CLIMATE RESPONSIVE ARCHITECTURE 3. Climate Responsive Design Lecture Notes Part 1: Extracted from Square One Archives, copyright Andrew Marsh
Passive solar building design uses a structure's windows, walls, and floors to collect, store, and distribute the sun's heat in the winter and reject solar heat in the summer. It can also maximize the use of natural light for interior illumination. illumination. The technology is called passive solar design, or climatic design. Unlike active systems, it doesn't involve the use of mechanical and electrical devices — such as electrical lights, pumps, fans, or electrical controls. Passive design can be used in most parts of the world. If designed by an experienced passive solar architect, buildings using passive solar design principles principles don't have to cost more up front than conventionally designed designed buildings. And when they do, the savings in energy bills quickly pay for themselves. Ad vantag van tages es Passive solar design is highly energy efficient, reducing a building's energy demands for lighting, winter heating, and summer cooling. Energy from the sun is free. Passive solar design also helps conserve valuable fossil fuel resources so that they can be directed toward other uses. Daylighting, a component of many passive solar designs, is one of the most costeffective means of reducing energy usage in buildings. A well-designed and built passive solar building does not have t o sacrifice aesthetics either. It can be as attractive as conventionally designed buildings and still save energy and money. Passive solar design also reduces greenhouse gases that contribute to global warming because it relies on solar energy, a renewable, nonpolluting resource. Disadvantages Where experienced solar architects and builders are not available, available, construction costs can run higher than for conventional homes, and mistakes can be made in the choice of building materials, especially window glass. Passive solar homes are often built using glass that, unfortunately, rejects solar energy. Choosing glass for passive solar designs isn't easy. The right glass choice depends on which side of the building (east, west, north, or south) the glass is installed and the climate in which you are building And along with daylighting comes heat. During the summer or in consistently warm climates, daylighting could actually increase energy use in a building by adding to its air-conditioning load. In addition, room and furniture layouts need to be planned carefully to avoid glare on equipment such as computers and t elevisions. elevisions.
PASSIVE DESIGN In a physical sense, a passive system is one that uses only locally available energy sources and utilises the natural flow paths of that energy to produce work. In other words, no auxiliary equipment (such as fans or pumps) are required to make the system to function - the transmission media is directed by induced convection currents or reflected/refracted to where it is needed to do the work. In an architectural design sense, the work that needs doing is usually the heating, cooling and lighting of enclosed spaces. The kinds of low-grade ambient energy systems available within most building sites are actually well suited to these tasks, as is evident by our ability to survive prior to the discovery of electricity. There are many sources of energy available locally within a building site. These include direct and diffuse radiation from the Sun, air movement from winds and temperature differences, biomass from vegetation, as well as geothermal and hydro-kinetic sources. Windows can be designed to allow in natural light and heat from the Sun, and opened to cooling afternoon breezes. Earth can be bermed high against rear walls to protect them from large changes in outdoor air temperatures. Alternatively inlet air can be drawn through underground cavities providing some level of geothermal cooling in summer and heating in winter. The effective use of these low-grade energy sources in a building requires only some careful thought and a little innovative design. Many projects have shown that such buildings do not have to cost any more than less carefully designed buildings, and can be significantly cheaper to run. The basic idea of passive design is to allow in daylight, heat and airflow only when they are most beneficial, and to exclude them when they are not. This includes the storage of ambient energies where possible, for distribution later when there may be greater need. The full range of passive techniques are considered, such as the correct orientation of the building, appropriate amounts of fenestration and shading, an efficient envelope, maximum use of daylighting and the appropriate level of thermal mass, as well as the use of renewable resources in preference to non-renewables. More conventional systems using fans and pumps can be used where a small initial energy input can be used to yield a relatively high output. This includes technologies such as evaporative cooling units and heat pumps. Good passive design for thermal comfort is based on the following six major principles: Orientation of frequently used areas towards the equator (north in the southern hemisphere, south in the northern hemisphere), to allow maximum sunshine when it is needed for warmth, and to more easily exclude the sun's heat when it is not. In areas near the equator, minimization of the size of east and west facades is desired so as to reduce solar gains f rom these hotter orientations.
Glazing used to trap the sun's warmth inside a space when it is needed, with adequate shading and protection of the building from unwanted heat gain or heat loss.
Thermal mass to store the heat from the sun when required, and provide a heat sink when the need is for cooling.
