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2015 Solar Decathlon: NexusHaus

The University of Texas at Austin, Technische Universität München

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U.S. Department of Energy


  • Darren Cattle, Abhishek Pratapa, Alejandro Silveyra, W. Alex Best, Travis Schneider, Yang Chen, Megan Recher, Kelsey Kaiser, Julia Park, Ryan McKeeman, Charles Upshaw, Kendall Claus, Jessica Janzen, Kristen Cetin, Arianna Hallenbeck, Ana Kauachi, Claire Haupt, Emily Heitzwebel, Kara Turner, Kaitlyn Gruener, Joshua Rhodes, Lauren Jones, Sean Moore, Reese Hatridge, Samantha Kambo, Julian Debo, Henry Wen, Michael Rahmatoulin, Alexandra Krippner, Ariel Padilla, Miren Urena, Andrea Tosi, Chiara Bonsignori, Aaron Hobbins, Vivek Shastry, Trey Farmer, Molly McNamara, Nari Shin, Hayley Smith, Anthony Abousleiman, Cheng Jia, Frank Ordia, Trond Bjarne Pettersen, Junji Kubo, Aina Tapias, Jose Maria Arribas Lopez, Mira Gloser, Miriam Santambrogio, Astrid Eyskens, Paloma Caballo, Rocio Romero Reolid, Irene Escude Moreno, Miguel Perez, Wolfgang Vidal, Federico Rebecchini, Enedia Lila, Bruna De Ranieri Cavani Ferramenta, Kristina Grondahl, Nicolo Temperi, Yvonne Berreiter, Rocia Pelaez Gutierrez, Alessandro Corso, Marta Ines Cot, Cibele De Avila, Luca Scubbi

Project Status

Student Work


784 sq. feet

Construction Cost

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Project Description


The NexusHaus is the entry of The University of Texas at Austin (UT) and Technische Universität München (TUM) for the 7th U.S. Department of Energy Solar Decathlon 2015.

Austin has been the fastest growing city in the nation for the last four years by currently 110 people net moving to Austin each day. As a result, the demand for affordable housing and the growth of suburban poverty has increased exponentially. The NexusHaus demonstrates the potential of combining energy and water to design a prototype of an affordable Accessory Dwelling Unit (ADU) as a unit of production that can easily augment the existing neighbourhood’s infrastructure without increasing demand for energy and water.

The design concept for the NexusHaus has been driven by the following overarching ideas: urban infill strategy via ADU development, affordable green building design, energy-water nexus, space extension, and smart technology. The two each 392 square foot modules consist of a day module that contains living, dining, and a kitchen, and a night module with a master bedroom, studio and a bathroom. The two can be placed in a number of different configurations depending on the site and the needs of the client.

The interior spaces can spill out onto fully shaded generous outdoor decks. These outdoor spaces are emblematic of the Austin experience, a sociable one that takes full advantage of temperate weather in the fall, winter, and spring. The canopy has a low light-transmittance to provide shading for the full height windows and doors and also captures the rainwater. The two modules are separated by a central space that is intended to be enclosed in the winter increasing the compactness of the entire structure, and capable of transforming itself into a ‘dog-trot-porch’ configuration seasonally.

NexusHaus minimizes on-peak consumption and maximizes on-peak production. Cooling and heating for the NexusHaus is provided by an air-source reversible heat pump with hydronic distribution to ductless fan coil units. The Integrated Thermal Energy and Rainwater Storage (ITHERST) system shifts cooling off-peak to low-demand night-time hours. This integrated thermal water storage system was developed specifically by Charles Upshaw, PhD candidate and the students’ team captain, for the NexusHaus as a proof-of-concept and is meant to provide an advanced design scenario by making use of systems not currently common in residential houses.

The NexusHaus focuses on water conservation and rainwater collection to supply all of its potable water needs. Rainwater will be captured from both the canopy and the roofs. The goal is to become one of the first permitted houses within the City of Austin that uses rainwater for potable water. Grey water collected from the bathroom sink, shower, and laundry is used to irrigate the landscape. All appliances and fixtures are highly water efficient. The rainwater/thermal storage tank, which is located in a conspicuous spot along the primary entrance, acts as a secondary storage volume for rainwater and gives the system additional capacity while also providing beneficial load shifting. The NexusHaus has also incorporated the use of an aquaponics system for on-site food production. Aquaponic systems combine aquaculture and hydroponics into a cohesive cyclical system for growing edible plants. 

In addition to the water and energy concepts, NexusHaus focuses on involving the residents in the everyday life of the building through a student-designed home management system called NexSmart. Residents will be able to maintain and create a customizable home that cares for them. NexSmart will also serve as an educational tool that gives residents agency and allows them to live more sustainably through understating their behavior.

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