Thermoacoustic Analysis for City Terrain Roughness of Warm Humid Climate FX Teddy Badai Samodra1 Laboratory of Architectural Science and Technology, Department of Architecture, Institut Teknologi Sepuluh Nopember (ITS), Surabaya, Indonesia
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Email address of corresponding author:
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ABSTRACT
The warm humid climate has specific contribution to increase the thermal and acoustic problem of the city. This paper presents analysis of thermoacoustic of this city terrain roughness with center of Surabaya as a case. The focus of this research is on the creating simultant solution for heating accumulation and noise production to the site and building. The thermal and acoustic accounting methods were performed for assessing site and building performance. Results highlighted that performances of building are depended on element configuration and dimension, material properties and its construction of both site and building relative to external climate conditions.
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Keywords: City Terrain Roughness, Noise Control, Themal Comfort, Thermoacoustic
1.
Introduction
Thermoacoustic effect is regarded as consisting of coupled thermal and acoustic pressure and motion. Previous research in thermoacoustics began with simple curiosity about the oscillating heat transfer between gas sound waves and solid boundaries. Thermoacoustic analysis can be harnessed to produce sustainable site planning of high density environment, both building and human activities. Thermal and acoustic problem is complementary, so it is not as difficult as thermal and humidity problem. The warm humid climate has specific contribution to increase the thermal and acoustic problem of the city. This region, especially in the lowland, city terrain roughness has hot environment all the days. Therefore, building heat gain is critical point and needs site control to provide thermal comfort. In other hand, noise control should be reached because of the human activities. 2.
Literature Review
Standards and regulations, which can be considered as inputs of some researches or projects should be improved to optimise the building envelope in order to obtain the comfort conditions (Oral, et al., 2004). If they are put into force, which take account of all aspects of the problem, as the optimisation of the performance of the building envelope controlling heat, light and sound should be achieved. Frontczak and Wargocki (2011) shows that the type of building, environmental climate and season influence thermal comfort. The solutions for controlling the indoor environment should include control of the thermal environment, the possibility of delegating control to occupants, and adjustments based on outdoor conditions, as well as the possibility of customizing the control. Concerning the combined effects on discomfort, the protocols including the warm conditions showed that the thermal sensations were not significantly different whereas the thermal comfort estimates differed (Pellerin and Candas, 2003). City terrain region has a large variety of forms and surface characteristic. Basically, the microclimate of these areas is influenced by several urban elements, such as the urban geometry, the greenery, and the properties of surfaces. It is clear that urban area without a proper use of these B2-58
elements is likely contributed to discomfort and inconvenience to the people as presented by Wong, et al. (2011). City is a complex urban environments and it can result in very different and often extreme comfort sensations even within short distances (Gulyas, et al., 2006). In this regon, taking façade noise levels and the WHO guideline into account, lots of people were exposed to daytime and nighttime transportation noise that would cause serious annoyance and sleep disturbance (Ko, et al, 2007). The large population of the city exposed to the nighttime transportation noise would attribute to the fact that nighttime traffic volume is not very different from daytime volume. In addition, central business districts and commercial sectors are generally very close to residential areas, and in some areas they are mixed with residential sectors. Kruger and Zannin (2004) define that the planning stage of a given architectural project, planners should have in mind: The importance of solar orientation, the correct dimensioning of ventilation and daylight openings, the correct choice of materials considering that each region has a distinct, particular climate type. The choice of the correct option for each one of these items will contribute to the improvement of environmental comfort of the building and consequently help rationalize the use of HVAC systems needed, therefore reducing energy consumption and promoting an adequate manner of using natural resources. The poor conservation state of doors and window frames has also contributed to the low acoustical performance of the façade (Kruger and Zannin, 2007). A more significant influence of the building materials (not only of the frames) was verified, however, in the thermal performance of both houses. Walls and roof materials were relevant not only in regulating heat gains and losses but also in the heat storage capacity of both building systems. The challenge for the building professionals is to assess these impacts, and consciously achieve healthy and comfortable living environment with minimal use of energy for heating and cooling. High density modifies the local microenvironment, which can be either favorable or unfavorable, depending on outdoor weather conditions (Niu, 2004). 3.
