Monitored over a four month period, a major UK food company has seen its energy bill drop by 50% in its’ freezing process. This has been achieved by the installation of Telemecanique Altivar variable speed drives, an innovative range of control technologies from Schneider Electric. The variable speed drive controls are linked to temperature probes that adjust the speed of the cooling fans according to the ambient needs of the process.
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The company manufactures frozen ready made meals at its factory in Carlisle including: potato topped pies, quiches, recipe dishes, crisp-bakes and party foods mainly for Marks & Spencer. The foods are quick frozen using refrigerant passed through water filled heat exchangers.
In the final stage, cooling of the foods used to be maintained by fan blown air passing over the heat exchangers (which contains the cooling water), this would then flow through the gas cooling heat exchanger. The air movement in this process used contact speed fans and relied on mechanical vanes to control airflow. As a result the fans ran at full duty irrespective of demand, consuming unnecessary electricity and delivering unreliable control.
There are 17 fans in use within the process, varying from 0.37kW up to 15kW. Each fan has now been fitted with an Altivar variable speed drive by Park Gate & Co., a Schneider Electric franchised distributor working in collaboration with the food processor’s engineers.
The use of variable speed control in continuous duty applications such as fans, pumps and compressors was recognised at the outset of the Climate Change Levy (CCL) as an opportunity for businesses to reduce energy consumption. After all, some two thirds of all electrical energy consumed by industry is through powering electric motors. However, in this case the food company’s application is unusual in that it makes clever use of sensing demand to vary the motor speed and usage.
Temperature probes have been located within the water cooling tower to feedback readings to the Altivar drives via a 0-10V interface. The signals feed into the drives’ inherent Proportional Integral Differential (PID) controller that enables scaling to in turn manage the motor speed and hence fan speed to meet the actual cooling requirements. The control set point that determines the fan speed function was also established in collaboration with the food processor’s engineering team who provided the data on optimum temperatures. It has already been noted, for example, that in winter months the fans rarely need to turn, where once they ran continuously.
To prove the success of the installation, engineers from Park Gate took empirical measurements of the energy savings. They used a kWh meter that produced “before and after” trends, over typical running periods. The traces showed significant reductions in power usage and provided firm evidence of electrical savings.
The food company is part of a much larger business, which has set energy reduction targets across its group of companies. Indeed, such is the success of the group in exceeding the Government’s target of reducing energy consumption by at least 2% per tonne of product that it has qualified for exemption from the CCL.
In addition to exemption from the CCL, the installation also qualified for tax reductions under the Inland Revenue’s Enhanced Capital Allowances (ECA) scheme. Businesses can write off the whole of the capital cost of their investment in these technologies against their taxable profits of the period during which they make the investment (unlike other equipment depreciation allowances that typically span five years for capital plant). Since all of Schneider Electric’s Telemecanique variable speed drives qualify under the ECA scheme, this presented no problems for the customer concerned.
The benefits in energy saving and capital allowance were further augmented by the improvement in the control of gas temperature, through the cooling process. The company now has enhanced process control; an improvement that will benefit both product quality and target shelf life. Additional savings have also been made through reduced maintenance when compared to the previous system.
In summary, a simple improvement to the refrigeration system has resulted in significant energy savings, sufficient for a four-month project payback and has delivered an improved process, contributing to overall quality and trace-ability requirements.
Schneider Electric provides customer focused offers to help businesses to monitor, meter and control water, air, gas & electricity around the plant, with the primary aim of reducing cost and maximising efficiency. The energy saving services offer includes analysis, installation reporting and also confirmation of savings made.
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