Method and apparatus for staged startup of air-cooled low charged packaged ammonia refrigeration system
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Solution Overview
Problem
Air-cooled ammonia refrigeration systems struggle to start during low-ambient conditions due to insufficient pressure delta across the condenser coils, which prevents proper oil flow and requires significant refrigerant charge, making it challenging for low-charge systems to operate effectively.
Innovation Solution
The implementation of motorized valves on condenser coil inlets, a main compressor discharge valve, bypass pressure regulator, check valves, and fan speed control allows individual coil sequencing and pressure regulation, eliminating the need for a stand-alone oil pump and minimizing refrigerant charge during startup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the condenser surface area is reduced to allow pressure buildup during startup, then the system can maintain discharge pressure, but the condenser cannot effectively condense vapor under low-ambient conditions
Solution Approach 1:
The condenser is divided into multiple independently controllable coil sections with individual motorized valves at each inlet. During startup, only one coil section is activated at a time, allowing the system to build discharge pressure with a limited effective condensing surface area. As startup progresses, additional coil sections are sequentially activated once pressure requirements are met, enabling the full condenser surface area to be utilized for effective vapor condensation.
2Stress or pressure
If isolating valves are used on condenser coil outlets to force liquid backup, then discharge pressure can be maintained, but significant refrigerant charge must be stored elsewhere in the system
Solution Approach 1:
Instead of closing valves at the condenser coil outlets to trap liquid refrigerant (prior art approach), the invention inverts the isolation mechanism by placing motorized valves at the coil inlets. This allows liquid refrigerant to flow freely through the active coil section while preventing it from reaching inactive sections. The check valves at coil outlets ensure liquid backup only in the active coil, eliminating the need for large refrigerant charge storage elsewhere in the system.
3Productivity
If the compressor discharges superheated vapor into the condenser during low-ambient conditions, then the condenser coils immediately condense vapor, but the discharge pressure cannot increase
Solution Approach 1:
Before allowing full vapor flow into the condenser during startup, the system preliminarily activates only one coil section with a motorized valve at its inlet. This preliminary action limits the condensing surface area to match the compressor's discharge capacity at low ambient conditions, allowing discharge pressure to build to the required level. Once pressure is established, additional coil sections are sequentially activated to handle increased vapor flow.
4Ease of operation
If screw compressors require minimum pressure delta across the housing, then proper oil flow can be maintained, but the air-cooled condenser cannot allow the delta pressure to build at startup
Solution Approach 1:
The system dynamically adjusts the number of active condenser coil sections during startup based on real-time discharge pressure conditions. Initially, only one coil section is active to allow pressure delta to build to the minimum level required for proper oil flow in screw compressors. As startup progresses and pressure requirements are met, additional coil sections are dynamically activated to maintain oil flow while handling increased vapor load.
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
Enables stable system operation during start-up and reduces the refrigerant charge required, allowing for efficient operation with less than six pounds of ammonia per ton of refrigeration capacity, while maintaining discharge pressure and oil flow.
Implementation Method 1
The condenser coil outlet contains vertically-oriented inline check valves to prevent liquid backflow when a coil is isolated.
Implementation Method 2
The compressor discharge line contains a single motorized valve for regulating discharge pressure.
Implementation Method 3
As the compressor discharges superheated vapor into the condenser, the cold condenser coils immediately condense any vapor
Implementation Method 4
the cold condenser coils immediately condense any vapor
Implementation Method 5
As the compressor discharges superheated vapor into the condenser
Data Source
AI summary
An apparatus for staged startup of air-cooled low charged packaged ammonia refrigeration system includes motorized valves on condenser coil inlets, a main compressor discharge motorized valve, a bypass pressure regulator valve in the main compressor piping, and check valves on the condenser outlets. The condenser inlet motorized valves provide precise control of gas feed to the condensers, so pressure can build without collapsing oil pressure. The condenser outlet contains check valves to prevent liquid backflow during coil isolation. The compressor discharge line contains a motorized valve for regulating discharge pressure at start-up. The motorized valve in the compressor discharge piping includes a bypass with a pressure regulator for precise regulation at minimum discharge pressure. Once discharge pressure rises above the setpoint, the condenser inlet solenoid coils open one at a time. The discharge pressure regulating motorized valve simultaneously regulates the discharge pressure until the condenser maintains discharge pressure.