|Climate Responsive Building - Appropriate Building Construction in Tropical and Subtropical Regions (SKAT, 1993, 324 p.)|
|3. Design rules|
The main points:
· Keep a balance between
· Seek solar radiation gain in winter and provide shading in summer
· Provide wind protection in winter and proper ventilation in summer
· Construct good-natured houses, with moderate heat storage capacity.
· Use medium sized windows
3.4.1 Climate and design in general
(also see Chapter 3.1, General guidelines)
The temperate and upland climate is characterized by three seasons. A hot and dry season, usually the longest period, is followed by a wet and warm season, the monsoon period. In the third season, the winter time, depending on the altitude, temperatures can drop far below the comfort level, especially at night, whereas daytime temperatures are moderate and the solar radiation intense. (also see Chapter 2.2)
Design objectives and response
This type of climate is the most complex one from the designers point of view.
Buildings must satisfy conflicting needs of hot-dry and warm-humid periods. Rules given in the respective previous chapters are hence partly applicable also in the temperate zone. In addition, in the upland areas, the designer must consider the principles of heat conservation and solar heat gain, and sometimes active heating as well.
As a consequence, solutions are often a compromise between these conflicting needs. Where incompatible needs arise, a careful analysis of the length and relative severity of seasons is required to find a balanced design.
Buildings should be of good-natured. They have to provide comfort in spite of climatic conditions which differ strongly with the seasons and in spite of sudden weather changes. They should not cool down too much during the cold nights and should not overheat during periods of strong radiant heat gain.
A moderate amount of thermal mass, together with moderately-sized openings and sufficient thermal insulation properties will provide acceptable conditions for the major part of the time.
3.4.2 Settlement Planning
(also see Chapter 3.1.2)
The main points
· Topography, south sloping
· Orientation, so as to benefit from the winter sun.
· Protection from winter winds.
· Form, semi-compact.
· Hazards, floods, landslides and falling rocks must be considered.
With conflicting seasonal requirements, different solutions may be equally appropriate. The advantages and disadvantages should be weighed together, considering not the extreme, but the prevailing climatic conditions. Buildings can be arranged rather freely. Settlements should be semi-compact to provide mutual shelter from wind in the cold season but also to take advantage of the sun radiation.
Nevertheless, the prevailing breezes in humid and hot seasons should not be cut off and sufficient shade should be provided.
220.127.116.11 Topographical location of settlements
Sun and wind orientation
In lowland regions settlements should be exposed to the wind and protected from the sun. In winter the opposite is required: Exposure to the sun and protection from the wind.
In upland regions, shelter against the wind and orientation for maximum solar radiation gain are required all the year round. Sites oriented south-southeast and located in the middle or the lower middle of a slope are preferred. Here solar gain is best. Excessive wind effects as well as cool air pools should be avoided. The layout of town structures should follow the same goal of sheltering against winds and utilizing the effects of the suns heat.
Especially in areas of intensive land use buildings should be located on south slopes, where the sun exposure is adequate.
Depressions should be avoided because cold air accumulates there. Above the bottom of the valley the microclimate is more favourable.
Houses should be located behind a wind shield, but be assured of exposure to the sun. This shield can be formed by existing or newly planted vegetation, by other structures or by topography.
To achieve a desired ventilation effect by vegetation, see Chapter 18.104.22.168.
In upland areas, there are naturally often high surrounding mountains shading the building sites, especially during winter when the sun is low; on the other hand, the need for warmth is greatest. When selecting a site, therefore, the horizon of the surrounding mountains together with the suns path should be studied carefully.
In this region, floods, storms and earthquakes often have to be considered, too. In mountainous regions, landslides and rockfalls require special attention.
22.214.171.124 Urban forms and external space
Aspects of proper sun orientation and wind protection should already be considered while working out the basic pattern of a settlement. This pattern should be of a semi-compact type.
The plot dimensions should allow the positioning of a building with its wider side facing south and sufficient distance from the neighbouring buildings. Provision for row buildings along the east-west axis may also be favoured.
