Passive Design with Natural Light and Air: Crucial Component of Change in the Cityscape
By: Ar. Jorge M. Mission Ph.D. UAP
(This article is written as an advocacy of UAP Mt Kanla-on Chapter (UAPMK) on its GREEN EARTH BLUE SKY agenda on environment and a contribution to the celebration of the 2012 World Day of Architecture with the theme “Architects are City Changers”. UAPMK is also assisting the Department of Energy –Visayas Field Office in disseminating the Guidelines on Energy Conserving Design of Buildings through its Information , Education ,and Communication Campaign (IECC) in implementing the country’s Energy Reform Agenda.)
Climate change has been an issue affecting human all over the globe today. It affects all spheres of human life –social , economic , political , cultural , and other personal human activities . Evident enough in the climate patterns , unstable temperature and its threat to human comfort , trigger challenges on creative ways for possible recovery of the lost resources of the earth in order to restore a greener earth and a bluer sky. Alternative approaches for a clean energy , reduction of carbon emission, new technology on renewable energy ,and the like ,continuously evolve. Information, education, and communication campaign has always become a program of private and government institutions.
Architectural edifices in the Philippines are not excluded from the phenomena. On – going challenges in building designs confront architects , and allied professionals to design buildings that are considered “green”. Creative approaches are openly called for effective design models. Energy efficiency and conservation in building designs are also the current focus and priority for a more functional facility and with the use of sustainable resources. Hence , building components are affected by the disastrous effects of climate change , - structural framings and foundation has to consider earthquakes; roofing and wall materials needs to resist heat ; openings and other innovative designs shall be provided with air and light ventilation and; and
vegetations or shrubberies for landscape entourage can be effective means for carbon sequestration or give its share in the carbon sink.
Eventually, these primary points will contribute in the change of cityscapes on Philippine architecture when building designs shall exploit obtainable and existing potential sources of energy .The use of natural light and air ventilation is significant enough to influence an impact in the conservation of energy. In addition, benefits of natural ventilation are numerous enough – from low maintenance and consumable cost, less hygiene problems, and psychological benefit of connectedness to nature. Architects , engineers and allied professionals are duty-bound to put into effect climate-adaptive designs and building technologies that will benefit clients , the community and stakeholders of the profession.
One of the concerns in celebrating the WDA is that, “Architects will play a crucial role in evolution by their capacity to meet the challenges of global urban sustainability and develop the tools needed to create resilient and sustainably liveable cities.” Further it is moving towards
“mitigating climate change, reducing polluting emissions, and better management of resources and energy.” Further , it aims for the structuring of cities ,to be socially inclusive , accessible and equitable , eliminating discrimination and precarious housing ; developing cities that can resist crises and cataclysms, whether natural or induced by man ; developing economic, educational and creative opportunities for all; and ensuring the security and sanitary conditions vital to all individuals. The following are noteworthy information, principles and concepts highlighting some salient provisions from the DOE Guidelines on Conservation on Building Designs (DOE-GECDB). Understanding these matters could help architects address issues confronting climate change by putting into concrete practice Passive Control approach as they integrate them in the design of buildings and other related architectural projects.
The Philippine Climate
According to Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA), Philippines have a Tropical Rainforest Climate with two (2) seasons – wet and dry. Dry season starts mid- November and ends up to mid of May. Cool and ocean breezes start on November up to the end of February. March to May as the hottest month and followed by a wet season from June to October being hot and humid. April and May has the hottest temperature from 28°C (83°F) up to 38°C (100°F) and rainfall varies but a rain year –round in most place of southern Luzon. An average temperature of 25.5°C (78°F) is during January as the coldest month.
Pagasa records there are 20 (or even more ) typhoons or “bagyos” across the country lasting for three (3) to four (4) days. Normally after downpours of heavy rain during nights and early mornings, steamy and sunny days follow on wet season.
There are 4 types of seasons: Type I-Two pronounced seasons: dry from November to April, wet during the rest of the year; Type II-No dry season with very pronounced rainfall from November to January. ; Type III-Seasons are not very pronounced; relatively dry from November to April and wet during the rest of the year. ; Type IV-Rainfall is more or less evenly distributed through the year.
