Danfoss NMD,NMS Variable Speed Compressor Controller Instruction Manual

Danfoss NMD, NMS Variable Speed Compressor Controller

Compressor Overview

Why Variable speed?

• Variable Speed offers the lowest energy consumption for applications by electronically self-adjusting the compressor’s speed to meet the cooling needs of the appliance, while improving the Coefficient of Performance (COP) by up to 40%.
• Commercial refrigeration manufacturers are focusing their efforts on producing more efficient applications to satisfy the demand for reduced operating costs of refrigeration equipment installed in supermarkets, retail premises, and restaurants, where energy savings have become a major concern.
• The accurate design of the application and the proper selection of components—such as efficient compressors, fan motors, increased insulation thickness of cabinet walls, larger condensers, and low-consumption lighting—are key to reducing the total energy consumption of the application.
• The compressor is one of the components with the highest impact in terms of energy consumption in an appliance.
• Variable Speed Compressors are the solution for obtaining maximum energy reduction, primarily because full compressor capacity is not always needed. This technology dynamically adapts the compressor’s cooling capacity to the appliance’s needs by adopting an electronically controlled running speed, optimizing the system’s performance.

The benefits obtained by using Variable Speed Compressors include:

• The ability to cover several standard compressor models of different cabinet volumes with just one compressor model.
• Reduction in compressor power consumption by up to 45% to 50% compared to standard compressors. This energy saving can be over 40% when considering the total appliance power consumption (attributable solely to the compressor).
• Reduction in pull-down time by operating at a higher speed when needed.
• Reduction in the number of start-ups/stops of the compressor.
• Modification of speed to achieve the longest possible duty cycle.
• Lower noise levels.
• Longer expected compressor life due to the compressor typically running at a lower speed than standard compressors.
• Drop-in electronic driver system for automatically self-adapting the compressor speed to the current thermal load.
• Compatibility with electromechanical and electronic thermostats.

Compressor dimensional drawings

Connectors

1. Suction
2. Service
3. Discharge

Specification

Compressor performances

Cooling Capacity [W] ASHRAE

Operating envelope

R290 LMBP

Electronic Driver

The controller drives the compressor at various specific speeds to better match the cooling needs of the refrigeration appliance. There are different inverter types, depending on the power supply type and control signal, as shown in the table.

General rules and wiring connections
The NVK and NVS series must always be powered through the dedicated electronic controller, supplied with the compressor as a separate device.

• Never connect the compressor’s hermetic pins directly to an AC or DC source.
• Do not attempt to fit an electronic driver different from the one supplied with the compressor, as the compressor will not operate and irreversible damage may occur.
• Do not remove the controller cover while powered on.

Terminal layout

• CN1: AC input
• CN2: Drop-in input
• CN3: Compressor
• CN4: Frequency input

Wiring diagram

External frequency steering input

Drop-in mode

Operating modes – speed control

Drop-in mode with thermostat

• Under this mode of operation, the compressor speed is controlled according to the appliance’s requirements. The optimal speed is evaluated based on the speed of the previous cycle and the time the compressor has been running or stopped.

  

• The advantages of Drop-in Control mode include:
  • Reduction in compressor power consumption compared to standard compressors.
  • Reduction in pull-down time by operating at a higher speed when needed.
  • Reduction in the number of start-ups/stops of the compressor.
  • Lower Sound Power Level due to the system typically running at a lower speed.
• The N206xx-Cxx series inverter is controlled by connecting terminal CN2 to the thermostat. The speed is determined by the controller’s rules (related to the operating rate and run time).
  Note: To ensure the signal is effectively identified, the signal input CN2 should be in phase with L, and the voltage between CN2 and N should be greater than 98VAC. When the input power of the inverter is lower than 10VAC for more than 3 minutes, the inverter is considered to be powered off.

Drop-In Mode Operation

The following describes the detailed operation in drop-in mode:

• Pull-Down Mode:
  1. The compressor initiates operation at 3900 RPM and maintains this speed for 15 minutes.
  2. Following this initial period, the compressor speed increases to 4200 RPM for an additional 15 minutes.
  3. Subsequently, the compressor speed increases to its maximum value and remains there until the thermostat opens. There is no time limit (set within the controller) for operation at maximum speed; the compressor continues at this speed until the thermostat reacts.
• First Cycle:
  After the Pull-Down phase, the first stabilized cycle will operate at 3900 RPM.
• Stabilized Conditions:
  During the stabilized cycle, the compressor speed is automatically adjusted based on the runtime of the previous cycle. The controller calculates the new speed using the following method:

  

• Speed Adjustment Logic:
  • If the Operating Rate is higher than 85%, the speed in the next cycle will be reduced by 300RPM.
  • If the Operating Rate is lower than 85%, the speed in the next cycle will be increased by 300RPM.

Examples:

• Example 1
  • If Tr = 10 minutes and Ts = 5 minutes, Operating Rate = 10 / (10 + 5) = 0.66 (66%).
  • In this case, the compressor speed will be increased in the next cycle to achieve an 85% Operating Rate.
• Example 2
  • If Tr = 40 minutes and Ts = 5 minutes, Operating Rate = 40 / (40 + 5) = 0.88 (88%).
  • In this case, the compressor speed will be reduced in the next cycle to achieve an 85% Operating Rate.
    In situations requiring higher cooling capacity (e.g., cabinet door opening, introduction of a warm load, increase in ambient temperature, or modification of thermostat settings), if the thermostat does not open within 30 minutes beyond the previous operating time (Tr), the compressor will re-enter Pull-Down Mode until the thermostat opens.

Static Defrost Mode:
Due to the absence of a dedicated defrost input, static defrost can be initiated by interrupting the controller’s power supply. To terminate the defrost cycle, the power supply to the compressor’s controller must be restored. Following this, the compressor will restart in Pull-Down Mode.

Frequency control mode
Under this mode of operation, the compressor speed is controlled through a frequency signal sent to the inverter. The compressor’s speed will follow the frequency signal, according to the relation described in Table 3 and illustrated in Graph 3.

Control signal characteristics
The frequency signal is a digital square wave, and its characteristics are described in Table 5.

Driver Protection Characteristics
The electronic driver is electronically protected against several possible malfunctions and failures. An LED light is installed on the driver board to display the intervention of any alarm and to identify its cause. The visual indication consists of a sequence of LED flashes repeating every 5 seconds until the alarm cause disappears. The code for the flashing sequence corresponding to each alarm is indicated in the following table.

Controller characteristics

Controller dimensions

Input and Output characteristics

Packaging and Ordering

Industrial Pack (compressors on pallet)

Single Pack (compressors packed individually in a carton box)

Danfoss Commercial Compressors

• Is a worldwide manufacturer of compressors and condensing units for refrigeration and HVAC applications. With a wide range of high-quality and innovative products, we help your company to find the best possible energy-efficient solution that respects the environment and reduces total life cycle costs.
• We have 40 years of experience within the development of hermetic compressors which has brought us amongst the global leaders in our business, and positioned us as distinct variable speed technology specialists. Today we operate from engineering and manufacturing facilities spanning three continents.