Insulation to reduce unwanted heat losses or heat gains through the roof, walls, doors, windows and floors.
Ventilation to provide fresh air and capture cooling breezes.
Zoning of internal spaces to allow different thermal requirements to be compartmentalised when required.
Buildings should be planned in such a way that benefit is obtained from shaded indoor and outdoor living areas when the weather is hot and sunny indoor and outdoor areas with wind protection when the weather is cold. Windows, glass doors, panels and skylights play a crucial role in admitting heat and light, and can have a significant impact on energy consumption. They are also the most difficult parts of the building envelope to adequately insulate. Care needs to be taken to ensure that windows are positioned, sized and protected so as to get the most benefit from winter sun while avoiding overheating in summer and heat loss in winter.
Thermal mass is basically the ability of a material to store heat. It can be easily incorporated into a building as part of the walls and floor. Thermal mass affects the t emperature within a building by:
Stabilising internal temperatures by providing heat source and heat sink surfaces for radiative, conductive and convective heat exchange processes.
Providing a time-lag in the equalisation of external and internal temperatures.
Providing a reduction in extreme temperature swings between outside and inside.
Material selection to capitalise on thermal mass is an important design consideration. For instance, heavyweight internal construction (high thermal mass) such as brick, solid concrete, stone, or earth can store the Sun's heat during winter days, releasing the warmth to the rooms in the night after it conducts through. Lightweight materials such as plasterboard and wood paneling are relatively low mass materials and will act as insulators to the thermal mass, reducing its effectiveness. Lightweight construction responds to temperature changes more rapidly. It is therefore suitable for rooms that need to heat or cool very quickly. For maximum energy efficiency in cold climates/seasons, thermal mass should be maximised in the equator-facing sides of a building. Any heat gained through the day can be lost through ventilation at night. In using this technique, the thermal mass is often referred to as a 'heat bank' and acts as a heat distributor, delaying the flow of heat out of the building by as much as 10-12 hours. Thermal mass design considerations include:
Where mass is used for warmth, it should be exposed to incident solar radiation.
Where mass is required for cooling, it is better placed in a shaded zone.
Buildings may be preheated using electric or hot water tubing embedded in the mass (mostly concrete floors).
Buildings may be pre-cooled using night-purge ventilation (opening the building up to cool breezes throughout the night), although this requires significant amounts of exposed mass, and may be necessary only at certain times of the year.
Thermal mass is particularly beneficial where there is a big difference between day and night outdoor temperatures
Insulation specifications are another important design feature. The building envelope provides a barrier against the extremes of the outdoor environment, allowing the thermal comfort levels indoors to be adjusted to suit the occupants. This might require heating or cooling depending on the season and location of the building. The energy required for heating or cooling will be greatly reduced if the building envelope is well insulated to reduce incidental losses. This means insulating the ceiling, walls and floor of the building, an easy task during construction, but often more difficult for existing buildings. Insulation reduces the rate at which heat flows through the building fabric, either outwards in winter or inwards in summer. In temperature controlled buildings, this will result in significant energy savings and increased thermal comfort. In passive buildings, it means that any low-grade energy available will be more effective at its job of heating or cooling. Insulation has an additional benefit it that it also reduces noise transfer through the fabric however its resistance to both fire and insects should be considered. Proper installation is also essential to maximise performance, and there often local and international standards to cover the fire safety and health aspects of installation. Ventilation of a building is critical during hot climates/seasons as the building must provide sufficient ventilation and breeze paths to assist with cooling. For warmer climates doors and windows should be positioned to facilitate prevailing cooling breezes. An analysis of local wind directions at different times of the year may be necessary in order to best locate windows and design systems to 'catch' or funnel the breezes through them.
To maintain indoor air quality, the opportunity to provide clear breeze paths through a building should be maximised to encourage air flow for night time cooling in summer and 'flushing out' the accommodation, by removing stale air that contains CO2, water vapour, and mould. Substantial savings can be made through proper zoning. Rooms requiring heating such as dining areas can be heated without having to include less frequently used rooms such as hallways, bathrooms or bedrooms. The following strategies could be incorporated into the design to allow for zoning in winter:
Air locks to the main entries to the building (for example, entry, laundry).
Similar activity rooms grouped together (for example, bedroom zone, living zone, wet or bathroom zone).
Grouped areas need to be sealed with tight fitting seals to all four sides of the door.
