NSF Early-concept Grants for Exploratory Research (EAGER):
Environmentally responsive, water harvesting and self-cooling building envelopes
Prof. Shu Yang, MSE CBE SEAS, University of Pennsylvania
Prof. William W. Braham, CEBD, University of Pennsylvania
Prof. Jie Yin, Mechanical Engineering, Temple University
Max Hakkarainen, CEBD, University of Pennsylvania
Evan Oskierko-Jeznacki, CEBD, University of Pennsylvania
Water Vapor harvesting for self-cooling
A "high risk-high payoff" approach to create an environmentally responsive building envelope that will address the two critical factors of building energy use and urban resilience deserve urgent attention. Given the high complexity of the problem, it will require highly explorative work that can transcend traditional disciplinary boundaries to address the grand challenges we face. This project exploits a drastically new and highly scalable approach, kirigami (cutting and folding), where reconfigurability and cooling processes are “materialized” in building envelopes that sense and actuate in response to environmental change (e.g. heat, humidity, and wind). The building envelopes will harvest dew water in the early morning and later release it via evaporation, thus, dramatically reducing the cooling load of building elements. This is similar to the effect of living plants on facades, but our building envelop will gather its own water, exploiting the natural day-night humidity cycle. In its harvest-evaporate form, it applies to the moist and marine climates of the US, where most of the population lives, and can be adapted as an evaporative surface in the drier regions.
Base materials of kirigami structures. As a proof-of-concept, we are using transparent PET films as a substrate to test various cut designs and absorbing materials for water vapor collection and evaporation, taking advantage of the daily moisture cycle to lower the daytime temperature of the building envelope. PET film is widely used as a backsheet in thin film solar cells due to its excellent optical transparency (> 90% transmittance in the visible wavelength) and long-term stable mechanical, thermal, and chemical properties under severe weather conditions. It also has low moisture permeability and low water absorption. Therefore, it will be a good candidate for kirigami-based building envelopes for outdoor uses. Al foil is used in buildings to prevent heat loss through floors by radiation (up to 93%) due to its low absorption and emissivity ratio (~ 5%). Al foil can reflect 95% of all radiant energy to block the flow of radiation with its reflective surface, thus reflecting the heat back into the building and preventing the heat loss. The attributes of Al foil including flexibility, high strength and durability, ease of lamination and coating, high heat conductivity and reflectivity, recyclability, and barrier efficiency to water vapor make it a good choice as the base material here.
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