Low temperature district heating (DH) is designed as 55/25oC for supply/return temperature to fulfill the low energy demand of future buildings. However, to secure the safety of domestic hot water, the supply temperature has to be kept around 60oC to avoid the existence of legionella, which reproduces rapidly at the temperature around 25oC- 45 oC. After several outbreaks of pheumonia and fever caused by legionella bacteria, most countries require 60 oC in the network and 50-55 oC at the faucets with periodic flush by hot water above 60 oC as disinfection solution. That makes obstacles of low temperature DH implementation. Therefore, effective solution of legionella bacteria is in urgent demand. To select optimal disinfection treatments for certain cases which are quite different in dimension or purpose of use, various methods were reviewed, including shock hyperchlorination, super heating, electric boiler, compact heat exchanger, water filter, chlorine dioxide, Monochloramine, UV sterilization, copper and silver electrodes. The implementary conditions, effect, limits as well as economic performance of them are demonstrated. For buildings with complicated networks and large volume, chemical approach is widely used, and oxidizing disinfectants have a better effect and economic performance. For buildings with DHW volume less than 3 liters, implementation of compact heat exchangers is an effective solution. By reviewing the efficacy of each method, the optimal solution for low temperature domestic hot water system is recommended by this study, which is of great use to realize low temperature DH system without any risk of legionella.
Proceedings of the 8th Conference on Sustainable Development of Energy, Water and Environment Systems, 2013
Legionella; Disinfection methods; Domestic hot water system; Control regulations
Main Research Area:
8th Conference on Sustainable Development of Energy, Water and Environment Systems (SDEWES 2013)