Harvesting Sunlight

Almost all of the earth's energy is derived from the sun; this energy is almost exclusively harvested by the unique ability of plants to convert the sun’s energy through photosynthesis. This process supplies humans with their vital support systems of oxygen, food, fuel, medicine and clothes. Even fossil fuels are the results of photosynthesis from millions of years ago. Our civilisation and our potential as human beings is inexorably and unavoidably entwined with developments in science, travel and plant exploitation. This scientific journey bloomed in the 19th century and, coupled with the impact of the industrial revolution, was the catalyst for a new type of architecture – the glasshouse.

Glasshouse design has been a constant inspiration for architects and engineers. A new approach to creating highly efficient transparent structures was inspired and influenced by two Scotsmen, Sir George Mackenzie and John Claudius Loudon. Mackenzie developed the curved glass house geometry that ran ‘parallel to the vaulted surface of the heavens’, tracking the sun for maximum gain of heat and light. Loudon patented the technique of utilising the malleable qualities of wrought iron, with curved sash bars that allowed bell shape and dome geometries. These new ideas – developed as a technological solution to creating artificial environments – went on to ignite a new approach to architecture and construction.

We wanted to rethink the ‘glass’ house as a true ‘green’ house, drawing on the analogy of a leaf and photosynthesis. To us this meant not just capturing heat and light but harvesting and storing and using it, just like trees which capture the sun's energy in its leaves through photosynthesis and proceeds to move and store the resource through transpiration. Our Leaf House was designed for a northern hemisphere location where the interior would be shaded and cooled from the excess heat of the summer and the captured energy could be used to temper the cold of the winter.

We wanted to follow this analogy into the structure and use renewable materials where possible. The structure is therefore made from wood gluelams with the minimal use of steel to keep it as light and transparent as possible. Inspired by aircraft design, the roof structure borrows from a timber and cable spanned aircraft wing, but with the geometry of a leaf. The central stem is made with timber arches and of this stem, bow-string trusses arch to the ground.

Like the cellulose structure of a leaf, we saw the roof structure as the means of supporting our ‘chlorophyll’ environmental control system: a number of layers that could both shade the interior and harvest the sun.

In translating these elements, our approach is to emulate the life systems of plants and to blend technology and nature in an expressive, meaningful and bold architecture.

The Leaf House was optimised in every orientation to gather the sun’s energy, dispersing some of the energy for immediate use in various building functions and storing the rest for future use in other seasons.

We were particularly inspired by the leaf of the Carnauba tree. The complex nature of the Carnauba leaf – with its ability to secrete wax through its leaves, apparently in defense against the hot winds and droughts of its native habitat – provides endless inspiration for developing a structure that also relies on its efficient and dynamic components to be self-sustaining and which can adapt itself to the environment. During the photosynthesis process chlorophyll, the green pigment in leaves, transforms the sun’s unusable sunlight energy into chemical energy to produce sugar (fuel/energy).

Six molecules of water and six molecules of CO2 produce one molecule of sugar and six molecules of oxygen:

6H2O + 6CO2C6H12O6 + 6O2

The leaf acts as the solar collector. The raw materials plants use for the process are water and CO2. The vehicle for the circulation of raw materials is the veins (xylem cells). The by-product of the process is sugar (energy) and oxygen. The energy is stored in the roots.

With this process as a starting point, an idea developed – an organic form, natural materials, the sun as energy source, the ground as energy storage, the structure as the channels for transporting energy, water as the conductor:

The heating and cooling of the various spaces would be provided by a closed loop geothermal heat pump system. The geothermal system water would connect to a bank of water-to-water reversible heat pumps located in a central mechanical room. A four-pipe HHW and CHW piping network would distribute heating and cooling to the various air handling units and other heat emitting equipment throughout the facility.

The geothermal system would offer several advantages over a ‘typical' boiler and chiller installation:

The geothermal system has no cooling tower. The geothermal well field, once installed and tested, requires virtually no maintenance.

Reversible heat pumps generate both heating and cooling using electricity as the primary energy source. The electricity required to run some of the pumps can be offset through the use of building integrated photovoltaics (BIPVs).

During the summer, heat is rejected to the ground through a water-to-water heat exchanger. Cool water is delivered to air handling equipment. Solar shading prevents excess heat gain from increasing the cooling load.

During the winter, heat is extracted from the ground. To increase the heating efficiency, heat from the solar thermal panels could be introduced to the geothermal loop during the heating seasons. The mass of the ground is able to store this heat and allows it to be utilised during the heating season. Solar shading elements will be positioned to allow passive solar heating from low-angle sun in the winter months.

We developed the leaf house structure with Dewhurst McFarlane and the environmental system with Buro Happold; our intention was to create a seamless fusion of engineering and architecture, an enclosure that defined space and controlled environment through structure and skin, just as nature operates. Although a theoretical project, it is a theme that we are continuing to explore.