R32 Expansion Valve Timing for Stable Compressor Discharge Temperature
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Solution Overview
Problem
Air conditioners using R32 as a refrigerant face challenges in stabilizing the temperature of the refrigerant discharged from the compressor in the low load range, where the amount of refrigerant circulating is reduced, leading to unstable control of the expansion valve and resulting in temperature fluctuations known as 'hunching'.
Innovation Solution
The control period for the opening degree of the expansion valve is extended in the low load range, with a smaller magnitude of change in the opening degree, allowing the temperature to stabilize before the next control, and the sampling time is adjusted based on the opening degree range, ensuring the refrigerant temperature reaches the target temperature without exceeding or falling short of it.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the opening degree of the expansion valve is controlled every predetermined period, then the control frequency is maintained, but the temperature of the discharged refrigerant cannot be stably controlled in the low load range
Solution Approach 1:
The control period is made variable rather than fixed. When the opening degree of the expansion valve is smaller than a predetermined value (low load range), the control period is set to a longer value. When the opening degree is equal to or larger than the predetermined value (high load range), the control period is set to a shorter value. This dynamic adjustment of control timing allows the system to adapt to different operating conditions, ensuring stable temperature control across all load ranges.
2Quantity of substance
If R32 is used as refrigerant to reduce circulating amount, then the refrigerating capacity per unit volume increases, but the temperature stabilization time becomes longer
Solution Approach 1:
The system predicts when the discharged refrigerant temperature will stabilize based on the current opening degree of the expansion valve. By using this prediction, the control system can plan ahead and set the next control timing appropriately, ensuring that control actions are taken at optimal moments rather than reacting to temperature fluctuations after they occur.
Solution Approach 2:
The control period parameter is changed based on the operating condition (opening degree range). In the low load range where temperature stabilization takes longer, a longer control period is used. In the high load range where stabilization is faster, a shorter control period is used. This parameter adaptation allows the control system to match the natural temperature stabilization characteristics of R32 under different operating conditions.
3Device complexity
If the opening degree control is performed with fixed timing, then the control logic is simple, but temperature hunching occurs in the low load range
Solution Approach 1:
The control system transitions from fixed timing to dynamic timing based on the opening degree of the expansion valve. By making the control period adaptive to the operating condition, the system eliminates temperature hunching while maintaining relatively simple control logic through clear conditional branching.
Solution Approach 2:
The control system uses feedback from the opening degree of the expansion valve to determine the appropriate control period. This feedback mechanism allows the system to automatically adjust its behavior based on current operating conditions, preventing temperature hunching without requiring complex control algorithms.
Data Source
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AI summary
This air conditioner using a refrigerant of R32 controls the opening degree of an expansion valve so as to stably control the temperature of the refrigerant discharged from a compressor. The air conditioner (10) includes a refrigerant circuit (11) in which a compressor (12), an outdoor heat exchanger (14), an expansion valve (15), and an indoor heat exchanger (16) are connected together, and through which HFC32 circulates as the refrigerant, and a controller (30) which performs an opening degree control every predetermined sampling time t to change the opening degree of the expansion valve (15) to a predetermined extent such that a discharge pipe temperature Tp of the compressor (12) reaches a target discharge pipe temperature Tpa. The sampling time t is set to be longer in a range where the opening degree of the expansion valve (15) is less than a predetermined value than in a range where the opening degree is equal to or more than the predetermined value.