When we talk about green buildings we refer to the application of techniques and principles for reducing the environmental footprint of ‘having’ and using a building. Constructing and maintaining a green building incorporates applying green principles at all stages; designing, building and using it.
In general green building practices may be divided in to two main categories; passive and active energy systems aiming at energy efficiency, energy saving and expolitation of renewable energy.
Bioclimatic Architecture and Passive Solar Systems
Passive green energy measures refer to what we can do to reduce the energy needs, thus energy consumption, of a building. Such measures include applying bioclimatic principles, using appropriate energy efficient materials to reduce wasted energy, using electrical appliances and lighting in an energy efficient manner and, in general, adopting an environmentally friendly lifestyle especially towards saving energy. A basic characteristic of passive systems, distinguishing them from active, is that to operate they rely on inherited thermal properties of materials in a system and do not require any external energy sources.
Applying bioclimatic principles in architectural design is when we design a building based on, and incorporating, the micro-climatic conditions of a given site aiming to secure comfortable internal climatic conditions (thermal comfort, visual comfort and good quality of internal air) and to minimise energy consumption and utilize renewable energy sources, such as solar, wind, water or geothermal energy.
Maintaining comfortable climatic condition in a building mainly translates to maintaining and controlling the temperature, humidity and lighting levels of the interior. To do so we need to consider the state and fluctuation of external climatic and environmental conditions during the day and night in all seasons plus all internal sources of influencing these climatic variables such as people living or working inside or visiting the building, all electrical appliances operating, and the usage-purpose of internal spaces etc. Applying bioclimatic principles such as thermal protection of the building, utilizing passive solar systems, applying techniques of natural ventilation, cooling and natural lighting and making optimum use of energy can greatly contribute to saving energy ‘from design stage’ in a building.
In general, bioclimatic building design is greatly dependant on the local climate of the site and includes the following principles.
- All year thermal protection of buildings by use of appropriate shading, effective insulation and air-sealing of building space and building openings (such as windows and other openings). Shading and proper insulation can keep excess heat from entering the building especially during hot summer months. Insulation and Air sealing are important elements towards increasing the energy efficiency of a building and reducing heating and cooling costs. A properly balanced implementation of insulation, ventilation, moisture control and air sealing can increase the building’s energy efficiency and reduce energy consumption.
- Exploitation of renewable energy potential, primarily solar energy which can be used for water and space heating during winter months and for natural lighting throughout the year. Appropriate orientation of a building at design stage especially of the building openings and glazing (windows, doors and transparent walls – south facing is most appropriate) can greatly affect the final energy behaviour of the building at its use; effective layout of internal spaces according to energy needs and integration with passive solar energy systems.
- Removal of excess heat that enters and accumulates in the building, especially in hot summer months, by use of natural cooling and ventilation which can be very effective during night-time.
- Ensuring adequate and even natural lighting by letting sunlight enter the building without accumulating excessive solar heat
- Incorporating bioclimatic techniques to improve the microclimate of the building’s exterior spaces, such as external orientation of spaces and shadings, using appropriate types of plants and trees to provide for natural shading and by following the aforementioned principles in general.
- Integral to the application of bioclimatic principles are the passive solar systems that operate ‘passively’, without electro-mechanical moving parts or external sources of energy and can provide for space heating, space cooling and space lighting from a natural source.
The passive solar design principles dictate that building structure and materials such as, walls, roof, floor and windows are designed to influence and assist the energy behaviour of the building towards inhabitable comfortable conditions. The aim is to take advantage of external micro-climatic conditions and passively collect, store and distribute gathered solar energy (solar heat) in the winter and reject it in the summer.
The design, structural and material elements considered in passive solar and bioclimatic architecture in general include placement and orientation of window openings, types of glazing, control of direct and indirect solar gains, heat storage, thermal insulation materials, solutions and methods (internal vs external thermal insulation), thermal mass and thermal resistance of materials, effective shading etc.
Use energy sensibly and efficiently electrical appliances and lighting
Apart from bioclimatic design, and utilisation of passive green energy systems that primarily deal with the energy needs of the building, to save energy we need also to consider the way we consume energy through using electrical appliances and lighting within the building. At home these appliances include refrigerator and freezer, washing machines and dryers, dishwashers, home audio equipment, television and other electronics, computers etc. Similar to the concept of energy efficiency of a building comes the concept of energy efferent equipment; Energy-Star-Qualified appliances provide a indication to consumers of the energy efficiency level of the appliance. Thus when purchasing such equipment we always need to consider, apart from purchasing cost, the appliances subsequent cost in consuming energy.
It is thus important to understand that the overall energy efficiency of a building is best achieved through a holistic approach integrating all aspects and stages of the building; from design, to construction and structural materials used to to build it to equipping it with energy efficient appliances and, of course, using appliances and installations sensibly and efficiently.
Active green energy systems refer to the use of technology applications (electrical or mechanical) for utilising or generating green power. Such systems may use solar collectors to collect solar energy in the form of heat, store it in a high temperature liquid and use it through an extended system with pipes, pumps and tanks, controls, mechanical and electrical parts for space heating or using hot water or generating energy. Thus, active energy systems may incorporate the use of renewable energy technologies, such as solar photovoltaic panels, solar thermal collectors, wind turbines, bio fuel systems, etc., to gather renewable energy to offset conventional energy, i.e. electricity generated from fossil fuels such as diesel and gas.
The most popular and widely used active systems are solar technologies utilised to convert solar energy to heat, such as solar heater systems, or directly to electricity with the use of photovoltaic PV panels. The use of renewable energy sources in general in buildings together with bioclimatic and passive energy efficiency measures already illustrated is a way leading to the concept of zero-energy-buildings, more popular term for zero energy homes.
A green building is not necessarily zero energy; the latter produce the same amount of energy as it consumes, on an annual basis. Therefore a zero energy building may in general be connected to the electric utility network both for receiving electricity or its needs in heating, cooling, lighting and operating devices and for storing excess electricity generated from renewable sources such as PV panels. The term zero-energy building implies that the energy it receives (on an annual basis) is covered by the energy it generates in a year.