JAKARTA GREEN BUILDING USER GUIDE VOL. 1 BUILDING ENVELOPE The Government of the Province of Jakarta Capital Special Territory In cooperation with: IFC in partnership with:
CODE REQUIREMENTS Building Envelope (BE) BE 01 Maximum OTTV The calculation should be done using the calculator available on this website http://greenbuilding.web.id Checklist for all code requirements lists the required documents is also available on this website http://greenbuilding.web.id
JAKARTA GREEN BUILDING USER GUIDE VOL. 1 BUILDING ENVELOPE table of contents INTRODUCTION 2 01 SCOPE 7 02 CODE REQUIREMENT 8 03 CODE EXPLANATION 9 04 DESIGN PRINCIPLES Heat Transfer through Building Envelope Building Forms and Orientations Window Area Glazing Materials External Shading Lightshelf Internal Shading Walls Roofs Infiltration 15 15 16 18 18 19 23 25 26 27 30 APPENDIX 33
Building Envelope: An Introduction THE FUNCTION OF BUILDING ENVELOPE Building envelope is comprised of opaque components (e.g. walls) and fenestration systems (e.g. windows) that divide the interior of a building from the exterior environment. Building envelope provides protection from the elements of external environment such as heat, radiation, wind, rain, noise, pollution etc.). Building envelope has a key role in reducing cooling and lighting energy consumption. For a typical mid and high rise building, the walls have considerably larger area than the roof. Therefore, care must be taken to control heat gain through the vertical surfaces, especially the windows. For low rise building where the roof becomes the larger part of the building envelope, heat transmission from the roof might be the determining factor of the overall cooling load. Additionally, windows and skylights in the building envelope dictate the amount of light that penetrates inside. By optimizing the window design, most buildings can significantly reduce their electric lighting without adding too much heat gain. ENERGY CONSUMPTION BREAKDOWN BUILDING ENVELOPE Building energy consumption in Indonesia is dominated by HVAC system regardless of the building type. As presented in Figure 1, HVAC accounts for about 47% to 65% of the total building energy consumption. The combined energy consumption for lighting and plug load contribute 15% to 25% of the total energy consumption. Therefore, reducing energy consumption for HVAC and lighting through passive and active design will significantly reduce the overall energy consumption of the building. 2
FIGURE. 01 Energy Consumption Breakdown for Various Building Type 1 Air Conditioning Lighting + outlet Elevator Building Energy Use (%) 100 60 40 20 17% 3% 15% 65% 13% 14% 16% 57% 16% 5% 22% 57% 14% 4% 27% 55% 6% 22% 25% 47% Others 0 Hotel Hospital Shopping Mall Office Building Government Office The source of cooling load can be organized into external heat gain (e.g. from walls, windows etc.) and internal heat gain (e.g. from lighting, equipment, people etc.). In buildings with large window openings heat gain from the windows and walls become the major part of the cooling load. As presented in Figure 2, external heat gain from windows and wall of a typical Jakarta office building is around 63%, while internal heat gain from equipment, lighting and occupancy is about 37%. This indicates large energy saving opportunities through properly designed building envelope to reduce cooling load. FIGURE. 02 Breakdown of Cooling Load for a Typical Jakarta Office Building 2 Equipment 23% Lighting 6% Walls 3% Occupancy 8% Windows 60% 1 Japan International Cooperation Agency (JICA).2009. A Study of Electricity Use in Multiple Jakarta Buildings. 2 International Finance Corporation (IFC). 2011. Jakarta Building Energy Efficiency Baseline and Saving Potential: Sensitivity Analysis. BUILDING ENVELOPE 3
CONSTRUCTION TREND In terms of thermal properties, building envelope constructions can be organized into two major types: curtain wall and brick and windows constructions. Curtain wall constructions, whether it is fully glass or combinations of glass and solid panel (e.g. aluminum composite panel) are popular for office buildings and more recently apartment buildings. Other building types, especially low rise buildings, tend to use brick and windows constructions. FIGURE. 03 Brick and Windows Constructions (Left) and Curtain Glass Wall Constructions 3 The primary reason given by architects and building owners for designing buildings with curtain walls is their commercial appeal. Large windows provide views that increase the value of the premises. However, in reality many of the users partially or fully draw the curtains/ blinds close due to glare and overheating. This blocks the view as well as daylight leading to unnecessarily high energy consumption for HVAC and lighting. BUILDING ENVELOPE 3 Jatmika Adi Suryabrata. 4
FIGURE. 04 Curtain Glass Wall Office with Fully Drawn Internal Shading and Electrical Light On 4 ENERGY SAVING POTENTIAL As stated above, building envelope can have a huge impact on the total building energy consumption as it can greatly modify the cooling load, especially by controlling radiation heat gain through the windows, and utilizing daylighting. The combined passive design strategies have a potential energy savings of roughly about 31% for office buildings. This can be achieved through building envelope designs to reduce external heat gain and utilizing daylighting. FIGURE. 05 Potential Energy Saving from HVAC and Lighting in a Typical Jakarta Office Building through Passive Design Strategies 5 Typical Office Energy Consumption Breakdown Elevator 4% Plug Load 14% Others 14% AC + Lighting 38% Potential Saving 31% Potential Energy Saving Wall Insulation Wall Reflectivity 0.3% 0.5% Daylighting 4.9% Glass WWR 7.3% 8.0% Shading 10.1% 4 Jatmika Adi Suryabrata. 5 International Finance Corporation (IFC). 2011. Jakarta Building Energy Efficiency Baseline and Saving Potential: Sensitivity Analysis. BUILDING ENVELOPE 5
