Passive solutions to reduce the need for cooling in buildings

Feng, Wei Working Paper Passive solutions to reduce the need for cooling in buildings ADBI Working Paper, No. 1387 Provided in Cooperation with: Asian Development Bank Institute (ADBI), Tokyo Suggested Citation: Feng, Wei (2023) : Passive solutions to reduce the need for cooling in buildings, ADBI Working Paper, No. 1387, Asian Development Bank Institute (ADBI), Tokyo, https://doi.org/10.56506/ABDS1960 This Version is available at: https://hdl.handle.net/10419/296781 Standard-Nutzungsbedingungen: Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden. Sie dürfen die Dokumente nicht für öffentliche oder kommerzielle Zwecke vervielfältigen, öffentlich ausstellen, öffentlich zugänglich machen, vertreiben oder anderweitig nutzen. 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If the documents have been made available under an Open Content Licence (especially Creative Commons Licences), you may exercise further usage rights as specified in the indicated licence. https://creativecommons.org/licenses/by-nc-nd/3.0/igo/ ADBI Working Paper Series PASSIVE SOLUTIONS TO REDUCE THE NEED FOR COOLING IN BUILDINGS Wei Feng No. 1387 May 2023 Asian Development Bank Institute The Working Paper series is a continuation of the formerly named Discussion Paper series; the numbering of the papers continued without interruption or change. ADBI’s working papers reflect initial ideas on a topic and are posted online for discussion. Some working papers may develop into other forms of publication. The Asian Development Bank refers to “China” as the People’s Republic of China. Suggested citation: Feng, W. 2023. Passive Solutions to Reduce the Need for Cooling in Buildings. ADBI Working Paper 1387. Tokyo: Asian Development Bank Institute. Available: https://doi.org/10.56506/ABDS1960 Please contact the authors for information about this paper. Email: [email protected], [email protected] Wei Feng is a research scientist at the Chinese Academy of Science of Shenzhen Institute of Advanced Technology, Shenzhen, Guangdong Province, People’s Republic of China and an affiliate scientist at the Lawrence Berkeley National Laboratory, Berkeley CA, United States. The views expressed in this paper are the views of the author and do not necessarily reflect the views or policies of ADBI, ADB, its Board of Directors, or the governments they represent. ADBI does not guarantee the accuracy of the data included in this paper and accepts no responsibility for any consequences of their use. Terminology used may not necessarily be consistent with ADB official terms. Discussion papers are subject to formal revision and correction before they are finalized and considered published. Asian Development Bank Institute Kasumigaseki Building, 8th Floor 3-2-5 Kasumigaseki, Chiyoda-ku Tokyo 100-6008, Japan Tel: +81-3-3593-5500 Fax: +81-3-3593-5571 URL: www.adbi.org E-mail: [email protected] © 2023 Asian Development Bank Institute ADBI Working Paper 1387 W. Feng Abstract This paper introduces designs, technologies, and best practices aimed at reducing the cooling energy demand in buildings. It covers the basic principles of why occupants need cooling to meet thermal comfort requirements and how heat is transferred into buildings from the outdoor environment. Passive designs help buildings make use of natural cooling resources and maximize free cooling opportunities such as natural ventilation. The paper summarizes best practices for each passive strategy used in buildings. As a result, architects and engineers will also be able to better orient functional spaces and design cooling operation strategies to provide cooling for spaces where and when needed. The building envelope provides the necessary insulation to stop heat transfer from a hot outdoor environment to an indoor one. Criteria for designing a high-performance building envelope are introduced. For fenestration systems, this paper covers energy-efficient technologies for glazing and shades to reduce solar heat gain. Cool roofs can effectively reflect sunlight back to the atmosphere and also significantly reduce buildings’ solar heat gain. Also, to create a cooler outdoor environment in cities, strategies are introduced to mitigate the urban heat island effect. Finally, policy recommendations are suggested, such as improving building codes and standards; creating labels and certifications for passive cooling technologies; establishing incentive programs to promote passive green buildings; educating architects, builders, and occupants; and developing sustainable city policies. Keywords: buildings, building envelope, cool roofs, thermal comfort, passive cooling, policies JEL Classification: R0 ADBI Working Paper 1387 W. Feng Contents 1. INTRODUCTION ....................................................................................................... 1 2. ADEQUATE BUILDING DESIGNS ............................................................................ 3 2.1 Building Orientation and Massing ................................................................... 3 2.2 Window-to-Wall Ratio .................................................................................... 4 2.3 Developing Energy-Efficient Space Conditioning Strategies .......................... 4 2.4 Summary of Best Practices in Building Design to Reduce Cooling Energy Demand ............................................................................................. 