Air Conditioning Free-Cooling Control to Prevent Pump Cavitation
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Solution Overview
Problem
Air conditioning systems typically operate in cooling mode even when outside ambient temperatures are low, resulting in low efficiency, whereas switching to free-cooling mode using ambient air for cooling is more efficient, but poses risks of pump cavitation and reliability issues during mode transitions.
Innovation Solution
An air conditioning system with a controller that initiates a refrigerant recovery sequence to ensure the pump operates reliably in free-cooling mode by recovering refrigerant from unused portions of the circuit, using sensors to manage pressure and prevent cavitation, and switching between cooling and free-cooling modes efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the air conditioning system operates in cooling mode using the compressor, then the system can provide reliable cooling, but energy efficiency deteriorates when outside ambient temperature is low
Solution Approach 1:
The system dynamically switches between cooling mode and free-cooling mode based on outside ambient temperature conditions. When the temperature is low, the system transitions to free-cooling mode using the pump and ventilated heat exchangers, thereby improving energy efficiency while maintaining cooling capability through adaptive operation
2Use of energy by moving object
If the system switches to free-cooling mode to improve energy efficiency, then energy consumption is reduced, but pump reliability deteriorates due to cavitation risks
Solution Approach 1:
Before switching to free-cooling mode, the system executes a refrigerant recovery sequence that actively pumps refrigerant from the evaporator and suction line into the condenser. This preliminary action ensures that liquid refrigerant is available at the pump inlet, preventing cavitation and protecting pump reliability while enabling energy-efficient free-cooling operation
Solution Approach 2:
The refrigerant recovery sequence acts as a preliminary countermeasure against the harmful effect of cavitation. By recovering refrigerant before mode switching, the system prevents the vacuum condition that would cause cavitation, thereby protecting the pump from damage while allowing free-cooling mode operation
3Use of energy by moving object
If the system switches from cooling mode to free-cooling mode, then energy efficiency is improved, but system stability deteriorates due to refrigerant distribution issues
Solution Approach 1:
The refrigerant recovery sequence is executed as a preliminary step before mode switching, actively redistributing refrigerant to ensure proper liquid refrigerant availability in the condenser. This preliminary refrigerant management action maintains system stability during the transition to free-cooling mode while enabling energy efficiency improvements
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 system improves energy efficiency by avoiding compressor usage in low ambient temperatures, enhances pump reliability by ensuring liquid refrigerant is available, and allows seamless transitions between operating modes, reducing the risk of pump damage from cavitation.
Implementation Method 1
a refrigeration circuit having a compressor and a pump; a recover-refrigerant sequence resident on the controller, the recover-refrigerant sequence being configured to pump the refrigerant
Implementation Method 2
The compressor compresses and circulates a refrigerant to chill or condition a working fluid
Implementation Method 3
In the free-cooling mode, one or more ventilated heat exchangers and pumps are activated so that the refrigerant is circulated by the pumps and is cooled by the outside ambient air
Data Source
AI summary
An air conditioning system having a cooling mode and a free-cooling mode. The system having a refrigeration circuit having a compressor and a pump; a suction pressure sensor for measuring a suction pressure of the compressor; a discharge pressure sensor for measuring a discharge pressure of the compressor; a controller for selectively operating in the cooling mode by circulating and compressing a refrigerant through the refrigeration circuit via the compressor or operating in the free-cooling mode by circulating the refrigerant through the refrigeration circuit via the pump; and a recover-refrigerant sequence resident on the controller, the recover-refrigerant sequence being configured to pump the refrigerant in a portion of the refrigeration circuit not used in the free-cooling mode to remaining portions of the refrigeration circuit used in the free-cooling mode when the controller switches from the cooling mode to the free-cooling mode.