In more detail, the energy saving potential through passive design has also been indicated by the results of simulation study revealing potential energy saving through reducing window area, applying external shadings, and improving glass performance are summarized in Table 1. TABLE. 01 Potential Energy Saving through Building Envelope for Various Building Types Potential Energy Saving through Building Envelope for Various Building Types 6 PASSIVE DESIGN STRATEGIES Office Retail Hotel Hospital Apartment School Shading 10.1% 4.6% 10.2% 8.8% 5.3% 1.9% WWR 8.0% 3.9% 8.7% 7.5% 2.3% 0.0% Glass 7.3% 3.2% 8.5% 8.0% 6.5% 4.2% Daylight link lighting system 4.9% NA NA NA NA 3.5% Wall Reflectivity 0.5% 0.3% 0.6% 0.3% 2.3% 2.6% Wall Insulation 0.3% 0.2% 1.0% 0.5% 3.2% -0.9% TOTAL 31.1% 12.2% 29.0% 25.1% 19.6% 11.3% As can be seen in Table 1, one of the most effective design strategies to reduce building energy consumption is by limiting heat gain through the windows. The combined passive design strategies that incorporate external shadings, reducing wall area and utilizing high performance glasses could lead to roughly 25% energy saving. Because solar radiation intensity is different for each orientation, controlling heat gain through fenestration system could also be achieved through appropriate building orientation. Results from this study highlight the important roles of architect to develop designs that are both saving energy and attractive. BUILDING ENVELOPE 6 International Finance Corporation (IFC). 2011. Jakarta Building Energy Efficiency Baseline and Saving Potential: Sensitivity Analysis. 6
01scope The Overall Thermal Transfer Value (OTTV) criterion for evaluating thermal performance of building envelope has been adopted. While it is a fairly robust way of quantifying building envelope s thermal performance, it has some limitations. The concept of OTTV is based on the assumption that the envelope of a building is completely enclosed. In the OTTV formulation, the following factors are not addressed or accounted for: Internal shading devices, such as draperies and blinds. Solar reflection or shading from adjacent buildings. Heat gain from Roof, which is covered separately through an RTTV calculation and is not required by this code. The OTTV requirement is applicable only for air-conditioned buildings. BUILDING ENVELOPE SCOPE 7
02code requirement REFERRING TO ARTICLE 6 The Overall Thermal Transfer Value (OTTV) for the building should not exceed 45 Watts/m 2. [3] Planning pertaining to OTTV shall refer to SNI 03-6389 concerning Conservation of Building Envelope Energy in Building Structures. BUILDING ENVELOPE CODE REQUIREMENT 8
code explanation 03An Overall Thermal Transfer Value (OTTV) is a measure of external heat gain transmitted through a unit area of the building envelope (W/m 2 ). Solar transmission through fenestration system is generally far greater than that of through opaque envelope. Therefore, designing windows must be carried out with caution to avoid excessive heat gain by controlling the window area, orientation, selection of high performance glazing materials and providing external shades. OTTV CALCULATIONS (1) Calculate OTTV for each orientation and building component (e.g. window, wall), using formula and spreadsheet below. (2) Calculate total OTTV by adding OTTV of each building component and orientation using formula and spreadsheet below (SNI 03-6389). (1) OTTV = [(Uw x (1-WWR)] x TD ek + (SC x WWR x SF) + (U f x WWR x T) A (2) OTTV total = (OTTV u x A u ) + (OTTV t x A t ) + (OTTV s x A s ) + (OTTV b x A b ) (A u + A t + A s + A b ) The formula for OTTV calculation above is elaborated in the spreadsheet below: SHEET. 01 Heat Conduction Through Walls No. ELEVATION North Wall South Wall West Wall East Wall TOTAL AREA Façade Area (A) m 2 Solar Absorbtion Factor (α) Total Opening Area (m 2 ) Window to Wall Ratio (WWR) (1-WWR) U-Value (Uw) w/m 2 k Tdeq OTTV A*OTTV BUILDING ENVELOPE CODE EXPLANATION 9
SHEET. 02 Heat Conduction Through Windows No. ELEVATION Façade Area (A) m 2 Total Opening Area (m 2 ) Window to Wall Ratio (WWR) U-Value (Uw) w/m 2 k T OTTV A*OTTV North Wall South Wall West Wall East Wall TOTAL AREA SHEET. 03 Solar Heat Gain Through Windows No. ELEVATION Façade Area (A) m 2 Total Opening Area (m 2 ) Window to Wall Ratio (WWR) Solar Factor (SF) Shading Coef. (SCk) Shading Coef. Effective (Sceff) Shading Coef (SC = SCk * Sceff) OTTV A*OTTV North Wall 130 South Wall 97 West Wall 243 East Wall 112 TOTAL AREA SHEET. 04 Summary No. ELEVATION Wall Con (W) Win Con (W) Win Sol (W) Total (W) Area (m 2 ) OTTV (W/m 2 ) North Wall South Wall West Wall East Wall TOTAL AREA Note: The values for building facades (total opening area, window to wall ratio and U-value) are determined by actual building geometry and thermal properties of its materials. The values for Solar Absorption Factor (α), TDek, T and Solar Factor (SF) is taken from tables in SNI 03-6389. SHGC = SC x 0,86. BUILDING ENVELOPE CODE EXPLANATION Roof Thermal Transfer Value (RTTV) calculations are not required for code compliance, since the code currently applies mostly to high rise building with relatively small roof area. 10
