The Algae Tower |
Contribution to the Taiwan Tower Conceptual Design Competion for Taichung at 2011.
The Algae Tower is a high-rise-building-project with an algae-bioreactor-facade using PBR for the cultivation of microalgae.
project name: Endless Tower
location: Taichung, Taiwan
client: City of Taichung
project team: Mark Blaschitz, Hannes Freiszmuth, Edith Hemmrich, Josef Roschitz, Carlos Tinoco de Castilla, Nikolaos Zachariadis
structural engineering: werkraum wien; B+G Ingenieure, Bollinger und Grohmann GmbH
building physics / material consulting: Arup GmbH, Berlin
The smallest footprint as possible and the shortest way of linking different functions: The Endless Tower is not only another tower in the world, it is a new generation of hybrid skyscraper buildings with a CO2 reducing and energy producing „Bioreactor-facade“. The proposed design for the Tower presents the City an iconic green landmark! The approximately 427m high tower will be a unique distinctive skyscraper with its representative illuminating facade of maple leafs, which might become a new symbol for the City. Besides its usage as an observation tower the building includes a spectacular museum, office areas and a big underground car park.
The skin of the Endless Tower looks and performs like a giant arbour as maple leaves cover the surface, representing the structure and providing external shading. Moreover the skin performs like a foliage canopy with the leaves conducting photo-synthesis by the integration of photobioreactors (PBR) for the cultivation of micro-algae. The PBR facilitate the mitigation of carbon by producing biomass, water and oxygen – powered by daylight.
PBR for the cultivation of microalgae
PBR are an established technology with a variety of systems available on the market. In principle PBR are transparent containers of glass and polymers that encapsulate an approx. 20mm cavity in which water as a medium and algae are circulating. The veins interconnect the leaves to a single cycle, with the biomass in form of algae being harvested at central location in the plant room of the basement, while the carbon is absorbed by every leaf.
The benefits of the PBR are many fold:
- they generate biomass as a renewable energy source, the biomass is storable solar energy and can be used as a fuel and transferred into electrical energy. Microalgae grows up to 30 times faster than macro-organisms and thus are an efficient provider of biomass.
- they generate heat, just like a solar collector. By heat exchanger the heat can be stored in a mass storage at the foundations of the tower. By a cooling pump, this energy can be used to cool the adjacent neighbourhoods.
- they absorb CO2 and in this way mitigate the effects of the powerplant.
- they produce water that can be used to cover the demand of the tower’s facilities.
The integration of PBR inside the leaves turns the structure into a generator for renewable energy allowing the tower and adjacent neighbourhoods to be self-sufficient from energy providers.
The cone shape of the Endless Tower has a total lateral surface area of approx. 37.150m˛; the maple leaves represent approx. 25 % of the skin, resulting in a total are of approx. 9.300 m˛ of PBR.
With a production of approx. 20 grams of dried biomass per m˛ and day, the net energy gain is over 40 KWh per m˛ and year, resulting into roughly 400 MWh per year through biomass and approx. the same amount of heat.
Over 200g CO2 per m˛ and day is mitigated by the PBR, resulting in a total mitigation of 2t CO2 per day. This equals the mitigation of a forest with the size of over 1km˛.
The architectural approach is directly transferred into a highly efficient structural concept. Its main components are the wide span slabs built as composite structures, the massive inner core with staggered diameter from bottom to the top and the load bearing triangulated tube at the characteristic outer facade.
The inner core is planned as a reinforced concrete (upper floors) respectively composite (lower floors) structure containing elevators, stairs, etc. which guarantee fire resistant and save escape routes. The facade structure is designed as a steel construction. The loads are transferred by a stable tube resulting from a triangular grid projected on the outer surface. The composite slabs will be flexibly connected to the facade and core. To secure lateral stability facade and inner core create a tube-in-tube system that is able to bear the high wind loads and of course stabilize the tower against earthquake hazard. If the owner requires a stiffer structure to minimize deflections of antennas or comparable, it will be easily possible to connect both tubes with outriggers to stiffen the bracing system. So the structural concept is flexible enough to react on the owners needs during planning phase without changes in the global concept.
A combined pile-raft-foundation is suggested for the foundation of the tower . This elastically bedded system is able to bear all loads without critical settlement. A ring beam (composite structure) is integrated in the slab above Level -1 to carry the load of the facade. It transfers all loads between the rising triangulated system and the regular column grid in the underground levels. All outer underground walls and the ground plate are combined to a water-resistant concrete tank.