Legionella safe & energy efficient domestic hot water with limited wat

Aim and goal

This project aims at evaluating how a limited domestic hot water (DHW) volume at reduced temperature will affect the growth of Legionella and how such a system could be implemented in real buildings.

Challenge

One important aspect in sustainable building is to optimize energy consumption, with DHW temperature being one essential factor. The optimal DHW temperature is often a balance between energy demands and microbial safety, in particular the risk of Legionella spp. at temperatures below 50 °C. Methods to remove Legionella used today has been shown to last for a short time and give rise to e.g. problems with leakage due to damage on the DHW installations. There is therefore a need to investigate novel approaches to solve this problem.

Solution

In new building constructions and renewal projects it is important to design the DHW system correct to minimize energy consumption and lower the risk of Legionella. One such approach would be to use a small volume of DHW, e.g. 3 L, and to heat the water instantaneously when needed. This approach has been tested in Germany and Denmark, but further evaluations are needed under Swedish conditions. There is also a need to study the Legionella biofilm formation under controlled conditions in such a system to be able to assess the risks in a long-term perspective.

Effect

The investigated system could potentially provide a stronger Legionella protection, and simultaneously allow a reduction of the DHW temperature with substantial reduction in the energy consumption.