When it comes to cooling and heating strategies in building design, the architect is challenged to find the most efficient, economic, and ecologic solution to ensure inhabitant’s thermal comfort. In most climates the natural energies to regulate the comfort through heating, cooling, humidifying, and drying are available all year long. It is the task of architecture to use them where they contribute to comfort. This means, to enable the building to absorb, save, release, reflect energy at the right moment. The study of passive strategies for a specific climate and building type can result in mostly or completely autonomous architecture – architecture that not only saves equipment and energy costs but makes a major contribution to nature and climate.
Sustainable Architecture: Natural Cooling and Heating
Why are natural and passive strategies so important?
In growing cities, the heat island effect shows its effects on the microclimate and generally the number of heatwaves is increasing. Means, like air-conditioners, which allow comfort in more extreme temperatures account nowadays for 10% of global energy consumption, consequently contributing to climate change. This vicious cycle lets the confrontation with natural strategies become fundamental.
Evaporative Cooling: Water Mirrors
Integrating water as an element of architectural projects can cool buildings through evaporation and air flow, depending on the climate. This methodology was recognized as early as the Romans, who often designed their homes around a central courtyard pool.
The future KFAS’ Headquarter Building in Kuwait, designed by TOPOTEK1, uses the availability of a large water mirror to pre-cool the air. The 40 cm deep pool is strategically positioned towards the predominant air currents, in front of building. Designed with a suspended volume the building catches the winds blowing from below. Then, the pre-cooled and humidified air is distributed inside the building, via the façade or the central courtyards.
Evaporative Cooling: Facade
Atelier Bow Wow, also applying evaporative cooling, compared their House & Atelier to a massive sweating rock with a dragon-like internal water vein. During construction, the architects dug a well from which well water is pumped up to the roof and streams down on the surface of the external wall. Covered with granule-faced asphalt, the wall absorbs water, which then evaporates due to the heat, cooling the outer walls of the building.
Thermal Mass: Cave Homes
Dense materials such as stone, concrete and earth each have several properties that allow a good insulation from heat. These include good thermal conductivity (ability to rerelease passive cooling), thermal lag (slow heat transmission), low reflectivity (lower redistribution of heat), and high volumetric heat capacity (elevated ability to store heat). When such materials are used in bulk, their insular qualities become especially potent, exemplified by ‘cave homes’ such as Kapsimalis Architects’ Summer Cave House in Santorini. The earth temperature only varies by a few degrees and is already stabilized at a depth of 1.5 to 2.5 m below the surface of the earth. This way buildings can easily be heated up during the winter and keep comfortable temperatures in summer.
Thermal Mass: Storage Walls
The passive use of solar energy with the aid of e.g. storage walls can help to maintain comfortable temperatures inside a building year-round. To achieve this, the surfaces’ placement should allow a high exposure to sunlight in winter and shading in summer. Of great importance is a good insulation of the building, otherwise the storage walls can increase the energy use.
Tadao Ando’s Poly Grand Theater in Shanghai consists of a massive reinforced concrete box surrounded by a transparent curtain wall that forms a double-skin glass-facade. The concrete box performs as a large thermal mass. In winter, the interior volume absorbs and stores the sun’s heat and releases it in the evening when the temperatures drop. In summer, the glass skin helps to reflect direct light of the concrete mass.
The Solar gain, meaning the generated heat as sun is absorbed by the building, is controlled by the building’s design and orientation, opaque-to-glazed areas ratio, heat reflection percentage, insulation level, and amount of nearby shading elements.
For the Dorotheen Quartier (Behnisch Architekten) these factors, the materiality and the specific roof architectural design were defined basing on shading and sun exposure studies. On the roof façade as well as the vertical glazing of the office, reflective fritting achieves sun protection, still allowing an optimal amount of lighting. The comfort concept employs thermally activated components, such as exposed concrete ceilings, and thermal storage capacity of interior surfaces what leads to reduced heating and cooling requirements.
The geothermal energy generated and stored in the interior of the earth is used as an energy source. Water in pipes absorbs the heat and the heat pump allows the water to circulate through the system, transferring the thermal energy to the building.
To ensure a good indoor climate Haas Cook Zemmrich STUDIO 2050 has designed specific rammed-earth elements for the new Alnatura Campus’ exterior walls. Rammed earth is an excellent heat store. A radiative system is integrated in the space-facing sides of the element, supplied by geothermal energy. It is heating or cooling the rammed-earth elements’ mass which slowly releases the necessary thermal energy.
Groundwater Heating & Cooling
The heat demand of the administration building of Südwestmetall in Esslingen is covered by a groundwater heat pump with an open loop well system as heat source. A relatively constant groundwater temperature of approx. 12°C throughout the year and the low-temperature heating system lead to a high heat pump COP and thus to very efficient energy generation. In addition, ground water is also used for cooling, covering the cooling demands of the chilled ceilings, and supply air conditioning. Integrated in-floor convectors serve as a fast-acting heating system.
A green roof significantly improves the indoor climate of a building as well as the local microclimate. In comparison to a conventional roof, where the air temperature can increase over 50°C, the area under a green roof cools down through the vegetations’ evapotranspiration and the shade it provides. Beside the basic division of green roofs in extensive and intensive green roofs, there is a difference between a wet and a dry roof. The wet roof absorbs and stores large amounts of heat, which reduces temperature fluctuation and can save energy needed for heating and cooling of the building. A dry roof acts as insulation. In summer, the green roof layers reduce the heat flow through the roof into the building. In winter, there is less heat emission.
As an alternative to green roofs, light-colored reflective roofs and facades can effectively cool interiors by redirecting sun rays and decreasing the heat absorption. Examples include roofs with sheet coverings, reflective tiles or shingles, or reflective paint. Glenn Murcutt’s Magney House in Australia additionally allows through its high roof construction existing heat to rise and escape areas in use.
Sources: archdaily.com | transsolar.com