Streets are best planned in the direction of summer winds, avoiding the direction of winter winds.
Public external space design
The outdoor space - as in all warm regions - should be actively used. It should be planned to provide a well-balanced mix of open, sunny areas for the cold season and shaded, well-ventilated areas for the warm period.
Open squares with groups of trees to provide shade are desirable. Planting of deciduous trees and pergolas with deciduous creepers are a possibility.
An analysis of traditional settlements provides valuable hints for appropriate solutions.
A good example is Bhumra, a village in the higher hilly region of West Nepal. This settlement also provides efficient wind protection and takes full advantage of the suns radiation. Flat roofs are actively used as outdoor living and working spaces, where favourable climatic conditions prevail during the daytime.
3.4.3 Building design
The main points
· Orientation and room placement
should be south facing.
· Form depends on precipitation pattern.
· Shade in summer and heat gain in winter is necessary.
· Ventilation must be controllable.
126.96.36.199 Orientation of buildings
(also see Chapter 188.8.131.52)
The orientation of the building greatly influences the solar heat gain; it should thus be carefully considered. Normally, buildings should have an elongated shape along the east-west axis. The southern front can easily be designed for proper utilization of the winter sun and for protection against the summer sun. Windows on the eastern side receive substantial heat during the morning, which may be highly appreciated in winter time. Usually, larger windows on the west side are to be avoided, as the solar heat gain through these would coincide with the highest air temperatures.
To achieve a proper sun penetration for natural lighting, solar heat gain and hygiene, the depth of the interior should not be excessive.
Buildings should be arranged so that they benefit from summer winds because this season is usually humid and a proper cross-ventilation is required for cooling and hygienic reasons (prevention of mould growth). Shelter should be provided from the winter winds.
184.108.40.206 Shape and volume
(also see Chapter 220.127.116.11)
Buildings are preferably rather compact. However, because of the conflicting climatic conditions, several solutions are possible, depending on local topographical conditions and functional requirements.
Requirements in upland regions
In upland areas, heating in winter becomes more important than cooling in summer. Hence, rather compact structures with minimal but proper sun-oriented exterior surfaces are desirable.
Buildings may be large and grouped close together. Row houses or adjoining buildings have the advantage of reduced heat loss.
Courtyard buildings with proper wind protection are a suitable solution.
The houses of Marpha, a village in the mountains of northern Nepal with a dry, cold and extremely windy climate, represent a good example.
Fig 3/153 Schematic layout of a house in Marpha, Nepal
18.104.22.168 Type and form of buildings
(also see Chapter 22.214.171.124)
A moderately compact internal room arrangement is of benefit for most of the year. Courtyard buildings are suitable, terraced buildings facing south may also be appropriate. In cooler areas, exposure of the main rooms to the winter sun is essential, whereas in warmer areas these rooms can also be placed north facing.
The concept of thermal zones
Heat losses can be efficiently reduced by dividing the house into zones with higher and lower heat demands, according to their functions. The zone with the higher heat demand, such as living rooms, is placed facing towards the sun (south). The zones with less heat requirements, e.g. sleeping areas, kitchen, stores, entrance etc., are arranged around the warm zone on the west, north and east side, providing protection against heat loss and wind. This zone functions as a thermal buffer. An external belt of vegetation or other adjoining buildings and parapet walls may provide additional protection.
This concept applies in the colder areas only.
Fig 3/154 Thermal zone layout for cold zones
Ventilation in warm zones
In the warmer areas, humidity can cause problems during the monsoon period, Hence, arrangements for a proper cross-ventilation are necessary. The separation of humidity-producing areas such as kitchen and bathrooms from the rest of the building is recommended.
Building components for different seasons
In this type of climate, it would seem reasonable, to conceive one part of the building for the cold period and another one for the warm period.
