For thermal comfort, the building must act as a barrier, transforming the outdoor climate to conditions suitable for indoor activities; the typical design process is a weighing of conflicting demands to reach a satisfactory compromise, such as between passive and active climatization, between privacy and solar access, between cross-ventilation and noise reduction, etc.
The climatic design process requires special attention. In 1974 the Building Research establishment in the UK was aware that a building can’t be design satisfactorily exclusively on economic, functional or formal grounds, just slightly adjusting to give a good indoor climate, since climate must be taken into account when deciding on the overall concept of a project, on the layout and orientation of buildings, on the shape and character of structures, on the spaces to be enclosed and the spaces between buildings. In other words, climate must be considered at the early design stage. \citet{al1974} distinguished between three stages in climatic design:
- forward analysis, which includes data collection and ends with a sketch design;
- plan development, which includes the design of solar controls, overall insulation properties, ventilation principles and activity adaptation;
- element design, which comprises closer examination and optimization of all individual building elements.
In the following section of the chapter, all the parameters that have to be considered during the design stage will be analyse in depth in both the climate locations assigned, so to define some passive strategies to reduce as much as possible the energy need for heating, cooling, ventilating and lightning.
Surroundings
The surroundings of a building have great influence on its indoor climate, whether it is in a city or in the countryside, providing for or protecting from certain winds, creating solar access or shading, etc, must be considered in each individual case.
- in Nome (Alaska), where there’s a Cold Subarctic climate, the urban fabric, site layout and building orientation should protect from cold winds. At the same time, solar access is important during the long, cold season when the sun is low. Glazed-over or covered urban spaces may be adequate, but risks of occasional overheating must be considered;
- in Nadi (Fiji Islands), where there’s a Torrid savanna climate, a compact urban plan is preferable for obtaining an acceptable microclimate in the hot season; narrow streets create shade and may act as cool ponds where buildings get their ventilation air. Moreover, highly reflective surfaces are thermally preferable to reduce solar gains, but they may create glare; finally, solar access during colder seasons may improve urban climate.
Form
The form of the building includes its main proportions, scale/volume, attachment etc. Roof form is often discussed; in fact, cylindrical and dome roofs have a higher heat transfer coefficient and larger area than flat roofs of the same base. As a result, the solar energy absorbing area is nearly the same, whereas the convection heat transfer area is higher for the curved types. The ceiling height is another issue related to roof form.
- in Nome (Alaska) a minimized and well-insulated building envelope that reduces heat losses is the most adequate. In particular, pitched roofs are suitable for rain protection;
- in Nadi (Fiji Islands) traditional buildings have often high rooms, especially those with domes or vaults which add to the room height, and thus also to the volume. A compact layout of buildings minimizes solar exposure in the summer and heat losses in the winter, if any. Courtyard houses create intermediate zones that can differ greatly from the outer climate.
Orientation
A North-South orientation of the main facades is preferable, since the summer sun penetrates façades and openings only marginally in these directions, while in winter when the path of the sun is lower, there is possibility of solar access.
- in Nome (Alaska) orientation for solar access is important, especially in winter. Double or triple glazing is required and large glazed areas may require shading in some directions if the summer is hot or also to avoid glare at West in late afternoon; windows in direction opposite from the equator, instead, should be minimized;
- in Nadi (Fiji Islands) North-South orientation of the main facades is preferable. Solar protection is important, especially towards the West, where afternoon sun coincides with high air temperatures. If there are prevailing winds suitable for cooling they can be caught by correctly placed openings or by special devices.
Materials
Building materials may be different for different building elements and they may play a greater role for the overall thermal performance. A standard recommendation is that local materials should be used as far as possible. However, the choice of materials should take into account, not only the production, transportation and construction costs and energy, but the life-cycle cost of the building, including the operation and the demolition and possible recycling of the material.
- in Nome (Alaska) thermal insulation of buildings is important to raise the temperature of inner surfaces for better comfort and to reduce the amount of energy used for heating;
- in Nadi (Fiji Islands) the great changes in day and night temperatures can be exploited by incorporating heavy materials to help to moderate the indoor climate. Some thermal insulation is advantageous, particularly of the roof, which receives the most solar radiation during hot periods; a lightweight and insulating envelope reduces the overall heat transfer, especially during winter, but requires heavy internal elements for heat storage. Spaces for night occupation only may be constructed in lightweight materials, allowing quick structural cooling in the evening.
Ventilation
Thermal comfort can be created by increasing air speed through cross ventilation, which promotes evaporative cooling of moist skin. In addition, the placement of openings for inlet and outlet of air is essential for directing the air current to the occupation zone and the presence of ventilated attic spaces, preferably with some ceiling insulation, reduce radiative heat transfer from the roof sheeting. Wind angles up to 45° to the openings are acceptable and may even give better ventilation rates than in a perpendicular direction.
- in Nome (Alaska) the ventilation rate should be kept at a minimum to reduce heat losses, but not so low that it causes health or moisture problems;
- in Nadi (Fiji Islands) adequately placed and designed openings can direct air-flow into the spaces normally occupied.
Structural cooling by night ventilation has been commonly adopted in hot and arid regions: during the daytime, a sufficient amount of internal building mass can serve as a heat sink to absorb, by radiation and natural convection, the heat penetrating into and generated inside the building. As a rule of thumb, night ventilation can create an indoor maximum temperature of 7–8 K below the outdoor maximum; during daytime, when the building is closed, the thermal mass is cooler than the indoor air, making the operative temperature lower, further enhancing the comfort.