Continuous Capacity Modulation
On many refrigeration systems the load will vary over a wide range, requiring the use of compressor capacity control. Traditional schemes of modulation include variable speed drives, unloaders, hot gas bypass or paralleling. Some of these solutions face various problems, as they are often complicated and difficult to design into existing equipment or often imply reliability concerns. Some require a high level of technical skills or an unaffordable first cost investment. Others do not provide the efficiency level or system stability originally promised. Now all these issues belong to the past with Copeland Scroll Digital™.
Based on the unique Copeland Compliant Scroll™ design, the digital modulation operates on a simple mechanism. Capacity control is achieved by separating the scroll sets axially over a small period of time. It is a simple mechanical solution allowing precise temperature control and system efficiency.
The modulation is achieved with a cycle time based on PWM (Pulse Width Modulation) control of a solenoid valve that operates a piston fitted rigidly to the upper scroll. This piston is actuated by gas pressure. The solenoid opens to allow the small modulation chamber to communicate with suction via the external tube.
Discharge pressure on the lower side of the piston forces it upwards, bringing with it the upper scroll – there is no compression. When the solenoid closes, pressure builds up in the modulation chamber. A small bleed hole speeds the pressure build up in the chamber. The upper scroll moves down to its normal contact position – compression resumes.
The compressor capacity is controlled by modulating the solenoid valve input over time as shown on the example below:
Cycle time: 20 sec Valve active/open: 12 sec and Valve inactive/ closed: 8 sec
Resulting capacity: 40%
Digital Scroll technology is a modulation solution that can easily and quickly be implemented into any existing system design as no other components are required.
Control Precision and Efficiency
Digital Scroll technology provides continuous, stepless modulation from 10–100% with no operating envelope restriction. As a result, system pressures and temperatures are tightly controlled. Tests showed a temperature variation of +/-0.5K in the display cases. More stable evaporating temperatures result in less dehumidification of the food, reduction of weight loss and preservation of food quality. Compressor cycling is reduced to a minimum, ensuring optimum system efficiency and longer life expectancy of the equipment. Low condensing capability down to 10°C also ensures the best seasonal efficiencies on the market.
The refrigerant flow back to a Digital Scroll compressor is identical to a standard scroll compressor, even at low capacity. The Digital Scroll compressor runs at full speed at all times, never slowing the oil flow to the compressor. Its reliability level is as high as in standard compressors. It does not cause motor overheating or resonance vibrations in the plant.
Features and Benefits
With Digital Scroll technology you can offer your customers (manufacturers, contractors, end-users):
- Simple, stepless, continuous modulation for precise temperature control
- Reduced energy consumption
- Highly flexible load matching from 10–100%
- An economical and reliable alternative to variable speed drive
- Longer lasting refrigeration equipment due to fewer compressor cycling
- With 10% to 100% digital modulation, the higher the number of evaporators in a refrigeration system, the more benefits you are able to offer to your customers.
Copeland Scroll™ Digital Model Overview