VRV oil return control method and system
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Solution Overview
Problem
Multi-split air conditioners face issues with oil accumulation in shut-off indoor units during heating mode, leading to a lack of oil in the compressor and damage, as the small opening degrees of expansion valves prevent oil return, and frequent oil return operations in cooling mode disrupt heating effectiveness.
Innovation Solution
An oil return control method that calculates an average exhaust pressure within an oil return period to determine whether to maintain heating or switch to cooling mode, adjusting compressor frequency and expansion valve openings to ensure oil return without affecting heating performance, by using a set threshold and predetermined limits to manage oil return processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the system switches to cooling mode to enable oil return, then oil return performance is improved, but heating effect deteriorates due to sharp room temperature drop
Solution Approach 1:
The patent changes the operating parameters by adjusting expansion valve opening degrees and compressor frequency to enable oil return while maintaining heating mode, rather than switching to cooling mode. This resolves the contradiction by finding alternative parameter adjustments that achieve oil return without sacrificing heating performance.
Solution Approach 2:
The system dynamically adjusts the opening degrees of expansion valves and compressor frequency based on real-time operating conditions to optimize oil return while maintaining heating effect. This dynamic adjustment allows the system to achieve oil return performance without switching modes, thereby preserving room temperature stability.
2Temperature
If expansion valve opening degree is kept small to optimize heating effect, then heating performance is improved, but oil return is prevented causing oil accumulation
Solution Approach 1:
The patent dynamically adjusts the expansion valve opening degree based on operating conditions such as compressor frequency and system state. During oil return periods, the opening degree is increased to facilitate oil return, then restored to optimize heating performance, resolving the contradiction between heating effect and oil return.
Solution Approach 2:
The system implements periodic oil return operations where expansion valve opening degrees are temporarily adjusted to enable oil return, then restored to optimize heating. This periodic action allows the system to alternately prioritize oil return and heating performance, preventing oil accumulation while maintaining overall heating effectiveness.
3Reliability
If compressor frequency is increased to improve oil return, then oil return performance is improved, but energy consumption increases
Solution Approach 1:
The patent implements periodic oil return operations where compressor frequency is temporarily increased to facilitate oil return, then restored to normal operating levels. This periodic high-frequency operation achieves necessary oil return while minimizing overall energy consumption compared to continuous high-frequency operation.
Solution Approach 2:
The system applies partial excessive action by temporarily increasing compressor frequency beyond normal operating levels specifically during oil return periods. This targeted excessive action achieves oil return performance without maintaining continuously high energy consumption, resolving the contradiction between oil return and energy efficiency.
Data Source
AI summary
An oil return control method for a multi-split air conditioner and a system accomplishing the same includes: calculating an average exhaust pressure within an oil return period Pd_AVG; determining whether the average exhaust pressure Pd_AVG≥the set threshold Pdthreshold; if Pd_AVG≥Pdthreshold, maintaining the multi-split air conditioner working in heating mode to ensure an acceptable oil return performance without affecting the air conditioning effect of indoor unit in heating mode; if Pd_AVG<Pdthreshold, switching the multi-split air conditioner to cooling mode, stopping a fan within those power-on indoor units and entering into a cooling oil return process and switching the multi-split air conditioner back to heating mode until the cooling oil return process ends.