REDUCING URBAN HEAT ISLAND EFFECT with THERMAL ...

Conference on Sustainable Building South East Asia, 11-13 April 2005, Malaysia

REDUCING URBAN HEAT ISLAND EFFECT with THERMAL COMFORT HOUSING and HONEYCOMB TOWNSHIPS

M. P. DAVIS, N. A. NORDIN Institute of Advanced Technology, Universiti Putra Malaysia UPM Serdang, Selangor,43650 Malaysia e-mail : [email protected] M. GHAZALI, M. J. DURAK Arkitek M. Ghazali 19-1 Jalan 1/76 Desa Pandan, Kuala Lumpur 55100, Malaysia e-mail : [email protected] G. REIMANN Faculty of Buildings & Energy, Technical University of Denmark Lyngby, 2800, Denmark e-mail : [email protected]

Abstract Urban houses in Malaysia are too hot for about half the days of the year and Kuala Lumpur has become the world’s worse urban heat island on record. However, these problems are not the inevitable consequences of urbanisation and can be corrected and avoided with a sensible application of the technologies available to prevent the thermal mass of houses and roads from absorbing solar radiation. This paper describes a technology known as Cool House to reduce the effects of urban heat island on occupants. ‘Cool House’ technology, developed at Universiti Putra Malaysia can achieve almost passive thermal comfort without airconditioning, even on the hottest days of the year. ‘Honeycomb townships’, a recent architectural invention by one of the authors, is a new method of subdividing land which saves greatly on roads, thereby permitting larger gardens and courtyard parks in front of the houses. Large fruit bearing fruit canopy trees can shade nearly half of the township from direct sunlight. The cooler environment and the creation of interconnected diverse microhabitats will allow the introduction of large numbers of birds and small non-aggressive native animals, bringing ‘Watchable Wildlife’ into highly populated urban centres. The adoption of this rather simple technology will potentially save Malaysia RM200 billion (USD52 billion) in saved electricity for air-conditioning urban houses and apartments over a 30 year period. Electricity savings on this scale will greatly benefit other developing countries intending to rapidly urbanise, particularly China, India and Indonesia with much larger populations. Keywords : Heat island, Thermal comfort, Energy efficiency, Wildlife technology, Honeycomb townships, Test reference year.

1. Introduction Many cities suffer from overheating, whereby the ambient air temperature in suburban and downtown urban areas can be 20C to 3 hotter than in rural areas. This is termed the urban heat island effect and is caused by fewer plants and trees and the greater absorption of solar radiation by more buildings and roads. These temperature increases, although seemingly small from an engineering viewpoint, have profound effects on human comfort. In the Malaysian humid tropics, urban houses overheat by about 30C which is the difference between human comfort and human misery (Davis et al, 2000). With urban development the temperature during the summer has been increasing over the last 30 to 80 years in many cities around the world by 0.10C to 0.40C per decade. For example, Shanghai in increasing by 0.10C per decade, Washington by 0.20C, Tokyo by 0.30C and Los Angeles and San Diego by 0.40C (Akbari, 2000). Designing houses, townships and cities which do not overheat compared to the surrounding rural environment will greatly improve their liveability and save a colossal amount of energy for cooling.

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M. P. Davis, N. A. Nordin, M. Ghazali, M. J. Durak, G. Reimann

2. Methods and Analysis

2.1 Outdoor Heat Stress Meteorological data collected between 1975 and 1995 from the Subang weather station, Kuala Lumpur, Malaysia reveals that the average outdoor temperature in Kuala Lumpur has increased by 1.20C during this 21 year period. This previously unreported data was part of a larger study to construct a Malaysian weather year, termed a Test Reference Year (Reimann et al 2000). As shown (Figure 1) Kuala Lumpur is getting hotter by 0.60C per decade. To our knowledge this is the world’s highest value so far reported for the urban heat island effect (Figure 2). This finding supports anecdotal subjective evidence from long term residents of Kuala Lumpur who claim city living is becoming more and more uncomfortable compared to the rural areas. An objective measure of heat stress imposed by the outdoor Malaysian environment during different periods of the year has been calculated from the Test Reference Year in a novel Thermal Discomfort index (Figure 3).