Methodology
Source: (Field Survey (2011) and Google Earth Image (2009))
Figure 1: Object/Area of Case Study
This paper presents analysis of thermoacoustic of this city terrain roughness with center of Surabaya as a case (See Figure 1.). Urip Simoharjo walk-up area is selected as case study and in this area consists of multivariation and characteristics of building and human activities. The focus of this research is on the creating simultant solution for heating accumulation and noise production to the site and building. The landscaping design and building envelope analysis are used to solve the problem as simulation variables. Moreover, outcomes are obtained for three scenarios models to site and building: Recommendation for specific and detail distance is used to control the noise and the heat from heavy work of human activities, landscaping design as barrier is used to reduce the noise beside as shading provider for optimize thermal comfort, and specific density of material is also used to eliminate noise, but it can accelerate the air flow. The numerological thermal and acoustic accounting methods are performed for assessing site and building performance. The analysis of open space and temperature will be developed to detect the B2-59
outdoor and indoor maximum temperature difference, and the relevant equation for the this difference is: ΔT = 7.45 + 3.97*ln(H/D) (1) where ΔT is maximum temperature difference, measured in 0C, H is average of buildings height, measured in meter, and D is average of distance among buildings, also measured in meter. In order to observe the comfort temperature and humidity, the analysis of wind speed for specific height will be applied, which is generally the wind speed of the outdoor environment: Vh = Vbl(h/hbl)φ (2) where Vh is wind speed at the h height (m/s), Vbl is wind speed at the top of boundary layer (m/s), h is the height of measurement (m), hbl is the height of boundary layer (m), and φ is the exponent of average wind speed. In detail of thermal observation, the analysis of surface temperature is conducted as equation (3). Ts = To + (I.αtotal/fo) (3) where Ts is surface temperature (exposed to direct sunlight) and To is outdoor temperature, both of them is measured in 0C, I is solar radiation intensity and measured in W/m2, αtotal is total of surface and material absorption value, and fo is conductance, measured in W/m2 0C. Correlations for noise reduction by distance derived analytically based on acoustics theory exist for simple logical description and analysis of noise reduction by exterior barrier is given by equation below: NR = 20 log [(2πN)0.5/tan(2πN)0.5] + 5 (4) where N= 0.006f.(A+B-D), measured in dB, f is Frequency (Hz), A+B = The nearest distance through barrier (meter), and D is the straight distance between sound source and receiver, mesured in meter. The last equation, used to simulate the noise reduction by composite transmission loss in building envelope, is defined as: TLc = 10 log (ΣS/ ΣτS) (5) Where TLc is composite transmission loss (dB), ΣS is composite area (m2), τ is sound transmission coefficient, and ΣτS is multiplication of sound transmission coefficient and composite area (m2).
Source: (Antaryama, et al., 2010)
Figure 2: Thermal Map of Surabaya in 2006
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4.
Results and Discussions
4.1 Environmental Analysis Generally, the characteristics city terrain roughness of warm humid climate climate are not as different as the other region. This area consists of high density building and produces thermoacoustic problems. The noise production from human activities come to follow the heat gain in the same time. The specific difference of the warm humid area from the other site is the accumulative of high temperature and heavy traffic of the environment and of course the high relative humidity and the fluctuation wind speed is significant. The high speed of lowland or coastal provides potential passive cooling. In contrast, it gives medium for air borne transfer from crowded street traffic which is felt not only by occupant of the building, but also by the pedestrian in curbside of this busy road. As presented by Figure 2., satellite image illustrates thermal map of Surabaya, the rapid development of the city (pusat kota) has contribution of the high temperature indication of the this environment. Over 34 0C of temperature is experienced for the central district of Surabaya. It is disadvantages if it is compared with location of the urban or suburban areas surroundings this city. The lowest temperature of that location indicates low movement of human activities. 4.2
Thermal Analysis
As result of the equation (1) above, maximum temperature difference (ΔT) is reached by the outdoor of the Urip Sumoharjo walk-up area in 11.82 0C as a result of 6m of average of buildings height and 2m of average of near distance among buildings (ΔT = 7.45 + 3.97*ln(6/2) 0C). This condition provides some consideration of landscape design to prevent of heat accumulation and to promote the sufficient of wind speed in creating of comfortable outdoor environment. The result of this equation indicates that the disadvantages of D (distance among buildings) of city terrain rouhness should be controlled by more efforts in presenting of air flow into building. The average of buildings height of this area is potential for creating turbulance air movement into limited space of the high density kampungs.
