ENERGY MANAGEMENT | TECHNOLOGY
How to assess a facility’s energy performance from electricity usage
Here is the method for creating a Performance Characteristic Line for an injection moulding plant, explained by Dr Robin Kent of Tangram Technology. Plot electricity use against produc- tion volume (processed amount of plastic) over a month as a scatter chart. Use a spreadsheet to find the equation of the linear line of best-fit and the correlation coefficient (R2) for the line. The intersection of the line of best-fit with the electricity usage axis is the ‘base load’. This is the energy
use when no effective production is taking place but machinery and services are available. This should be approximately 30% of the total load. The slope of the linear line of best-fit is the ‘process load’ for the site and shows the average energy being used to process each kilogram of polymer. The process load is process specific and for injection moulding, the value of the process load should be in the region of 0.9-1.6 kWh/kg. The correlation coefficient (R2)
n Investigate process parameter changes, for example hold pressure, screw back speed, barrel temperatures and packing time, to minimise energy use.
n If mould temperature controllers are used to heat the mould then look at the temperature of the feed and return hoses. Insulate as necessary to reduce losses from these.
n Always examine the motor and control options when choosing a new machine. They may increase the purchase cost but will pay back in the medium to long term. The main change in injection moulding in the past 15 years has been the more widespread use of all-electric machines and servo motor driven hydraulic machines. “Older generation machines using fixed speed motors and fixed speed pumps can be described as ‘energy hogs’,” says Kent. “You may save some money by not investing in a new machine, but you are paying every day through the energy costs. However, in reality, hardware and software are not the only things that make the difference. Good people can make even old machines energy efficient and save money.” He continues: “Professional
energy managers and consultants can be used; however, they will never know a moulder’s site and process as well as they do. The difference is that they will know where to look and what to expect and identify things of importance
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should be less than 0.7, which indi- cates good consistency of energy use. However, this is not the same as good energy management. This indicates that the site is consistent and makes improvement easier to manage. A poor correlation coefficient (R2) is
greater than 0.7, which indicates poor consistency of energy use. This is generally considered the same as poor energy management. This indicates that the site is inconsistent and makes improvement difficult to manage.
and where to make the savings. However, there are many people and organisations offering energy consultancy and obviously they are not all equal. If your energy management consultancy focuses on the lights – about 5% of the energy use at an injection moulding site - and says nothing about the machines, which represent about 66% of energy use, then you know that you have got the wrong one.”
In conclusion, Kent says that an injection moulding site with good energy management will look exactly the same as a plant that is well managed in all other areas. Energy management is not a new task, it has simply been raised in impor- tance. Site managers have always been given people, machines and materials and told to make good products. Energy is now simply part of this mix and has a higher priority than before. He adds that it is always possible to see if a plant is well managed by look- ing at the site, the machines and the people — the site and machines are clean, everything is well-maintained and the profes- sionalism and enthusiasm of the people is evident. Sites with good energy management look the same, he says. Conversely, it is
Left: The new XL variant of the Engel E-temp temperature control units provides higher pump capacity. This now makes it possible for one temperature control unit to replace several smaller temperature control units that operate at the same temperature
June 2020 | INJECTION WORLD 47
IMAGE: ENGEL
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