5 3. FREE COOLING SOLUTIONS .................................................................................. 6 3.1 Natural Ventilation and Free Cooling.............................................................. 6 3.2 Other Free Cooling Solutions ......................................................................... 8 4. HIGH-PERFORMANCE BUILDING ENVELOPE ....................................................... 8 4.1 Opaque Building Envelope ............................................................................. 9 4.2 Building Fenestration Systems ..................................................................... 10 4.3 Examples of Advanced Envelope Design to Reduce Cooling Load .............. 13 4.4 Summary of Best Practices in Building Envelope Design to Reduce Cooling Load ................................................................................................ 13 5. COOL ROOFS AND SURFACES ............................................................................ 14 5.1 Cool Roofs ................................................................................................... 14 5.2 Cool Walls.................................................................................................... 17 5.3 Summary of Best Practices on Cool Roofs................................................... 17 6. URBAN PLANNING TO REDUCE THE URBAN HEAT ISLAND EFFECT ............... 18 7. POLICY INSTRUMENTS TO REDUCE COOLING DEMAND.................................. 20 7.1 Building Codes and Standards ..................................................................... 21 7.2 Labels and Certifications .............................................................................. 22 7.3 Incentive Policies ......................................................................................... 22 7.4 Capacity Building and Cultivating Passive Cooling Behaviors ...................... 22 7.5 Sustainable Urban Planning Policies............................................................ 23 7.6 Million Cool Roof Challenge ......................................................................... 23 8. PASSIVE COOLING BUILDING DESIGN AND CASE STUDY ................................ 23 8.1 School of Design and Environment 4 Net-Zero Energy Building ................... 23 8.2 Passive Design of the Shenzhen Institute of Building Research ................... 24 9. CONCLUSION AND POLICY RECOMMENDATIONS ............................................. 25 REFERENCES ................................................................................................................... 27 ADBI Working Paper 1387 W. Feng 1 1. INTRODUCTION Space cooling is needed when building occupants feel uncomfortable because of a rise in room air temperature and/or relative humidity. When occupants feel uncomfortable, they often turn on fans or air-conditioning, which consumes energy. Identifying how to make occupants feel comfortable without using mechanical cooling is critical to reduce cooling energy demand. Each of us may have a different ambient temperature we feel comfortable with, and there are a number of standards that attempt to define a common range of comfortable temperature and humidity levels. For instance, the American Society of Heating Refrigeration and Air-Conditioning Engineers’ (ASHRAE) Standard 55 defines the temperature and humidity ranges for occupant thermal comfort zones, as shown in Figure 1. Air-conditioning tends to be used outside of such comfort zones, cooling when the temperature is higher than the range. Figure 1: Thermal Comfort Zones with Temperature and Relative Humidity Ranges Source: ASHRAE Standard 55. Rises in indoor temperature are often caused by heat transfer from the exterior environment to buildings as well as by internal heat gain. The occupants’ metabolic rate and clothing choices can also affect their thermal comfort and use of space cooling. The amount of cooling energy needed to cool a space to meet the occupants’ thermal comfort criteria is called the “cooling load”. Figure 2 illustrates building heat gains from different sources. In cooling seasons, solar radiation passing through a building’s windows and skylights is one of the major sources of indoor heat gain (radiation heat gain). Heat can also be transferred through the building envelope into the indoor space when the outdoor temperature is high. Heat transfer conduction can also happen when solar radiation is received on an opaque building surface, and the rise in a building’s external surface temperature causes heat flux into its interior space (conduction and convection heat gain). Interior heat gain can also cause the indoor temperature to rise and the cooling load to increase. Interior heat can be emitted from human bodies, as well as indoor electrical devices such as lighting, computers, cooking devices, and appliances. Moisture changes in an indoor environment can also cause discomfort. To reduce the amount of moisture in the indoor environment (such as moisture generated from a shower), cooling energy is often needed to absorb it or condense the moisture into water. The amount of energy used to remove moisture from the air is often called “latent heat,” while the energy expended to condition the indoor air temperature is called “sensible heat.” In hot and humid climates or buildings that generate a lot of indoor moisture, properly managing moisture and removing it from indoors