Control device, condensing unit, control method, and control program
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In refrigerating apparatuses with parallel compressors and solenoid and expansion valves, the middle pressure cannot be effectively controlled when the circulation amount of refrigerant is low, leading to increased pressure and reduced coefficient of performance (COP).
Innovation Solution
A control device and method that adjusts the solenoid valve and electronic expansion valve in parallel configuration to manage refrigerant flow, closing the solenoid valve when specific conditions are met to allow the expansion valve to control middle pressure, thereby maintaining optimal refrigerant circulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the solenoid valve with fixed opening degree is used in parallel with the expansion valve, then the circulation amount processing in a wide area is improved, but the middle pressure cannot be controlled when the circulation amount is low
Solution Approach 1:
The system dynamically switches between fixed opening degree mode (solenoid valve open) for high circulation amounts and variable opening degree mode (expansion valve controlled) for low circulation amounts. The control device determines the operating mode based on circulation amount detection, enabling the system to adapt its pressure control mechanism to match the current operational requirements.
Solution Approach 2:
The pressure control function is segmented into two distinct operational modes: one utilizing the solenoid valve for high circulation scenarios and another utilizing the expansion valve for low circulation scenarios. This segmentation allows each valve type to operate in its optimal performance range, with the control device managing the transition between modes.
2Productivity
If the expansion valve opening degree is reduced to control low circulation amount, then the circulation control is improved, but the middle pressure increases
Solution Approach 1:
The control device acts as an intermediary that coordinates between the solenoid valve and expansion valve operations. By detecting circulation amount and determining the appropriate operational mode, the control device prevents the middle pressure increase that would otherwise result from excessive expansion valve restriction, ensuring optimal pressure levels while maintaining circulation control.
3Device complexity
If the solenoid valve remains open during low circulation, then the system simplicity is maintained, but the COP decreases due to increased middle pressure
Solution Approach 1:
The control device implements feedback-based operation by continuously detecting the circulation amount and adjusting the solenoid valve state accordingly. When circulation amount falls below a predetermined threshold, the control device closes the solenoid valve to prevent middle pressure increase and COP degradation. This feedback mechanism maintains system simplicity while optimizing 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 suppresses middle pressure and improves COP by adjusting valve operations based on temperature and circulation conditions, enhancing system efficiency.
Implementation Method 1
a gas cooler that cools a refrigerant compressed by the compressors to a high pressure equal to or higher than a critical pressure during a normal operation
Implementation Method 2
a solenoid valve that has a fixed opening degree and an electronic expansion valve that has a variable opening degree, the solenoid valve and the electronic expansion valve being provided in parallel on an upstream side of the middle pressure receiver
Implementation Method 3
an electronic expansion valve that has a variable opening degree... the electronic expansion valve has a minimum opening degree
Data Source
Figure 1
Figure 2~4
Figure 5
AI summary
Provided are a control device, a condensing unit, a control method, and a control program with which it is possible to control the middle pressure of a refrigerant circuit. A control device (30) controls a refrigerant circuit which comprises: compressors (11, 12) that are provided in parallel; gas coolers (51, 52) that cool a refrigerant compressed by the compressors (11, 12) to a high pressure equal to or higher than the critical pressure during normal operation; a middle pressure receiver (9) for storing a middle pressure liquid refrigerant cooled by the gas coolers (51, 52); and a solenoid valve SVG and an electronic expansion valve EEVG provided in parallel on the upstream side of the middle pressure receiver (9) and on the downstream side of the gas coolers (51, 52). The control device performs control of changing the solenoid valve SVG from opening to closing upon determination of satisfaction of all conditions that: the high-pressure saturation temperature is equal to or lower than the critical temperature; the evaporation temperature set value is a value at which the inhalation density is equal to or lower than 50% with respect to the set maximum evaporation temperature; the middle pressure measurement value exceeds a target middle pressure; and the electronic expansion valve EEVG has the minimum opening degree.