Water and Energy Systems in the Built Environment

Abstract

The water and wastewater infrastructure of the built environment is currently operated as a linear system that delivers potable water and removes wastewater, carrying away the energy and resource potential embedded in the streams that pass through buildings. Recovering this potential through integrated water-energy systems is technically feasible, but adoption remains limited by fragmented assessment methods, divergent stakeholder priorities, and institutional structures that do not align with the resource-efficient configurations such systems require. This thesis investigates how water and energy systems in the built environment can be assessed and developed to be more sustainable, energy and resource-efficient, through four interconnected studies.

A comparative characterization of numerous water streams in a typical building was developed, integrating volume, quality, and energy content into a single reference for source-first system selection. Two rounds of semi-structured interviews with thirteen stakeholders spanning regulatory agencies, municipalities, water utilities, property owners, and consultants identified evaluation criteria covering resource efficiency, socioeconomic, and resilience dimensions. These were synthesized into a modular, decision-support framework structured around five stages: conceptualization of the project, description and classification of the site, technical-solution library, system assessment, and multi-criteria decision analysis. The framework was demonstrated through a proof-of-concept application and shown to produce consistent rankings across a wide range of weight configurations.

Two integrated case studies were numerically modelled, with key components validated against pilot installations in Gothenburg. A rainwater-based system combining evaporative cooling with toilet flushing was simulated. Using the suggested rainwater catchment area and tank size, energy savings of 19–28 % in commercial buildings during cooling periods were achieved, with residential savings falling as low as 1–7 % annually with negative energy savings for certain sizes. This was mainly due to limited cooling demand and high parasitic losses. An integrated greywater reuse and heat recovery system at the HSB Living Lab delivered approximately 22–23 % energy savings and 92 % water savings for toilet flushing, with the main trade-off appearing not as competing water- and energy-saving objectives but as a moderate increase in treated-water residence time.

Across the four studies, good technical performance emerges as necessary but is not the only constraint for implementation. Stakeholder priorities, such as environmental, cost and health aspects, are essential, but institutional barriers, such as split incentives, regulatory uncertainty, and the cost-price principle must be aligned to form an optimal environment for system implementation realization. In addition, the decentralization-centralization trade-off for downstream resource recovery has to be considered to avoid suboptimization. Further institutional alignment across climate adaptation, water management, and energy efficiency policy is a precondition for translating technical systems and stakeholder priorities into implementation at scale.

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