A proposed new UK framework for the sizing of domestic hot and cold water systems for medium-large scale residential buildings

There now exists relatively widespread concern across the building services and public health engineering communities that the loading units approach used for the sizing of domestic hot and cold water systems is no longer fit for purpose. In addition to the known variance and diverging results calculated using relevant codified documents, anecdotal evidence also suggests significant over-sizing of pipes; an aspect of design that impacts directly upon system performance, space-take, energy consumption and potentially water quality parameters.
This paper summarises the report from Phase 1 of the LUNA (Loading Units Normalisation Assessment) project, which recommended that a new framework for the sizing of domestic hot and cold water systems for medium-large scale residential buildings be adopted in the UK[13]. Both case study and measured data are summarised, where datasets were compared to establish the differences between estimated and ‘actual’ values of flow. The paper also presents a preliminary analysis of the lower threshold for the definition of mid-small size residential dwellings, below which the method adopted is mapped to selected design flow rates.