Journal article

In-building waste water heat recovery: urban-scale methods for the characterisation of water streams and the assessment of energy savings and costs

Residential domestic hot water (DHW) energy consumption represented 16% of the EU household heating demand in 2013. With the improvement of the building envelop, DHW contribution to energy consumption is expected to increase signi cantly, with values between 20% to 32% in single family buildings, and between 35% to almost 50% in multifamily buildings. This energy, currently lost to the environment, can be recovered by waste water heat recovery (WWHR) systems inside buildings (in-building solution). However, the characterisation of residential grey water streams at urban scale has barely been addressed. Also, the impact of such solutions on the total heating consumption and the related costs has not been assessed in detail for di erent types of residential buildings or for urban systems. The characterisation and geoallocation method of grey water streams as to mass ow and tem- perature level is therefore addressed. A method to quantify the energy saving potential and costs at urban scale of in-building WWHR systems in residential buildings is also proposed. These methods are applied in two case-studies, rst as retro tting solution in a city in Luxembourg and, second, as optimisation measure for high e ciency residential buildings. Grey water heat recovery would reduce the residential fuel consumption of the city by 6.3%. An integrated approach combining grey water heat recovery for hot water preheating and a heat pump yields up to 28% and 41% electricity savings for passive single family houses and multifamily buildings, respectively. With the detailed characterisation of various grey water streams in function of inhabitant number and end-use occurrence, the quanti cation of the energy savings and costs through heat recovery is improved. The outcomes of urban energy and cost assessments concerning grey water heat recovery are more speci c, as the results at building level are aggregated to the considered geographical scope. The proposed method therefore complements current urban energy and cost assessments with the detailed integration of in-building grey water heat recovery systems.

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