Indoor Expansion Valve Control for Stable CO2 Refrigeration
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Solution Overview
Problem
In refrigeration systems using carbon dioxide for supercritical refrigeration cycles, the outlet refrigerant temperature of indoor heat exchangers becomes unstable due to changes in high-pressure refrigerant pressure, leading to frequent adjustments of indoor expansion valves and instability in refrigeration capability.
Innovation Solution
A refrigeration system with a controller that adjusts the opening degrees of control valves for indoor heat exchangers to maintain a deviation of outlet refrigerant temperatures from an average value, stabilizing the refrigeration capability even with pressure changes, and using deviations from an average target refrigerant temperature based on room air temperature to control the refrigerant flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the opening degree of the indoor expansion valve is frequently adjusted to track the outlet refrigerant temperature, then the outlet refrigerant temperature can follow the target temperature, but the valve opening degree becomes unstable and the refrigeration capability becomes unstable
Solution Approach 1:
The control method performs preliminary calculation of the required valve opening degree based on predicted outlet refrigerant temperature, rather than reacting to temperature deviations after they occur. This allows the valve to be positioned proactively, reducing frequent adjustments and improving stability.
Solution Approach 2:
The system implements feedback control by continuously monitoring the outlet refrigerant temperature and comparing it with the target temperature, then adjusting the valve opening degree based on the temperature difference and its rate of change to maintain stable refrigeration capability.
2Speed
If the outlet refrigerant temperature is used as a direct parameter for control, then the control response is direct, but the valve opening degree needs frequent adjustment due to pressure changes, leading to instability
Solution Approach 1:
The control method calculates the required valve opening degree in advance based on the relationship between outlet refrigerant temperature and valve opening degree, considering the current high-pressure refrigerant pressure. This preliminary calculation reduces the need for frequent adjustments while maintaining direct temperature control.
Solution Approach 2:
The system changes the control parameter from direct outlet temperature tracking to a calculated valve opening degree that accounts for pressure variations. This parameter transformation allows the valve to operate more stably while still achieving the desired temperature control.
3Temperature
If the opening degree of the indoor expansion valve is adjusted to reduce refrigerant circulation, then the outlet refrigerant temperature increases, but this requires frequent adjustments when pressure changes, increasing system complexity
Solution Approach 1:
The control method transforms the control approach by changing from direct temperature-based valve adjustment to a calculated opening degree based on the relationship between temperature, pressure, and valve position. This reduces control complexity while achieving temperature control.
Solution Approach 2:
The system uses feedback control to monitor outlet refrigerant temperature and adjust the valve opening degree accordingly, reducing the need for complex control logic while maintaining effective temperature control through continuous monitoring and adjustment.
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 reduces the need for frequent adjustments of control valves, stabilizes the outlet refrigerant temperature, and enhances the comfort and energy efficiency of air conditioning by matching refrigerant flow with required capabilities, thereby reducing unnecessary compressor input.
Implementation Method 1
a compressor (22), configured to compress the refrigerant to have a critical pressure or more
Implementation Method 2
a heat-source side heat exchanger (23)... and a plurality of application side heat exchangers (33a, 33b)... during heat dissipation
Data Source
AI summary
An air conditioner (1) includes a refrigerant circuit (10) configured to perform a supercritical refrigeration cycle and including: an outdoor circuit (21) including a compressor (22), an outdoor heat exchanger (23), and an outdoor expansion valve (24); and two indoor circuits (31a, 31b) including indoor heat exchangers (33a, 33b) and indoor expansion valves (34a, 34b). The air conditioner (1) further includes a controller (50) configured to control outlet refrigerant temperatures of the indoor heat exchangers (33a, 33b). The controller (50) includes a valve control part (50a) configured to adjust the opening degrees of the indoor expansion valves (34a, 34b) such that a deviation of the outlet refrigerant temperature of each of the indoor heat exchangers (33a, 33b) from an average value of the outlet refrigerant temperatures of all the indoor heat exchangers (33a, 33b) approaches a deviation of a target value which is a deviation, from the average value, of a target refrigerant temperature of the outlet refrigerant temperature of each of the indoor heat exchangers (33a, 33b).