One solution would be a building type which is also useful in
hot-dry and maritime areas, consisting of a ground floor with massive walls and
an upper floor of a light structure . The ground floor would be relatively cool
in the daytime and relatively warm at night. The light structure on the upper
floor would perform the opposite way. As a consequence, in the winter time the
inhabitants would use the upper floor in the daytime and the ground floor at
night. In the summer time the pattern would be reversed.
(see Chapter 126.96.36.199)
It would even be possible to use different sites in different climatic regions - a warm one in winter and a cool one in summer - and to migrate from one place to the other.
In reality, however, for both economical and organizational reasons, such day and night rooms or summer and winter houses are often not feasible, and a building or room has to be designed to serve all year round. The large range of thermal conditions requires the utilization of radiation and wind effects, as well as protection from them. Hence, the arrangements have to play a dual role.
188.8.131.52 Immediate external space
(also see Chapter 184.108.40.206)
The outdoor space should also be designed as a compromise with
ventilation and shade in summer, and wind protection and solar radiation gain in
winter. The vegetation should be planned accordingly, to provide partly sunny
and partly shaded spaces. Deciduous trees are an excellent medium with which to
achieve this goal.
(also see Chapter 220.127.116.11)
3.4.4 Building components
(also see Chapter 3.1.4)
The main points
· Medium heat storage capacity
and time lag is required.
· Thermal insulation is needed in upland areas.
· Reflectivity and emissivity is less important.
Thermal storage and time lag
Heat accumulated during the daytime should be stored by an adequate thermal capacity of the walls, ceilings and floors to balance the temperature. A properly dimensioned thermal mass means that rooms do not overheat during days with high temperature and high solar radiation gain, and do not cool out too much at night, or even during the following cooler day.
The retention of nighttime low temperatures is desirable in the hot-dry season. In the cold season the retention in the evening of heat gained during the daytime is desirable. Both can be achieved with a solid floor, wall and roof structure with a time lag of some 9 to 12 hours. This thermal capacity is preferably provided by internal walls, floors and roof, permitting the outer walls to be used more freely for large openings which will help to meet the requirements of the warm-humid period.
If the thermal mass of the west wall is used for balancing the night temperature, its time lag should be about 6 hours, as it gains heat in the afternoon hours only.
A too excessive thermal mass should be avoided. This is especially important in upland areas. A large thermal mass would make the space almost unheatable during the evening hours of the cold season. The time lag should not exceed 8 hours, which is equivalent to the time lag of a concrete wall of 20 cm thickness.
If thermal insulation is used, it should be placed on the outside of walls and roof, so that the beneficial effect of the thermal storage capacity is not reduced.
In upland areas, conductive and radiant heat losses should be minimized. As a consequence, the use of thermal insulation material may be appropriate.
At least as important is, however, an airtight construction. Thermal insulation is only effective in a building with no or very little air leakage.
As a rule of thumb, in upland areas, a well insulated and relatively airtight building requires about 1-kWh heat storage capacity per 1-m² of south facing glazed area.
Reflectivity and emissivity
In cool upland regions it is important that during the daytime radiant heat is absorbed in the building shell and radiant heat loss at night is minimized.
As a consequence, the outer surfaces should posses absorption capacity but low emissivity.
Absorbant surfaces are generally darker and non-shiny. Such surfaces should, however, only be used for buildings with a high thermal capacity. Low thermal capacity buildings would immediately overheat.
18.104.22.168 Foundation, basement and floors
(also see Chapter 22.214.171.124)
The floor may be in direct contact to the ground, with medium insulation and thermal storage capacity. In upland regions, materials with low thermal transmission properties are suitable (e.g. timber). In addition, thermal insulation may be required. Floor areas receiving direct solar radiation should possess absorption properties and a heat storage capacity.
(also see Chapter 126.96.36.199)
The cooler the climate, the better the thermal insulation and air-tightness of the outer walls should be.
A medium heat storage capacity of internal and outer walls is appropriate to avoid overheating in the daytime and keep the night temperature at comfort level.
