Photobioreactors as adaptive shading devices
by Jan Wurm, 3 March 2012
Mike Davies concept of the polyvalent wall is still a popular reference for all of us researching smart facades beyond mechanical systems. Using multiple coated glass panes that integrate electrically and chemically active layers, the polyvalent wall is able to adjust the transparency to internal requirements and external conditions.
Since 1981 modern glazing technology has come a long way. The complex multi layered build-up of state of the art glazing products allow the integration of most requirements of modern building envelopes: thermal insulation, adjustable shading by means of electrochromic coatings and even energy generation through integrated photovoltaics. However, because most of the material resources would be lost at the end of its life, the multi-layered composite glazing build-ups contradict the principles of Cradle to Cradle. We ask therefore if there is a smarter solution for adaptive shading devices based on fewer components and material combinations?
The utilisation of bio-chemical processes represents one alternative. Photosynthesis generates biomass by absorbing day-light and CO2. Because cell division rates respond directly to the external conditions, trees and plants have long been used in landscaping as Smart Shading Devices. Higher plants go through a relatively slow yearly cycle, but micro-organisms such as algae respond to changing conditions within hours. But the question is: can micro-organisms be utilised to shade buildings?
Since 2009 Arup Germany has been leading a research collaboration with COLT International and SSC, a small enterprise specialised in hydrobiological processes. The collaboration is about the integration into buildings of photobioreactors (PBR). The poject is funded by the initiative ZukunftBau of the German Federal Ministry of Transport, Building and Urban Development. So what are photobioreactors?
Photobioreactors are transparent containers which create a controlled environment for photosynthesis. Recent years, has seen the development of the Flat Panel Uplift Bioreactor. In a Flat Panel Uplift Bioreactor, pressurised air is introduced at the bottom of the panel. The air bubbles rise up inside the cavity creating strong turbulence which is beneficial for the algae growth. This kind of photobioreactor has a photosynthesis production rate that is approximately ten times higher than tubular glass reactors which had been used up till this point.
Within the photobioreactor, heat is generated through the solar thermal effect. This heat needs to be dissipated to prevent the overheating of the system. Indeed, for a stable production rate the temperature needs to be kept below 40°C. If this is done through a heat exchanger, the thermal energy can be recovered and used for heating–the bioreactor performs like a solar collector.
The shading factor depends on the density of cells. With a cell division rate of maximum one per day, the shading factor can be doubled within a day if the continuous harvesting process is suspended. The system represents an interactive, adaptive shading system. During times of high solar radiation the density of the cells increases, blocking the light. In contrast, the light transmission can be increased by an intensified harvesting process.
Because they can be completely recycled at the end of their life, Flat Panel Uplift Bioreactors represent and exciting technology that adheres to the principles of Cradle to Cradle.
Early in 2012 the research consortium installed the first operational prototypes of external louvers with integrated photobioreactors. The prototypes are approximately 2.60m high and 60cm wide and consist of four panes of monolithic glass. The panes form a central cavity of 18mm for the circulation of the medium and 16mm insulating cavities on either side. The glass panes are clamped along the entire perimeter to facilitate easy de-mounting. The bottom profile of the louver integrates all the pipes and valves that are required to service the photobioreactor. The prototypes are currently being tested and the results are promising. An entire façade with integrated PBR will be fitted in 2013 on the Smart Material House in Hamburg, designed by SPLITTERWERK Architects for the International Building Exhibition in Hamburg. This project will be the first to utilise bio-chemical processes in building components, generating biomass and heat, absorbing CO2 and providing adaptive shading.
This technology can play an important part in establishing surplus energy houses as a building standard. This opens the possibility of creating zero carbon neighborhoods. With the possibilities of local and decentralised generation of energy, directly at the site of the consumer and the associated short supply chains of local grids, entirely new perspectives arise for planning on urban scale. The interaction and cross-linkage between the individual building and its context, both with respect to generation and consumption of energy and emissions and capabilities to store and mitigate emissions will be more and more to the fore.
For a balanced eco-efficiency on the scale of a building cluster, a neighborhood or even a region, it is possible to define and embed the environmental characteristics of energy intensive building typologies with the natural and technical processes in the area. The PBR technology is linking both cycles and in this sense a truly smart, multi-functional component based on Cradle to Cradle thinking.
Jan Wurm is an Associate at Arup in Berlin and a visiting professor at the Danish Technical University in Copenhagen. Jan’s passion is in architectural engineering: the interaction of technology, building materials and structure and the architectural form itself. His work on structural use of glass for the building envelope has made him an acknowledged and internationally recognised expert in this field. His book Structural Glass was published in German, English and Mandarin by Birkhäuser. After having worked for three years in Arup Materials Consulting and Arup Facade Engineering in London, Jan transferred to the Berlin office in 2008 to lead Arups European Region Materials Group.