Low Flow showers

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Specifying Low Flow showers in the DHW dialogue can reduce the demand for a DHW system by up to 35%. However, in many cases, low-flow showers and showers employing Waste Water Heat Recovery may not reduce the demand at all.


The SBEM database includes a field representing the Shower Fraction for an Activity. This can take a value as high as 0.88 (ie 88% of hot water demand is from showers) or as low as zero. For the majority of activities, the value is zero.

A DHW System will likely serve multiple types of activity so a saving as high as 35% would be unusual, however, activities with a high shower fraction also have a very high demand for hot water so a value close to this is feasible.

Note: that all activities with a shower fraction of 0.88 are 'Changing Room with Showers' activities. All these have an exceptional DHW demand that often skews a BRUKL or EPC calculation. Employing low-flow technology in such buildings may well significantly reduce ratings.


The following activities have a shower fraction of 0.7. DHW systems supplying these could have a reduced demand of 28% with all low flow showers.



The following activities have a shower fraction of 0.12. DHW systems supplying these could have a reduced demand of 5% with only low-flow showers. All other activities will be unaffected by the presence of low flow or WWHR showers.