AC drives in heating, ventilation and air conditioning (HVAC) applications
40% of all energy in Europe and North America is consumed in buildings. The biggest share of this energy is consumed in heating, ventilation and air conditioning (HVAC) applications.
With the rising energy cost and concerns about the CO2 levels and global warming, it is crucial to use all means available to reduce the energy consumption in heating, ventilation and air conditioning (HVAC) applications. The savings potential in HVAC applictions is big.
The key thing is to start looking more at lifetime costs of HVAC system, where energy cost plays a big role, rather than the initial investment in HVAC system. To give an example, 90% of the lifetime costs of the pump or fan is energy.
The majority of HVAC applications where AC drives (microdrives) are used are
1. fans
2. pumps
3. compressors.
Figure: The main components of an HVAC system includes air circulation, water cooling circuits and water heating circuits.
1. Fans and pumps
Using an AC drive to control the fan or pump output rather than using dampers, vanes, valves or on/off control brings substantial energy savings, if the required output is less than nominal most of the time.
The AC drive (VFD) controls the speed of the pump and fan by changing the electrical energy supplied rather than damping the air- or water flow. It is like reducing the speed of a car by pressing less on the accelerator instead of using the brake to slow down the speed. The payback time of an AC drive is typically one year or less.
Graph: Electrical power consumed by pump at partial loads is significantly less with an AC drive than with valve or on/off control.
Other benefits of using AC drive (Frequency Converter, Frequency Changer) to control the speed of fan or pump are:
Smooth ramp up and ramp down causes less stress to the mechanics of fans and pumps and to air ducts and water piping
Slowing down the speed rather than damping the output will result in lower noise levels
Tuning the HVAC system during and after the commissioning is easier when the flexibility of an AC drive is used
2. Compressors
Compressors in heating, ventilation and air conditioning (HVAC) are often used in chillers for cooling water, which again is used for cooling air. Utilising AC drives (Adjustable Frequency Drives) in compressor applications will potentially bring energy savings compared to on/off control.
Energy savings are achieved by optimising the system setup of compressor, chilled water circulation and condenser water circulation. The optimum set point for chilled water temperature and condenser water temperature is based on outdoor and indoor temperature and humidity.
The energy savings are most effectively achieved by tuning the system rather than optimizing individual functions. The AC drive gives the flexibility of tuning the setup of the system to operate in the most energy efficient operational point.
Other benefits while using ac drives (Variable Frequency Drives, Adjustable Speed Drives)
Reduced number of starts and stops reduces the wear of the compressor
The piping and mechanics are stressed less in ramp up or –down situations
Reduced noise level in low load situations
Possibility to use high speed compressors
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Application case of AC drives (variable speed drives) for HVAC
Powtran Technology Co., Ltd. (Shenzhen POWTRAN Technology Co., Ltd., DaLian Powtran Technology Co., Ltd.)