is as important as conditioning the indoor space temperature. It is worth mentioning that in developing regions and low-income communities, residents may not be able to afford space conditioning. Passive cooling solutions (Peters and Sayin 2022a,b) are preferable ADBI Working Paper 1387 W. Feng 2 low-cost solutions. This paper will also cover passive design strategies for buildings such as natural ventilation, cool roofs and surfaces, and using fans to provide good thermal comfort. Cooling is also needed for refrigeration purposes to keep food fresh and to keep medicine effective (e.g., vaccines). Storing food in a refrigerator is a common way to keep food fresh. In addition to home refrigerators and commercial refrigeration cabinets, refrigeration is also commonly found in cold chains to ship food or medical products from one place to another, often around the world. Refrigeration systems are often installed in trucks and shipping containers, as well as in warehouses. Figure 2: Building Space Heat Gains Source: Author’s own. As passive cooling can effectively cut energy demand for mechanical cooling, the passive cooling design and technologies introduced in this paper are especially suitable to promote cost-effective cooling methods focusing on low-income communities. To identify methods for reducing the cooling load in built environments, this paper discusses many basic principles, including better building designs, highperformance building envelope systems, the use of cool roofs and reflective surfaces, and sustainable urban planning. Besides technological solutions, financing solutions are needed to scale green and energy-efficient cooling systems. Various financing tools are available to facilitate the purchase, installation, and energy-efficient operation of cooling technologies. Commercial financial instruments often include loans, equity investments, and risk mitigants. With financing institutes paying more attention to climate change, certain financing opportunities can be leveraged for cooling solutions, such as the utilization of climate funds, funding for refrigerant replacement, and improvements in energy efficiency. Due to the low-cost features of passive measures, when promoting energyefficient, green, and net-zero carbon buildings, policy priorities should be given to passive cooling solutions. ADBI Working Paper 1387 W. Feng 3 The objective of this paper is to introduce the technical opportunities for implementing passive cooling measures and provide policy instruments for governments to advance the adoption of passive solutions. This paper introduces several passive cooling approaches, such as adequate building designs (Section 2), free cooling and natural ventilation (Section 3), high-performance building envelopes (Section 4), cool roofs and surfaces (Section 5), and urban planning methods to reduce urban heat island effects (Section 6). It then provides policy instruments to help countries and regions implement passive cooling measures in buildings (Section 7). Comprehensive case studies provide examples of implementation of these passive measures. 2. ADEQUATE BUILDING DESIGNS Building design is the first and foremost approach that can be used to help reduce cooling load without the installation of expensive building technologies. To reduce cooling load, the key building design aims are to avoid building solar heat gain and to make use of its natural cooling environment to enhance energy-free cooling. 2.1 Building Orientation and Massing Properly orienting a building to reduce solar heat gain can effectively reduce the cooling energy demand. The shape of a building and building envelope material types also have a strong influence on cooling energy use. During the design stage, energy simulation analysis is often needed to calculate the cooling energy demand under different design strategies, given the constraints of the site, landscape, and shade analysis from the exterior environment. The general principles of orientation and massing design are used to ensure buildings receive as little heat transfer from the outdoor environment (including solar radiation) as possible. Most green building designs require buildings to utilize daylight. Finding a balance between energy savings, daylight utilization, and cooling load reductions needs to be considered in the design stage. Another design strategy is to have buildings close to natural cooling resources, such as a river, pond, lake, or green vegetation. The adjacent cool resources can provide natural breezes that are useful for building ventilation. Understanding the local \wind profile and optimizing the building’s orientation can maximize its free cooling opportunities. It is also important to analyze the building’s interior functional space, as not all functional spaces need mechanical cooling all the time. Assigning some zones (e.g., corridors, staircases) that do not need much air-conditioning to locations that receive large amounts of solar gain is also a good design strategy (Figure 3). ADBI Working Paper 1387 W. Feng 4 Figure 3: Orientation and Massing Strategies to Reduce Unoccupied Space Conditioning Energy Source: Author’s own. 2.2 Window-to-Wall Ratio The window-to-wall ratio (WWR) is the ratio of the window areas to the total facade area. The WWR value ranges between 0 and 1. Properly designing a building’s window areas is important to reduce cooling energy demand, as well as to utilize