Dear Editor,
The adoption of building designs, which are totally unsuitable for our hot and humid climate, has been an increasing trend on the coast of Guyana over the last few decades. Building designs are being adopted primarily on aesthetic considerations, without regard to the environment. The result is that buildings are now requiring a significant amount of air-conditioning, as internal conditions would be extremely uncomfortable without it. Some designs even increase the need for internal artificial lighting during the day. Accordingly, there is a sharply increasing demand for electricity for cooling, and to a lesser extent, lighting.
At this time when we are promoting energy efficiency and preservation of the environment, our focus should be on erecting buildings that are energy efficient. This means adopting designs and developing buildings that are appropriate for our climatic conditions. Designs should, as much as possible, utilise passive cooling and ventilation, and natural lighting.
Until about the mid 1970s, our buildings use to be more energy efficient. Buildings were primarily made of wood, a material which has a low thermal mass. Buildings had roofs with the apexes high above floor level and no ceilings. Roofs were fully boarded before being covered with zinc sheets; the boards acted somewhat as thermal insulation. The buildings had a lot more windows – some even had roof-windows. Internally, there were several feet of space between the top of a wall and the roof. In addition, there was usually a 4-inch or so space between the floor and the bottom of a wall. Invariably, our buildings were white in colour to reflect most of the sunlight and reduce heat transfer to the inside. These and other design features facilitated (i) proper ventilation and air circulation; (ii) reduced solar heat gain; (iii) passive cooling; and (iv) the admission of sufficient natural light in buildings. As such, there was little or no need for air-conditioning to cool the buildings, or for electric lighting during the day.
In contrast, our buildings today are made predominantly of concrete, a material with a high thermal mass. The switch to concrete was based on economics; concrete lasts longer than wood and requires less maintenance. Apart from the use of concrete, building designs now incorporate lower roofs with ceilings. Typically, ceilings are placed just about 9 to 10 feet above the floor. Internal walls, particularly bedroom walls in houses, no longer have any space above or below them. Perhaps this is an effort to improve bedroom privacy, but internal air circulation is restricted. Also, white buildings are less dominant; buildings are now of every colour except, maybe, black. I recently saw a dark-blue building. It appears that people are painting their buildings with their favourite colour. The heat transfer effect the colour of the paint has on a building is not a consideration.
With the prevailing building designs, the concrete would absorb significant solar heat during the day, transferring some heat to the inside air in the process. At nights, the absorbed heat is slowly released to the atmosphere in and out of the building. As a result, thermal comfort inside the building is rather difficult to achieve, even during the sleeping hours at nights, without some auxiliary system. What exacerbates the thermal discomfort in our concrete buildings is the use of high concrete fences around the buildings, and the paving of large areas of surrounding yard space with concrete or similar materials. The retention and radiation of solar heat from these structures contribute to higher temperatures within the buildings.
Generally, the use of high-mass, concrete building construction is not recommended for a hot, humid climate such as ours, particularly with the limited diurnal temperature range. Passive cooling in our climate is normally more effective in low mass buildings. However, with innovative designs, comfortable indoor conditions can be achieved in concrete buildings using passive cooling. The key is to use well insulated and shaded thermal mass designs to reduce solar heat gain. In addition, the designs should facilitate adequate ventilation and air circulation.
In a paper entitled ‘Cooling Buildings in Hot Humid Climates – a Decision Model for Ventilation’ by J C Bonetti, H Corvacho and F Brandão Alves, the following design strategy is recommended:
1. solar protection of windows and walls;
2. to consider high and large openings to promote ventilation and indirect lighting;
3. to enhance air circulation with high ceiling levels;
4. to promote ventilation through the roof and to choose reflective roofs with separate and insulated ceilings;
5. to adopt elevated floors to allow for its cooling and to reinforce ventilation;
6. to design an open internal layout;
7. to choose lightweight constructions duly insulated;
8. to strengthen new urban design solutions which may facilitate natural ventilation of the area, considering namely wind corridors: to design both building and landscaping in order to use in the best way the available cooling winds and, if necessary, to deflect them;
9. to plan the use of shade-producing trees since they filter the sunlight, reduce air temperature and reduce glare from bright overcast skies.
A change in building design practice should be part of the promotion of energy efficiency in this country. This means encouraging the design of buildings that are appropriate to our climate, reducing the need for air conditioning and daytime artificial lighting. The optimised use of natural ventilation for cooling buildings should be the first consideration in any design. The use of natural lighting should also be optimised. Ensuing buildings would, therefore, be more energy efficient with little or no electricity demand for cooling, or for electric lighting during the daylight hours.
This does not mean that buildings should not be aesthetically appealing. Local architects and building designers should be conducting research to develop buildings that meet certain economic, aesthetic and energy efficiency considerations.
Yours faithfully,
Horace Williams
Electrical Engineer