The Thermal Human and Visual Comfort
The climatic condition of the country is much affecting the built-environment of any region. Due to this, thermal human comfort and good lighting or proper Illumination from natural light source in non-air conditioned buildings and spaces are called for in order to produce energy conserving architectural designs , appropriate engineering , and aesthetically sound buildings of any type –residential, commercial, religious, public and private institutions, and the like. Thermal human comfort is directly affected with solar heat , and in fact to some extent will affect indoor air quality (IAQ). Good natural light ventilation could serve good and healthy visual comfort to the user, however be noted that only with effective means of control or devices shall be provided in order to retain acceptable temperature and evade the increase of solar heat gain to create thermal discomfort.
The DOE-GECDB gives the general principles of thermal comfort. It enumerates the main variables that affect human comfort as to the following: dry bulb temperature; relative humidity or wet bulb temperature; air movement; ventilation; and thermal radiation from hot surface (ceiling, walls, and glass window). It also includes indoor air quality.These variables are significant inputs to consider in the building design process.
1. Dry bulb temperature, usually referred as “air temperature”, is one consideration in a building that is affecting the interior environment. Air temperature affects human comfort. When heat discomfort occurs , cooling is necessary. This means that the use of power or motor gadgets, equipments or appliances will depend on the heat gain accumulated within the room or space that requires high cooling requirement in hot environment. Therefore, the lower the air temperature, the less necessary in the use of these energy consuming equipments in order to cool the place. In an actual experiment in the locality of Bacolod City, outdoor dry bulb temperature marks 42°C at 1:00 pm , and for indoor bulb temperature is 33°C at 2:30 pm . An early morning indoor temperature at 6:00 am could get 27°C so far. If an indoor temperature could only be maintained at average of 27°C for the rest of daytime, possibly electric bill will become lower and shall be meaningful.
2.Relative Humidity or wet-bulb temperature , an indication of the amount of moisture in the air, is another factor to look into in achieving thermal comfort. The recommended humidity level to achieve the most comfortable environment is 40% –50 % , nevertheless, a range from 30% to 60% will also be acceptable . However ,in comparison to the DOE-GECDB , the 60% relative humidity is already the maximum for air conditioned buildings where 50% shall serve as the minimum.
3.Air movement adds another function in achieving thermal comfort in the design of building at the same time to cause energy conservation. Building orientation on the windward side where the source of wind comes from , shall be the basis of site planning. Leeward , the opposite side of the windward , is understood as a better position where the building could release hot air. Air movement in warm or humid conditions can cause heat loss without any change in air temperature.
Effective entry or inlets (infiltration for air leakage) of air could be achieved when openings of the structure are well oriented to the windward side as it gets positive wind pressure. Exit or outlets (exfiltration for air leakage) of air will always be effective when openings are also provided on the leeward side as it generates negative wind pressure. Air movement significantly contributes to air circulation inside the building in terms of air change depending on the type of buildings. Usually air change depends on , coefficient of discharge (Ce or effectiveness of opening , 0.5 -0.6 for perpendicular wind ,and 0.25 -0.30 for diagonal wind ), area of opening ,and wind velocity. Generally , a space may need (four) 4 air change per hour.
4.Ventilation -Natural light and air : Thermal comfort will always be the consideration especially in hot and humid country like Philippines. For energy conserving designs, natural ventilation could help ease the warm environment with sufficient supply of air. “In order to breathe air, a human being needs 21 % of oxygen.” When a ventilation rate drops below the level of 16.5 %, a person will lose consciousness. Interior space must be very well ventilated not only in terms air but also with light.
The DOE guideline states that “as a general rule, ventilation rate of 2.8 m3/min to 5.7 m3/min per person is adequate in practice if the average indoor air temperature rise of not more than 14 ºC is to be maintained as a result of body heat. Where power-driven and other heat sources are present, a higher ventilation rate is necessary.”
Further DOE-GECGB address the aspect on –Natural Ventilation by Window Opening:” The influence on the size of windows on the internal air movement depends to a great extent on whether a room is cross-ventilated. If a window is located on one wall of a room, its size has a little effect on the internal air velocity. However, an even distribution of windows, and the correct choices of sashes, will help to improve the ventilation even the windows are located in one wall.
Two natural air ventilation types of method could be integrated in the design process, -the stack effect, and the wind-induced method. Stack effect may only be effective when openings are available at higher heights where hot air inside the room can be released. Due to buoyancy effect hot air rises up because it is less dense than cool air.