daylight. Nowadays, architects often like to design large window area facades, as windows tend to cost less and are easy to build compared with opaque walls. However, large window areas often mean more solar radiation will be received by the building and may increase its cooling demand. Several countries’ building energy codes and standards have developed regulations to limit the WWR in new building designs. For example, the US ASHRAE Standard 90.1 limits the WWR to 40%. Should a building need to build a WWR value larger than 40%, the design team needs to consider more aggressive energy conservation measures to prove that increasing the WWR will not significantly increase the building’s cooling energy use. Often, advanced shading methods and daylighting utilization strategies are adopted when designers choose a large WWR. Section 5.2 introduces methods for designing a building fenestration system to achieve good cooling energy savings. 2.3 Developing Energy-Efficient Space Conditioning Strategies Deciding which kind of cooling service needs to be deployed for each building zone, and at what time it must be deployed, are very important design issues. The design of cooling strategies should be developed at the same time as zoning and WWR design strategies are decided upon. Overall, not all the zones in a building need the same quality of cooling throughout an entire cooling season. Some zones, such as a data center, may need mechanical cooling 24/7 to maintain a constant indoor air temperature, while zones like corridors may not need such a high quality of cooling as office spaces. The general principle for providing mechanical cooling is to develop a “partial-time partial-space” strategy that only provides mechanical cooling for a space at the time when it is needed, and to maximize the natural ventilation and free cooling opportunities. ADBI Working Paper 1387 W. Feng 11 In addition to window thermal conductivity requirements, solar heat gain properties are also important. As the basic function of an exterior window is to enable exterior light to come into the indoor space, we often use visible light transmittance (VT) to describe the percentage of visible light transmitted through window glasses. A clear glass usually has a VT of 75%–92%, while color or coated glasses have a much lower VT value. When sunlight is transmitted from windows into buildings, heat is also transferred through solar radiation. The percentage of solar radiation admitted (transmitted and/or absorbed) through a window assembly is defined as the solar heat gain coefficient (SGHC) and is another important parameter when selecting a window. Building codes and standards often have requirements of minimum VT and SGHC values in different climate zones. To reduce cooling load, architects and engineers often want to use low SGHC value windows to reduce solar heat gain and cooling load. However, a low SHGC may also mean a low VT and reduce the building’s ability to utilize daylight. Low thermal emissivity (low-E) windows, which stop infrared heat exchange between indoor and outdoor environments, have become increasingly common. Spectrum-selective glasses can further block solar radiation by allowing the specific spectrum of solar rays transmitted and thus reduce a window assembly’s SGHC. Window film and coating technology developments have made “smart windows” possible. A thermochromic window can change its color based on the amount of solar radiation it receives, thereby changing the SGHC and VT values. When the solar radiation received by the window is ample, the thermochromic window reduces this transmittance. The electrochromic window uses electric control to adjust the window’s transparency level. Instead of passively adjusting as the thermochromic window does, the electrochromic window can engage occupants and integrate with a building’s modern control system to adjust the window’s transparency to reduce cooling load and utilize daylight. To help building owners select energy-efficient fenestration systems, labels and rating systems are developed to disclose fenestration system performance data. The National Fenestration Rating Council (NFRC) in the United States has developed a windows rating label (Figure 7) to show building users the U-value, SGHC, VT, and air leakage data. Figure 7: Window Label from the National Fenestration Rating Council in the United States Source: US NFRC (2022). ADBI Working Paper 1387 W. Feng 12 4.2.2 Shades To further reduce cooling load, window shading devices are often attached to windows to block solar radiation heat gain. Shades can be installed on a building’s exterior surfaces, interior surfaces, or in the middle of glass window panes. Exterior shading devices are effective in blocking solar heat gain outside of a building. Exterior shades can be installed horizontally as overhangs or vertically as fins. Overall, overhangs are effective in blocking solar heat gain when the solar altitude angle is high (e.g., at noon). Vertical fin shades are effective for blocking solar radiation when the solar attitude angle is not too high, and are especially helpful for mitigating direct solar radiation-caused glare. Interior shades such as blinds and screens are also helpful for reducing a building’s solar heat gain and cooling load. Unlike exterior shades, interior shades are often installed for each window, so occupants have the freedom to adjust their position. Advanced shades not only block