Energy Management: A Basic Guide
| By Robin Kent, Tangram Technology Energy management – why worry? Energy management is a fundamental to sustainable manufacturing and yet many companies have no clear idea of where to start in the measurement and management of energy. Indeed, few companies have carried out even the most basic actions to reduce their energy consumption. Yet this is one of the easiest actions that they can take to improve sustainability, to reduce costs and to improve competitiveness. A variable cost The plastics processing industry regards energy as a fixed and uncontrollable overhead cost but this is untrue. Energy is a variable and controllable cost and most processors can reduce energy usage by up to 30% and increase profits by up to 30% through simple management, maintenance and investment actions. Energy use in plastics processing is a combination of two components: Total energy use = Base Load + Process Load The base load is the fixed element of energy use, it is incurred irrespective of whether production is taking place or not and it does not change as output changes. This is the load used for heating, lighting, air leaks from compressors and pumps operating when there is no production at all. The process load is the variable element of energy use and for most plastics processes it varies directly with the production volume. This is the load used to actually run injection moulding machines, extruders or other process machinery. The base and process loads can be easily found using available information: Record the energy usage (in kWh) and the related production volumes (in kg) for at least 12 weekly or monthly periods. Plot these using a scatter chart and find the equation of the best-fit line for the data. The best-fit line is the Performance Characteristic Line (PCL) and a typical result for most processes will be as shown in Figure 1:  Figure 1: A Performance Characteristic Line for an injection moulding site
The equation of the line of best fit for this data is: kWh = 1.5751 x Production volume + 152,440 R2 = 0.9397 The good R2 value (0.9397) indicates that the data set is relatively consistent with the line of best fit - not all data is this good. The equation of the best-fit line can be used to separate the base and process loads:
The PCL shows that energy use varies directly with production volume and can be used to assess a site’s energy performance. Simply feed the production volume into the equation for the PCL and the result is the predicted energy usage for the given production volume. For the site shown in Figure 1, if the production volume is 200,000 kg, then the predicted energy use will be: kWh = 1.5751 x 200,000 + 152,440 = 467,460 kWh Production accountability for energy use is possible by comparing the predicted and actual energy use for the actual monthly production volume. The simple PCL approach provides a vital tool that can be used to set targets and assess performance of any plastics processing site based on a historical performance. The PCL can also be used to forecast a site’s future energy use based on the sales forecast. Simply translate the sales forecast into monthly production volumes and use the PCL to predict the energy use and cost by month. The PCL gives plastics processing site vital information on where to start looking for energy usage and cost reductions. Sites can:
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| Where are we using energy? Understanding where a site is using energy is fundamental to managing usage. For most plastics processing sites the approximate energy use distribution is as shown in Figure 2:  Figure 2: Approximate energy distribution in plastics processing
Before starting work, sites need to establish where they are using energy and one of the best tools is an ‘energy map’ of the site. A typical site energy map is shown in Figure 3 shows where the site is using energy and how much is being used in each area. This can be used to target the high usage areas, e.g. it is rarely worthwhile worrying about lighting – the usage is small and it is better to concentrate on bigger usage areas for bigger gains. |
What can we do to reduce energy usage? Figure 3: A typical site energy map
Management and measurement Energy management is the same as the management of any other resource. If you are not managing it then it is managing you and measurement is fundamental. Measurement leads to management: but only if it is on the real management agenda.
Maintenance Machine selection and operation Maintenance is not simply the maintenance of the machinery. It is a whole range of activities that do not require significant investment and yet can have a remarkable effect on energy usage and costs. Maintenance is about how the site is operated.
Machines use energy even when idling and this can be anything from 52% and 97.5% of the full energy consumption. An idling machine is not ‘free’. Idle periods of greater than 45 minutes may make it cheaper to switch off and restart. Find the minimum stand-by settings and establish setting sheets so that operators always leave machines in this condition when not producing.
Services For any service, the best approach is to ‘minimize the demand and then optimize the supply’.
Investment The cost of the energy used during the lifetime of almost any piece of capital equipment will be more than the initial purchase cost and the initial purchase cost or payback should not dominate the decision-making process. Instead focus on the ‘whole life’ cost of the investment and look at the long term cash flow to find the product with the greatest benefit. Improved energy efficient technology now makes it possible to re-equip a factory for permanently lower operating costs. Typical projects have paybacks from under 4 years and often as low as 9 months. Investment in energy efficiency projects can significantly improve profits.
The real secret The real secret is not in the technical aspects - it is in the management attitude. A desire to reduce costs through good energy management and an effective implementation and monitoring programme will always produce the results and the commercial benefits. |