Figure 1 Average temperature vs year

Figure 2. Heat island effect

One unit of thermal discomfort is defined here as the heat stress suffered by a person wearing light tropical clothing whilst resting outdoors for one hour in the shade with no wind whilst the average ambient temperature is 10C above the upper thermal comfort level (estimated to be 280C for the Malaysian humid tropics, Davis et al 2000). For example, a person under these conditions when the average ambient temperature between 1pm and 2 pm is 330C suffers, by definition, 5 units of thermal discomfort. These units per hour, summed over 24 hours, provide a quantitative measure of human heat stress for that particular day. The results reveal that the population of Malaysia suffers outdoor heat stress throughout the year; there is no cool season (Figure 3). Whilst Malaysia, being close to the equator, is hot every day of the year, this index reveals for the first time the true but rather hidden seasonality as felt by humans. Two 455


heat-waves, imposing 40 units of thermal discomfort per day, occur regularly in March and May whilst the 4 months from September to December are much more pleasant, imposing only 15 units of thermal discomfort per day.

Figure 3. Malaysian reference weather year

2.2 Indoor Heat Stress The indoor temperature of residential houses in Malaysia has been extensively studied over the last ten years by researchers at the Centre for Thermal Comfort Studies at Universiti Putra Malaysia (Davis et al 1995, 1997, 2002, 2003). Whilst the traditional well ventilated wooden houses in the rural areas are near ambient houses, closely following the outdoor temperature, all of the modern concrete houses built over the last 50 years in Malaysia are grossly overheated (Figure 4).

Figure 4. Temperature inside a concrete house

In this example a single story concrete terrace house during a heat-wave is way above the upper thermal comfort level every minute of the night and day. However, the outdoor environment is perfectly comfortable for 14 hours per day. Experiments such as this during different times of the year, using a miniature temperature data-logging technique (Davis et al, 1995), has established that all 2 million modern concrete houses cause two to three times more thermal discomfort (heat stress) than the outdoor environment (Table 1). Our general, though rather sad, conclusion is that the Malaysian urban population would be far more thermally comfortable if, they abandoned their houses and lived under trees.

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Table 1. Thermal discomfort

This absurd situation has provided the motivation to design thermally comfortable houses without the high electricity cost of air-conditioning which has been estimated by computer simulation to be more than the house construction cost over a 30 year period (Davis et al, 2003). The general problem of gross overheating in Malaysian urban houses is illustrated (Figure 5). The closed attic space becomes up to 140C hotter than outdoor ambient temperature. This excessive heat is transmitted through the bedroom ceilings and becomes stored in the concrete walls and floor slabs. Unlike wooden houses, Malaysia’s concrete houses therefore heat up like ovens during the day and barely cool down at night. The term ‘sweat boxes’ is aptly applied to Malaysia’s 1.7 million terrace houses. The principle source of the problem is the absorption of solar radiation by the concrete roof tiles and the transmission of the heat into the non-ventilated attic space. Over the years, Malaysian attics have become less and less ventilated, to prevent the spread of fire and to keep out rain, birds and vermin. However, replacing the concrete tiles with a metal roof and insulating the roofs with glass wool or rockwool has proved highly effective in reducing the sealed attic space temperature to outdoor ambient (Davis & Nordin, 2003). This is illustrated (Figure 6). Renovating a double storey house in this way reduced the thermal discomfort in the bedrooms and living areas by 80% (Figure 7).

Figure 5. Indoor temperature vs outdoor ambient temperature

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ON A VERY HOT DAY

0

Temperature C 50

(1 June 2001, Serdang, Selangor) Single-storey terrace houses ROOF SPACE TEMPERATURES

48 0C

45

NORMAL ROOF

40

COOL ROOF 0

35 C 35

30 0C upper thermal comfort level

30

25 7 AM

11 AM

3 PM

7 PM

11 PM

3 AM

Time

Figure 6. Thermal comfort level for very hot day temperature

Figure 7. Thermal discomfort per 24 hours

Computer simulation, using BSim software linked to the Malaysian climatic test reference year, has demonstrated that further improvements in thermal comfort can be achieved by shading the walls, to reduce solar heat gain, and by mechanically ventilating buildings at night, to expel hot air and introduce cool night time air. Thus bungalows (Figure 8) and apartments (Figure 9) have been designed which, according to computer simulation, will stay within the thermal comfort zone without the need for airconditioning, even on the hottest day of the year. HOTTEST DAY OF YEAR (8 March)