solar beam radiation but redirect some solar beams into the interior space to provide daylighting benefits. So choosing a shading device should balance cooling energy savings with its ability to utilize daylight. In some window assembly products, shades are also installed in the middle of windowpanes. Compared with interior shades, exterior shades are more effective in blocking solar radiation outside of a building instead of inside. However, with exterior shades, as they are directly exposed to outdoor environments, their maintenance and automatic operation could make a shading system expensive to operate, especially for high-rise buildings. The advancement of window technology has made it possible to integrate windows and shades with a built environment control system and intelligently control the window operation and reduce the building’s cooling load. The opening of windows and the operation of window shades can be sensed as a part of the building control system; the system knows when the building is operated in natural ventilation mode and when it is operated using mechanical cooling (Figure 8). Lighting controls can also be integrated with the shade operation to make use of daylight and save lighting energy use. Figure 8: Integrative Controls for Shading, Lighting, Heating, Ventilation, and Air-Conditioning Source: Lawrence Berkeley National Laboratory (2015). ADBI Working Paper 1387 W. Feng 13 4.3 Examples of Advanced Envelope Design to Reduce Cooling Load A building fenestration system and its shade can be used to enhance natural ventilation. Figure 9 shows how a high-rise building design in Zhuhai, PRC, uses solar photovoltaic (PV) shades as overhangs to block solar radiation and generate electricity. The overhang is designed with an airflow path to allow air to pass through the back of the PV panel to naturally cool down the PV panel and increase its efficiency. During shoulder seasons, when the building is operated in natural ventilation mode with a window open, the outdoor air can be slightly warmed by the PV panel overhang and reduce the building’s heating energy demand (Feng et al. 2019). Figure 9: PV Overhang Shades Design for a High-Rise Building in Zhuhai, PRC Source: Xingye Solar Co. (2019), personal communication. Traditional buildings are operated with a fixed WWR and external shades. A case building in Shandong Province, PRC, demonstrates the use of operable external shades to change the building’s WWR and optimize shading effects. During a winter evening, the operable shades can fully close. The back of the shading panel has insulation material. When fully closed, it can reduce the building’s heat loss. During daytime in the summer, the shades are optimized to open at different angles based on the orientation to allow the space to utilize daylight but block sunlight heat gain. PV can not only be used in exterior shading devices but can also be installed in the middle of windowpanes to reduce cooling load and generate electricity. Results from one PV shade window technology (produced by Solaria) test at the Lawrence Berkeley National Laboratory showed that a window with PV shades can reduce energy by 15%, compared with traditional low-E windows. 4.4 Summary of Best Practices in Building Envelope Design to Reduce Cooling Load To summarize, the advanced design of building envelope systems can greatly help buildings reduce their cooling energy demand. Below is a summary of the best practices in designing and operating building envelope systems: • Design a building to ensure its walls, roofs, and windows meet building energy codes and standard thermal property requirements. • Select windows with a low SGHC value to avoid solar heat gain, but also pay attention to visible light transmittance so the building can utilize daylight. • Use interior and exterior shading devices to shade solar radiation and reduce daylight glare. ADBI Working Paper 1387 W. Feng 14 • Develop and apply building fenestration system labels to enable customers to select high-performance windows. • Integrate window and shade operation with building control systems to coordinate envelope operation with indoor cooling operation strategies. • Use simulation software tools to assess building fenestration system daylighting and heat transfer performance. 5. COOL ROOFS AND SURFACES Solar radiation is the major heat gain source and the reason for buildings to operate their cooling system in the summer. The roof is the key component in a building’s envelope system and is directly affected by solar radiation. Dark materials tend to absorb more heat than light-color materials. Roofs are often made with dark colors and have a great capacity to absorb sunlight, heat buildings, and affect the surrounding environment. The roof-absorbed heat from solar radiation often transmits into the indoor space and adds cooling energy demand. Hot dark roofs, when emitting heat to the surrounding environment, can also cause urban heat island effects, which in turn aggravate building heat gain and reduce the efficiency of air-conditioning systems (Akbari, Menon, and Rosenfeld 2009). Figure 10 illustrates how a roof receives, absorbs, and reflects solar energy, and emits heat. Figure 10: How a Roof Receives, Absorbs, and Reflects Solar Energy, and Emits Heat Source: Lawrence Berkeley National Laboratory (2019). 