Thermal Control and Basic Psychrometric Processes REFERENCES 1. Koenigsberger, O.H., T.G.Ingersoll, A.Mayhew and S.V.Szokolay (1973). Manual of tropical housing and building, Longman, London. 2.
Szokolay, S.V. (1980). Environmental science handbook, The Construction Press Ltd., Lancaster, England.
3.
Vaughn Bradshaw (1993). Building control systems , John Wliey & Sons, Inc.
4.
Smith, B.J., G.M.Phillips and M.E.Sweeney (1982). Environmental Science , Longman.
OBJECTIVES To discuss simple means of thermal control To introduce the basic psychrometric processes relating to the building
MEANS OF THERMAL CONTROL Thermal control requirements • deviation of outdoor (climatic) conditions from desired (design) conditions Outdoor conditions - Comfort conditions = Required controls • Required controls passive (building) active (energy-based installations)
Thermal control strategy • utilise passive controls to their full potential economy - ethics (conservation) Required controls - Passive controls = Active controls
Objectives of climatic design • when cold discomfort conditions prevail prevent heat loss utilise heat gain from sun and other sources • when hot discomfort conditions prevail prevent heat gain maximise heat dissipation • when conditions vary diurnally between cold and hot discomfort - even out the variations Generic architectural features and their climatic control functions * Mass (weight of construction) • mass produces thermal capacity • thermal capacity moderates the periodic heat flow through the building envelope • important and useful in large diurnal temp. climates • thermal mass characterised in terms of time-lag (φ) and decrement factor (μ) • low mass ⇒ low thermal capacity ⇒ quick response • high mass ⇒ high thermal capacity ⇒ slow response • periodic heat flow • use thermal mass to control when peak temperatures should occur, as well as the degree of attenuation • architectural features relating to mass are : envelope roof - floor internal partitions Glass • a most common architectural feature
• •
•
•
windows - glass curtain walls glass atriums transmitter of radiant (solar) energy - heat and light control of amount of radiant energy admitted depends on spectral transmittance (solar-optical) characteristics shading devices spectral transmittance characteristics solar : α + ρ + τ = 1 light : τvis = surface luminance measured through the transparent material under test / surface transmittance types of glass clear - heat-reflecting - heat-absorbing - double glazing • shading devices control the amount of solar energy admission external - internal
Insulation • impedes heat flow - retains heat inside • types of insulation resistive (bulk) - radiative - capacitive • insulation may be applied in walls - roofs floors -
retards heat inflow
ceilings
Ventilation • changes internal temperature, depending on the nature and extent of temperature differential between internal and outdoor air temperatures • enhances convective cooling, but can also introduce convective heating • enhances evaporative haet loss • indoor air flow patterns determined by following factors orientation - external features - cross-ventilation position of openings - size of openings - control of openings Orientation • main design purpose when relying on orientation is to control the amount of solar radiation falling on the facades • solar radiation receieved on horizontal & tilted (usually vertical) walls vary on the same site • the solar radiation profile is markedly dependent on orientation and latitude horizontal surfaces receive the greatest solar radiation at higher latitudes, the wall facing the Equator receives the next highest radiation in winter, but receives very little in summer in equatorial regions north and south walls receive the least intensity and that for only short periods of the year east and west facing walls receive the second highest intensities in the equatorial location, and consistently large intensities even at higher latitudes • in equatorial regions, if solar heat is to be avoided, the main windows should face north and south • in higher latitudes window should face the equator to maximise the availability of solar heating during winter, while simple horizontal shading is sufficient to provide shading during summer • east and west (especially) facing windows should be avoided
Shading devices • main purpose is to exclude solar radiation • effectiveness expressed in terms of shading coefficients (SC) SC = Solar heat gain through any glass and shading system combination / solar heat gain through a 3 mm unshaded clear glass • various types - internal - external • external types more useful as heat is rejected Material colour • essentially affects the absorptivity of solar radiation Shape • determines the heat loss/gain via conduction, convection and radiation • compact vs open Solar control • sunlight penetration both beneficial and a problem - depending on thermal needs and times of year in temperate and cold climates - in warm humid climates, solar admission must be avoided maximally • methods for solar control building orientation special glasses ~ heat absorbing ~ heat reflecting shading devices → blinds and curtains ~ internal → horizontal → vertical → eggcrate ~ external Sun Path diagrams • indicates sun position throughout the year • facilitates direct reading of solar altitude and azimuth at any time of the day for a selected date of each month