MAXIMUM TEMPERATURE OUTDOORS

39.40C

35.60C

29.60C

34.20C

29.80C

32.80C

30.80C

NORMAL BUNGALOW

UPM COOL BUNGALOW

Figure 8 Maximum temperature for hottest day of the year

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Figure 9. Simulated performance on hottest day of year

3. Honeycomb Housing Honeycomb Housing is a new patent pending invention for subdividing land discovered in 2003 by one of the present authors, architect Mazlin Ghazali. Instead of building rows of monotonous houses on rectangular plots of land, houses are built on triangular land within larger hexagonal-shaped land. Each hexagon is a cul-de-sac containing 5 to 14 houses all surrounding a small community park with large trees shading the road (see Figure 10).

Figure 10. Honeycomb Housing

The novel, wide frontage houses currently being designed include bungalows, back to back semidetached, quarter-detached, triplexes and sextuplets. Honeycomb housing creates small, friendly neighbourhood communities with ‘defensible space’. The hexagons efficiently interlock to form a ‘honeycomb’, interconnected with looping roads that are safe for children, pedestrians and cyclists. Since the roads are internal rather than around the perimeter of houses, the road area can be substantially reduced compared to terrace housing. For example a honeycomb township containing 258 houses was compared, using our Honeycomb mathematical software, with a conventional terrace house township also contain 258 houses (Table 2). The land saved by reduced roads, including the socially useless back lanes, was 23% in the honeycomb layout. This allowed for 100% bigger gardens for the consumer and 20% more saleable land for the developer. The Honeycomb layout, 16.5 houses per acre achieved an 8% higher housing density, compared to only 15.2 houses per acre for terrace row housing. Honeycomb layouts have other inherent advantages. Since the houses are not built in rows they do not require a level building site, only a level footprint for each housing block. This is far more environment friendly than terrace housing and causes minimal disturbance to the top soil and the natural water run off. Honeycomb roads are shorter and winding which creates slow moving traffic, safer for children, cyclists and pedestrians.

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4. Reducing Heat Island effect Kuala Lumpur is getting hotter, faster than any other recorded city in the world. New townships in Malaysia are repeating this mistake. Townships are being created from virgin jungle or plantations by totally clearing all trees and ground cover and cutting the hills and filling the valleys for easy terrace house construction. The high density of housing with token gardens and excessive road areas and back lanes leaves almost no suitable land to restore tree cover and green environment. Urban areas have become concrete jungles and heat islands, perhaps 40C hotter than the surrounding rural areas. This is particularly noticeable in Selangor with a population density of 526 persons per square kilometre compared to only 35 in Sabah and 17 in Sarawak. Honeycomb housing layouts can permit a very lush urban landscape in the gardens and neighbourhood parks. The winding roads can also be tree lined to provide shade. The aim is to recreate a rainforest type canopy over the township as the trees mature over a 5 to 10 year period to reduce the heat island effect. From our Honeycomb mathematical model, we have estimated the potential tree canopy area of the above honeycomb township to be 46%, compared to only 15% for a row housing, typical of a Malaysian terrace house township (Table 2) Table 2 Comparison between terrace and honeycomb housing

Discussion The successful urbanisation of Malaysia from a rural agricultural economy in two generations has become an inspiration to other developing countries. However, in the rush to modernise and alleviate poverty, serious mistakes in urban development have been made, albeit unwittingly. Evidence presented in this paper establishes that Kuala Lumpur is getting hotter faster than any other recorded city in the world. Random household surveys conducted by Universiti Putra Malaysia have also established that terrace houses, the major housing form in urban Malaysia, are considered by residents to be too hot on about half the days of the year (Davis and Nordin, 2002). These problems should be seen as mistakes that Malaysia has made, rather than the inevitable consequences of urbanisation. Other developing countries can avoid these mistakes with a sensible application of the technologies outlined in this paper. The Cool House technology developed at Universiti Putra Malaysia and reviewed here has the potential to solve the general problem of overheating in Malaysia’s urban housing. The insulation, ventilation and shading technology is not really novel. However, the use of indoor climate computer simulation programs linked to an accurate weather year for Malaysia provides a powerful tool for combining and optimising these separate technologies. As demonstrated in an earlier paper regarding energy efficient housing for China and Arab countries (Davis et al 2003), this method can be extended to any other climate, allowing energy efficient buildings to be perfected at the design stage, rather than expensively modifying houses after construction. Renovation of existing houses using this technology and the construction of the new designs of thermal comfort houses and apartments can have an enormous impact on air-conditioning electricity consumption, potentially saving Malaysia RM200 billion (USD 52 billion) over the next 30 years (Davis et al 2003). No country who wishes to rapidly urbanise can afford to ignore electricity savings on this scale, particularly other developing countries with far higher populations than Malaysia such as China, India and Indonesia. Modifying the indoor climate is clearly achievable with existing technology, correctly applied for any particular climate and culture. Preventing the thermal mass of buildings from heating up during the 460


