Receiver Vent and Dual Expansion Valve Control in Air Conditioners
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Solution Overview
Problem
Air conditioning apparatuses with refrigerant circuits featuring expansion valves on both sides of a receiver face challenges in suction wetting control, particularly when using R32 as refrigerant, as they struggle to maintain the desired dryness state, leading to potential liquid compression and increased compressor discharge temperature.
Innovation Solution
Incorporating a receiver gas vent pipe and valve to control gas refrigerant flow to the compressor, combined with upstream expansion valve subcooling control and downstream expansion valve suction wetting control, to stabilize refrigerant flow rates and maintain the refrigerant in a liquid state, ensuring high controllability and accurate suction wetting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If gas refrigerant is injected from the receiver into the compressor and expansion valves are provided on both upstream and downstream sides of the receiver, then the refrigeration cycle operation is improved, but the controllability of suction wetting control deteriorates
Solution Approach 1:
The patent divides the single expansion valve function into two separate expansion valves positioned on the upstream and downstream sides of the receiver. This segmentation allows independent control of refrigerant flow into and out of the receiver, enabling precise suction wetting control while maintaining efficient refrigeration cycle operation. The upstream expansion valve controls refrigerant injection into the receiver, while the downstream expansion valve controls refrigerant flow from the receiver to the evaporator.
Solution Approach 2:
The patent employs dynamic control of both expansion valves based on real-time operating conditions. The controller adjusts the opening degrees of the upstream and downstream expansion valves independently according to compressor suction pressure, temperature, and refrigerant flow conditions. This dynamic adjustment enables adaptive suction wetting control that maintains optimal performance across varying operating conditions while preventing liquid compression.
2Reliability
If the compressor suctions in refrigerant with high dryness, then liquid compression is prevented, but the discharge temperature increases excessively
Solution Approach 1:
The patent implements a feedback control system that continuously monitors compressor suction conditions and adjusts the expansion valve openings accordingly. Sensors detect suction pressure, temperature, and refrigerant state, and the controller uses this feedback to dynamically adjust the upstream and downstream expansion valves. This closed-loop control maintains refrigerant dryness within the optimal range, preventing both liquid compression and excessive discharge temperature increases.
Solution Approach 2:
The patent controls the degree of superheat (a key parameter) by adjusting expansion valve openings based on operating conditions. By dynamically changing the superheat parameter within an optimal range rather than maintaining a fixed value, the system prevents liquid compression when superheat is too low and prevents excessive discharge temperature when superheat is too high. This parameter-based control approach resolves the contradiction between reliability and temperature management.
3Temperature
If the compressor suctions in refrigerant with low dryness, then discharge temperature is reduced, but liquid compression occurs
Solution Approach 1:
The upstream expansion valve performs preliminary action by controlling the amount of refrigerant injected into the receiver before it reaches the compressor suction. By pre-regulating refrigerant flow and state in the receiver, the system ensures that the compressor receives refrigerant with appropriate dryness characteristics. This preliminary control prevents liquid compression at the compressor inlet while the downstream expansion valve subsequently controls the refrigerant flow to the evaporator.
Solution Approach 2:
The receiver acts as an intermediary between the upstream and downstream expansion valves, and between the compressor and evaporator. It provides a buffer zone where refrigerant can be stored, mixed, and conditioned before being delivered to the evaporator. The receiver's intermediate position allows the upstream expansion valve to control refrigerant injection and the downstream expansion valve to control outlet flow, enabling precise control of suction refrigerant state and preventing liquid compression while managing discharge temperature.
Data Source
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AI summary
In an air conditioning apparatus (1), gas vent control is performed so that gas refrigerant is led from a receiver (25) to the suction side of a compressor (21) via a receiver gas vent pipe (30) by opening a receiver gas vent valve (30a), upstream side expansion valve subcooling control is performed so that the opening of an upstream side expansion valve (24, 26) is changed such that the subcooling of refrigerant is set to target subcooling at the outlet of a radiator (23, 41), and downstream side expansion valve suction wetting control is performed so that the opening of a downstream side expansion valve (26, 24) is changed such that refrigerant is in a wetting state and the dryness is set to target dryness at the outlet of a evaporator (41, 23).