Energy Saving on Compressor

ABB drives reduce refrigeration costs

Any refrigeration system with a wide variation in operating hours or with a heat load that is less than the peak load can benefit from an AC drive.

Many refrigeration systems that use pumps, fans and compressors are still using inefficient on/off or two-speed control for the condenser fans and significant savings can be made by using an AC drive to directly control the speed of the electric motor.

Here is a True Example-

Poole’s Pies of Wigan is hoping to make an 11 per cent cut in the cost of electricity following the installation of ABB drives within its refrigeration plant.

The reduction will see costs cut by more than GBP6,200, giving a payback for the project of 2.3 years.

Owned by David Whelan, the company employs 100 staff and can produce 200,000 meat pies a day, as well as 80,000 other puff-pastry products.

The installation of a new production line, complete with spiral freezer, designed for the manufacture of a variety of puff-pastry products, prompted the company to look at improving its energy efficiency.

For many companies in the food manufacturing sector, refrigeration can account for 70-80 per cent of the electricity bill, so any savings made in this area are likely to be significant.

Installed by Seward Refrigeration, the refrigeration system operates on pumped ammonia refrigerant at an operating temperature of -40C.

Seward Refrigeration chose ABB drives to run two of the major components in the refrigeration system.The condenser is an evaporative type with the fan controlled by an ABB standard drive.

Variable speed operation of the fan gives significant reduction in power even for a small reduction in speed.

For example, a 10 per cent speed reduction gives 30 per cent less energy consumption.

A single 315kW screw compressor is used to provide refrigerant for the spiral freezer.

The use of an ABB drive permits energy saving at part-load conditions.

The screw compressor can operate at speeds between 1,500 and 3,600rpm at 100 per cent slide valve position.

With this mode of operation, the machine operates at optimum efficiency for any given speed.

‘Although the full load efficiency of screw compressors is good, part-load performance with slide valve control is generally poor,’ said Brian Seward of Seward Refrigeration.

‘With variable speed control of the compressor at Poole’s Pies we now have good efficiency at both part load and full load,’ he added.

The screw compressor uses a low harmonic ABB industrial drive, which minimises harmonic interference on the mains supply and avoids the use of complex solutions to ensure conformity with G5/4 requirements.

Other advantages of the ABB industrial drive include operation at unity power factor, allowing reactive power charges to be avoided.

The stand-alone design of the drive gives it a small footprint, minimising space requirements in the control room.

Since refrigeration systems typically run 24 hours, most fan and pump applications are potential candidates for AC drives.

Where drive belts are used on the fan systems, the AC drive reduces belt stress and maintenance costs.

Converting these systems to AC drive control can reduce the energy consumption Efficiently.

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