Environmental impacts and benefits of heat recovery in kitchens
This study explored how to sustainably recover heat from drain water in commercial kitchens, based on experience gained at Penrhyn Castle demonstration site.
We determined the environmental impacts associated with manufacture and installation of a drain water heat recovery system comprising all necessary equipment such as an in-line heat exchanger and connecting pipework and fittings. Through a Life Cycle Assessment (LCA), environmental impacts starting from raw material extraction and ending with recycling and/or disposal of the equipment were quantified. The majority of the environmental burden is caused through the manufacture of copper parts such as the heat exchanger, especially when made from primary, rather than recycled, copper. Smart material choice can dramatically reduce impacts: recycled copper or newly developed heat transferring materials such as polymer based heat exchangers, or polyethylene instead of metallic pipework.
Comparing the environmental burden of a heat recovery system retrofitted to a commercial kitchen with the avoided burden from the energy replaced through heat recovery.
The environmental burdens of heat recovery manufacture and installation were then compared to the environmental benefits of reduced water heating achieved through heat recovery.
How long does it take for energy savings to payback the environmental footprint of system installation? In the Penrhyn Castle case study, carbon emissions are offset easily within a considered 10-year lifetime of the heat recovery system, no matter if renewable or fossil fuels for water heating are replaced through the recovered heat. We did notice some trade-offs though, when considering other environmental impacts such as resource depletion, owing to large amounts of metal used in heat exchange systems.
Impacts per kWh compared: heat recovery from kitchen drain water vs. other energy sources for heating water. Recovering heat reduces environmental impacts even when replacing renewable heat, especially for climate change mitigation (GWP – Global Warming Potential). Other impact categories shown: AP – Acidification Potential, FEtoxP – Freshwater Ecotoxicity Potential, RDP – Resource Depletion Potential. H. recov – Heat recovery from kitchen drain water. From: Schestak et al. 2020.
Trade-offs can be negated when heat recovery systems are used in kitchens with higher water consumption, where large heat recovery potential offsets all impacts of installation. For a heat recovery system consisting of a copper heat exchanger and pipework of 10 m, full environmental payback within 10 years can be achieved from water consumption rates of about 555 l/day. The installation of a heat recovery system can provide environmental benefits not only when electricity from a non-renewable source or gas is replaced, but also in the case of replacing solar or geothermal energy, or wood pellets. If heat recovery was applied in the over 200,000 commercial food outlets in the UK, about 500,000 tonnes of CO2 equivalents could be saved per year. That is equivalent to taking 260,000 cars off the road.
For the full scientific study, click here.