5.1 Cool Roofs Studies have found that a roof can be much cooler under sunlight if it reflects most of the sunlight instead of absorbing it. The ratio of reflected sunlight from a roof surface to the total sunlight solar radiation received is defined as “solar reflectance.” Having high solar reflectance is one of the key characteristics necessary for a cool roof. Another ADBI Working Paper 1387 W. Feng 15 key characteristic of a cool roof is having high thermal emittance. “Thermal emittance” is the ability of a roof to emit heat primarily through infrared radiation. As thermal radiation happens in a much longer spectrum (4–80 microns) in sunlight compared with solar radiation (0.3–2.5 microns), these two parameters are intended as factors that characterize a cool roof. A dark roof usually has a solar reflectance value of 0.05–0.2 and a thermal emittance of 0.9, while a typical cool roof has a solar reflectance of about 0.7 and a thermal emittance of 0.2. It should be noted that not all cool roofs are white, although white materials tend to reflect a significant amount of solar energy. Colored roofing materials can also have good solar reflectance. As more than half of solar energy is transmitted via invisible sunlight, a colored roof, if properly designed, can also be a cool roof (Levinson and Akbari 2010). 5.1.1 Types of Cool Roof Technology Several cool roof technologies have been developed for both new constructions and retrofitting existing buildings. The single-ply membrane is a single-layer cool roof membrane material that can be rolled onto a roof. The technology is a good solution for the fast installation of a cool roof, and the membrane can be attached to an existing roof surface with fasteners, adhesives, or using ballasts. The single-ply membrane is also suitable for retrofitting an existing roof by placing the cool roof material on top of the existing roofing structure. Elastomeric coating is a liquid surfacing material (acrylic, elastomeric, or asphaltic) and can be applied to different roof types, especially built-up and metal roofs. Elastomeric coating is available in different colors, not just white. Painted metal is a roofing product made with metal with painted or factory-coated cool roof colors. Finally, ballast roofing materials are used to combine a cool roof with a stone or concrete paver. The goal is to weigh down the waterproof layers of the roof. Ballast material can also add to the thermal mass of the surface layer, thereby reducing heat conduction into the interior space. Low-cost cool roof solutions such as painting it a light or white color are effective methods for turning an existing dark roof into a cool roof. Paint is a cost-effective solution for developing countries that are not able to afford complex cool roof solutions. Paint can also be applied to pitched-roof surfaces. When applying cool roof paints, attention must be paid to the weatherization degradation effects of the paints. It is desirable to select durable paint and the cool roof reflectance can last longer throughout a building’s lifetime. In addition to cool roofs, other roofing technologies can help reduce a building’s cool energy use. A “green roof” refers to using green plants and vegetation on a roof surface to create shade and using plants to absorb the solar heat gain. A green roof often includes several layers of roofing materials, including vegetation, growing soil, irrigation, a drainage layer, a root barrier, a waterproofing membrane, and a structure deck. A “PV roof” refers to a roof where PV panels are installed on a building’s rooftop. PV does not directly save cooling energy use, but the electricity generated by the panels can offset cooling energy consumption. PV panels can also create good shade and reduce a roof’s solar heat gain. A solar thermal panel is another way to harvest solar radiation. Solar thermal technologies can produce hot water and are popular in Asian buildings. ADBI Working Paper 1387 W. Feng 16 5.1.2 Standards and Labels To promote the adoption of cool roofs in buildings, cool roof regulations are often embedded in building energy codes and standards. Based on applicable climate zones and the level of steepness of the roof, solar reflectance (SR) and thermal emittance (TE) values are often required for cool performance. Testing methods are needed to test roof product solar reflectance and thermal emittance. A few countries in Asia have developed cool roof testing standards based on analysis from Asia-Pacific Economic Cooperation (APEC) (Table 2). Table 2: Testing Standards of Cool Roof Properties in Asia (APEC EWG 2020) Economies Roof Standards Comment People’s Republic of China GBT31389, JGJ287, JGJ359, JGT235-2014 GBT31389 specifies the testing standard for reflectance and emittance. JGJ and JGT are standards of product performance Hong Kong, China No specific standard for testing reflectance and emittance Uses OTTV and OTTR in the economy’s building code. Indonesia Currently no standard for reflectance or emittance of cool roof Table for reflectance and emittance is provided in the economy’s building code and standard Japan JIS_K05602, JIS_K_05675, JSTM-J-7601, JSTM-J-7602, JSTM-J-6151, JIS-R-3107 JIS R 3017 is the standard for measuring glazing product emittance and is also used for measuring opaque surfaces Republic of Korea Information not available Malaysia Currently no standard for reflectance or emittance of cool roof The economy’s code MS1525 requires the calculation of RTTV; however, it does not reference the testing procedure. Table for reflectance