If an AHU (air handling unit) or associated pumps do not have inverters fitted, then the chances are the air and water flow created by the motors are controlled by the partial opening and closing of dampers in the ducting, or valves where water is moved around.
To gain HVAC flow control this is sometimes done manually or electronically through the use of dampers or valves.
This is not ideal as the motor is still running at full speed when dampers are used to attempt control. A comparison to this; it’s like driving your car with your foot down on the accelerator whilst applying the brakes at the same time to get the required speed! Whilst I am sure most people wouldn’t drive like this, I am baffled why they apply this method to gain a measure of control of an electric motor.
HVAC Flow Control
It makes far more sense to control the speed of the motor to give more effective HVAC flow control. This is how inverters work, an inverter controlling the speed of your motor will allow you to open the dampers and valves fully and decrease or increase the air and water flow through varying the motor speed.
Not only will an inverter give you far better control it will also allow considerable energy savings. To get a 50% energy saving you may think you have to halve the speed of the motor, however, this is not so, due to Cube Law which applies to centrifugal pumps and fans, whereby, if you run a pump or fan at 80% speed (50Hz down to 40Hz) then a 50% energy saving will be achieved. To find out more about how Cube Law works, please click here.
To achieve HVAC flow control with inverters there are other advantages to be gained:
- Lower noise levels
- Longer motor life
- Less turbulence
- Gentle start up
- Improved power factor
So remember as with our example of driving a car, take your foot off the brake and ease off the accelerator to slow down! Fit inverters!
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