Living Green # 6 Green Glass That is Really ‘GREEN’

My previous article mentioned about green glass that is not necessarily ‘green’. It might make you unhappy with your own apartments; especially if you have full-height windows and just figure out that it is too hot in summer and you are paying too much on energy bills. So, energy conservation is one of your concerns. Of course, we prefer glass windows to opaque walls. Daylight and view are the reason that some of us want to live in high-rise condominiums. However, you might want to know how much is too much for glass area in your apartments. What is the optimum area of glass for a house to be energy-efficient? The answer may be plain simple – just enough to make use of daylight and take a good view.

Having enough daylight means that the living room is so well- illuminated that you do not need to turn on the light during the daytimes. My own research suggests that a window area of about 50% of the total wall area is more than enough for daylight without too much solar heat. Unfortunately, it is the ‘good view’ that is difficult to justify whether it is good enough. Of course, if your 200-sq.m. condo unit is on the 30th floor of a building located on the bank of Chaopraya River, you would want as much transparent area as possible; and if you can afford that condo, you don’t need to worry much about energy bills, do you? Maybe or maybe not.

For the rest of us who cannot afford that premium condo, energy bill is definitely of concern. Furthermore, the view outside of our windows might not be good enough to spend extra money to look at. However, condominium developers still feel that full-height window is a must for marketing a city condo, and the most simple and inexpensive way for them to call it ‘green’ is to install green glass on our windows. I once said that green glass saves energy only when it is compared with clear glass, but having full-height green glass windows like what in cold-climate countries will not help you save on energy bills at all. Unfortunately, city condos installed with full-height green glass windows are mushrooming as the architects and developers are not those who pay for the energy bills. So, it seems that customers themselves need to be more educated and aware of what they will buy. For the government, they should be more stringent on the building energy codes simply because Thailand is not one of the OPEC countries!!.

In terms of energy conservation, actually, new buildings are required by laws to limit the amount of heat gain through the envelopes. The measure is know as OTTV—The Overall Thermal Transfer Value, which describes the amount of heat gain through building envelopes; the maximum value is 45 Watt per one unit area of exterior walls. A rule of thumb says that; in order to pass the law, if a building is designed with a window area of more than 30% of the total wall area, it needs a special kind of treatments; using either higher-efficient glasses or better insulations in the exterior walls, otherwise, the building needs to install external shading devices. If this energy code is enforced fully, we will see more energy-efficient buildings that not only help the condominium owners save on their energy bills, but also help Thailand import less energy from OPEC.

So, if all condos are using green glass, how do you justify if they are really energy-efficient or ‘green’ enough? There are a few things you need to look at. First, are the full-height glass windows oriented toward the south or the west? If so, your room will get too much solar heat. It is the first thing to avoid. Second, do the windows have sunshades? Proper shadings could cut down the solar heat gain by 30%. Sunshade is the fundamental design for buildings in hot-humid climates, even though many architects and developers feel it is quite obsolete to build a condo that has a ‘regional’ or ‘eastern’ look. It is sometimes even worse that it is the customers themselves who ask for ‘western’ looking buildings, and they are willing to pay for extra energy cost!! There is nothing much I can say about them.

The last thing is the color of ceilings. Light-colored ceiling allows more daylight to penetrate into the room by means of reflection. Regarding daylight, it is worthwhile to look at some special treatments on building facades that serve more than one function. Almost every green building design handbook has a section called ‘Lightshelf’. Lightshelf is a device that not only provides solar shading, but also improves quality of daylight. This way, direct sunlight is blocked from entering the space, while the room is better illuminated by the daylight reflected from the top of the lightshelf.

Here you see that shading devices can be designed to do more. Another good example that I found while searching for some nice façade pictures is a unique element put on the façade of an apartment building in Mexico City. It is designed by a Mexican design firm named Hierve-Diseñería. On the façade, there are 7,900 blown green glass spheres hanging outside in order to provide shading and, of course, create a really nice decoration. Although, there is no exact energy saving calculation available for this creative use of ‘green’ exterior shading; and headstrong environmentalists might question if the glasses were recycled ones, I believe it is worth looking at and thinking about being both ‘green’ and pretty. Let’s discuss furthermore about being ‘green’ that is not necessarily looking outdated.

ผศ.ดร. อรรจน์ เศรษฐบุตร

Asst. Professor Dr. Atch Sreshthaputra

Faculty of Architecture, Chulalongkorn University

Chairman of Green Building Program. The Association of Siamese Architects.

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