Figure 3: Wind Speed for Specific Height
Figure 3. shows the wind speed for specific height of the object. Base on the wind gradient analysis, the four levels of walk-up flat building feel the difference of the wind speed. Thus, the opportunity for passive cooling is experienced in difference way for the occupants. Base on equation (2), the wind speed is measured at avereage occupant height (1.7m) for every level: V2.3 = Vbl2(h2.3/hbl2)φ2, V5.5 = Vbl2(h5.5/hbl2)φ2, V8.7 = Vbl2(h8.7/hbl2)φ2, and V11.9 = Vbl2(h11.9/hbl2)φ2 and the results are: V2.3 = 1.44 m/s, V5.5 = 2.06 m/s, V8.7 = 2.37 m/s, and V11.9 = 2.68 m/s. Minimum requirement of wind speed to reduce accumulation of highest temperature and humidity of Surabaya is 0.25 m/s. Base on this datum, all of the floors meet with standard. This condition indicates that vertical development like walk-up flat is one of good recommendation for sustainable design, not only because of the urgent requirement of building space but also because of the accomodation for outdoor and indoor thermal comfort. The natural dehumidication is still obtained by the building with the wind acceleration despite in city terrain roughness. Air movement reaches the building B2-61
because the site provides irregular of building height and distance and it gives the advantage. The higher building has wind catcher role for the lower building. The multivariation of limited space plays like opening at the building scale with difference distance to direct the wind reaches the building.
Figure 4: Site Shading
The latitute location for 7 of South hemisphere makes the probability of hottest month is in February and October when the sun moves on this place. The first of general suggestion for thermal problems is site shading, it means that the site of the object study uses the shading from surroundings building, especially in the east and west building with higher levels. The site analysis of the object study area using solar chart can be seen in Figure 4. This figure explores that the site of walk-up flat is not shaded perfectly by the surroundings. The site is shaded by commercial and food court building for the east area at 06.00-07.30 and by west kampung for the west area at 16.3018.00. That result is unexpected because the building or site needs shading in the ciritical hours with low altitude angle (at 10.00 or 14.00). The following recommendation to solve this problem is analysis for building envelope. The analysis of surface temperature results that 36,6 0C is reached by the brick light coloured and exposed wall to the direct contact with solar radiation base on equation (3). This surface temperature is produced by 28.9 0C of outdoor temperature, 495.32 W/m2 of solar radiation intensity (at 10.00 and 120 solar altitude), 0.3 of total of surface and material absorption coefficient, and 18.9 W/m2 degC for east wall-normal. In order to avoid of heat gain by this way, the development of sun screen/shading devices should be analysed. As presented by Figure 5., the measurement date/month is 17 October/26 February, the measurement time is at 10.00, and the opening orientation is 105 deg (east south east). By this condition, the analysis of solar chart is resulting 580 of the vertical shading angle and 120 of the horisontal shading angle. The 580 of the vertical shading angle affects the horizontal sun shading device and the 120 of the horisontal shading angle affects the vertical sun shading device. The dimension of sun shading device complies with a request for opening dimension to prevent sunlight interruption into indoor environment, for example for this walk-up building, the vertical sun shading device has 0.33 m of the length only, but the horisontal one is 1.50 m and 1.00 m of the length with a note that the opening is divided into 2 parts of height (0.48 m) with 0.23 m and 0.13 m of the lenght of additional cover in the edge in order to reduces of the lenght of sun shading device.