GRAPHICAL CALCULATION OF OTTV OTTV can be calculated using the formula describe in detail in SNI 03-6389. However, OTTV calculation using the formula could be troublesome and difficult to review. A simpler methods of calculating OTTV is using spreadsheet based OTTV calculation tool available on DPPB s website needs to be filled out and submitted for code compliance. If reputable building energy simulation is used for the building, OTTV calculations from the program can also be used. While designing OTTV can be calculated using a graphical design tool presented in Figure 6, which shows combination values of SHGC, OTTV and WWR for a specific orientation of the envelope 7.With this design tool, the value of the WWR of a window with certain SHGC can be easily determined to meet the OTTV Code 45 W/m 2. The graph is valid for a typical brick wall construction with U-value of 1,039 W/ m 2 -K and 8 mm single pane windows without external shades. As heat transmission through the opaque envelope are not critical, this design tool can also be applied for other wall constructions of similar U-value. 7 Ibnu Saud, 2012. Unpublished thesis. Department of Architecture and Planning, Gadjah Mada University. BUILDING ENVELOPE CODE EXPLANATION 11
FIGURE. 06 OTTV Values for Various WWR and SHGC for Eight Major Orientations WWR North Wall (0 o ) WWR North East Wall (45 o ) OTTV (W/m2) 150 140 130 120 110 100 90 70 60 50 40 30 20 10 0 WWR 130 70% 120 65% 70% 110 60% 65% 55% 100 60% 50% 55% 90 45% 50% 40% 45% 40% 70 35% 35% 60 30% 30% 25% 50 25% 20% 20% 40 15% 30 15% 10% 10% 20 5% 5% 10 0% 0% 0 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 SHGC OTTV (W/m2) 150 140 SHGC WWR WWR East Wall (90 o ) WWR South East Wall (135 o ) OTTV (W/m2) 150 140 130 120 110 100 90 70 60 50 40 30 20 10 0 SHGC WWR 70% 140 65% 130 60% 120 55% 110 50% 70% 100 65% 45% 90 60% 40% 55% 35% 50% 30% 70 45% 40% 25% 60 35% 50 30% 20% 25% 15% 40 20% 10% 30 15% 20 10% 5% 10 5% 0% 0% 0 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 OTTV (W/m2) 150 SHGC WWR WWR South Wall (1 o ) WWR South West Wall (225 o ) OTTV (W/m2) 150 140 130 120 110 100 90 70 60 50 40 30 20 10 0 120 70% 110 65% 100 60% WWR 55% 90 50% 70% 45% 65% 60% 70 40% 55% 60 35% 50% 45% 30% 40% 50 35% 25% 30% 40 20% 25% 20% 30 15% 15% 20 10% 10% 10 5% 5% 0% 0 0% 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 SHGC OTTV (W/m2) 150 140 130 SHGC WWR BUILDING ENVELOPE CODE EXPLANATION These tables are also available in appendix. WWR West Wall (270 o ) WWR North West Wall (315 o ) WWR OTTV (W/m2) 150 140 130 120 110 100 90 70 60 50 40 30 20 10 0 70% 150 65% 60% 140 70% 130 65% 55% 120 60% 50% 110 55% 45% 100 50% 40% 90 45% 35% 40% 30% 70 35% 25% 30% 60 25% 20% 50 20% 15% 40 15% 10% 30 10% 5% 20 10 5% 0% 0 0% 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 SHGC OTTV (W/m2) SHGC WWR 12
To illustrate the application of the graphs for determining WWR for each wall orientation to meet the building code, an example of simple 20 m x 40 m rectangular building is outlined below. North WWR? West WWR 0% South WWR? East WWR 10% 20 m Window = 8mm single pane glass SHGC = 0.7 U-value = 5.2 Opaque = brick wall U-value = 1,039 W/m 2 -K Floor to floor height 4m 40 m What is the maximum WWR for North and South windows to meet the maximum OTTV of 45 W/m 2? STEP. 1 Using the east wall graph above, determine the OTTV for east and west wall. Results: OTTV for East and West wall are 24 W/m 2 and 3 W/m 2 respectively. WWR East Wall (90 o ) OTTV (W/m2) 150 140 130 120 110 100 90 70 60 50 40 30 20 10 0 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 SHGC WWR 70% 65% 60% 55% 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% (1) SHGC 0.7 (2) OTTV 24 W/m 2 (3) WWR 10% STEP. 2 Calculate the OTTV for North and South Wall. SURFACE ORIENTATION OTTV (w/m 2 ) Surface Area (m 2 ) Total External Heat Gain (W) (OTTV) (A) (OTTVx A) East (e) 24 1920 West (w) 3 240 North (n)?? South (s)?? TOTAL OTTV Total = 45 4 20 To calculate the OTTV for North and South walls, the following formula can be utilized: (OTTV 1 x A 1 ) + (OTTV 2 x A 2 ) +... + (OTTV i x A i ) A 1 + A 2 +... + A i BUILDING ENVELOPE CODE EXPLANATION 13
SURFACE ORIENTATION OTTV (w/m 2 ) Surface Area (m 2 ) Total External Heat Gain (W) (OTTV) (A) (OTTVxA) East (e) 24 1920 West (w) 3 240 North (n) 60.75 9720 South (s) 60.75 9720 TOTAL 45 4 20 STEP. 3 Determine the WWR of North and South wall using the graphs in Figure 6. It is shown in the figure below that to meet the 45 W/m 2 requirements, the WWR for North and South wall must be smaller than 43% and 62%. WWR North Wall (0 o ) WWR South Wall (1 o ) OTTV (W/m2) 150 140 130 120 110 100 90 70 60 50 40 30 20 10 0 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 SHGC (1) SHGC 0.7 (2) OTTV 60.75 W/m2 (3) WWR 43% WWR 70% 65% 60% 55% 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% OTTV (W/m2) 150 140 130 120 110 100 90 70 60 50 40 30 20 10 0 SHGC WWR 70% 65% 60% 55% 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 (1) SHGC 0.7 (2) OTTV 60.75 W/m2 (3) WWR 62% Having external shadings may improve significantly the performance of the windows by blocking solar radiation leading to lower SHGC values. The SHGC or SC values of the fenestration system combining the effect of glazing materials and external shading devices can be calculated using the following formula (SNI 03-6389): SC = SC k x SC eff BUILDING ENVELOPE CODE EXPLANATION The values of SCeff for various external shading configurations and orientations are provided in SNI 03-6389 SC = Shading coefficient of the fenestration system SCk = shading coefficient of the glazing materials SCeff = shading coefficient of the shading devices SHGC = 0.86 SC 14