Effectivity of cross ventilation happens when two walls are provided with openings. Even by experience, extent of its effectivity however is also affected by orientation of the building to avail prevailing winds, the shape of the structure, uninterrupted airflow from outside, and to a lesser extent, the arrangement of rooms and the position of interior partitions. No how matter a room could be well ventilated, it has to be noted that Heat Index, the human-perceived equivalent temperature, could still effect. Possibly, when the temperature is 90 °F (32 °C) with very high humidity, the heat index can be about 105 °F (41 °C).
Provisions for natural ventilation and lighting in the DOE-GECDB states that, “in natural regulations, it is specified that every building shall be provided with: natural lighting by means of windows, skylights, fan-lights, doors, and other approved natural light transmitting media; and natural ventilation by means of windows, skylights, fanlights, doors, louvers or similar ventilation openings.”
5. Thermal radiation and the Overall Thermal Transfer Value: Heat gain inside the building is always brought by thermal radiation or heat conduction received by the building envelope such as opaque external walls, glass windows, opaque roof, and skylight. An architect and his allied professionals, must have sufficient data of materials and their characteristics , mechanical or chemical properties , in order to know what materials to specify whether it could contribute or avoid heat gain by conduction of building component in terms of “U” value (a measure of how much heat will pass through a thermal object), or “R” value, (resistance to heat flow). The guidelines specify that, in the case of a non-air-conditioned building, any external wall abutting a habitable room shall have U-value of not more than 3.5 W/m2ºK.
The Overall Thermal Transfer Value (OTTV) of the building envelope determines the quality of the building whether it is energy conserving or energy efficient. Although the OTTV is normally used for air--conditioned buildings, it would be a guiding principle in the architectural design process to consider natural ventilation.
DOE-GECDB elaborates that OTTV concept means, “the solar heat gain through building envelope constitutes a substantial share of heat load in a building, which will have to be eventually absorbed by the air-conditioning system at the expense of energy input. To minimize solar heat gain into a building is therefore the first and foremost consideration in the design of energy efficient building. The architectural techniques used to achieve such purpose are too numerous to mention. Siting and orientation of a rectangular building to avoid exposure of its long facades to face east and west, for instance, is a simple means of reducing solar heat gain if the building sites permits. Appropriate choice of building shape to minimize building envelope area and selection of light colors for wall finish to reflect solar radiation are other common sense design alternatives to lower solar heat input.”
6. Indoor Air Quality: Passive design with natural air and light contributes to indoor air quality. Humidity control and ventilation already mentioned earlier are also affecting indoor air quality. Other aspects are filtration level, sanitation, and odor. Filtration level concerns with the level of respirable particle (smoke, dust, etc.) found in the place. Presence of bacteria, molds, and viruses cause sanitation problems, while unsatisfactory odors are brought by volatile organic compounds (paints, pesticides, cleaning liquids) shall be avoided. It will take effective number of air change to remove these pollutants to maintain a habitable indoor air quality.
Being “Green” and Natural
There are other attributes to describe what a Green House , a Green Building or any of its components - eco-friendly; environment friendly; sustainable building; eco–architecture; green architecture, green engineering , green technology etc...To certain extent, it can also be attributed to a “natural building” ,although it differs in terms of technology application. Buildings and houses in order to be labeled as green and natural, must always give visible effect in terms of energy conservation and energy efficiency. Green rating systems are established; standards and labeling for household appliances; energy management; energy audit; and recognition awards are advocated to promote energy conservation and efficiency. A new Enercon Law is also expected.
Sufficient definitions were already established in other venues in understanding what a green building ,a house or structure is. However, the definition by Engr. Nestor Archival may be easier to understand that could summarize the information discussed earlier. Archival, who topped the Pitong Pinoy Awards, describes a GREEN HOUSE as “the structure and the environs that shelter, protect, and nurture life. It is the habitat for safe, healthy and happy living. It is a house where one can breathe clean air; a house that is not too cold and not too warm; a house that is not too humid and too dry; a house that gets light from the sun during the day; a house that can let air move in and out as desirable; a house that conserves water and energy; a house that
was constructed with mostly local materials, some of which may be reused or recycled; a house conducive to sustainable living.”
Passive Control Approaches and Design Possibilities.
