In WMG’s first article on heat recovery we discussed the opportunity to save money and reduce emissions via the capture of waste heat from industrial processes. Heat that is currently being wasted in industrial processes has massive potential as the country makes the transition to Net Zero and in a climate of energy supply uncertainty.

If this potential can be realised by UK manufacturers it will provide a significant boost to reducing emissions and energy costs– without having to cost the earth. This opportunity is greater now than it has ever been with the average gas price paid by manufacturing industries more than doubling from Q1 2021 to Q1 2022 according to BEIS, with further increases expected into 2023.

The first article in this series specifically highlighted how the transfer of heat for secondary uses can be cheaper, more efficient, and simpler than the conversion of heat to other energy types. Transferring heat for a secondary use means moving heat around your facility, typically from a high temperature source to a lower temperature sink.

This article focuses on a case study at Sarginsons – an aluminium foundry in Coventry that is using wasted heat from a compressor for space heating.

The project focusses on the recovery of wasted heat from two 55 kW compressors, one fixed and one variable load, that the foundry uses to provide compressed air for processes around the site. Compressors are one of the most common sources of wasted heat in manufacturing, approximately 70% of all manufacturing companies use compressed air for some aspect of their operations. It is estimated that 10 per cent of all the industrial electricity consumed in Europe is used to generate compressed air. Another reason compressors provide such an opportunity for manufacturers is that they are inherently inefficient. For a typical compressor only 5-10% of input energy is converted productively, whilst an astonishing 80% is lost as heat. The diagram shows the overall efficiencies for compressors.

Figure 1

As shown above, the potential for energy savings is there and is extremely widespread. The Sarginsons project focusses on a low-cost solution to recover some of the heat that is being wasted by the compressors. In this case, a simple duct system was proposed to move the warm air that was given off by the compressors around the facility for space heating during the winter. Currently, workshop areas are being heated by electric heaters with plans to install further electric heaters to provide sufficient heat for shopfloor workers. By utilising the waste heat from the compressors, cost can be saved from the purchase of the heaters themselves and the electricity needed to power them. Additionally, reusing previously wasted heat provides a zero-carbon alternative to traditional heating methods that is simple to implement.

Using waste heat from the compressor means six, 1.2kW electric heaters across 2 workshops can be replaced. The table below shows the savings (based on UK average prices for a medium sized business in Q2 2022) that can be achieved by replacing these electric heaters with previously wasted heat. 1651 kgCO2e is equivalent to the amount of CO2 absorbed by 66 trees in one year – a terrific message for an SME to be able to publicise.

Project costs depend on a variety of factors, such as:

 What is the distance between the compressor from the heat sink?

 Is there a duct install capability on-site or will you need an external contractor?

 What size ducting do you need?

 How much control of the system do you want and how complicated does it need to be?

A simple duct over a few meters can cost as little as £100 in material costs. Adding dampers to control air flow and bends to work around existing machinery adds complexity and cost. However, implementing a project like this can always remain low cost with potential for sub-annual payback periods, even if it becomes more complex when fitted to your site.

In addition to having a good business case, reuse of waste heat demonstrates to customers a business is serious about finding practical sustainability solutions.

The final project cost for Sarginsons was calculated at £750 giving a payback of under 7 months:

Electric Power Saved 7776 kWh

Financial Savings £1,353

Emissions Savings 1,651 kgCO2e

Project Cost £750

This project demonstrates that reducing emissions need not be a financial burden for manufacturers but an incentive to save money. Waste heat recovery can provide low-hanging fruit for smaller manufacturers in terms of energy and carbon saving.

Rick Davies, Engineering Director at Sarginsons Industries Ltd comments:

“We knew that excess heat was being given off by this equipment but didn’t think about how we could capture and utilise it. WMG helped us see how relatively easy it is to recover waste heat and recoup investment in a very short timeframe. In the current climate of spiralling energy costs I would recommend every manufacturer takes a look at the significant potential saving waste heat offers for their bottom line”

With around 70% of manufacturers using compressed air in the UK, and a host of other waste heat sources that can be utilised at a given site, the opportunity here is clearly a massive one and WMG has shown how it can be realised. The next edition of this series will cover the final implementation of the project to validate energy saving estimates and give an indication of what a system like this could look like.

This HVM Catapult funded project by WMG shows how considerable amounts of wasted heat from compressors can be captured and reused on-site. It should be noted that waste heat recovery is not the only way compressors can be made more efficient, and the method outlined above is not the only way to recover wasted heat. Some compressor manufacturers offer built-in waste heat recovery options or retrofits and the British Compressed Air Society has published a white paper on how to make your compressed air system as efficient as possible.

To discuss how WMG can work with your business please contact us at: wmgbusiness@warwick.ac.uk