Energy and Water Autonomy for Off-Grid Waterfront Floating Structures

Waterfront communities are the most susceptible to climate change and to extreme weather events. Beyond the risk of flooding itself, centralized water and energy systems are prone to failure under dynamic storm conditions; the connectivity of sewage and water supply in waterfront neighborhoods is often compromised during storms. For instance, in 2012, during Hurricane Sandy, supply and distribution chains to Red Hook, Brooklyn were disrupted and sewers were backed up, which resulted in untreated wastewater flooding the streets.

The RETI Center’s BlueCity Lab (BCL) project was born in response to these failures. The BCL will be a water-borne physical space and community support structure sited in Red Hook’s Gowanus Bay (Figure 1a; Nandan et al 2020). In parallel, the Philadelphia Water Department has been working on a floating classroom on the Schuylkill River in Philadelphia (Figure 1b; Philadelphia Inquirer).

Floating structures are designed to adapt to rising waters. In past demonstrations in the Netherlands, such structures have proved capable of withstanding sea level rise as well as the increased frequency and intensity of storms (Edidin 2005). However, because of their siting on water, they present a major operational challenge: they must operate off-grid as connections to central water and energy infrastructure become difficult or even unfeasible. Instead, such structures must be designed to be self-sufficient; their requirements raise specific questions on water and energy autonomy at the building scale. My lab at the University of Pennsylvania Weitzman School of Design, the Thermal Architecture Lab, is part of a collaboration with the RETI Center and the Water Center at Penn, to develop energy and water autonomous systems for off-grid floating structures.

Building Self-Sufficiency Frameworks for Energy and Water Use

Energy autonomous buildings are a branch of the Zero Energy Building (ZEB) typology, characterized by a lack of connection to the grid. They are designed with their own energy supply and storage system and with reduced energy needs achieved through efficiency (Torcellini et a. 2006). Similarly, the water autonomous building, or the Zero Water Building (ZWB), is a novel framework for a building that maintains water-usage independence by employing strategies such as rainwater collection and on-site remediation (Harputlugil et al. 2020). We use these frameworks of water and energy autonomy to develop a model for an off-grid, floating, self-sufficient building.

Residing on Water as an Opportunity

Floating waterfront structures present many potential advantages in relation to both energy and water self-sufficiency. First, due to their siting, such structures are typically not shaded by the surrounding urban context, which allows access to abundant solar energy in comparison with most urban sites. Additionally, their siting in an open space increases their access to wind; this can be useful for turbine energy production as well as for the building’s natural ventilation. In certain cases where strong enough water currents are available, floating structures can also benefit from tidal energy production. Residing on the water also constitutes an advantage: water can be used as a heat sink for summer cooling and as a heat source for winter heating, as water temperature is more constant and less variable due to its thermal inertia.

Design Strategies

In order to make the RETI Center’s BlueCity Lab self-sufficient in both energy and water usage we have worked together with the BCL design team, Gita Nandan, Zehra Kuz, and Tim Gilman, and with our collaborator Dr. Forrest Meggers (Princeton University), to integrate the following strategies into the BCL design process:

Passive Design

Passive design can reduce the energy demand of a building significantly through architectural strategies that moderate the exchange of heat between the building and its environment. These design strategies include building orientation and massing, envelope design, and material selection. We conducted a parametric orientation study to understand its impact on energy demand throughout the different seasons in order to propose ways to minimize the cooling and heating load (Figure 2). We studied natural ventilation and the prevalent wind directions on the site to help determine the best placement of openings in the envelope. Additionally, we examined building envelope materials and the ratio between glazed and opaque façade portions in order to propose a design solution that balances year-round daylight access and prevents excessive heat loss in the cold season. As many of the BCL’s planned educational activities will take place during the daytime, our analysis and design decisions prioritized daylighting to minimize the artificial light energy load.

Figure 2. An illustration of a parametric study of the building orientation and façade design for optimizing multiple variables including solar heat gain, daylighting, and solar power supply, using Ladybug Tools and Design Explorer software. Image credit: Mrinalini Verma and Dorit Aviv.

Energy Supply

In addition to building orientation, form, and materials, we studied energy supply potential through our simulations. The variations in the adjacent illustration show not only building heat gain and loss but also potential energy supply from solar panels positioned on the roof. We propose locating solar panels on the BCL’s roof and south-facing façade to produce sufficient energy for the building’s operation. Small wind turbines and tidal-power technologies are additional possible energy sources to maintain self-sufficiency. A battery is required as part of the energy supply system to store energy from peak periods. Additionally, to mitigate risks in relying on intermittent power sources, we propose embedded sensors and adaptive controls that can help moderate the building’s systems according to available supply and weather conditions.

Low Energy Building Systems

We developed a scheme for a low-energy integrated heating and cooling system that minimizes the building’s mechanical system energy load. Collected data from the bottom of the Gowanus Bay in Red Hook, where the BCL will be built, indicates that the water temperature remains close to 20°C during the summer and stays consistently above the average air temperature during the winter. By using the bay water year-round as a heat sink or a heat source for a high-efficiency heat pump, we can minimize energy expended on heating and cooling. The pump will moderate the water temperature of a hydronic radiant system embedded in the building’s surfaces for indoor thermal control. Natural ventilation will provide fresh air and additional cooling capacity when climatically possible.

Water Supply

The roof of the BCL is designed to allow for the collection of rainwater into a central tank. In our analysis, we found that rainwater collection alone will not support the full operations of the BCL and proposed additional potential options for water harvesting and remediation. Low-tech solar desalination techniques would work well in this context due to the availability of bay water, and adaptive materials such as hydrogels could be used for atmospheric water harvesting thanks to the high humidity level at the site. The weight of the water collection tank must be considered as part of the balance of forces required to achieve buoyancy.

Water and Waste Treatment

The BCL must remediate its own wastewater as well as the polluted water of the Gowanus Bay in which it resides. The BCL’s design team specified a biophilic concrete for use at the hull and the base of the floating garden pods surrounding the BCL (Figure 1a, Figure 3) to attract marine and marsh organisms which, in turn, will engage in and accelerate the breakdown of the pollutants in the water.

We have also studied additional methods for water treatment: a greenhouse at the top floor of the BCL can be modeled as a Living Machine—a wastewater remediation technology that combines elements of conventional biological water purification systems with plants and other organisms; an anaerobic digester can be placed in the hull for solid waste treatment. Figure 3, below, depicts these water supply and remediation strategies, as well as the energy systems explored in this study.

Figure 3. Diagram of water and energy self-sufficient systems for the BlueCity Lab floating structure. Image credit: Mrinalini Verma and Dorit Aviv.

In conclusion, this research for a floating waterfront structure raised significant questions on energy and water self-sufficiency in architectural design. Self-sufficient buildings, while presenting many challenges, also offer the advantage of autonomous system design and operation. These systems do not rely on the urban grid and are designed to be adaptive to changing weather conditions. This study is part of ongoing research at the Thermal Architecture Lab aimed at developing applicable solutions for climate-resilient building prototypes.

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