Refrigerant Circuit Oil Return Control for Stable Heating Capacity
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Solution Overview
Problem
In refrigerant circuit systems, the oil return operation often results in excessive heating capacity and increased pressure due to increased compressor frequency, which can lead to inefficient heating capacity matching the load during heating operations.
Innovation Solution
A control device that sets a higher enthalpy on the outlet side of the condenser and adjusts the expansion valve opening degree to maintain a target temperature higher than normal operation, thereby controlling the refrigerant circulation amount and preventing excessive heating capacity during oil return operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the frequency of the compressor is increased during the oil return operation, then the circulation amount of the refrigerant is increased and the oil return operation can be stably performed, but the heating capacity becomes excessive and the pressure increases
Solution Approach 1:
The invention changes the target temperature parameter on the outlet side of the condenser during oil return operation. Specifically, the target temperature is set to be higher than the normal operation target temperature (which is typically 3-5°C above the utilization-side medium temperature). By raising the target temperature, the enthalpy on the outlet side of the condenser increases, which reduces the heating capacity and prevents excessive pressure rise while still maintaining sufficient refrigerant circulation for stable oil return operation.
2Speed
If the frequency of the compressor is increased during the oil return operation, then the flow rate of the refrigerant in the pipe is maintained at a constant speed necessary for recovering the refrigerator oil, but the heating capacity becomes excessive
Solution Approach 1:
The invention applies parameter changes by adjusting the target temperature on the outlet side of the condenser. This temperature parameter is raised above the normal operation setting, which directly affects the enthalpy of the refrigerant at the condenser outlet. This enthalpy increase reduces the heating capacity while the compressor frequency increase maintains the refrigerant flow rate at the necessary speed for oil return.
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 allows for stable oil return operations while maintaining heating capacity corresponding to the load, preventing excessive heating and pressure increases, thus ensuring efficient refrigerant circuit performance.
Implementation Method 1
a condenser configured to condense the compressed refrigerant
Implementation Method 2
a first expansion valve configured to depressurize the condensed refrigerant
Implementation Method 3
an evaporator configured to evaporate the refrigerant depressurized in the second expansion valve
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A control device (100) capable of performing an oil return operation corresponding to a load is provided. The control device (100) which controls a refrigerant circuit system (1) controls an enthalpy difference (Δi, Δi') between an inlet side and an outlet side of a condenser (11) and a frequency of a compressor (10A, 10B) so that a difference between a heating capacity of a refrigerant circuit system during an oil return operation in a heating cycle (Q') and that of the refrigerant circuit system during a normal operation (Q) is within a predetermined range. The enthalpy difference (Δi, Δi') during the oil return operation is controlled to be smaller than that during the normal operation by setting a target temperature (T') on an outlet side of a condenser (11) to be higher than a temperature during the normal operation.