Benchmarking and Energy Performance

3.5 Benchmarking and Energy Performance

Benchmarking of energy consumption internally (historical / trend analysis) and externally (across similar industries) are two powerful tools for performance assessment and logical evolution of avenues for improvement. Historical data well documented helps to bring out energy consumption and cost trends month-wise / day-wise. Trend analysis of energy consumption, cost, relevant production features, specific energy consumption, help to understand effects of capacity utilization on energy use efficiency and costs on a broader scale.

External benchmarking relates to inter-unit comparison across a group of similar units. However, it would be important to ascertain similarities, as otherwise findings can be grossly misleading. Few comparative factors, which need to be looked into while benchmarking externally are:

• Scale of operation
• Vintage of technology
• Raw material specifications and quality
• Product specifications and quality

Benchmarking energy performance permits

• Quantification of fixed and variable energy consumption trends vis-à-vis production levels
• Comparison of the industry energy performance with respect to various production levels (capacity utilization)
• Identification of best practices (based on the external benchmarking data)
• Scope and margin available for energy consumption and cost reduction
• Basis for monitoring and target setting exercises.

The benchmark parameters can be:

• Gross production related

e.g. kWh/MT clinker or cement produced (cement plant)

e.g. kWh/kg yarn produced (Textile unit)

e.g. kWh/MT, kCal/kg, paper produced (Paper plant)

e.g. kCal/kWh Power produced (Heat rate of a power plant)

e.g. Million kilocals/MT Urea or Ammonia (Fertilizer plant)

e.g. kWh/MT of liquid metal output (in a foundry)

• Equipment / utility related

e.g. kW/ton of refrigeration (on Air conditioning plant)

e.g. % thermal efficiency of a boiler plant

e.g. % cooling tower effectiveness in a cooling tower

e.g. kWh/NM3 of compressed air generated

e.g. kWh /litre in a diesel power generation plant.

While such benchmarks are referred to, related crucial process parameters need mentioning for meaningful comparison among peers. For instance, in the above case:

• For a cement plant – type of cement, blaine number (fineness) i.e. Portland and process used (wet/dry) are to be reported alongside kWh/MT figure.
• For a textile unit – average count, type of yarn i.e. polyester/cotton, is to be reported along side kWh/square meter.
• For a paper plant – paper type, raw material (recycling extent), GSM quality is some important factors to be reported along with kWh/MT, kCal/Kg figures.
• For a power plant / cogeneration plant – plant % loading, condenser vacuum, inlet cooling water temperature, would be important factors to be mentioned alongside heat rate (kCal/kWh).
• For a fertilizer plant – capacity utilization(%) and on-stream factor are two inputs worth comparing while mentioning specific energy consumption
• For a foundry unit – melt output, furnace type, composition (mild steel, high carbon steel/cast iron etc.) raw material mix, number or power trips could be some useful operating parameters to be reported while mentioning specific energy consumption data.
• For an Air conditioning (A/c) plant – Chilled water temperature level and refrigeration load (TR) are crucial for comparing kW/TR.
• For a boiler plant – fuel quality, type, steam pressure, temperature, flow, are useful comparators alongside thermal efficiency and more importantly, whether thermal efficiency is on gross calorific value basis or net calorific value basis or whether the computation is by direct method or indirect heat loss method, may mean a lot in benchmarking exercise for meaningful comparison
• Cooling tower effectiveness – ambient air wet/dry bulb temperature, relative humidity, air and circulating water flows are required to be reported to make meaningful sense.
• Compressed air specific power consumption – is to be compared at similar inlet air temperature and pressure of generation.
• Diesel power plant performance – is to be compared at similar loading %, steady run condition etc.

Plant Energy Performance

Plant energy performance (PEP) is the measure of whether a plant is now using more or less energy to manufacture its products than it did in the past: a measure of how well the energy management programme is doing. It compares the change in energy consumption from one year to the other considering production output. Plant energy performance monitoring compares plant energy use at a reference year with the subsequent years to determine the improvement that has been made.

However, a plant production output may vary from year to year and the output has a significant bearing on plant energy use. For a meaningful comparison, it is necessary to determine the energy that would have been required to produce this year production output, if the plant had operated in the same way as it did during the reference year. This calculated value can then be compared with the actual value to determine the improvement or deterioration that has taken place since the reference year.

Production factor

Production factor is used to determine the energy that would have been required to produce this year’s production output if the plant had operated in the same way as it did in the reference year. It is the ratio of production in the current year to that in the reference year.

Reference Year Equivalent Energy Use

The reference year’s energy use that would have been used to produce the current year’s production output may be called the “reference year energy use equivalent” or “reference year equivalent” for short. The reference year equivalent is obtained by multiplying the reference year energy use by the production factor (obtained above)

 Reference year equivalent = Reference year energy use x Production factor

The improvement or deterioration from the reference year is called “energy performance” and is a measure of the plant’s energy management progress. It is the reduction or increase in the current year’s energy use over the reference, and is calculated by subtracting the current year’s energy use from the reference years equivalent. The result is divided by the reference year equivalent and multiplied by 100 to obtain a percentage.

The energy performance is the percentage of energy saved at the current rate of use compared to the reference year rate of use. The greater the improvement, the higher the number will be.

Monthly Energy Performance

Experience however, has shown that once a plant has started measuring yearly energy performance, management wants more frequent performance information in order to monitor and control energy use on an on-going basis. PEP can just as easily be used for monthly reporting as yearly reporting.