Low return temperature from domestic hot-water system based on instantaneous heat exchanger with chemical-based disinfection solution

Abstract

Thermal treatment for sterilising domestic hot-water systems requires a circulation temperature higher than 50 °C, which is not suitable for low-temperature district heating systems. Chemical treatment is a temperature-independent sterilisation method for hot-water systems. This study demonstrates that the heat exchanger-based domestic hot-water system of a multi-family building can operate without the risk of Legionella through the use of a chemical sterilisation method. This solution enables the reduction of the circulation temperature to 45 °C to satisfy the comfort requirements. Three temperature operation strategies were tested in the circulation loop. According to the results, the Legionella concentration was minimised. The operation of several thermostatic control valves in the risers was found to be problematic as this resulted in high return temperatures to the heat exchanger. The use of the chemical sterilisation method allows the reduction of the supply temperature below 50 °C and the exclusion of most of the vertical pipelines from the circulation loop . This results in a low return temperature of 40 °C and a reduction in the circulation heat loss up to 66%.