Energy Management Made Simple

June 15, 2016 11:08 am
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In recent weeks I’ve visited some real large-scale production sites. Prior to my visits I wouldn’t have been surprised to find their annual utility bills amounted to a hefty sum, made up of a fairly traditional mix of compressed air, fridge plant, steam boilers, water and waste water treatment. The true spend surpassed my initial ideas when it turned out that all 3 sites were actually spending upwards of £5m per annum; the reality was that all 3 were making an annual profit of less than their utility bill.

What surprised me most however, was the fact that there wasn’t any form of utility management programme in place, and in none of the cases was there any evidence of any accountability for utility spend. In addition, there was little or no understanding of the key energy efficiency measures.

A typical production site is connected to the grid to purchase electricity and gas. Whilst some of the electricity will be used direct to power electric motors for example, in many instances it will swiftly be converted into compressed air and “coolth”, through a refrigeration system. Likewise, whilst gas may be used directly to supply heat, it is often first converted into steam. Steam and coolth are then distributed around the site before being consumed. With this in mind, in order to manage the energy spend we need to understand how the energy flows around the site:

  • Procurement from the utility company
  • Conversion to a different energy form for distribution
  • Distribution around the site
  • Usage
  • Recovery of residual energy

Like all activity on a production site, there are a number of key metrics that give us the key management information we need to effectively manage this process. Focusing on frozen food manufacturers in this example, consider the conversion of electricity into “coolth” in a refrigeration system…

Fridge Compressors

In a frozen food business, the fridge compressors are likely to be a significant part of the overall electrical consumption for the site – in a recent example they represented 80% of their circa £1m per annum electricity bill. They are, also, a badly understood asset. Often maintained by third parties through contracts with no efficiency measures, filled with toxic gases and housed in locked rooms for which the Site General Manager has no key, they are shrouded in mystery and, at best, ignored. At worst they are operated in an inefficient manner, substantially increasing site energy bills.

Refrigeration systems have a low profile until they fail, causing product to defrost and an ammonia release into the atmosphere.

A typical fridge plant will be a mechanical vapour compression (MVC) system utilising the latent heat of evaporation to lower the temperature. The refrigerant gas is compressed, increasing the temperature. It is then condensed to a liquid, still at high pressure, and the waste heat rejected to atmosphere through a cooling tower or evaporative condenser. The liquid then passes through an expansion valve thus reducing the pressure. It then passes through a heat exchanger where it boils off, extracting heat from the surroundings and reducing the temperature. At this point it is passed back to the compressor and the cycle begins again.

The coolth is often distributed to the process through a secondary refrigerant system. Assuming this to be the case, the main energy consumers in the process are:

  • Compressor
  • Condenser
  • Secondary refrigerant circulation pumps

The key performance measure of the fridge system is the coefficient of performance (COP). This is defined as:

COP = energy removed from the process in the evaporator/energy to the fridge compressor

Whilst this does not tell the whole story, it is a good starting point. The COP depends on many factors, not least the target temperature. It is the COP that is often badly understood, or not understood at all. This is particularly relevant at this time. R22 refrigerant is now banned, and many older refrigeration systems have been converted to alternate gasses such as RS52. However, this was often done with consideration for the capital cost only, with no visibility of the reduction in COP and the consequent increase in a site’s electrical bill.

Summary

If you don’t measure it, you can’t manage it! Refrigeration systems will make up a fundamental part of the cost base in any site where temperatures need to be reduced. The efficiency of these systems is often not known as it is not built into the measures for the service contract. In order to control this major cost, you need an efficiency measure. Once you have this, you can start to discuss with your service partner how to increase it.

For additional information on Coriolis’s Energy Management Capability and how to use it to enhance your business, please contact us.

 

Written by Richard Jeffers, Coriolis Ltd