Heat recovery from greywater tested under real conditions

The CSTB's R&D experimental set-up, Simulhome, in Nantes. Photo : Aurélien Mahot - Clan d'œil

A research team of the CSTB worked on estimating the potential for instant heat recovery from greywater, thanks to the experimental installation Simulhome at the Aquasim test facility. Simulhome reproduces domestic water use realistically, in a standard-equipped housing unit.

Analyzing how various solutions perform, while they are in use

Systems for instant heat recovery from greywater can be installed downstream from a shower base, to recover some of the heat of the water that is being discharged to the sewer. The recovered energy can be used to reduce the amount of energy used to produce domestic hot water.

The CSTB sought to quantify, on the scale of a household, the potential for heat recovery in three installation configurations: sending the preheated water back to the water heater, sending it directly to the cold side of the shower mixer valve, or sending it back to both places (water heater and shower mixer valve) at the same time.

The performance of the heat exchangers can already be measured according to recognized protocols, under a given set of conditions. But the CSTB wanted to compare these results with the reality of how the solutions perform in a home, where the users adjust the flow rate and the mixing of the hot and cold water, and where the temperature of the cold water varies, etc.

Full-scale test as close as possible to reality

Simulating the behavior of a heat exchanger at full scale in an environment identical to the environment of a housing unit: this is the objective of the Simulhome experimental set-up. It was developed by the CSTB at Aquasim, its test facility in Nantes, which studies the water cycle at the scale of the building and its plot of land.

Simulhome comprises a complete household plumbing system, with 7 draw-off points: toilet, shower/bathtub, bathroom sink, kitchen sink, water heater, dishwasher and washing machine. The set-up reproduces standard patterns of water use: shower at 8 am, kitchen at noon, dishwasher at 8 pm, etc. Sixteen temperature sensors, six flow meters, three energy meters, two smart water meters and two pressure sensors (for hot and cold water) are used for monitoring water use.

Results: the study showed that the best yield is achieved when water is sent to the mixer valve and the water heater simultaneously. These findings help assess the system's potential to recover heat from greywater.

Innovation in research at the European scale

This study is part of the Wisdom, R&D project, supported by the European Commission. The aim of the program is to optimize the management of water resources, and so it explores the entire water cycle, from the extraction of water before it is used, to its return to the environment after usage and treatment. The project has eleven public and private European partners, including the CSTB, which provides its major facility, Aquasim, and its expertise in sustainable water management.

Find out more: