List of fi gures
3.2.4 Spatial organisation
The development site should be as large as possible. It can be proven that damage to the natural environ- ment is directly linked to the density of the users’
population. Furthermore, a large size of the resort site will allow for (relatively) unconstrained positioning of the resort buildings and generous space left be- tween them. This should allow for adequate exposure of the buildings’ broad side to the winds prevailing in the area. Generally, in hot humid regions such as the coastal tropics buildings should be fully exposed to cooling winds (Figure 3.3).
In order to ensure free movement of air through the site, resort buildings should be located a fair dis- tance from each other; this also avoids obstructing land–sea breezes. In the layout organisation, a paral- lel tendency is preferred. Probably the best solution would be to set the buildings in a single row following a shoreline. However, one must remember that their sun–wind orientation is, in this climate, crucial to their thermal performance. Generally, the long axis should be aligned in an east–west direction. The pre- ferred orientation is that of the long axis of the build- ing pointed west 5in the southern and +5in the northern hemisphere with a 10tolerance (i.e. facing from 255–275, or 265–285, direction). Longer walls would then face south and north, limiting their ex- posure to ‘low-angle’ solar radiation (Figure 3.4).
Another important factor is the prevailing wind direction. Orientating buildings so that their long facades are exactly perpendicular to the wind direc- tion (i.e. facing the wind) is not required. It has been shown in some studies (compare Givoni, 1962) that a Figure 3.1 Every large body of water acts as a heat sink
during the day.
better and more even distribution of air flowing through the building, without compromising air ve- locity, is achieved when the wind is oblique to the inlet openings – at approximately 45. Further im- provement can be observed when inlet and outlet openings are located in opposite walls. If the open- ings were located in adjacent walls, better cross-ven- tilation resulted from the inlet opening being
perpendicular to the wind direction. Furthermore, for best ventilation effects, the area of openings serv- ing as outlets should be maximised (Figures 3.5–3.8).
Buildings of the resort should be connected by shaded pathways. Paving, however, should be avoided. Both the vegetation and topography should provide maximum shade and support air movement through the site. Whenever possible, buildings should occupy either the crest or foot of a hill (the two locations where wind and breeze speeds are recorded at their highest) and avoid its west and east Figure 3.3 Flow of air around a group of buildings.
Figure 3.4 Recommended orientation for best shading effects.
Figure 3.6 Comparison of air speed inside the room achieved by varying inlet and outlet sizes.
Figure 3.7 High-branched trees, such as palms, provide shade and let the air flow freely around the building.
Figure 3.8 ‘Cooling path’ provided for the breeze before it enters the building. Hard surface heats the air, which rises drawing more air through the building.
Figure 3.9a–e Use of vegetation in redirecting airflows through the site.
Figure 3.9 (Continued)
side, which are the worst in terms of exposure to solar irradiation. Furthermore, moving buildings as close as practicable to the shoreline (but beyond the zone endangered by tides and storm surges) is recom- mended. Ideally, a building location would be in a
‘saddle’ between two hills, particularly if both sides were open to wide and flat areas, for example to the sea. The funnelling effect at such a position is virtu- ally guaranteeing nearly continuous air movement through the site.
Care should be taken in planting new trees and shrubs to achieve maximum shading benefits on the east and west sides. This could be combined with the enhancement of breezes through a ‘funnel effect’, although the benefits can be expected for a rather narrow wind incidence angle only (see above).
Elements of the landscape design (including vegeta- tion) can also create high and low pressure areas around a building in reference to its openings, direct- ing and accelerating beneficial air streams into the building. It is important that landscape elements ef- fectively shade ‘air paths’ to ensure that air entering the building is of a relatively low temperature (Figure 3.9a–e).
Taking advantage of wind/breeze incidence could be more important than protecting the building’s perimeter from solar irradiation. In the tropics, the sun at noon can take either a south or north position. It stays very high over the horizon for most of the day, twice a year directly overhead, and even small eaves are sufficient to shade vertical elements of the building structure, with the excep- tion of east and west orientated walls. The roof is the element receiving most solar irradiation and this does not change much with its tilt or orientation. Pro- blems related to irradiation of walls are caused by the sunrays coming at lower angles. The solution could be to position the long axis of a building as close as practicable to an east–west direction. That would decrease the area of surfaces exposed to this insolation. Still prevalent is the opinion that the problem of insolation can easily be dealt with by shading the east and west walls. This would suggest that in any case wind consideration should take pre- cedence over sun-related orientation. Nowadays, however, some experts question this opinion.
Appropriate site planning can help reduce the problem of humidity build-ups. Preventing excessive Figure 3.9 (Continued)
humidity on the site in naturally humid climates can be done by allowing for free air movement through it and by locating humidity sources (swimming pools, decorative ponds, etc.) far from resort buildings. Lo- cating the buildings away from larger masses of veg- etation would also probably be beneficial in this respect.
One of the more important planning issues is functional zoning of a resort. Its ‘naturally noisy’
parts, such as dining rooms, playgrounds, entertain- ment areas, the reception and roads, should be sepa- rated from guest units. Moving them apart and/or introducing vegetation as sound and visual barriers can do this.
3.3
Constructional design
Key recommendations in brief:
* Lightweight structural systems should be selected ahead of heavy ones for most eco-resort applica- tions;
* Heavyweight, well-insulated and sealed systems should be used in all air-conditioned buildings;
* Consider hybrid structure for guest units: light- weight for night-time use part and heavy for the daytime one;
* Provide good insulation for roofs with the
‘parasol’ option as an alternative.
There are three competing views regarding the most appropriate climate-responsive building struc- ture in warm and humid climatic regions. They champion the following structural types:
* low mass or lightweight structure;
* large mass or heavyweight structure;
* a combination of both former types in a hybrid structure.
The most popular views, supported by vernacular building traditions in the wet tropics, give preference to lightweight solutions. It has been argued that the lesser mass of such buildings reduces the structure’s thermal time lag, which in turn causes internal tem- perature swings to follow more closely the external temperature profile. This short response time has been seen as necessary because of the relatively small diurnal temperature differences characteristic of the zone. With this view, the indoor environment bene- fits from small drops in evening/night temperatures occurring without significant delays. The same views hold that small diurnal temperature ranges do not warrant use of thermal mass. The mass is almost cer- tainly counter-productive when used in the struc- tures of guest bedrooms. Lightweight constructions are preferable there because they do not support sta- bilising temperatures at concurrent high relative hu- midity (night-time) conditions. In these conditions, the envelope should also have a low insulating value if the building is fully cross-ventilated.
In this type of building the indoor temperature can never be lower than the one outdoors but lack of insulation – allowing for unimpeded heat transfers – ensures that it will not be significantly higher either.
Nevertheless, surfaces exposed to solar radiation, es- pecially roofs, should be well insulated. It is worth
noting that well located mass inside the structure can help to overcome undesired temperature fluctua- tions and winter overcooling, which can and does occur even in tropical environments.
The second view favours heavyweight buildings.
Research carried out in tropical Australia (Cox, 1993) found that heavyweight buildings were the least over- heated. Therefore, it was concluded, a heavyweight structure is climatically the most suitable solution when used in combination with other passive mea- sures, such as shading and night-time ventilation.
While the research findings demonstrated the supe- riority of a predominantly heavyweight structure, factors like siting and orientation were excluded from considerations. This limitation may have been ac- ceptable in the case of a building project undertaken in an urban environment where limited size and re- stricted orientation of building sites are their domi- nant and usually predetermined qualities.
Locality microclimate’s characteristics have a much greater impact on the building’s performance if one can remove these urban limitations. This is often the case with resort sites. There are also signif- icant differences between residents’ dwellings and the resort in terms of time of use. Furthermore, a psychometric comfort zone (see Figure 2.8) specified for a dwelling, being different from that of a resort, influences lengths of periods accounted for as
‘overheated’ and ‘underheated’. This can substantial- ly distort our view of comfortable conditions in the resort. Finally, the research only compared light- weight versus heavyweight buildings. Cox’s study, although acknowledging such a possibility, did not attempt to test the thermal performance of the third option: hybrid light–heavy structures (Figure 3.10).
The hybrid structure uses heavyweight fabric for daytime living areas downstairs and a lightweight superstructure for spaces used at night. The concept was first offered by Drysdale in the late 1940s (Drys- dale, 1975) and since then the hybrid approach, de- veloped along the lines of logical deduction, has gained much support. It has been argued that a heavyweight daytime part of the building, without mechanical ventilation but using its capacitive insu- lation, offers a level of performance which is on par with that of a mechanically ventilated lightweight structure. The bedroom part of the building, on the other hand, benefits from the thermal behaviour of a
lightweight structure. The concept has undergone very limited testing in practical situations and remains largely a theoretical conjecture. Neverthe- less, the hybrid alternative could prove to be the most appropriate solution for eco-resorts in the coastal tro- pics.
In the case of some resort buildings, however, it does not seem necessary to use this type of structure.
