Following the success of the secret life of chillers, the secret life of Variable Speed Drives (VSD) might be equally important.
Variable Speed Drives (VSD), also known as Variable Frequency Drives (VFD) can replace motor starters and lower energy costs, but this graph above (real data) shows the motor speed remains pretty constant all day long.
Considering these drives are essentially digital, it can be surprisingly difficult to access the raw data! VSD’s often have internal memory, not open to the BMS, so the data must be retrieve manually.
While some drives can be programmed to perform specific routines, the full benefit is derived when they can be automatically controlled. most VSD’s accept control pair to regulate the motor speed from 0-100% from a 0-10v or 4-20mA signal, but faults can be really difficult to detect without the raw data.
And considering the drive is essentially a digital motor starter, it can be surprisingly difficult to access the raw data! VSD’s often have internal memory, and some have slots for removable SD cards, that can be used to collect data, but collecting data by hand every three days is tiresome.
To save energy, we arrange an automatic control to signal the VSD to vary the motor speed. Perhaps we might design the system to vary the AHU fan speed depending on the room air temperature, or the carbon dioxide content of the room. But finding problems, and wasted energy is exceedingly difficult without obtaining the raw data from the VSD memory.
So, the secret life of VSD’s might not be as exciting as a chiller, but equally important for energy saving. For air-conditioned hotels and offices, we target the air conditioning plant for savings first because it’s the largest proportion of your energy bill.
It would be remiss not to mention that VSD’s provide soft start functionality, replacing the traditional motor starter, and reducing the mechanical stress during start-up, and increasing the longevity of the HVAC equipment. Call Kelcroft today and ask to speak with energy expert John A. Herbert he has decades of international cost saving experience.
About the Author
John A. Herbert is a veteran Building Services engineer, with more than 30 years experience, he was educated in the United Kingdom and has been working in Asia for more than two decades advising international and local companies how to lower energy costs. He is a Hong Kong Registered Energy Assessor (REA), and a BEAM Professional.