Exchange waste water for cash and carbon savings

By Isabel Schestak, Post-doctoral researcher, Bangor University

Commercial kitchens in the UK hospitality and food service sector consume more energy for the preparation of meals than cooking in domestic kitchens. However, they can also play a vital role in climate change mitigation. The heat in the drain water of commercial kitchens is a valuable source of energy, which – when recovered – saves energy for hot water heating and hence carbon emissions but also costs. Researchers from Bangor University/Wales and Trinity College Dublin/Ireland, working in the Dwr Uisce project, have installed a heat recovery system at a demonstration site restaurant of the National Trust at Penrhyn Castle/Wales, and found that approximately 30% of water heating energy can be saved through harvesting the free heat being normally just flushed down the drain of a kitchen.

The technology is simple: a heat exchanger – a double walled copper pipe – replaces a part of the kitchen’s drain, through which heat is transferred from the warm drain water to the cold incoming water. The boiler receives the pre-warmed water and requires less energy to heat the water to the desired temperature. If all food outlets in the UK were to install a heat recovery system, an estimated 500,000 tonnes of CO2e could be saved every year, equivalent to taking 260,000 cars off the road, making a significant contribution towards a net zero hospitality sector (Schestak et al., 2020). The researchers developed an Excel-based tool for operators of commercial kitchens which can estimate the individual savings potential for a specific kitchen, for both costs and carbon emissions (Schestak et al., 2021). For instance, a restaurant with a water consumption of 2,000 m3/year could recover approx. 16,000 kWh/year and save 4,000 kg CO2 equivalent – considering that natural gas is replaced. With a gas price of 3 p/kWh this translates to savings of about £5,000 for 10 years of operation. If the kitchen uses electricity for water heating at a rate of 14 p/kWh, heat recovery would save £22,000 in 10 years.

An analysis of the commercial kitchens in the UK showed that the majority would be able to achieve a financial payback within less than 10 years after considering the installation costs of the heat recovery system (Spriet and McNabola, 2019).

The technology and the tool will be introduced through a free 1-hr online webinar open to all interested stakeholders involved with commercial kitchens such as in hotels, restaurants, pubs, cafes, canteens etc.: Register now: “Don’t flush money down the kitchen drain!”,  March 15, at 10-11am GMT. You will learn how heat recovery from kitchen drains works, incl. showcasing of the demonstration site in Bangor, Wales; and get an individual estimate for the savings achievable in your case using the Excel-tool.

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