Surfaces should generally have medium colors. In warmer regions a bright surface with higher reflectivity is appropriate. Absorptive, dark surfaces are possible in recessed areas, where the summer sun does not reach.
In upland regions joints between construction elements should be well-sealed against air penetration. The application of a wallpaper to the inner surface is efficient in this respect.
188.8.131.52 Openings and windows
(also see Chapter 184.108.40.206)
Size and placement
Windows should be of medium size with openings on opposite walls for proper cross-ventilation during the humid period.
On the west and north side windows should be small. As a rule of thumb, the total window area should not exceed 25% of the floor area.
In upland areas, as many windows as possible should be located on the south side of the building to utilize the heating effect of solar radiation. However, the glazed area should not exceed 50% of the south elevation because of extensive heat loss at night.
Excessive glazing can lead to overheating. This can be counteracted by
· the provision of adequate
· the provision of ventilation,
· sufficient heat storage capacity.
Windows should be equipped with tightly closing glazed panels, which provide protection against heat loss during the cold season and also against flow of heat and dusty air during the dry and hot season.
Construction details for windows
The joints between the window frames and the adjoining walls are an often neglected detail. They should be airtight and, therefore, carefully sealed.
Fig 3/157 Airtight joints
b) Double glazing
Double glazed leaves could be an advantage. However, it is not easy to build them to function properly, because the space between the two glazed panels needs to be accessible for cleaning.
More important than double glazing is good workmanship, particularly with regard to the grooves. To achieve air-tightness is the most crucial point, because the loss of warm air trough the grooves usually accounts for much more than the loss of heat by conduction through window panes. Double-groove window panels could bring a considerable improvement, suitable hinges, however, are often not available.
Fig 3/158 Double groove window
d) Double leaves
Another possible improvement, which utilizes conventional hinges, is the use of double leaves, one opening to the outside and the other to the inside. The technique is simple, but has the disadvantage that the application of mosquito screens is almost impossible.
Fig 3/159 Double leaf window
e) Solid shutters
Instead of a second glazed leave a solid timber panel can also be used. This would provide a better heat insulating effect for cold nights as well as for hot daytime conditions.
For additional thermal insulation at night heavy drapes closing rather tightly against the window frame can also be used.
g) Insulated shutters
A very efficient, but rather expensive solution is the use of insulated internal shutters, placed inside or outside of the window leaves.
h) Timber quality
For the construction of windows and doors it is very important to use well-seasoned timber. Only then will panels remain straight and airtight.
(also see Chapter 220.127.116.11)
The roof should protect the building from precipitation and therefore be carefully waterproofed.
The roof should provide protection against heat gain in summer and heat loss in winter. The roof should, therefore, have thermal insulation properties.
Usually a multilayer construction is required. The reflectivity and emissivity of the outer surface is then of minor importance.
The construction should have a medium heat storage capacity to balance temperature fluctuations between the daytime and evening hours, and also in case of sudden weather changes. This storage mass must be situated inside the insulation layer.
In upland regions the construction should be airtight, the joints between construction elements requiring special care.
3.4.5 Special topics
18.104.22.168 Shading devices
(also see Chapter 22.214.171.124)
In the hot period, windows must be protected from solar radiation and glare. In the cold season, however, solar heat gain through openings is desired. Hence, shading devices should be movable, which involves a somewhat complicated mechanism and also the attendance of the inhabitants. (see example in Chapter 4.9)
An other possibility is a well-balanced design aiming at an optimal direct solar gain in winter and good shading in summer. (see example in Chapter 4.6)
A careful climatic analysis will provide an assessment, at what time direct gain is desirable and when not. To determine the shape and size of appropriate shading devices, design aids as described in Chapter 2.2.1 are given.
Fig 3/160 Solar angle consideration
Shading of walls
Walls do not need extra shading devices in this type of climate, provided they possess reasonably good insulation and reflective properties.
(Form of building, roof overhangs etc. see Chapter 126.96.36.199)
Deciduous trees are suitable for shading purposes. Such shading trees are best located on the east and west side of a building. Vegetation which is too dense and too close to the building should be avoided because of dampness effect.