There are possible approaches in order to apply Passive control in buildings and houses. The utilization of natural resources and potential energies of the locality must be first utilized in order to avoid or lessen the use of any mechanical means of ventilation, yet retains comfort benefits to the occupant.
By professional judgement, natural light and natural air ventilation, and the Overall Thermal Transfer Value (OTTV) of buildings are closely correlated. They are symbiotic in terms of thermal comfort at the same time affecting lighting and visual qualities of space as well. This would mean that every building component as a channel of solar heat gain causing the generation of overall thermal transfer inside the building space must be given attention. This would even consider from the very start of site selection to site planning and development as part of the building design process.
In site selection, whether in the urban or rural area , off-site factors and its context are initial parameters to consider ,like wind direction and pressure , solar orientation , adjacent buildings , outdoor temperature, flood history , noise ,smell and others are essential in the design process. The location of a structure will influence much the quality of building design and an advantage for new projects especially during the pre-design phase. Energy conserving building design starts from site selection. Retrofitting may only be a solution for old buildings.Studying the Comprehensive Land Use Plan (CLUP) of a place, may help in choosing a practical building location while places adapting New Urbanism or Ebenezer Howard’s Garden Cities of Tomorrow , may benefit claims of these planning concepts in greening the structure.
In the case for site development planning, the shape of a building and its exposure to solar heat shall be given attention. Shorter side exposed to sun is best to avoid accumulation of heat through solar radiation on walls and windows. In addition, trees, shrubs, flora and of other type of vegetation that will cover the building will prevent solar heat from entering the building.
For buildings, external walls, roof, windows, skylights, are components of building envelop that determines the Overall Thermal Transfer Value. Generally, using appropriate materials with effective heat resistance from a direct solar radiation will prevent if not reduce heat gain. Type of roofing materials, innovative strategies, provisions of adequate ventilation, insulation, are crucial features of design adaptations. The use of skylights can always help save energy while harnessing the power of the sun for lighting the space.
The type of materials and performance of external walls to serve as thermal mass in absorbing thermal energy , the method of construction to be used for external walls, a well- arranged location of openings for air or wind infiltration are a productive design approaches. Installation of an appropriately -sized windows to allow natural air for cross ventilation and type of windows specified whether awning; jalousie; sliding, or maybe louvered, would help direct or redirect the
wind for proper building ventilation. Sun shading or hot daylight blocking can be introduced through window canopies , overhangs , outer screen , or trellis . In addition glass windows can prevent or minimize effects of solar radiation through glass films or interior blinds. When possible ,sunscreen shall be provided at the exterior side of windows. Much favourable technique when interior walls shall be provided with cuts in the lower portion and the same at the higher portion for hot air release and sound air circulation.
“Passive design aims to optimize the building form ,orientation ,façade design and space planning together with overall site layout to make maximum use of the natural environment in order to provide occupant comfort with minimum use of energy and mechanical systems. “
Summary and Conclusion
Passive control design may not be the ultimate answer to satisfy occupants when it comes to outstanding comfort. But, by taking full advantage of natural and renewable energy resources before using any mechanical means or any active control system to ventilate the space is a sustainable approach that would contribute in mitigating climate change, reducing carbon emissions and even to zero energy consumptions. With these issues confronting world today, architecture in the Philippines must adapt or be responsive to the climate and the immediate context of its environment. Eventually therefore, when all of these technical norms and principles given are relatively and habitually observed, Passive Design with prime considerations on natural light and air will always be one Crucial Component of Change in the Cityscape.
Truly enough , this will make ARCHITECTS AS CITY CHANGERS , indeed!
References and Suggested Readings:
Department of Energy (DOE) –Guidelines for Energy Conserving Design of Buildings-Updated 2007
DOE-National Energy Efficiency and Conservation Program (NEECP)
DOE-Energy Management and Energy Audit (PowerPoint Presentation)
DOE-Energy Reform Agenda ((PowerPoint Presentation)
UAP Memorandum Circular No. 08, S. 2012
Natural ventilation: Stack Ventilation
Cross Ventilation in House Designs for Natural Passive Air Flow
http://www.sustainability.vic.gov.au/resources/documents/Air_movement.pdf) What Rooms Do Not Require Natural Light & Ventilation? | eHow.com http://www.ehow.com/list_7597999_rooms-require-natural-light-ventilation.html#ixzz1zBEQHDXs