Vapor quality
Reducing Charge is Not a Compromise – It’s a Design Choice
Written by: Michael Elstrøm
A cold storage facility in northern Germany faced a common problem: How do you maintain stable operation when the system rarely runs at full load?
The system operated across three temperature levels:
- -42°C for blast freezing
- -32°C for cold storage
- -10°C for loading docks
With frequent partial load conditions, the risk is clear:
Flooded evaporators. Wet suction lines. Reduced performance.
The original solution was a traditional pumped overfeed system with an ammonia charge of 5 tonnes. That solution works. But it is not optimal.
A Different Approach
Instead of accepting the limitations, the operator chose a different path: Direct control of vapor quality inside the evaporator. “The design was chosen as a replica of existing, well performing systems.”
With Vapor Quality Sensors, the system measures what actually matters: what is happening inside the pipe in real time. This enables precise control, compressor protection and eliminates the need for superheat control.
Reducing Refrigerant Charge
By moving from a pumped overfeed system to a DX system with sensor-based control:
- Ammonia charge reduced from 5 tonnes to 2.2 tonnes
- System complexity reduced
- Operational stability improved
This is not a marginal gain. It is a fundamental change in system design.
Energy Performance
After two years of operation:
- 36 kWh/m³/year vs 47 kWh/m³/year
This corresponds to a 24% reduction in energy consumption. These results were achieved under real operating conditions across all temperature levels (-42°C / -32°C / -10°C).
Installation Matters
Accurate measurement depends on correct installation. Incorrect placement introduces delays that affect control.
To ensure reliable operation:
- Avoid weld areas
- Verify installation
- Ensure calibration
Control is only as good as the data you rely on.
Conclusion
You can run a traditional system, or you can control the process.
The result is lower charge, lower energy consumption and a more stable operation. Not by adding complexity, but by measuring what actually matters.
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