Community Research and Development Information Service - CORDIS

Recycling the heat in hot water

Hot water is taken for granted in western societies. However, preparation and storage of hot water is a costly process that consumes a great deal of energy.
Recycling the heat in hot water
The hot water for dishwashers, washing machines and showers, the production of which accounts for approximately 90 % of the energy usage of these appliances in Europe, is discharged into sewers. Recovery of the heat in the still-warm wastewater could significantly decrease energy consumption and help meet legislative requirements for sustainable management techniques in heating and plumbing.

The EU-funded project ‘The development of a new domestic heat recovery technology for low grade heat in waste water’ (LOW-HEAT) sought to capitalise on the heat energy in this warm water stream from everyday household usage to supplement domestic boilers.

Conventional heat exchangers are not suitable for heat recovery under low-flow conditions such as those in household wastewater disposal. In addition, the wastewater has a variety of contaminants including chemicals and solid matter that could both decrease system efficiency and life-span as well as create undesirable odours.

Thus, the researchers set out to develop innovative technologies including equipment and controlling software to overcome the inherent problems of wastewater re-use and make it both feasible and cost effective.

Specifically, the investigators developed a system consisting of three components: an innovative heat exchanger, a drain device and a radio frequency (RF) controller. The system enabled automatic activation of the pump when a temperature over 30 degrees Celsius was detected. The software was capable of enabling clearance of filter blockages by temporarily reversing pump action. Finally, the RF controller provided the end user with information related to cost, energy savings and maintenance requirements.

The system facilitated recovery of up to 50 % of the wasted heat energy, significantly reducing energy consumption and carbon dioxide (CO2) emissions. The cost analysis demonstrated a payback time of four years for a fully operational system, making it a viable and competitive alternative to commercially available systems.

The LOW-HEAT project outcomes resulted in an award for energy efficiency, a patent for the technology and European recognition of the potential for exploitation. Thus, the researchers provided an important stimulus for greener homes and businesses and a competitive edge for the European heating and plumbing industry.

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