ACR Journal

February | March 2023 EFFICIENCY 14 At the recent Institute of Refrigeration conference, held in Birmingham at the beginning of December, speakers were invited to put a question to the audience at the end of their talk. Dr Andy Pearson, Group Managing Director of Star Refrigeration, presented his recent work developing new methods of energy benchmarking for cold stores and asked “If benchmarking is so good then why is it not being advocated as vigorously as possible by everybody involved in the cold storage industry?” The importance of energy benchmarking Volume 9 No.2 With gas and electricity prices reaching record heights energy e ciency is clearly a key topic for most businesses but a lot of people don’t seem to know what to do about it. It is relatively easy to tell whether someone is really interested in the energy performance of their facility. All that is needed is to ask them whether they sub- meter their electrical consumption so that they can tell which parts of the system are using the energy. Without this level of granularity the only thing that people can do, faced with rising energy bills, is despair. With this information it is possible to construct a cost-saving plan, often without much capital investment. Information is critical to the success of any benchmarking activity. Ideally, the information should be gathered automatically and stored for long-term analysis of trends and developments. It should be easily verified to provide a sense check on the numbers presented and should not be a ected by occasional gaps in the recording caused for example by power outages or component downtime. It should be delivered to the plant supervisor and key decision makers in an easily understood format, preferably graphically, but the raw data behind the graphs should also be available for more detailed analysis if required. Modern industrial refrigeration systems already are equipped with su cient computing and storage capacity to do this. There are three key elements to a benchmarking programme. It should be possible to track a facility’s performance over time to judge whether it is improving or declining. It should also be possible to compare the facility under examination with other facilities operated by the same owner or even competitors’ facilities. It should then be possible to use recorded data to predict the direction of travel of the trend in order to assess the benefit of taking early action to improve performance and to assess the financial benefit, if any, of action already taken. Each of these aspects of benchmarking is considered here. The first element is easily achieved by dividing the annual energy consumption of the site (which can be read o the electricity bill) by the volume of the refrigerated space (which is just length x width x height and doesn’t change with time). Consistency is key: use the same measure of electricity consumption each time and the same volume figure. This calculation can be automated quite easily if the energy data recent work, published at the International Congress of Refrigeration in Montreal in 2019, identified that some modern facilities were better than the 1994 guide and so a revised best practice metric was proposed. This was based on the equation S = 15500V -0.63 where S is the specific energy consumption and V is the volume of the refrigerated space. If V is in cubic metres then the specific energy consumption (SEC) best practice identified by this equation is in kWh per m 3 per year. <caption> Figure 1 – Specific Energy Consumption compared with best practice metrics is stored in a computer or plc and can be adjusted to give a rolling 12 month figure. In 1994 the Energy Technology Support Unit (ETSU), part of the UK’s Department of Energy, published a Good Practice Guide for cold store e ciency which included a best practice metric based on energy per cubic metre. This is shown in the graph in Figure 1 as the yellow line. More recent work, published at the International Congress of Refrigeration in Montreal in 2019, identified that some modern facilities were better than the 1994 guide and so a revised best practice metric was proposed. This was based on the equation S = 15500V-0.63 where S is the specific energy consumption and V is the volume of the refrigerated space. If V is in cubic metres then the specific energy consumption (SEC) best practice identified by this equation is in kWh per m3 per year. For the site plotted in Figure 1 the annual energy use is 1,875 MWh and the Figure 1 – Specific Energy Consumption compared with best practice metrics