04design principles HEAT TRANSFER THROUGH BUILDING ENVELOPE In externally dominated cooling load buildings, energy consumption for HVAC system is mainly determined by heat transfer through its building envelope components including: Heat transfer through windows, Heat transfer through walls, Heat transfer through roofs, Infiltration and exfiltration rates through cracks, windows and doors openings. There are a number of design principles that could be applied to reduce heat gain through the building envelope: Designing building form and orientation to minimize building envelope exposure to east and west solar radiation. Reducing heat transmissions through windows by reducing the window area, providing properly designed external shades and selecting high performance glazing materials. Reducing heat transmissions through walls by having sufficient insulation. Reducing heat transmissions through roofs by having higher reflectivity, emissivity and insulation values. Reducing infiltration and exfiltration by properly sealed the building and controlling the door and window openings. FIGURE. 07 Heat Transfer Components through Building Envelopes Direct Solar Radiation Long Wave Radiation Convection Short Wave Radiation Conduction Heat Transmission through windows 40x - 130x Heat Transmission through brick walls 1x BUILDING ENVELOPE DESIGN PRINCIPLES 15
Thermal transfer through the building envelopes can be categorized as radiation, conduction and convection through walls and windows. Out of these, direct radiation through windows is the most critical in Jakarta. Results from simulation studies indicates that for a typical building envelope constructions and materials, thermal transfer through windows is roughly 40 to 130 times greater than that of walls. Even for the best high performance glazing available, heat transfer through windows is significantly higher compared to brick wall. Therefore, controlling thermal transfer through the windows is essential to the successfulness of the overall passive design strategies to reduce cooling load. Another form of heat transfer that may increase cooling load considerably is infiltration and exfiltration through building envelope cracks, openings of windows and doors. BUILDING FORMS AND ORIENTATIONS Due to daily and annual movement of the sun, solar radiation received by building envelope varies for each orientation. For Jakarta and other location of similar latitude, west facing vertical surfaces receive a daily average of 303 W/m 2 solar radiation, while that of east, north and south receive a daily average of 268 W/m 2, 207 W/m 2, and 165 W/m 2 solar radiation respectively. Horizontal surfaces (roof) receive a daily average of 527 W/m 2, which is significantly higher than any vertical surface (wal). FIGURE. 08 Average Daily Solar Radiation on Horizontal Roof and Vertical Surfaces of Major Orientations Yearly Average of Surface Exterior Solar Incident on West, South, East, North, and Horizontal Surfaces (W/m 2 ) 1000 West South East North Horizontal Surface Exterior Solar Incident (W/m 2 ) 0 600 400 200 BUILDING ENVELOPE DESIGN PRINCIPLES 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Hourly Data 16
FIGURE. 09 Building form elongated east west to minimize solar heat gain and maximize daylighting. Left: Faculty of Social and Political Science, UIN, Jakarta. Right: Ministry of Marine Affairs and Fisheries Head Office, Jakarta 8 To avoid excessive solar radiation heat gain, major building envelope surfaces with windows should be oriented north and south whenever possible. This allows the window to receive diffuse daylight from the sky while minimizing direct solar heat gain. Furthermore, services areas with predominantly opaque walls could be located at east and west ends of the building to function as thermal buffer spaces. Opaque walls with high thermal mass Circulation N Services Stairs The comparative solar heat gain represented by OTTV values for various building forms and orientations is presented in Figure 10. The OTTV values are for simple rectangular building with window strips (SHGC 0.4) and the same floor area. FIGURE. 10 The Impact of Building Forms and Orientations on OTTV (W/m 2 ) 0 o W 90 o N 45 o 135 o E 1:1 1:2 1:3 S WWR 70% 50% 30% 1:1 1:2 1:3 0 o 0 o 45 o 0 o 45 o 90 o 135 o 45 o 90 o 135 o 66.79 67.56 62.75 67.68 71.25 67.86 59.75 66.72 72.46 66.99 49.99 50.57 47.02 50.74 53.41 50.84 44.82 50.09 54.37 50.24 32.44 32.81 30.58 33 34.73 33.03 29.19 32.64 35.4 32.68 Source: Ibnu Saud, 2012. Unpublished thesis. Department of Architecture and Planning, Gadjah Mada University. 8 Jatmika Adi Suryabrata. BUILDING ENVELOPE DESIGN PRINCIPLES 17
WINDOW AREA The proportion of window area has a considerable influence on cooling load since it determines the total amount of solar radiation through window area. This is because window glazing allows more heat gain to the interior space than opaque envelope, and therefore a larger window to wall ratio (WWR) usually lead to higher cooling load. Reducing window area is one the most effective solutions to reduce cooling load and overall building energy consumption. Since window construction is typically costlier than wall construction, reducing WWR may reduce construction cost as well. Results from a simulation study of typical Jakarta buildings shows that reducing window area by half can reduce energy consumption up to 10%. TABLE. 