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Danfoss - Principles / Advantages of Inverter Drives

Benefits / Principles / Advantages of Inverter Drives

The VLT® HVAC Drive

Dedicated for Building Services applications; its optimised features make it the perfect cost effective match for fans, pumps and compressors in buildings fitted with sophisticated HVAC systems – VLT® HVAC Drive is a must for intelligent buildings.

Motor Independency for Building Services

Frequency converter control of fans, pumps and compressor motors brings significant energy and operational benefits in terms of simple and flexible overall control.

Legislation has reinforced the need for higher efficient systems, resulting in a more diverse offering of high efficient induction, permanent magnet and synchronous reluctance motors.

Danfoss Drives are at the forefront by providing a solution where one drive fits all motor types. This gives motor independency to installers, OEM and end users, helping to future proof the building services system. Maximum possible energy savings can therefore be achieved using the best motor technology for the application whilst reducing total cost of ownership.

Freedom of Choice – One VLT® Drive for all motors.

EC+ Technology for Building Services

When building an HVAC system, to get the highest performance and system efficiency, the individual components (motor, drive and fan) need to be flexible and broadly compatible with each other.

If you specify a high-efficiency motor that is only compatible with lower efficiency fans, the overall system efficiency would suffer and would not reflect the high performance and investment in the individual components.

Danfoss Drives EC+ concept allows ventilation system designers to combine a VLT® HVAC Drive with the most efficient fan and permanent magnet motor. A practical example can be seen in the EC version of radial fans with external-rotor motors illustrated below.

To achieve extremely compact construction, the motor extends into the intake area of the impeller. This impairs the efficiency of the fan, and therefore the efficiency of the entire ventilation unit. As a result, high motor efficiency does not lead to high system efficiency.

New Multi-Fan Control

Plug Fans and Axial Fans in parallel are becoming more and more popular in AHU, RTU, condensor and multi-fan applications. Use of high efficiency PM Motors has so far required separate drives for each motor.

Danfoss Drives now take technology development to the next level with the Multi-fan feature enabling one VLT® HVAC Drive to control multiple fans with IE5 permanent magnet motors.

Refrigeration Systems

The performance of a refrigeration system is expressed using the Energy Efficiency Ratio (EER) or the Co-efficient of Performance (COP). This is the ratio of the generated cooling or heating capacity to the power consumed and is usually based on full-load operation. However, it is not enough to rate refrigeration units at just one load level, since most refrigeration systems operate under partial load conditions. This means that significant energy savings can be obtained using speed control.

Refrigeration System without Speed Control

In a refrigeration system without speed control the refrigerant compressor always runs at full speed, regardless of the cooling capacity required. The cooling output is regulated by the evaporator, which is filled by the expansion device. Since the expansion valve constantly tries to fill the evaporator optimally, this adjustment causes the pressure to change and therefore creates oscillation in the system. Because of this oscillation, the evaporator never properly fills and operates ineffectively and therefore the cooling capacity of the refrigerant is not optimal.

Refrigeration System with Speed Control

Continuous variable speed control by VLT® Refrigeration Drive FC103 makes intelligent capacity control possible. By creating stability whilst balancing the capacity to the actual load, system wide COP/EER improves providing significant energy savings. Intelligent compressor and condenser fan control is a “must” in any optimised refrigeration system.

The following positive effects can be achieved in a refrigeration system with variable-speed compressor operation:


  • Stable suction pressure
  • Increased capacity using smaller compressor
  • Built-in soft starter function
  • Reduced mechanical load
  • Fewer starts & stops extends lifetime
  • Eliminate mechanical capacity control

Condenser Fan Control

  • Load dependent capacity control
  • Stable condensing pressure
  • Reduced charge of refrigerant
  • Less dirt build up on condenser
  • Stand-alone optimised control with VLT® Refrigeration Drive FC103

Pumps in A/C or Indirect Cooling Systems & Fans in Air-Conditioning Systems

  • Coolant pump capacity according to demand
  • Stable coolant flow & pressure
  • Optimised operation of air handling units
  • High efficiency
  • Airflow according to demand
  • Stand-alone optimised control with VLT® Refrigeration Drive FC103
  • Operate from direct signal (0/4-20mA or 0-10v DC)

Depending on the application, speed control can result in energy savings ranging from 10% to as much as 70%.

Click the PDF image to view the technical information in full

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