The Copeland Scroll Digital operates in two stages - the "loaded state" and the “unloaded state”. Copeland Scroll Digital is equipped with an external solenoid valve. When the solenoid valve receives a 220 V signal, the upper scroll moves up about one millimeter. This movement makes a gap between the orbited scroll and the fixed scroll; in addition there is no axial seal between these two scrolls. The compressor cannot compress the refrigerant even though the motor is still running. The capacity output is 100% in the loaded stage and 0% in the unloaded stage. The average capacity is a time-averaged summation of the loaded state and the unloaded state. For example. in a 20-second cycle time, if the loaded state time is 10 seconds and the unloaded state time is 10 seconds, the compressor modulation is 50% ((10 seconds x 100% + 10 seconds x 0%)/ 20).
In the fixed speed compressor, there is an internal temperature protection mechanism, the thermal disc (TOD). This is a bimetallic device that opens when the scroll temperature exceeds 143°C . In The Copeland Scroll Digital, there is no internal TOD, as there is a space constraint. Instead of the TOD, there is a discharge thermostat that measures the hot gas temperature.
In the standard Copeland scroll, there is a discharge valve that is mounted near the compressor discharge pipe. This valve helps to ensure that the shutdown duration is minimized. In the Copeland Scroll Digital, there is no discharge valve. During tandem operation, to ensure that no hot gas bypasses into the Copeland Scroll Digital through the discharge port, an external check valve is used.
For a standard single Copeland Scroll Digital up to six HP, there is no need for an external check valve. However, in a tandem configuration, a check valve in the discharge line is recommended.
When the compressor operates in low capacity, the time of unloaded stage is longer. The power consumption is very low during the unloaded stage--only 10% of the full power used during theloaded stage. This low power consumption cannot create compressor heat, so it does not require fluid injection.
The Copeland Scroll Digital compressor runs with constant speed in the loaded and unloaded stages. Since the motor continues running, it does not need starting current when the stage changes from the unloaded state into the loaded state. The current fluctuation is so much lower that it does not influence other electrical equipment.
The starting current for the Copeland Scroll Digital is the same as a standard scroll. This is because the starting current is a function of the Locked Rotor Current, which remains the same for all Scroll Compressors. It is possible to start the Copeland Scroll Digital in an unloaded state which lowers the current consumption.
The unloaded power consumption is about 10% of full-load power. This low power consumption during the unloaded state provides high energy efficiency ratio (EER) at part-load operation.
The external solenoid in the Copeland Scroll Digital is a specially-designed long-life valve. It should never be replaced by a standard solenoid valve. This valve has a life of 40 million cycles – equivalent to 15 years of continuous operation. All of the components in the Copeland Scroll Digital have been qualified to handle continuous loading and unloading.
The cycle time is an integral part of the Copeland Scroll Digital operation. The cycle time consists of 220V and 0V signals to the external solenoid valve. The 220V signal to the solenoid valve activates the unloaded state and the 0V signal activates the loaded state. Time averaging of the loaded and unloaded state delivers the average capacity. The maximum cycle time recommended by Copeland is 30 seconds. Any cycle time longer than 30 seconds can affect motor cooling and adversely affect the life of the compressor. Copeland has determined through experimentation an optimal cycle time curve; at every capacity output there is an optimal cycle time. Please contact Emerson Climate Technologies Application Engineer to know more about the optimal cycle time.
There is a sound difference between the loaded and unloaded state. In terms of the average sound pressure, the loaded state has a higher sound pressure of two dbA compared with the unloaded state. The quality of the sound in both states is different as well. If sound is an issue, a sound jacket on the compressor is very effective. Alternately, the compressor can be mounted in a sound insulated compartment.
The Copeland Scroll Digital has been designed with the same rigor as the standard Copeland scroll. The robustness of the Copeland Scroll Digital is as good as a standard Copeland scroll. Since the Copeland Scroll Digital will make very few stops and starts during it lifetime, bearing wear will not be as severe as on fixed speed scrolls that start and stop more frequently.