Compressor Start Valve Control to Reduce Refrigerant-Oil Solubility
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Solution Overview
Problem
New environmentally friendly refrigerants used in transport refrigeration systems exhibit high solubility in oil at low ambient temperatures, leading to viscosity degradation and potential component failure due to low evaporation flooded start conditions.
Innovation Solution
A method and system that actively control a valve in the refrigerant line upstream of the compressor to lower the saturated suction temperature of the refrigerant below ambient temperature by a threshold temperature difference, thereby reducing solubility and improving oil viscosity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If new environmentally friendly refrigerants are used, then environmental compliance is improved, but oil viscosity degradation occurs due to high solubility at low ambient temperatures
Solution Approach 1:
The system changes the temperature parameter of the refrigerant by actively controlling the expansion valve to subcool the refrigerant below ambient temperature. This parameter change reduces refrigerant solubility in the oil, thereby preventing viscosity degradation and maintaining lubrication reliability during compressor startup.
Solution Approach 2:
The system performs preliminary subcooling of the refrigerant before it enters the compressor during startup conditions. By actively controlling the expansion valve to lower the refrigerant temperature below ambient temperature in advance, the system prevents solubility-related viscosity degradation before it occurs, ensuring reliable lubrication from the start.
2Reliability
If active valve control is implemented, then refrigerant solubility is reduced and oil viscosity is improved, but system complexity increases
Solution Approach 1:
The expansion valve serves multiple functions: it controls refrigerant flow to the evaporator for cooling purposes and simultaneously acts as a subcooling control device to manage refrigerant solubility during startup. This multi-functionality reduces the need for separate dedicated subcooling valves, thereby limiting the increase in system complexity.
Solution Approach 2:
The system uses feedback from temperature sensors and compressor startup detection to actively modulate the expansion valve position. This feedback control ensures the refrigerant is subcooled to the appropriate degree below ambient temperature, optimizing solubility management while avoiding excessive valve actuation that would unnecessarily complicate the control system.
3Reliability
If refrigerant temperature is lowered below ambient temperature, then solubility is reduced and lubrication is improved, but energy consumption increases
Solution Approach 1:
The active subcooling control via the expansion valve is applied periodically or transiently during compressor startup conditions rather than continuously during normal operation. This periodic action limits the additional energy consumption to only when necessary, maintaining lubrication reliability during critical startup phases without incurring continuous energy penalties during steady-state operation.
Solution Approach 2:
The system applies partial subcooling, lowering the refrigerant temperature below ambient temperature by a controlled margin rather than excessive cooling. This partial action is sufficient to reduce solubility and improve lubrication during startup while minimizing the energy penalty associated with over-subcooling, thereby balancing lubrication performance with energy efficiency.
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 solution effectively increases the viscosity of the refrigerant-oil mixture, enhancing compressor reliability and lubrication performance during start-up and initial operation, especially in low ambient temperature conditions.
Implementation Method 1
adjusting the valve, adjustment of the valve including actively controlling the valve to thereby adjust the pressure of the refrigerant to lower a saturated suction temperature of the refrigerant
Implementation Method 2
an evaporator for drawing heat out of the box by drawing or pushing return air across refrigerant-containing coils within the evaporator. This step vaporizes any remaining liquid refrigerant
Implementation Method 3
a condenser to cool the pressurized vapor from the compressor, thereby changing the state of the refrigerant from a gas to a liquid. Ambient air may be blown across the refrigerant coils in the condenser to effect the heat exchange
Data Source
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AI summary
A method of managing a compressor start operation, the method comprising controlling a valve 250, 275 disposed upstream of a compressor 210 to lower a saturated suction temperature of a refrigerant to be below an ambient temperature while starting the compressor 210.