A Water-Energy Nexus approach for Integrated Design and Operation of Water and Energy Systems in Buildings

The water-energy management at a building scale is gaining attention. Greywater and rainwater can be treated and reused for non-potable end-use through an on-site wastewater recovery system. However, reducing the building’s water use increases the building’s energy use. That’s why it is necessary to consider the interactions and trade-offs between water and energy to prevent shifting problems from the water sector to the energy sector. This study evaluates the water-energy system at a building scale through a multi-objective approach. It includes water (network water, wastewater and rainwater) and energy (space heating, hot water and electricity demand). Different water resources (network water, greywater and rainwater) and different water demands quality are considered. According to the results, CHP (combined heat and power) technology is the most efficient in terms of water-energy supply at a buildings scale. Rainwater harvesting for non-potable purpose is interesting through the GDM (gravity-driven membrane) treatment with a membrane area around 8 m2. A decrease of 88% of the network water consumption is achieved by increases the total cost only by 7%. Rainwater harvesting should be prioritized over greywater reuse. The volume of the rainwater storage varies from 0-1900L. The independence of the network water for non-potable use increases the total cost of 39% with a volume of the rainwater storage variating from 1900-2600L. In conclusion, it is better to invest in rainwater harvesting instead of greywater reuse.