the precision of systems relying solely on thermal expansion devices, ensuring consistent refrigeration across multiple zones.
Implementation Method 1
a refrigeration circuit having a compressor, a condenser, a thermal expansion device, an evaporator and a solenoid valve
Implementation Method 2
a thermal expansion device and an evaporator coil
Implementation Method 3
The evaporator coil(s) may be configured to exchange heat with indoor air of, for example, the transport unit to regulate a temperature inside the transport unit
Data Source
AI summary
A system and method for temperature control for a Transport Refrigeration System (TRS) is provided. Particularly, a method for temperature control of an internal space of a refrigerated transport unit is provided. The method includes determining a measured internal space temperature within the internal space of the refrigerated transport unit. The method also includes calculating, via a TRS controller, a temperature difference between the measured internal space temperature and a desired set point temperature. Also, the method includes adjusting, via the TRS controller, a duty cycle percentage of a liquid line solenoid valve and/or a hot gas solenoid valve based on the temperature difference to control an amount of refrigerant directed to the thermal expansion device and the evaporator and/or an amount of hot gas directed to the evaporator.