daytime is a very effective strategy for passively achieving indoor thermal comfort in hot climates and also lowers the radiation from the buildings to the outdoor environment, helping to reduce the heat island effect. However, the urban roads in Malaysia are also a major contributor to the heat island effect. The roads are surfaced in black bitumen and fully exposed to direct sunlight which optimises the absorption of solar radiation, grossly overheats the roads and the subsurface layer of hardcore. Roads also comprise almost half the of the land area of Malaysian terrace house townships. Urban roads are therefore an enormous heat sink in Malaysia and need to be shaded from direct sunlight by canopy trees. This is not possible in the grid land subdivision typified by terrace housing. Only very small trees can grow since their roots are blocked by drains at the front and sewer pipes at the back lanes and offer virtually no shade to the roads. New Malaysian townships are becoming increasingly like desert townships, too hot and devoid of nature. Honeycomb townships offer a sensible and environmentally friendly strategy for preventing the roads from overheating. The large central parks in front of the houses allows very large trees to grow in land undisturbed by drains or sewage pipes, providing almost complete shade to the courtyard roads as they mature to 12 to 18 meters in height. The short winding roads can also accommodate shades trees on both sides, providing a tunnel of tree which filters most of the sunlight. The design of Honeycomb townships has led to the emergence of Urban Wildlife technology at Universiti Putra Malaysia, a well established agricultural based university with a full complement of biological faculties. A collection of some 600 species of fruit and berry bearing trees and bushes collected from the rainforests are now being propagated in polybags in a commercial nursery of over 1 million trees in Tanjung Malim run by James Kingham, a collaborator in this project. Each species of tree will provide food for a range of insects and bird life. By selecting and planting a variety of these trees and bushes in honeycomb townships, a rich food chain and diverse microhabitats can be established in urban areas, supporting large populations of semidomesticated but free ranging birds and non-aggressive small native animals such as squirrels and mouse deer as well a as visiting migratory birds. This natural food chain can be supplement with food supplied by residents to achieve higher densities of wildlife, cared for particularly by knowledgeable school children and retired residents. Conclusions Thermal comfort honeycomb townships provide a blueprint for cooler, environmentally friendly and energy efficient houses, towns and cities of the future, potentially overcoming the heat island effect suffered by many of the world’s cities. The thermal comfort technology, combined with Honeycomb land subdivision and the emerging urban wildlife technology, is now at the commercially ready stage and is beginning to attract the serious attention of Housing Developers and Government Housing Ministries in Malaysia. The technology can be applied particularly to new towns and cities worldwide, in any climate. Nature and wildlife can become an intimate part of all urban areas, even desert cities, using a sensible and sensitive application of this technology to improve human welfare. References Akbari H. (2000). Heat Island Group, Website www. http://eetd.lbl.gov/HeatIsland/HighTemps/ Davis M.P., Rajion M.A. and Farimah C.T.N.I. (1995). A new sheep shed which overcomes heat stress and disease losses in the Malaysian humid tropics. Ann. Zootech. 44, Suppl. 324, Elsevier/INDR. Davis M.P., Shanmugavelu S. and Adam n.M.(1997). Overheating in Malaysan Houses. Proceedings Affordable Quality

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Davis M.P. and Nordin N.A. (2002). Cool House Technology. Buletin Ingenieur Mal;aysia, 12, March pp42-50. Davis M.P. and Nordin N.A. (2003). UPM Cool Roof- A national Plan. Building and Investment 2, pp83-85. Davis M.P. et al (2003). Thermal comfort housing for Malaysia, China and Arab countries. Buletin Ingenieur Malaysia 13,

June pp35-40. Reimann G., Davis M.P. and Zain-Ahmed A. (2000). Energy Simulations for Tropical Buildings using Malaysian Weather Data,

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