Maintaining the quality of DHW in district-heating schemes
With the growing use of district heating in residential buildings, SAV System has expressed concern that the quality of domestic hot water is being compromised through inadequate control. Sales director Jan Hansen, explains, ‘The main problem lies in the use of heat-interface units that lack useful control functionality, as this results in lack of responsiveness and poor temperature control of domestic hot water.’
He elaborates, ‘For example, if there is no differential-pressure control or effective control in the heat-interface unit (HIE), the temperature variation of the DHW can be as much as ±15 K. So in a system designed for a DHW temperature of 50°C, the actual temperature could range from 35 to 65°C.
‘Such units are often installed because they are seen as being relatively cheap.’
In contrast, SAV’s FlatStation HIUs incorporate a differential-pressure control valve to ensure that the differential pressure remains at around 35 kPa in every unit, irrespective of its location in the distribution system. The result is that DHW temperature is controlled to within ±2 K.
These HIUs also incorporate an integral idle temperature controller in the control valve to ensure that the water in the supply pipe remains warm to ensure responsive DHW, even when space-heating loads are low.
Jan Hansen concludes, ‘Historically, HIUs in district-heating schemes have been treated as accessories rather than as a key element in the system. This is something that has to change if we are to avoid disappointing the end user and embarrassing the specifier.’