A number of behavioural differences between resi- dents and visitors to the tropical coast make it poss- ible to consider only a part of a resort as the one crucial to the tourists’ perception of comfort. As we have argued, it is the part designated for night-time use, i.e. the guest units. Constructional design of oth- er buildings should give priority to limitation of the impact that the buildings and associated construc- tion processes make on the environment. From this point of view, lightweight structures seem to be a better option than heavy ones by a large margin.
Builders themselves can move elements of a light- weight structure and, because of this, the need for lifting equipment is usually substantially reduced.
Furthermore, these elements can be brought to the site using all means of transportation including bur- den animals – there is no need for roads or cranes.
Most technologies used in lightweight structures do not require powered machinery or tools, which results in less environmental impact during the con- struction stages. Having been traditionally used in vernacular tropical buildings, these technologies, more often than the heavyweight ones, can draw on locally available materials and utilise locally available building skills. Flow-on benefits include low embod- ied energy and less undesirable socio-economic impacts. Finally, yet importantly, lightweight struc- tures can be removed leaving almost no trace behind – a feat not as easily achievable with heavyweight ones.
Figure 3.10 Section showing the principle of a hybrid structure.
3.4
Building design
The building envelope – a system of roofs, walls with all openings, and floors both on the ground and suspended – is the ultimate barrier between the indoors and the world outside. The barrier works like a filter, employing building fabric and various design features.
In a hot and humid climate, there appear to be only two considerable ameliorating effects achievable with the help of purely passive climate control. They are:
* reduction in the amount of total radiation; and
* increase of airflow.
Other effects, such as supply of cool air and de- humidification, are difficult to achieve without some support from powered devices and would probably require conscious cooperation on the part of the occupants. This, in turn, would require some sort of preparatory measures, such as instruction and train- ing. Thus, an attempt to achieve such effects is seem- ingly impractical in a tourist resort. There are also psychological consequences (see Section 2.4) of cer- tain design solutions, which also could be employed.
However, these solutions appear to be largely past experience/culture-dependent and require much more research before conclusive results, leading to their practical implementation, can be expected.
Let us pause for a moment and consider the actu- al magnitude of the design task. A brief developed on a basis of climatic recommendations alone would be- come, most probably, a document full of mutually exclusive demands. For instance, in order to reduce roof area and solar irradiation and to increase expo- sure to sea breezes, it would be advisable to build multi-storey buildings. However, this is contradictory to the resort character and, quite obviously, invasive to the landscape. Moreover, high-rise buildings de- mand, on average, more energy than any others, pres- ent a more difficult-to-control acoustic environment, are much more expensive in difficult foundation con- ditions so frequently found on the tropical coast, and are more intrusive (to say the least) in environmental terms.
A compromise solution would be to accommo- date tourist resorts in buildings of a few storeys. Guest bedrooms could be located upstairs while rooms re- quiring more defined thermal control during the day- time could be moved downstairs. The upper parts of
the resort buildings should preferably be lightweight structures designed to prevent any considerable heat gains. Such a solution could be problematic when looked at from another angle: cyclonic winds occur- ring in the tropics during the summer season can cause extensive damage to light structures and endan- ger their occupants. Other examples such as better daylighting, achieved by increasing the size of win- dows, in most instances will increase heat gains. Larg- er windows, on one hand, will increase intrusion of external noise but, on the other hand, provide psy- chologically beneficial visual contact with the out- side. Noise in the background is undesirable in itself but potentially useful to aid speech privacy as a mask- ing sound. Sunshades would control the period of solar irradiation but reduce the level of available day- light. This list of contradictions could be extended.
V. Olgyay (1963) carried out studies for optimum building shape for a range of climatic zones. For hot–
humid zones he recommended rectangular building shape with the short to long wall aspect ratio of 1:1.7.
This recommendation applies, however, primarily to dwellings as it improves their overall day–night per- formance. Resort performance emphasis is on the night-time, and the ability to dissipate heat (by means of effective cross-ventilation easiest available in narrow, spread-out buildings) is, perhaps, more important than preventing heat gains. Notwithstand- ing, exposure of eastern and western walls to the sun should be minimised and the building elongated to catch prevailing winds and to aid cross-ventilation.
A catalogue of means available to architectural designers is presented in this section. Some of these means could greatly influence the indoor climate of a resort. In the given conditions, some may only pro- duce marginal changes and others would make no measurable impact. However the range of available means seems to be large enough to select the ones, in most locations, that will control parameters of the indoor environment to a desired extent.