and emittance is provided in the economy’s building standard Philippines Currently no standard for reflectance or emittance of cool roof The economy’s building energy code is under public review Singapore Information not available There is no known testing standard for reflectance and emittance measurement Thailand ASTM E 903-82, JIS R 3106 1998, ASTM E 1980-01, ASTM C 1371-98, BS EN 12898 To date, the tests for reflectance of coating have been done in compliance with JIS R 3106. However, changing to JIS K 5602:2008 is under consideration Viet Nam QCVN 09:2017/BXD Specifies reflectance and emittance requirements for calculating resistance. However, there is no testing standard for reflectance and emittance measurement Source: APEC (2020). As roofing materials’ performance always ages with time, cool roof standards often require initial and/or aged values of ST and TE. Some standards also allow the installation of a cool roof to be traded off against its roof insulation level, U-value, or R-value. That is, if a cool roof is used, a roof tends to absorb less solar radiation energy, so the roof’s insulation level could be slightly reduced compared to a roof with no cool roof installed. The US Green Building Council (USGBC) Leadership in Energy and Environmental Design green building standard awards up to two points for applying cool roofs and mitigating urban heat island effects. The Cool Roof Rating Council (CRRC) in the United States also developed cool roof labels to help customers select cool roof ADBI Working Paper 1387 W. Feng 17 products. On a rating label, the cool roof product’s initial and aged SR and TE values need to be documented (Figure 11). Figure 11: Cool Roof Rating Label Source: US Cool Roof Rating Council (2022). 5.1.3 Potential Disadvantages of Cool Roofs Using a white color roof can also cause glare when it reflects sunlight to adjacent buildings. To avoid glare impacts, a colored cool roof could be more appropriate for low-rise buildings. The application of a cool roof on a building needs to take into consideration its seasonal impacts. To develop cool roof standards, a comprehensive regional analysis in a country needs to be conducted to trade off cooling energy savings by applying a cool roof against its heating energy penalty. 5.2 Cool Walls A wall only receives about 50% of solar heat gain compared with the same area of a roof. However, a building has a much bigger exterior wall surface area than its roof. Especially in cities with many high-rise buildings, walls could play much greater roles in reflecting sunlight and help mitigate the urban heat island effect. Cool color paints are the most common technology used for cool walls. Unlike a roof, half of the sunlight reflected from a wall may be sent to its neighboring buildings or absorbed by the city. Therefore, having retroreflective wall materials or coating could enhance the reflection of solar energy back to the sky, as well as reducing potential reflection glare. 5.3 Summary of Best Practices on Cool Roofs Below is a summary of the best practices for cool roofs: • Develop cool roof-based building energy codes, standards, and green building labels. • Develop various types of cool roof technologies. • Develop standards and criteria for cool roof product performance testing. • Set up cool roof product rating systems. • Establish education and dissemination programs to teach designers and building owners to adopt cool surfaces. ADBI Working Paper 1387 W. Feng 18 6. URBAN PLANNING TO REDUCE THE URBAN HEAT ISLAND EFFECT The urban heat island effect is a phenomenon that occurs during the daytime where an urban area has a much higher air temperature than its surrounding suburban and rural areas (Figure 12). Human activities such as vehicle exhaust heat emissions, energy use in factories, and exchange of heat from air-conditioning systems are major causes of urban heat island effects. Another major cause is urban infrastructure such as buildings and pavements that replace trees and enhance solar energy absorption in urban areas. Figure 12: Urban Heat Island Effect Source: Lawrence Berkeley National Laboratory (2019b). Urban heat island effects can have several impacts in increasing building energy use and worsening outdoor air quality. A hot urban environment can increase heat transfer from the outdoor environment to the indoors and raise cooling energy demand. Also, a hot outdoor environment can slow an air-conditioner system condenser side heat exchange and reduce cooling system efficiency. The increased electricity demand on cooling energy use can also cause stress to the power grid and possible blackouts. Hot outdoor air can also accelerate the formation of ozone and outdoor pollutant emissions such as nitrogen oxides and volatile organic compounds. It can also cause human health effects such as respiratory syndrome and heat stroke. Better urban planning can reduce urban heat island effects caused by human activities. Planning commercial-residential mixed-use urban districts can reduce commute distances and decrease the heat exhaust from cars. Urban planning to encourage the use of public transport can also reduce the urban heat island effect. Moving high energy demand industrial facilities outside of a city can shift the heat emission from cities to suburban or rural areas and relieve the increase in urban temperatures. There are several ways to mitigate the urban heat island effect through better