02 The Impact of WWR on Energy Saving (%) for Various Building Type. (0.0% Saving is the Base Case) The impact of WWR on energy saving (%) for various building type. (0.0% saving is the base case) 9 WWR Office Retail Hotel Hospital Apartment School 69% (0.0%) (0.0%) (0.0%) (0.0%) 53% 3.7% 2.0% 4.6% 3.9% 40% 8.0% 3.9% 8.7% 7.5% (0.0%) -1.8% 34% 9.5% 4.9% 10.6% 9.1% 2.3% (0.0%) 20% 13.2% 7.1% 14.5% 12.6% 6.8% 5.4% GLAZING MATERIALS Window glazing can have a wide range of different properties with respect to light, radiation and heat. The principal fundamental properties for glazing are solar transmittance, solar absorptance, solar reflectance, and light transmittance. Thermal transmission for glazing material is measured in terms of U-value for conduction and Solar Heat Gain Coefficient (SHGC) or Shading Coefficient (SC) for solar radiation. Note that SHGC = 0.86 SC. BUILDING ENVELOPE DESIGN PRINCIPLES Typical U-values, light (visible) transmittance and SHGC of currently available glass in Jakarta is presented in Table 3. Custom offline tinted glasses with various SHGC and light transmittance values and colors are also available locally, Better performance glasses with SHGC as low as 0.2 are globally available. However, such application is currently limited due to high cost. Alternatively, additional coating that can be applied by local industries is also available. The relatively low cost offline coating can improve SHGC to as low as 0.2. 9 International Finance Corporation (IFC). 2011. Jakarta Building Energy Efficiency Baseline and Saving Potential: Sensitivity Analysis. 18
TABLE. 03 U Values, Light Transmittance and SHGC Values of Typical Glass Locally Available in Indonesia U values, light transmittance and SHGC values of typical glass SINGLE GLASS 8mm Clear Tinted Reflective Low-e U-Value 4.94 5.18 5.18 4.54 Visual Transmission (%) 89 55 42 48 35 67 SC 0.95 0.51 0.57 0.42 0.53 0.40 0.69 SHGC 0.82 0.44 0.49 0.36 0.46 0.34 0.59 For Indonesian climate where temperature differences between indoor and outdoor are relatively small, improving the SHGC is more effective than that of U-value. In other words, having double glazing to reduce conduction heat gain through windows usually is not cost effective. For example, reducing SHGC from 0.67 to 0.38 will reduce total energy consumption by 8%. While adding clear glass to form double glazing with the same SHGC to improve U-value from 5.8 to 3.4 will only reduce total energy consumption by about 1%. To highlight the significant impact of SHGC on total energy consumption, results from a simulation studies for various building types are summarized in Table 4. For all cases the U-value and visible transmittance is kept constant at 5.8 W/m 2 and 0.7% respectively. SHGC of 0.6 is the base case. TABLE. 04 The Impact of SHGC on Energy Saving (%) for Typical Buildings in Jakarta (U-Value 5.8 W/m 2 /K; Visible Transmittance 0.57). 10 The impact of SHGC on energy saving (%) for typical buildings in Jakarta WWR Office Retail Hotel Hospital Apartment School 0.6 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.5 5.7% 2.4% 5.1% 5.7% 3.7% 3.2% 0.4 8.4% 3.7% 8.5% 8.2% 6.1% 5.1% 0.3 11.0% 5.1% 11.9% 10.8% 8.4% 6.7% 0.2 14.4% 6.6% 15.4% 13.3% 10.6% 7.5% EXTERNAL SHADING External shadings are more effective in reducing solar heat gain than internal shading devices because it blocks the solar radiation before it reaches the building envelope. External shadings should be carefully design not only to reduce cooling load but also to create aesthetically appealing architecture, while allowing sufficient daylight for the interior spaces. 10 International Finance Corporation (IFC). 2011. Jakarta Building Energy Efficiency Baseline and Saving Potential: Sensitivity Analysis. BUILDING ENVELOPE DESIGN PRINCIPLES 19
The geometry of the shading devices must be designed in response to the sun path, which leads to different shapes and sizes for different orientations. In general, horizontal shading devices are more appropriate for south and north oriented windows where direct sunrays come from high altitude angles. Slated vertical fins can effectively block solar radiation from low altitude angles of east and west oriented windows. For more accurate results, sun path diagrams, either manual or computer generated should be utilized for developing shading designs. FIGURE. 11 Vertical Fins Blocking Solar Radiation from Low Altitude Angles (Top Left) 11 and Horizontal Shading (Top Right) 12, and Egg Crate as Double Façade (Bottom). 13 The impact of generic external shading devices on expected energy saving for various building types has been studied using hourly computer simulations. For all simulations, the base case is no horizontal shading (over hang) for office, retail, hotel, and hospital; and 300 mm horizontal shading for apartment and school. In addition, base case WWR for apartment and school are 40% and 35% respectively, while for that of others is 69%. These base case differences represent typical existing conditions in Jakarta. The smaller window area for apartment and school has led to lesser energy saving from external shading devices. BUILDING ENVELOPE DESIGN PRINCIPLES There are many ways of achieving vertical shadow angle (VSA) using a single horizontal overhang, pergola, multiple horizontal overhang with smaller depth as shown in Figure 12. 11 Jatmika Adi Suryabrata. 12 Wiratman Architecture. 13 Jatmika Adi Suryabrata. 20