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4.3
Acoustic Analysis
Figure 5: Sun Shading Devices
The sound pressure for average street traffic/heavy traffic is 0.2 Pa if it is felt in curbside of busy road, 5m from the source (http://www.sengpielaudio.com/TableOfSoundPressureLevels.htm). With 5 m distance sound pressure level and 2.10-5 Pa of the reference sound pressure, the sound pressure level is 80 dB (LP = 20 log (0.2/0.00002 dB) and it is over the standard noise level for flat (maximum 30dB). The distance between building as receiver of noise and the source is 30 m and with this distance the new value of sound pressure level is 20 log (0.0056/0.00002) dB = 49 dB with a note that sound pressure change become 1/(30/5)2 0.2 Pa = (1/36) 0.2 Pa = 0.0056. This new value does not meet with the standard and it needs 19 dB reduction with environmental barrier or building envelope control. The barrier of the site should meet with the wind acceleration into building and the view from/to in site/out site as aesthetic issue. Therefore, the maximum of the height of barrier is 2.3 m as the 1st floor reference height (see Figure 6.). In this case, it can be tried that 2 m is the height of barrier to make NR (Noise Reduction). With 1000 Hz of frequency, 30 m of the straight distance between sound source and receiver, 30.02 m of the nearest distance through barrier, the NR is 20 log [(2x3.14x1.32)0.5/tan(2 x3.14x1.32)0.5] + 5 dB and the result is 40.2 dB (see equation (4)). With the 40.2 dB NR, the sound pressure level is decreasing become 49-40.2dB = 8.8 dB and it is under the maximum requirement (30 dB), so it is sufficient to standard. The other strategy to noise level is analysis of building envelope. This analysis can be conducted by noise reduction with composite transmission loss, TLc = 10 log (ΣS/ ΣτS or see equation (5). With 114 mm brick wall with 13 mm layer of plaster on each side, TLbrick = 50 dB for 1000Hz, so sound transmission coefficient of the brick (τbrick) is 0.00001. With 2 cm hollow wood door, TLwood = 18 dB for 1000 Hz, so sound transmission coefficient of the wood (τwood) is 0.016. With 6 mm single/monolithic glass of window, TLglass= 34 dB, so sound transmission coefficient of the glass(τglass) is 0.000398. The composite area (ΣS) is 9.6 m2, wood area (Swood) is 1.51 m2, glass area (Sglass) is 0.83 m2, and brick area (Sbrick) is 7.26 m2. Base on all that data, composite transmission loss (TLc) is 10 log (ΣScomposite/ ΣτS) dB = 10 log [9.6/( Sbrick x τbrick + Swood x τwood + Sglass x τglass)] dB = 25.92 dB. Wall composite noise reduction is 49-25.92 = 23.08 dB (< 30 dB) and it is also sufficient to standard.
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5.
Conclusion
Figure 6: Environmental Barrier
This paper discussed the thermoacoustic in general normative analysis with specific of subtantive calculation method for several critical point of the problem solution. Thermal and acoustic are oberseved one by one but still considered each others. Results of this research highlighted that performances of thermal and acoustic of building are depended on element configuration and dimension, material properties and its construction of both site and building relative to external climate conditions. For landscape planning and design, this paper recommends that thermal problem is not easy to solve because of the high density of terrain roughness, but the acoustic problem such as noise influnce from the crowded traffic and commercial activities can be controlled by the convensional method using environmental barrier in the way that it still considers the air flow to the site or building (thermal problem). For the context of the building envelope, both unexpected heat and sound as the thermal and acoustic key issues are eliminated by the existing building. The little major issues discussed in this paper such as the mapping of thermoacoustic, detailed influnce of human acitivities, greenery influnces, and computerised simulation method will be pursued in our further studies. Acknowledgement
The Author expresses a gratitude to the Laboratory of Architectural Science and Technology, Department of Architecture - ITS for a helping technical support. References
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