The client is a large retail group and operates a few distribution centres (DC) throughout the country which serve a large quantity of retail outlets. Due to confidentiality purposes the name of the client cannot be revealed.
The client is in the process of transitioning the supply chain and wanted to use this opportunity to review what has historically worked well and to ensure the principles related to this are incorporated in the future solution to maximize the investment made in systems and infrastructure.
The refrigeration facility at the DC forms a major part of the cold chain and can be very costly if not managed efficiently. The cost of electricity as an energy source is the biggest input cost for maintaining the cold chain. More efficient use of electricity will also reduce the carbon footprint of the cold chain. The purpose was to conduct an energy audit to test the energy efficiency of the refrigeration equipment to provide an adequate cold storage environment.
Energy Audit Methodology
The energy audit was done by recording and analysing the energy consumption and product throughput during the sample period over 12 months. The space utilization and energy consumption were measured in terms of product throughput and benchmarked against similar South African cold storage facilities.
In this assessment the energy consumption was measured and then compared to the benefit obtained by that electricity consumed. This benefit was measured in the amount of electricity used to cool a unit volume (in cubic meters) and also the amount of product that received this benefit in the cold chain. The business purpose of a retailer is to sell product to customers, the cold chain is there to prolong the quality of perishables, and therefore it just make sense to analyse the energy efficiency in comparison with the product throughput.
Data in the form of electricity consumed at the DC was collected by energy consumption meters fitted at appropriate positions on the distribution boards. The data collected by the latter was then converted into KWh. The unit of measure of kWh/m² (kWh per square meter floor area) is an acceptable measure for office space and general store areas. The measurement of refrigeration energy efficiency requires that the measure be adapted to kWh/m³ (kWh per cubic meter cooling space) for the volume of space to be cooled, e.g. the cold rooms and cabinets. A more refined measure is the amount of kWh electricity used per ton of product kept under cooling per day (kWh/ton-day). The latter two measurements were used in this cold chain assessment to determine the energy efficiency of the DC by benchmarking these values against other similar refrigeration facilities in South Africa.
The facility used in the order of 4.8m kWh electricity per year at a cost of R2.85m in 2012. The electricity consumption for the non-refrigeration portion is 66% of the total. This is very high compared to other similar facilities and should be investigated further (outside the scope of the client request).
- The benchmarking results show that the DC is buying electricity at a very low unit cost.
- The refrigeration equipment is very efficient and well maintained.
- The refrigeration plant has the capacity for the current levels of product throughput.
- The cold storage space utilization is very low and result in wasted cold volume.
- The average temperature in the cold stores was higher than the specified maximum.
- The temperature analysis has shown hotter temperatures at the cold room doors which is an indication of heat ingress through the doors leading to energy waste.
Proposed Action Plan
Action 1: Decrease the refrigeration setting to bring the temperature in specification.
(This will increase the energy consumption but need to be done to maintain product quality. The DC cold stores temperature were too high while they have more than enough refrigeration capacity.)
Action 2: Improve the utilization of the cold stores by increasing the product throughput or reducing the cold room size.
(The latter option would require capital spend for partitioning – costing handled by DC)
Action 3: Improve the door seals to prevent heat ingress at doors.
(Capital required: R50 000)
The table below shows that electricity savings of up to 62% is possible when operations are benchmarked against other similar cold storage facilities. This can be achieved by better utilization of cold storage space and the alterations to reduce heat ingress through the doors.
Actions taken by DC:
- The operating personnel responsible for cold store temperature were trained in the correct procedures for temperature setting and management control was introduced to assure that the product is stored within specified temperature regimes. This was done on the first day after receiving the audit findings.
- The utilization of cold storage space will be handled in the bigger supply chain project and the outcome is still unknown.
- The door seals have been repaired and the client has requested a repeat of the temperature analysis at the same period next year to test temperature ingress.
The client is a large apple packhouse operation in the Western Cape where apples are stored, sorted and packed for the export market. Due to confidentiality purposes the name of the client cannot be revealed.
The main energy source is electricity obtained from Eskom. Apples are harvested by farmers during February to April and then stored in controlled atmosphere cold stores for up to 10 months at the packhouse facility. Short term storage is done with regulated atmosphere cold stores and forced air cooling for packed pallets. The cold storage and packing operations continues throughout the year.
A previous energy audit was done at this client during 2010. One of the recommendations was to implement an energy information model for better energy management. This model was implemented and maintained during 2012 and 2013. The client requested a second energy audit during 2013 to assist with the development of a detailed action plan.
Energy Audit Methodology
Information gathered in the energy model was analyzed to obtain a better view on the electricity consumption patterns in the facility. The assessment was done for the electricity consumption period from January 2012 to December 2012. During this period almost 7.1GWh of electricity was used at a cost of R4.59m, an average unit cost of R0.67/kWh. The electricity balance (see below) shows that 89% of the electricity is consumed in cold storage operations. The client agreed that this significant energy user should be the focus point of the improvement action plan.
A checklist was compiled from literature on best practices for energy efficiency in refrigeration applications. This checklist was followed as a guideline to evaluate all the cold storage operations at this packhouse as an input towards developing the improvement action plan.
The major findings of this energy audit are twofold:
- Technical improvements can be made to improve the energy efficiency of the facility. These steps are summarized in the table below.
- It was clear that there was a lack of energy management skills at the packhouse. The energy information was gathered in the model, but nobody really attended to the information and acted upon it. The audit also indicated that some of the information was not correctly captured, which may lead to false conclusions. The technical people were found to be very competent in running the cold stores, but during their busy season they do not have time for energy management activities.
Proposed Action Plan
The proposed technical action plan is summarized in the table below. These actions would require an investment of R390 000 and will lead to an energy saving of R1.35m per year. The projected saving of 1.84GWh per year is a saving of 26% on the electricity consumption of the packhouse facility.
A good energy management approach is essential for sustainable energy improvement. The packhouse has implemented sub metering and an energy information model to assist in energy management. The information should provide a baseline against which performance improvement can be measured. The following improvements to this approach were recommended:
- Determine the roles and responsibilities for energy management at Valley.
- Revise the data for 2012 and establish a baseline.
- Revise the data for 2013 and determine improvement against the baseline.
- Set improvement targets for 2014 and beyond.
- Continue with short interval control during 2014 based on weekly results.
- Allocate resources for the energy management actions or subcontract.
A solar PV analysis was done for the packhouse. A 741kWp system is recommended before excess power is fed back into the grid. This system will cover 5200 square meters of existing roofing space. The total investment cost is R9,6m after tax rebates. The costs of the proposed solar PV system equates to effectively paying only 34.7 cents/kWh over the next 25 years. The projected average cost of electricity obtained from Eskom is R2.66 /kWh over the next 25 years.
Actions taken by the Packhouse:
- The outcome of the energy audit was received with great appreciation by the packhouse. The action items requiring capital investment were put on the budget for next year.
- The packhouse is also negotiating with an outside energy consultant to assist with the energy management process during next year. This will include the energy projects for improved refrigeration control.