Fig 3/161 Deciduous trees provide access to winter sun but protect against summer sun
Vegetation cover on facades(also see Chapter 188.8.131.52 )
A green cover on outer walls and roof has many advantages:
· It protects the walls against
· The wind velocity on the surface is reduced and with it the cooling-off period.
· Glare is eliminated
(also see Chapter 184.108.40.206)
In winter time, a dense green coverage can be a disadvantage because desired the solar heat gain may be reduced. By using deciduous plants this effect can be avoided.
220.127.116.11 Natural ventilation
(also see Chapter 18.104.22.168)
Relation to winds
Protection against cold winter winds should be balanced by proper ventilation during hot and humid periods. Therefore, regulated air movement is a primary requirement. This can be achieved by well planned openings with shutters.
Preferably, special openings for ventilation should be provided. Two small openings, one at a high level and one at a low level, or ventilating stacks may be solutions (see Chapter 3.1.4). The disadvantage of such special arrangements lies in the fact that they are often neglected by the inhabitants, with the result that warm or cold air enters the room at undesired times.
The warmer the climate and the higher the humidity, the more important is it to provide cross-ventilation.
To counteract the winter wind direction, evergreen windbreakers are desirable. However, trees should not block the prevailing summer breezes. Evergreen trees are best for wind protection, whereas deciduous trees are suitable for shading purposes.
The way plants can be arranged to achieve the desired ventilation effect is described in detail in Chapter 22.214.171.124.
Fig 3/162 Regulation of ventilation by evergreens and deciduous bushes
126.96.36.199 Passive heating
This section deals only with heating. Cooling methods are described in Chapter 188.8.131.52 and 184.108.40.206.
Elements of passive solar heating
The possibilities of space heating by means of passive solar radiation have been excessively dealt with in the technical literature of recent years, but the main principles have been known for a long time. Traditional buildings often include a fine synthesis of a balanced use of solar energy. The advantages are obvious: the consumption of firewood or other fuels can be reduced, which, in these days, is extremely important ecologically.
The basic idea was formulated by Socrates, who designed a concept with three elements:
· Capturing as much winter sun
· Keeping out solar radiation in summer time
· Using a thermal buffer zone towards the north
1. Summer sun
2. Winter sun
3. Covered verandah
4. Living room
5. Storeroom as thermal buffer zone
6. Insulated wall towards the north
Fig 3/163 The concept designed by Socrates
The function of the solar gain process using glazed surfaces is based on the greenhouse effect. This means that solar radiation can easily pass through glass. When it strikes an absorptive surface behind the glass, it is converted into longwave heat radiation which cannot pass directly through the glass anymore. As a result the materials behind the glass heat up.
Passive solar systems
Three main principles used for passive solar gain can be distinguished: direct solar gain, indirect solar gain and attached green house.
Passive solar gain
The suns rays enter through the windows into the rooms which are required to be heated and the heat is stored in the walls, floors and ceilings.
Using direct solar energy in a building requires that the majority of windows are located on the south elevation. The suns rays enter the building through the windows and strike the floors, walls and objects in the rooms, where the greatest part is absorbed and converted into heat.
Fig 3/164 The floor as collector and heat storage mass
Fig 3/165 Internal walls as collector and heat storage mass
Fig 3/166 The ceiling as collector and heat storage mass
In order to retain the heat and to avoid overheating of the rooms in daytime heat storage capacity is needed. This implies that the major part of the materials used in the inside of the building (inside the thermal insulation) must have good heat absorption and heat storage properties.
Indirect solar gain
The suns rays are captured by various kinds of solar collectors, where the accumulated heat can be transferred to the room in a controlled way.
Commonly known systems are:
a) Trombe wall
A massive wall with a dark surface is placed behind a glazed surface. It absorbs the suns rays and conducts the heat slowly through the wall to the inside of the building. From here the heat is transferred to the rooms both by radiation and by convection.
