The challenge 

Heat recovery is a significant challenge for the food sector. In commercial kitchens, food is heated from chilled very quickly, which requires a lot of energy and a lot of heat, most of which is wasted.

To reduce the environmental impact of commercial kitchens, there was a need to develop a new system to reduce waste heat and make steps towards meeting net zero targets. 

This solution is not without challenge. Any system has to perform highly and overcome obstacles like grease and flame protection, while working to recover low-grade waste and reintroduce it to the kitchen’s system.

Lancashire firm Dext had an idea: what if they could recycle heat waste from commercial kitchens in a way that would reduce energy costs and environmental impact?

What we did

Using sector-leading modelling techniques, including computational fluid dynamics (CFD), our academics helped Dext to develop a radiative heat recovery panel that could be installed close to cookers and chargrills in the form of a splashback.

The DexTherm heat recovery panel absorbed waste heat and transferred it into a sealed water circuit, which was then circulated through a coil in a cylinder, providing hot water for the kitchen and substantial energy savings. The system had the advantage of performing well in difficult operating circumstances as well as being effective, robust, relatively low-cost and easy to clean.  

Today, this innovative splashback is used in more than 400 Nando’s restaurants across the UK. 

Building on their initial success, the next project was to develop a bigger, more powerful heat recovery system that could sit within a kitchen’s extract duct. In 2013, Dext secured a Knowledge Transfer Partnership to employ a graduate mechanical engineer to work with our expert academics to make this vision a reality. Following the success of this partnership, KTP associate Gareth has become Dext’s Technical Director and is integral to the ongoing development of the company. 

During the Knowledge Transfer Partnership, the team scoped an experimental manufacturing solution, which resulted in a prototype heat exchanger and heat pump plant. The plant needed to recover the waste heat from the kitchen air extractor and provide hot water, space heating and cooling for the entire restaurant. It also needed to operate within dirty and greasy air streams without system fouling or failure.  

A custom wind tunnel was made specifically for the project, creating the opportunity for comprehensive test data and further validation of the computational models and selection software to improve the performance of the heat exchanger. 

In 2014, the experimental system was successfully installed in a restaurant to evaluate its performance.  Following the installation, proof of concept was achieved which provided a strong and encouraging business case, it was a good idea, but it could be developed.  Dext knew a full research and engineering project was needed to unlock the potential of such a system and reduce its complexity.

In 2015, Dext collaborated with Hallam’s National Centre of Excellence for Food Engineering (NCEFE) who helped set up a consortium with Dext, William Jackson Food Group and DCI Refrigeration.

The consortium successfully secured funding through the competitive Innovate UK ‘Improving Food Supply Chain Efficiency’ fund. The result was a £600k project to develop a fully-fledged new heat recovery system based on the prototype.  

The project brought together all the previous experiments and prototype testing to create a full scale, comprehensive  development project. The ‘living lab’ facility was located in the Advanced Technology Park in the outskirts of Sheffield to develop the DexThermic ‘Dirty Air Heat Exchanger’ (DAHX). 

Initially, small-scale prototypes were tested and validated against the CFD models, and as the science stacked up, the ambition for the project increased.  In 2018, the final year of the UKRI project, the third scale prototype became a reality. 

Drawing heavily on Gareth’s Ministry of Defence production engineering background, the result was an efficient and cost-effective system, made from aluminium and stainless steel, using a technically advanced design and manufacturing process, which didn’t collect oily residues. 

The low air pressure drop design allowed for the unit to be fitted to the existing air handling system and showcased its resistance against grease build up.

The result

The product proved its ability to recover enough waste heat from the cooking process, and from the body heat of diners in the restaurant, to provide space heating and hot water for the entire restaurant. 

Dext has also developed ‘DexTcalc’. Based on comprehensive test data and complex computational modelling, this predictive software can accurately calculate forecasted energy reductions and cost savings for potential new clients. 

A full-size trial at Nando's Parrs Wood further proved the product’s robust performance and, after some very positive press in 2023, the Dext team have deservedly received a tidal wave of enquiries for their pioneering heat recovery system. 

The collaboratively created and academically tested sustainable innovation, DexThermic is the result of vision, passion and engineering expertise being focused on the hospitality sector with amazing results! 

“An idea, however good it may be, can only come to successful fruition if you can prove its worth, and Sheffield Hallam Uni gave Dext that opportunity. We were able to turn an idea into a real, robust, ready-for-market product thanks to the academic team and the facilities made available to us. Where else would we get our hands on a full-scale specially built environmental wind tunnel?!

“Now our sustainable heat exchange system is taking the UK catering industry by storm and we have all the data to prove its merit.”

Neil Bracewell, Dext Commercial Director.