FIGURE. 12 Generic Types of External Shadings: Overhang and Its Energy Saving Potential 14 VSA o Office Retail Hotel Hospital Apartment School 0 2 4 6 8 10 12 14 16 Energy Saving (%) 70 o VSA 50 o VSA As depicted in the simulation results above, external shading devices are very effective for reducing cooling load from the windows, where as much as around 14% of energy saving can be obtained through the installation of egg crate. The effectiveness of the shading varies depending on the WWR, orientations and selection of glazing materials. In general, higher energy saving through shading can be achieved where the building has high WWR and SHGC. Therefore, designing fenestration system (windows) should be carried out comprehensively to include all possible strategies to obtain best results. 14 International Finance Corporation (IFC). 2011. Jakarta Building Energy Efficiency Baseline and Saving Potential: Sensitivity Analysis. BUILDING ENVELOPE DESIGN PRINCIPLES 21
FIGURE. 13 Generic Types of External Shadings: Vertical Fins (Top) and Egg Crate (Bottom) with Energy Saving Potential 15 HSA o HSA o Office Retail Hotel Hospital Apartment School 0 2 4 6 8 10 12 14 16 Energy Saving (%) 70 o HSA 50 o HSA Office Retail Hotel Hospital Apartment School BUILDING ENVELOPE DESIGN PRINCIPLES 0 2 4 6 8 10 12 14 16 Energy Saving (%) 70 o HSA & VSA 50 o HSA & VSA 15 International Finance Corporation (IFC). 2011. Jakarta Building Energy Efficiency Baseline and Saving Potential: Sensitivity Analysis. 22
FIGURE. 14 Reducing Heat Transmission with Shading 16 38.07 25.34 21.24 N N N 51.53 48.22 38.58 W E W E W E S S S 36.51 33.78 32.14 27.51 20.07 18.81 No Shading Total Heat Transmission= 41.33 W/m 2 60 cm Shading Total Heat Transmission= 30.13 W/m 2 90 cm Shading Total Heat Transmission= 26.50 W/m 2 LIGHTSHELF Further discussion on lightshelves is presented in the Lighting Section. Light shelf is a horizontal element that divides windows into upper part for daylighting and lower part for vision and reflects daylight coming from the upper part of the windows to provide better daylight distribution into the deeper part of the interior. At the same time, it can also work as a horizontal shade for the lower part of the window to reduce heat gain and glare. The glass above lightshelves should have higher VT, whereas the one below lightshelves could have lower SGHC and VT. This would optimize light penetration without letting in too much heat. For better daylight distribution the upper surface of the lightshelf as well as the ceiling must have a high reflectance. 16 Rachmat Syahrullah, 2012. Unpublished thesis. Department of Architecture and Planning, Gadjah Mada university. BUILDING ENVELOPE DESIGN PRINCIPLES 23
FIGURE. 15 Example of Typical Lightshelf Performance 17 6.00 m 6.00 m 6.00 m 350 lux 350 lux 350 lux No Shading Average Heat Transmission= 47.44 W/m 2 Overhang Average Heat Transmission= 31.93 W/m 2 Lightshelf Average Heat Transmission= 33.01 W/m 2 As Figure 16 shows, lightshelves can create more uniform daylight distribution and deeper penetration by bouncing the daylight off the ceiling. Brighter ceiling near the windows may also reduce the sensation of glare because of reduced contrast between interior surfaces (ceiling) and the outdoor environment. FIGURE. 16 Application of Lightshelves 18 BUILDING ENVELOPE DESIGN PRINCIPLES 17 Rachmat Syahrullah, 2012. Unpublished thesis. Department of Architecture and Planning, Gadjah Mada university. 18 Jatmika Adi Suryabrata. 24
INTERNAL SHADING Internal shadings block solar radiation after passing window glazing and preventing direct solar radiation on the occupant and deeper parts of the interior. However, Internal shadings are not as effective as external shading in reducing cooling load because the radiant heat is already enter the interior through the window glass and is radiated and convected inside the interior space, which eventually become a cooling load for the HVAC system. Light colors internal shadings with reflective linings are more effective than dark color as more radiant heat is reflected back outside through the window glazing. FIGURE. 17 Thermal Performance of Fenestration System No Shading Heat absorbed reradiated and convected in the interior and become major source of cooling load and thermal discomfort Average Heat Transmission= 47.44 W/m 2 Internal Shading Reradiated heat is trapped and eventually convected in the interior; may improve thermal comfort Average Heat Transmission= 24.14 W/m 2 External Shading Reradiated heat is convected away; improve thermal comfort and reduce cooling load Average Heat Transmission= 20.08 W/m 2 Internal shadings are generally fully adjustable to cater the individual needs of the occupants and come with various design and colors to match the interiors. In terms of design, internal shading can be distinguished into roller shades, horizontal blinds, vertical blinds and drapes. Among those, horizontal blinds have better performance by reflecting daylight to the ceiling to improve daylight performance into the deep part of the interiors. The main problem with manually operated internal shades is that the users rarely adjust the shades in accord with the sun movement (e.g. reopen the shades whenever there is no glare or excessive heat gain). Because internal shades also reduce daylight performance, this may lead to much higher energy consumption for lighting. To avoid the problem, either the occupants can be trained in the proper use of blinds and shades or motorized internal shades can be utilized to respond to the different activities requirements or intensity of the sunlight. The operation can be controlled remotely and automatically via sensors. BUILDING ENVELOPE DESIGN PRINCIPLES 25
