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| High rise buildings in Shenzhen China |
I still remember the draughty, chill of the air-conditioned “computer room”. It was thought that computers couldn’t possibly survive the heat and dust of India without climate control as they might get damaged internally. I am also old enough to remember when most office buildings were naturally ventilated, even in sultry Madras. The offices were filled with stacks of papers anchored from the outside breeze and indoor fans by paperweights.
In a span of just 20 years, offices in tropical Asia have changed from offering windows that open to air-tight spaces that are fully air-conditioned. Air-conditioning as an engineering technology is, of course, miraculous and amazing! It delivers, with no nonsense or fuss, dry air and constant temperature which teleports us from the tropics to the alps in an instant. It’s not surprising therefore that Lee Kuan Yew, Singapore’s first Prime minister, who transformed the tiny outpost into one of Asia's wealthiest, singled out the air-conditioner as the most important invention in boosting Singapore’s economy.
Mumbai architect and Professor at Harvard University, Rahul Mehrotra, has a different viewpoint. He believes that this trend towards glass-walled air-conditioned skyscrapers, which he calls the “architecture of impatient capital”, is the product of investment capital that wants fast predictable returns from speculative construction. This commodities architecture has little time or patience for subtle climatic design and openable windows.
The truth is that given the choice, most of us would prefer greater control over our work environments, including the opportunity to prop open a window. Since openable windows actually curb energy consumption, there’s no reason to insist that they be sealed shut. So why don’t we design our work places with windows that open? And what will it take for us to get a breath of fresh air during the workday without leaving our offices to do so?
Why They Don’t Make Office Buildings with Openable Windows?
In the words of Isaac Asimov, “Your assumptions are your windows on the world.” Here are some reasons why it’s assumed that open-and-close windows in an office building are a bad idea:
Openable windows have become unfashionable and interrupt the cool lines of modern architecture. They are assumed to be more expensive than sealed glass facades. They make the owner liable should things or people fall out and allow air, noise, rain and insects to enter. It is also easier to design sealed air-conditioned environments, where a designer doesn’t have to account for employees that could open the windows on a hot day.
Investors would like deep floor plans that pack as many employees on one floor as possible making cross ventilation, interior courtyards and light-wells difficult to achieve.
Saving Energy While Improving Comfort and Productivity
In actuality, well-designed, naturally-ventilated buildings lead to profitability in many ways. They have the potential to cut the energy use of air-conditioned buildings in half.
Access to fresh air also results in better employee outputs. Natural ventilation can increase productivity by up to 11 percent, showing that the profitability of a building’s design can be tied directly to the workforce inside. There’s also the satisfaction derived from self-assessed productivity and the perception of control according to Adrian Leaman and Bill Boardass, as well as a deeper connection to the outdoors.
In addition to a sense of well-being, employees in naturally-ventilated buildings are healthier. One study shows employees in air-conditioned buildings display a greater rate of negative health impacts than those that work in naturally-ventilated buildings.
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| Analysis using free online EDGE APP |
9 Practical Technologies That Can Bring Back Openable Windows in Offices.
Much has been written on ventilation design concepts such as double-skin façade, biomimicry, stack effect ventilation, Venturi effect ventilation, segmented atriums for skyscrapers, solar chimney and passive own draught ventilation. While these are inspirational ideas for “aggressive” passive architecture, they don’t provide easily implemented solutions to the challenges of today’s designers in Asia, where most buildings are built.
Let’s look at some of the more practical technologies that can be applied to almost any high rise office building in order to design a façade with windows that open:
1. Window Switch: This inexpensive device is integrated into the HVAC system, preventing wasted energy from employees opening windows at inopportune times. When the HVAC system senses a particular window is open, the cooling air supply to that zone turns off, allowing ventilation and the temperature to float. A similar “on-again, off-again” approach is a “traffic light” system that informs employees when it’s a good time to open the window. Studies have shown that these kinds of devices can save on annual energy costs by 40 percent.
2. Powered Window Actuators: We have them in cars, so why not in buildings? Taking measurements of various conditions inside and outside a building, such as wind speed, dust particulate volume, and temperature levels, sensors can be programmed to open vents automatically at various positions to suit specific conditions. These devices are cost-effective, as a single sensor can control a number of vents.
Window actuators allow a machine-based approach to open windows when conditions are ideal or when the building’s design prevents human access to hard-to-reach vents. By introducing a simple device with a programmed algorithm, the efficiency of the HVAC system can be instantly improved.
3. Monsoon Windows: For office buildings in the tropics, windows have to be closed when it rains heavily, which results in shutting off airflow. With monsoon windows, a rain sensor closes windows when it rains, however, there is still airflow into the interior.
