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The Costs Of Cooling

The naked truth about the costs of cooling

Air-conditioning is hard to avoid in this climate, but there are other methods to keep the heat down in homes

Elizabeth Horscroft – Updated on Jul 02, 2008 – SCMP

Academics and environmentalists say if it is too hot in the home take off your clothes because it is less damaging to the environment than air-conditioning.

Li Yuguo, of the University of Hong Kong Department of Mechanical Engineering, said the problem was that people in Hong Kong were overdressed – they wear stifling formal business wear in a sub-tropical climate which should be shed as soon as they get home from work.

“People need to make the transition when they get home and shed a layer of clothing,” Professor Li said.

Use common sense to keep cool this summer. Professor Li said air-conditioning accounted for about 60 to 70 per cent of electricity consumption in Hong Kong, so using more efficient alternatives would save money.

Dressing for the climate is a good start. An open window (with insect screen) is another free and easy option.

If it is hot and humid outside an open window will not cool your home, but it will ventilate it, which has health benefits.

He said keeping windows open was a good way to replenish stale air, and people should not be too concerned about pollution because, from the 10th floor up of a building, the air was cleaner and the sun’s radiation killed bacteria.

“We still need to be careful about the particulates in the air though,” he said, adding that east-facing flats benefited from prevailing easterly winds, so leaving windows open helped ventilate and cool.

According to Professor Li, flats in Chai Wan benefit the most. “[People living in] flats facing west spend a lot more money on cooling,” he said.

Diane Urmeneta, an interior designer at I. F. Collection, said cross-ventilation was the best way to make the most of a natural breeze. “Having windows on two sides of the room, or opposite sides of the home, will allow this. But casement windows do not work well because strong winds can easily blow them shut. Sliding panels with screens work best and offer maximum exposure.”

Tinted windows also cooled the home by blocking the sun’s rays, but they toned down views so most people did not like this option.

More popular were heavy curtain materials or curtains with detachable blackout linings, and the use of energy-saving light bulbs that did not emit too much heat, Ms Urmeneta said.

According to Professor Li, Hong Kong buildings suffer from poorly sealed windows which let in hot air.

Properly sealing windows and doors helped keep homes cool in summer and warm in winter. Carefully chosen accessories cooled the home too.

“Indoor plants help because they are a natural way of keeping the air clean and fresh … as long as they are taken care of properly,” Ms Urmeneta said. She suggested that rooms be finished in shades of blue and green because they had “a more calming and cooling effect” compared with warm reds and yellows.

Another alternative is roof gardens. Sam C. M. Hui of the University of Hong Kong’s Department of Mechanical Engineering, said that building owners could improve thermal comfort and reduce energy consumption of air-conditioners by taking advantage of the thermal insulation that a green roof provided.

“Green roofs contribute positively to the improvement of the thermal performance of a building because they can reduce solar radiation, daily temperature variations and annual thermal fluctuations,” Dr Hui said.

Using natural cooling methods, however, only goes so far. So, according to the CLP Power website, ceiling or table fans are a good alternative because they consume only 5 to 10 per cent of the electricity that air-conditioners do.

Professor Li said fans cooled rooms by two to three degrees Celsius. As good an alternative as fans are, they cannot replace air-conditioning. But the toxic coolant, high energy consumption and their pollution impact on the environment continue to be a problem.

Environmental educator Jenny Quinton suggested looking at the problem through the eyes of a child. “Children are surprised when they find out that we are getting most of our electricity from burning coal, but they can quickly make the connection between how running the air-con 24/7 equates to the power companies shovelling more coal into the system and that that equates to yucky air and global warming,” she said.

Ms Quinton, who leads environmental programmes for children at the Ark Eden project in Mui Wo on Lantau Island, said: “Air-con is what we should try to avoid if we want to be part of the solution.”

But, given that air-conditioning is a must, look for models with a “grade one” energy label. According to the Hong Kong government’s Electrical and Mechanical Services Department, these will use less electricity than a grade three and significantly less than a grade five air-conditioner.

Using air-conditioners with fans is also a good alternative.

Professor Li said: “Setting air-conditioning at 24 degrees [Celsius] will be comfortable. But, additional air movement from ceiling fans will make the room temperature about 26 to 27 degrees [Celsius] which may be perfectly fine for many people.”

Setting the temperature slightly higher when sleeping – because the body temperature is lower – also helps. According to Friends of the Earth, setting the temperature slightly on the high side can save 3 per cent of electricity costs.

But leaving air-conditioners on when not in the home is a no-no. Ms Quinton said: “Leaving an air-conditioner on for an hour uses the same amount of electricity as leaving a light on for four days.”

Hard-core energy users can cut down by monitoring their electricity bills as they change their consumption habits. “Cut energy bills month by month, year by year and continuously educate yourself, family and company [on saving power],” Ms Quinton said.

This article is the first in a two-part series on how to cool a home in an energy efficient way. Next week: How installing green roofs can help cool buildings and reduce energy consumption.

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