Domestic hot water (DHW) refers to the hot water used in sinks, showers and baths in any type of building (not just domestic dwellings). As such, it is different from the hot water contained within heating pipe-work, although water for both purposes is often generated by the same system. Unlike water in heating systems, DHW is potable as people may consume it deliberately or accidentally during bathing / showering.
Typically, hot water generated by a heat source such as a boiler or combined heat and power unit goes through one stage of heat exchange before the resultant DHW is stored in a vessel, such as a calorifier. It is then available when the need for DHW arises. However, systems equipped with SAV’s Flatstation HIUs (heat interface units) can generate DHW instantaneously within a user dwelling using hot water from a central plant room. Each HIU uses a compact plate heat exchanger to maintain separation of the two systems.
DHW is normally supplied to taps and showers at temperatures of between 50 – 60 degrees Celcius, and to a professional kitchen at 65 degrees C so as to satisfy hygiene standards. DHW should be stored at temperatures above 60 degrees C, to ensure there is sufficient heat to kill off Legionella bacteria. This storage temperature can then be reduced at tap outlets by using blender valves to mix with cold water.