urban and infrastructure planning: ADBI Working Paper 1387 W. Feng 19 • Good vegetation to create shades in an urban environment Trees provide pleasant shade for the urban environment and can mitigate solar heat gain by urban surfaces. They can also absorb solar radiation from the sunlight without increasing outdoor air temperature and releasing moisture into the atmosphere. • Cool roofs and walls The cool roofs and walls discussed previously not only reduce the cooling energy demand for a building itself, but also, collectively, the reflective features of building envelopes can enable cities to absorb less solar radiation heat in the summer. Researchers have found that using a cool roof can effectively reduce the noon temperature of the PRC’s Pearl River Delta cities by 0.8 degrees Celsius (°C) during ordinary summer days, and 1.2 °C during heatwave events (Figure 13). • Cool pavement Dark color pavements, often made with asphalt-based material, can absorb a great amount of solar energy. In the summer, we sometimes find that some pavements become “melted” due to a large amount of heat absorption and the high temperature of the road surface. The hot pavements continuously emit heat back into the urban air and aggravate the urban heat island effect. As pavements make up about a third of the urban surface, reducing pavement heat absorption and using cool pavements has become critically important. “Cool pavements,” similarly to cool roofs, refer to pavements using reflective materials that reflect more solar energy than traditional pavements and stay cool. Concrete pavements can reflect 30%–50% of received solar energy. Some color-coated asphalt pavements can achieve solar reflectance of 50%. Cool pavements can also bring in better outdoor thermal comfort for people walking and exercising in cities. • Water features Water is a natural resource for free cooling. Lakes and ponds not only reflect solar energy, but their water temperature is often lower than the outdoor air temperature in the daytime, and the heat absorbed by water won’t increase the outdoor temperature rise. The heat absorbed by water can also be converted into latent heat through water evaporation. Spraying water can create mists that can cool the surrounding environment. • Create urban wind channels Understanding the dominant wind directions in the summer, and planning for a city to take advantage of those winds, can help enhance air movement through a city and assist in mitigating the urban heat island effect. Planners often need to consider certain wind flow channels and refrain from using dense high-rise buildings that block upstream wind flow. • District cooling Air-conditioning systems need to exhaust heat to the outdoor environment and thus aggravate the urban heat island effect. However, district cooling systems can locate the cooling central plant in suburban areas, where the urban heat island effect is not significant, and provide centralized chilled water to buildings in cities. Some advanced district cooling systems can utilize water from underground, rivers, lakes, and even seawater to exchange heat. In this case, ADBI Working Paper 1387 W. Feng 20 heat is ejected into the water instead of to the outdoor air, and therefore will not worsen urban heat island effects. Figure 13: Urban Heat Island Mitigation Using Cool Roofs Source: Cao et al. (2015). 7. POLICY INSTRUMENTS TO REDUCE COOLING DEMAND Several policy barriers to applying passive cooling measures exist. In some countries, codes and standards are not stringent enough to require the adoption of passive cooling design and technologies—the building and construction market lacks labels and certifications to disclose passive cooling products’ key performance data; building owners lack incentives to develop passive construction; and architects, builders, and occupants are not aware of the importance of passive design and do not know how to design or operate passive technologies. There is also a lack of sustainable city policies to create a cooler outdoor environment and a need to establish international passive cooling programs such as the Million Cool Roof Challenge to scale up the global adoption of affordable passive cooling solutions. Policy instruments are important to overcome existing barriers and accelerate passive cooling market adoption. Regulatory, information, and incentive policies are available to scale up green cooling applications. According to previous analysis, regulatory policy development should focus on upgrading building codes and standards to encourage the adoption of passive measures in buildings. Information policies should focus on developing label and certification programs to promote passive cooling technologies. Incentive programs are important in providing financial and/or building construction incentives for buildings to adopt passive cooling measures. Moreover, capacity building policies are needed to educate architects, developers, and occupants to take part in the passive cooling built environment and sustainable urban planning. ADBI Working Paper 1387 W. Feng 27 REFERENCES ADB (2021) People’s Republic of China: Developing a Climate Friendly Cooling Sector through Market and Financing Innovation, Project Number: 52249-003, September 2021, https://www.adb.org/sites/default/files/project-documents/ 52249/52249-003-tacr-en.pdf. Akbari, H., S. Menon, and A. Rosenfeld. 2009. 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