Case Study Super market refrigeration
- Installed 22kw VSD on 18.5Kw motor after 2 months baseline recording of power consumption of the total total refrigeration switchboard (mid and low temp rack + all cases and condensers).
- We programmed the drive to work with a Programmable Logic Controller linked to the refrigeration management system based on the system pressure required.
- The Drive was programmed to run above normal speed of 50Hz up to 60Hz to accommodate peak demand and prevent compressor 2 and 3 cycling on as often.
- We also programmed the drive to idle down to around 30Hz to maintain constant pressure and prevent Compressor 1 from cycling off.
- Preventing compressors cycling on and off is one key energy saving measures. Start up load can be 5-7 times normal operating load.
Operation
- The VSD controlled the motor perfectly supplying constant pressure.
- Readings showed the pressure ranges in the system were much narrower.
- Harmonics at certain frequencies caused some excessive vibration –those frequencies were identified and removed in the ramping process. •
- Plumbing needed to be reinforced after it was identified that a weak point could be a problem
NORMAL OPERATION
• 1200Kw per day = $166 • 35,500Kw per month = $4,970
VARIABLE SPEED DRIVE
• 960Kw per day = $134 • 29,500Kw per month = $4,130
Based on average charge of 14 cents per Kwh from July electricity bill.
Savings 9 months of the year of around $850 per month •
Summer months will be less but still measurable •