Saving energy with Variable Speed Drives (VSD’s)

  What are Variable Speed Drives?
  Variable Speed Drives - Case Study
  Variable Speed Drive Tips

Saving energy with Variable Speed Drives
You can significantly reduce your energy costs through the application of variable speed drives. Read on for more information on VSD’s.

What are Variable Speed Drives?  

Variable speed drives (VSD’s) allow loads driven by AC induction motors (such as fans and pumps) to operate in a wide range of speeds compared to the motor fixed speed. (VSD’s are also called variable-frequency drives, adjustable-speed drives, variable-frequency inverters, or frequency converters).
VSD installations can reduce energy (in some cases energy savings can exceed 50 percent), improve power factor and process precision, and provide other performance benefits such as soft starting and over speed capability. They also can eliminate the need for expensive and energy wasting throttling mechanisms such as control valves and outlet dampers. 
Typical Applications of Variable Speed Drives
VSD’s have been used to provide significant savings in a number of applications. These include: 
  • Variable air volume (VAV) air conditioning systems.  
  • Chilled water pumping (eg secondary chilled water pumps).  
  • Exhaust air systems (eg dust extraction, paint shop exhaust, and fume cupboards).  
  • Refrigeration systems. 

Modern compressors (including air and refrigeration compressors) can also include VSD’s for energy efficiency in some applications.  

Variable Speed Drives - Case Study
Building Saves Energy and Improves Comfort
A major Hotel/High-rise Building/Department Store installed variable speed drives on its air conditioning fans, improving conditions, reducing noise and cutting fan-related energy costs by about 30% . 

Project Description 
The building such as Hotel has a large number of air handling units supplying air conditioning to its guests’ rooms. As the guests’ rooms are occupied, more air needs to be supplied to maintain the comfort of each room. As a result, the fans supplying the air need to vary their output, based on the number of rooms occupied.
The initial installation had throttling dampers installed in the supply air duct work. As the requirement for airflow decreased the dampers closed to reduce airflow to the rooms.
Not only was this method of flow control inefficient in terms of energy use, it resulted in noise (as the dampers closed against the fan generated air pressure) and also required regular maintenance to keep the dampers operating.
The hotel identified that installing variable speed drives (VSDs) on the fans would not only result in energy savings but also provide improved system performance and lower maintenance costs .
 The hotel installed a trial VSD on one of its air handling unit supply air fans and, based on the results, decided to install VSDs on each of the guests’ rooms air handling unit supply air fans.
 The work included disconnecting the existing supply air dampers, upgrading the air conditioning control systems and installing the new VSDs.
 Based on monitoring carried out before and after installation of the VSDs, savings achieved were approximately 30% of fan energy costs.
 Based on the monitored results the initial payback period will be 32 months. This does not include the maintenance savings.
 This case demonstrates that it is possible to improve energy performance and service delivery at the same time. The upgrade was very well received by both hotel management and their guests.

Efficiency measure(s)

Installation of VSDs on fans

Potential users

Offices Building , hotels, hospitals, Department store

Expected payback period

Less than 36 months

Note: Whilst care has been taken in the preparation of this material, it is intended to provide a general idea about what can be achieved in a particular situation. Quantitative indicators may vary with time and changing circumstances. Each situation is different, requiring its own evaluation; and therefore the results given above should not be taken as being directly transferable to other circumstances. Names and addresses have been withheld for privacy reasons.

Further Information
To find out how you can reduce your energy costs contact Western Power’s Energy Consultants today  by