[LCE23] Low hanging fruit in decarbonisation of buildings? Wastewater Heat Recovery (WWHR) systems

Every day, more than 22,000,000 m³ of hot water are consumed by European homes alone. It is a major source of energy consumption for new housing, and yet 80 percent of this heat ends up in sewers and is wasted. Considering hot water is mostly used in showers, recovering waste heat from shower drains could be a simple way to save up to 70 percent wasted energy and related CO2 emissions.


  • Robert Pinter, European Copper Institute
  • Hugo Durou, WWHR Europe



Low hanging fruit in decarbonisation of buildings? Wastewater Heat Recovery (WWHR) systems

Links & resources



1) Is there a publication on the energy and CO2 calculations in the presentation?

>Details in the white paper: https://issuu.com/copperinarchitecture/docs/wwhr-white_paper

2) I have heard about similar systems that apply to a large building or neighbourhood. Could you explain whether it makes economic sense to do this at scale, rather than for individual showers

>There are two type of collective WWHR systems: 1/ medium (8 k€ for up to 100 rooms or appartments) 2/ large (1 to 2 M€ for a whole neighborhood). Roughly, for up to 20 appartments individual WWHRS are the cheaper option, beyond 20 appartments medium is usually cheaper. Large WWHRS (1 to 2 M€) usually require a big demand for heat nearby (swimming pool, facility...).

3) Do you have an estimate of capital cost and instalation cost in new build and in retrofit?

>New buildings can be designed at an early stage. Capital cost 200 to 2000 € for individual WWHR systems and 100 to 400 € per appartment for collective WWHR systems.

4) What be the payback from installing a WWHR system for a typical family shower system: (a) full investment, (b) marginal extra investment if the shower were to be upgraded anyway?

>WWHRS hardware costs 200 to 2000€, installation costs (a) 200 to 1000 € or (b) 50 to 200 €.

5) If annual cost savings are €50-150, what is the payback period for such installation?

>It ranges from 2 to 10 years, depending on the WWHRS and energy cost.

6) Why not include oils/ solid fuel/ etc in your total EU saving potential? After all, a lot of this energy will be used for showers.

>Electricity and natural gas represents 66% of energy source for water heating in EU households. In a simplified method only these two main sources were taken into account (energy savings, GHG emissions) to demonstrate order of magnitude.

7) Do you have an estimate of the embedded carbon in the manufacture of these systems

>Systems range from 1 kg to 10 kg per individual unit.

8) What is the expected lifetime and mainenance cost?

>Most WWHR systems are completely still with no moving parts, so expect a lifespan from 30 to 50 year just as regular piping. WWHR systems with automated backflush required a battery to be recharged every 15 years.

9) What about the maintenance costs (cleaning) of the heat exchanger? I assume the freqency must be quite high.

>It depends on the users (hair, length of showers, type of soap). Automated backflush system are set to one cleaning every 10 days. Cost is hard to compute as most users do the cleaning themselves or it is automated.

10) How do you treat the dirt and/or hair in the drain water from shower?

>Three methods: 1/ dismanteling the unit and clean it by hand. 2/ use brushed sold by the manufacturer 3/ some units have automated backflush cleaning.

11) In the total consumption savings and GHG emissions calculations by 2030, is the increase in the next years of renewable energy power production (or distributed power generation) share taken into account?

>The GHG emissions are calculated assuming gas and electricity as heat source only and with current CO2 kg/kWh coefficients. Growing share of renewable energy will, of course, influence avoided emissions in the future but recovered amount of energy will stay constant.

12) I understand that WWHR can also be used for space heating and coolling. Could you comment on that possibility?

>Usage for heating and cooling requires large number of users to ensure there is a continuous flow of wastewater - as much as possible. It is most seen with district-sized WWHR.