WALLS The correlation between conductance (k), resistance (R) and U-values can be seen in the following equations: Opaque envelopes (walls) generally comprise of several layers of materials of different thickness and thermal properties. The combine conductance (k) values and resistance (R) values of each material layers defines the overall thermal properties of the opaque envelope (U-values). The lower the U values the better since the lower the thermal transfer. R= t 1 ; Uvalue= k R 1 + R 2 +... R n Masonry construction of clay brick or aerated concrete block with plaster finish in both sides is common application for wall construction in Indonesia. It is widely used, especially for low rise building, due to economic reasons. More recently, concrete panel is being used to replace masonry construction, especially for high rise building. In terms of heat transfer, the application of masonry or concrete panel generally is sufficient as the outdoor-indoor temperature differentials are relatively small. Consequently, applying insulation layer on masonry wall may not be cost effective. Another common envelope construction is curtain wall employing glass and opaque panels (e.g. aluminum composite). In terms of thermal properties, curtail walls are very susceptible to heat transfer and therefore insulation layer is essential to improve the thermal performance of building envelope and to reduce cooling load. The application of opaque envelope with lower U-value is preferable compared to curtain glass wall. Opaque envelopes are not only significantly reduce the heat transmission and cooling load, but also reduce Mean Radiant Temperature (MRT) in the interior spaces. MRT is the average of interior surface temperature, the lower the better. Together with air temperature, MRT affects thermal comfort level in the form of operative temperature, which is the average value of air temperature and MRT. BUILDING ENVELOPE DESIGN PRINCIPLES As presented in Figure 18, inside surface temperature of glazing materials can be significantly higher than that of masonry walls. Therefore, although the air temperature is within the comfort zone (e.g. 25 o C), the operative temperature can be higher (e.g. 28 o C) if the building envelope is dominated by window glazing. In other words, although the air temperature measure at 25 o C, it feels like 28 o C. In this case, air temperature must be set lower (e.g. 22-23 o C) to reach the comfort level, leading to higher energy consumption. 26
FIGURE. 18 Surface Temperature Decrement on Inside Surface Wall Outdoor Indoor Outdoor Indoor Outdoor Indoor 33 o C 25 o C 33 o C 25 o C 33 o C 25 o C Orientation : West Wall Date : 09/23 16:00:00 1 SHGC 0.4 Glass 2 Plaster + Brick + Plaster 3 90 cm Shading 46.1 o C Inside Surface 3 42.2 o C Inside Surface 1 1 2 2 36.6 o C Inside Surface 2 West 46.1 o C 42.2 o C 36.6 o C North 35.6 o C 33.9 o C 32.1 o C East 47.4 o C 40.8 o C 35.8 o C South 34.1 o C 34.1 o C 32.2 o C ROOFS In single story or low rise building with large roof area, roof may become the major source of heat gain. To minimize heat gain through the roof, materials with high reflectivity and emissivity shall be selected. Because roof materials usually has high U-value (high heat transmission), adding an insulation layer may reduce cooling load significantly. Having roof with high reflectivity and emissivity will also reduce the urban heat island phenomenon. Alternatively, a green roof could be applied to reduce heat transmission through the roof. Although U-value of green roof is difficult to determine, naturally green roof has an excellent thermal properties because of its thick construction layers. The U values of green roof vary greatly depending on the construction layers, moisture content and type of the plants. Green roof also reduce urban heat island phenomenon because much of the solar radiation is absorbed by the plants for evaporation and transpiration. Heat transfer through the roof, which may significantly affect the cooling load, can be calculated using Roof Thermal Transfer Value (RTTV) equations, as described in SNI 03-6389 concerning Conservation of Building Envelope Energy in Building Structures. BUILDING ENVELOPE DESIGN PRINCIPLES 27
FIGURE. 19 Green Roof (Left) and Metal Roof With Insulation Layer (Right) Plants Growing medium Filter Fleece Drainage layer Suitable waterpooling membrane Concrete slab Profiled metal cuter sheet Earthwool factory clad roll Vapour control layer Profiled metal cuter sheet Rail and bracket Generally, thermal performance of building materials is expressed in U-value. The U-value (or U-factor) is the overall heat transfer coefficient that describes how well a material can conduct heat. It measures the rate of heat transfer through a building element over a given area, under standardized conditions. A smaller U-value is better at reducing heat transfer. BUILDING ENVELOPE DESIGN PRINCIPLES Figure 20 shows the results from a simulation study revealing the significant impact of adding insulation layer on reducing heat transfer of common building envelope constructions. Note that roofs (horizontal surfaces) receive much higher solar radiation than walls (vertical surfaces), therefore better thermal performance (lower U-value) of roof constructions should be applied than that of walls. As depicted in Figure 20, adding 40 mm insulation layer under the concrete roof has significantly reduced the heat transmissions from 23.58 W/m 2 to only 4.10 W/m 2. Insulation layer has far greater effect for metal roof sheet, where the heat transmissions is reduced from 88.75 W/m 2 to 13.94 W/m 2. Similarly, adding insulation layer on common curtain wall construction of Aluminum composite panel with gypsum board, will reduce the heat transmission by more than 50%. 28