Adobe and burned clay bricks are the materials with the best properties for trombe wall constructions.
A disadvantage of the trombe wall is that it covers a great part of the south facing elevation and thus prevents the provision of windows on this side.
Fig 3/167 Trombe wall with insulated shutter on the outside
b) Solar wall
The solar wall consists of highly absorptive, light materials between a glazed surface and heat insulation. Solar radiant heat is collected. This is then emitted to the air between the glasspane and the surface of the collector, which transfers the heat to the rooms.
Solar walls can be constructed of corrugated, matt black painted
metal sheeting or other building materials which heat up quickly and which are
resistant to high temperatures. They can be incorporated into the building
elevation, but they can also be arranged in a detached way. In order to prevent
the heat from escaping to the outside, the glazed window walls in front of the
solar walls have to be constructed in a well sealed way. The system is also
known as air-loop heating.
(see example in Chapter 4.9)
Fig 3/168 Solar wall as an air heating device with internal storage mass
During the warm period of the year, solar walls can be used as a
cooling device, creating increased ventilation.
(also see 220.127.116.11)
Fig 3/169 Solar wall as cooling device
c) Solar collector
Solar collectors using water as a heat transmitting medium are the most efficient ones. The system also offers more flexibility in the design because water can easily be transported to the desired place in a controlled manner. However, the technology requires more expertise and skill than the construction of thermal walls. At high altitudes, there is a danger of freezing.
Fig 3/170 Solar collector as detached device
As a rough rule of thumb, in upland regions where the
temperature varies approximately between 0°C and 10°C, the solar
collector surface should be about 1/3rd of the heated floor area, provided the
building is moderately well constructed.
(Example of space heating by a solar collector see Chapter 4.6)
Danger of freezing
In mountainous regions, with temperatures far below freezing point, the use of water as a heat transmitting medium is not possible. An anti-freezing agent would be required, but in many cases its availability and use cannot be guarantied. Here, systems using air as a transmitting medium are appropriate. However, such systems are less efficient.
Collector at low level
For them to operate in a purely passive way, all these water and air-loop systems, also called thermo-syphons, require placing the collector at a lower level than the heat outlet, for them to operate in a purely passive way. The reason is that a heated medium expands and is thus lighter than a cooler one. It therefore rises, which is the basic principle of any such system.
Collector at high level
If, for certain reasons, the collector is located above the heat outlet, an active element is required to transport the heat to the desired place. Such elements would be circulation pumps or fans. These systems are more complex in terms of construction, as well as in terms of operation. They are more expensive and also depend on a second energy source, usually electricity.
d) Water wall
(see Chapter 3.1)
Instead of masonry the wall consists of a metal tank filled with water. Compared to the trombe wall this system conducts heat much more rapidly because the wall has far less thermal lag and the water convects during heating. The great heat capacity of water permits for rather thin walls.
e) Roof pond
(see Chapter 3.1)
Water walls and roof ponds could be suitable, but are technically demanding.
f) Heat gain through an attached greenhouse
A greenhouse is built onto the south wall of a house and functions as a solar collector. During the day excess heat is transferred by convection into the house, where it is stored in the floor, walls or ceiling, or in a special heat storage element. The greenhouse can also be combined with the principles of a trombe or solar wall.
The floor of a greenhouse as heat storage
The main advantage of the greenhouse is the attractive additional room it offers, which can be used as living space during cold but sunny hours, and as a place to raise vegetables and flowers as well.
To avoid overheating of the greenhouse, movable shading devices, preferably placed on the outside, have to be considered. Large ventilation openings are usually also required.
The walls of the greenhouse as heat storage area
If a greenhouse is used during the cold season when there is no sunshine, it can easily become a source of heat loss rather than heat gain. This is also the case during cool nights if it is not properly closed off from the rest of the building.
Free standing heat storage in greenhouse
Fig 3/172 Solar gain by attached greenhouse shown during day and night function