FIGURE. 20 Examples of Typical Building Envelope Materials and Its Heat Transmission (W/m 2 ) 120 mm Concrete Roof U-value Average heat transmission No insulation 2.410 23.58 W/m 2 40 mm insulation 0.557 4.10 W/m 2 Metal Roof U-value Average heat transmission No insulation 5.306 88.75 W/m 2 40 mm insulation 0.638 13.94 W/m 2 100 mm insulation 0.275 5.72 W/m 2 Aluminium Composite Panel (ACP) ACP + air gap + gypsumboard ACP + air gap + gypsumboard + insulation + gypsumboard plaster + aerated concrete brick + plaster U-value Average heat transmission 6.674 43.70 W/m 2 2.779 24.74 W/m 2 0.529 11.70 W/m 2 1.039 11.83 W/m 2 BUILDING ENVELOPE DESIGN PRINCIPLES 29
INFILTRATION Infiltration is the unintentional introduction of external air into a building. This could occur through cracks in walls, roofs, or the door and window openings. It could also happen through exterior doors and windows that are left open. This air leakage could be exacerbated by wind, negative pressurization of the building etc. Infiltration can increase the cooling energy consumption in Jakarta, because the incoming air has to be cooled and dehumidified. If the building interiors are positively pressurized, the interior air could start leaking outside. This is known as exfiltration. Infiltration and exfiltration occur not only through building envelope separating indoor and outdoor, but also between conditioned and unconditioned spaces (e.g. staircase) within the building. In Indonesia, air tightness is not properly addressed in construction practices. Besides making sure all significant cracks in the building are closed, occupants should be trained to close all exterior windows and doors when not in use. FIGURE. 21 Infiltration and Exfiltration Through Windows Opening and Cracks 19 BUILDING ENVELOPE DESIGN PRINCIPLES 19 Jatmika Adi Suryabrata. 30
CASE STUDY The building envelope of the Ministry of Public Works building in Jakarta is designed to reduce solar radiation and optimize natural lighting. Significant energy saving is achieved through configuring building form and orientation, and envelope design (50% Window- Wall ratio, reflective glass, exterior shading) to avoid exessive solar heat gain from east and west, yet allowing diffuse daylight to enter the interior spaces from north and south oriented windows with lightshelves. Daylight and electric lighting integration with photo sensors, water cooled chiller with VSD and VAV are employed to further reduce energy consumption. With an average of 140 kwh/ m 2 /year, the building enjoys over 40% energy saving compared to normal office building in Jakarta. The building has received Platinum certification from Green Building Council Indonesia. FIGURE. 22 Average Daily Solar Radiation on Horizontal Roof and Vertical Surfaces of Major Orientations BUILDING ENVELOPE DESIGN PRINCIPLES 31
FIGURE. 22 (continued) Average Daily Solar Radiation on Horizontal Roof and Vertical Surfaces of Major Orientations Building Form and Direction Original block plan: Larger area of the building is oreinted to east and west Modified building form: 1. Narrow building form 2. Reduce surface ecposure of the working space to east and west sun 3. Orienting windows to north and south Building Envelope, Shading, and Daylight 1. Stopsol darkblue + insulation 2. Lightshelves for better daylight distribution 3. Narrow building span 4. Translucent interior partition OTTV = 28,1 W/m 2 Return air Lightshelves Thermal isulation BUILDING ENVELOPE DESIGN PRINCIPLES 32
appendix APPENDIX A. OTTV Values for WWR North Wall (0 o ) OTTV (W/m 2 ) WWR 150 140 130 120 110 100 90 70 60 50 40 30 20 10 0 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 70% 65% 60% 55% 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% SHGC BUILDING ENVELOPE DESIGN APPENDIX PRINCIPLES 33
APPENDIX B. OTTV Values for WWR North East Wall (45 o ) OTTV (W/m 2 ) WWR 150 140 130 120 110 100 90 70 60 50 40 30 20 10 0 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 SHGC 70% 65% 60% 55% 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% BUILDING ENVELOPE APPENDIX 34
APPENDIX C. OTTV Values for WWR East Wall (90 o ) OTTV (W/m 2 ) WWR 150 140 130 120 110 100 90 70 60 50 40 30 20 10 0 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 SHGC 70% 65% 60% 55% 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% BUILDING ENVELOPE APPENDIX 35
APPENDIX D. OTTV Values for WWR South East Wall (135 o ) OTTV (W/m 2 ) WWR 150 140 130 120 110 100 90 70 60 50 40 30 20 10 0 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 SHGC 70% 65% 60% 55% 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% BUILDING ENVELOPE APPENDIX 36
APPENDIX E. OTTV Values for WWR South Wall (1 o ) OTTV (W/m 2 ) WWR 150 140 130 120 110 100 90 70 60 50 40 30 20 10 0 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 SHGC 70% 65% 60% 55% 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% BUILDING ENVELOPE APPENDIX 37
APPENDIX F. OTTV Values for WWR South West Wall (225 o ) OTTV (W/m 2 ) WWR 150 140 130 120 110 100 90 70 60 50 40 30 20 10 0 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 SHGC 70% 65% 60% 55% 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% BUILDING ENVELOPE APPENDIX 38
APPENDIX G. OTTV Values for WWR West Wall (270 o ) OTTV (W/m 2 ) 150 140 130 120 110 100 90 70 60 WWR 70% 65% 60% 55% 50% 45% 40% 35% 30% 25% 50 20% 40 30 20 10 0 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 SHGC 15% 10% 5% 0% BUILDING ENVELOPE APPENDIX 39
APPENDIX H. OTTV Values for WWR North West Wall (315 o ) OTTV (W/m 2 ) WWR 150 140 130 120 110 100 90 70 60 50 40 30 20 10 0 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 SHGC 70% 65% 60% 55% 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% BUILDING ENVELOPE APPENDIX 40
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