4. Full fresh air mode: just like with cars where one can turn off the AC and have the fan on outside air mode left on, the mechanical systems in offices can be designed to have a ‘full fresh air’ mode. The windows can, of course, be left open to flush out internal heat gains and humidity.
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Hybrid Modes of an Office Building in Masdar City, Abu Dhabi. Source: WSP Group, UK
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5. Night Ventilation Cooling: In the sub-tropics, where the outdoor temperature in the evening is generally lower, night ventilation (also called “night-purge ventilation” or “night flushing”) is an effective approach by which the cool outside air helps reduce the heat accumulated in the exposed building structure. Windows can either be left open manually or automated to open after the occupation period to provide night-time cooling.
A structural slab ventilation system (such as offered by TermoDeck) can help store the cooler night-time temperature in the thermal mass of the building for the following day.
6. Noise Cancellation Design: Openable windows are only possible in certain urban settings when noise cancellation has been considered in the design process. The Sun Ship building in Freiberg, Germany has double wall layers with a staggered vertical air inlet and outlet. The front-facing side has a grill and weatherproofing and a large ventilation panel (watch a video of the ventilation concept). Baffles allow the panel to be opened during the day with minimum noise penetration.
Such double-wall plenum structures can be combined with other mitigation measures, such as sound absorbers and active noise control, for enhanced performance. Air-quality sensors paired with actuators can control external noise as well as pollutants within the occupied space.
7. Insect Screens: Insect screens are desirable for open windows in the tropics where serious illnesses are spread by insects. Smooth, rounded wires or threads forming the mesh of insect screens have non-linear resistance to airflow, with resistance actually higher at lower wind speeds. Where insect screens are placed close to openings there may be difficulty operating certain types of sashes, but magnetically held screens are now available.
8. Slimmer Plan Depth: Before the advent of air conditioning and electric lighting, office buildings in New York City were designed with deliberately narrow U, E and H-shaped floor plans to facilitate daylight and natural ventilation. Today, the Royal Institute of British Architects recommends a floor plan depth of no more than 15 meters in order to take advantage of cross ventilation. Similarly, the Netherlands has strict regulations on access to natural light and outside views in workplaces, which require buildings to be designed with narrow plan depths.
A ratio of greater surface to floor area will increase the capex of an office but with a significant potential for lower running costs and higher worker productivity, which can be marketed at a premium. Narrow buildings with natural ventilation are also less negatively impacted by times when ventilation systems are inactive (such as power outages), as they are less dependent on daylight and artificial cooling.
9. Ceiling Fans: In a study on the cooling effect and energy-saving potential of ceiling fans, Professor Steven Szokolay shows that the combined approach of openable windows and ceiling fans in Asian offices can significantly delay resorting to air conditioning. The Infosys office in Hyderabad, India has openable windows and ceiling fans that offer a perceived cooling effect of up to 5.6°C, enabling the building manager to adjust the thermostat higher while maintaining thermal comfort.
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| Infosys Building for Software Development in Electronic City, Bangalore Source: McD BERL |
Perception of Style and Comfort
Beyond technology and design, if openable windows and natural ventilation are to have a significant impact on energy consumption and thermal comfort, our preconceived notion of comfort and style will need to be rethought.
A comparative study of two office buildings in Bangkok one with AC and other without, shows that the offices with natural ventilation were comfortable with temperatures up to 310C. In fact, field research across multiple countries has shown that the human sense of comfort is closely linked to the outdoor temperature and not a constant 240C + 20C. We could save a lot of cooling energy and provide more comfort by linking algorithms to the program of Building Management Systems (BMS) to link the internal temperature settings to the outside temperature.
One wouldn’t dress in a Burmese longyi or to Arabic thawb to play a football game so why do we wear suits derived from British Victorian era to offices in warm and humid Asia? Clothes act as an insulation material and reduce the body’s heat loss. Therefore, the more appropriate the clothing for the climate, the higher the office temperature could be set at. In response to this, some governments are trying to raise awareness and mandate behavioural change. For example, governments in both Japan and Pakistan are mandating office workers to dress down, ditching their suits and ties for open-necked, short-sleeved shirts-instead of carrying sweaters to protect themselves from over-chilled air.
Opening the Window of Opportunity
In the past, we expected perfect comfort from naturally ventilated buildings which was unrealistic and pretty impossible in most parts of the world. However, with the realization that an Asia with a future full of gas-guzzling, impenetrable office buildings will seal our collective destiny towards a 6-degree warmer world it may be time to be realistic about what natural ventilation can effectively deliver through good design and innovation.
In the quest for modern buildings in tropical Asia to achieve better building performance, a hybrid practice needs to emerge based on the array of options available that blend mechanical and natural ventilation. Designing ‘intentional’ mixed mode buildings with openable windows but being mindful of noise, dust and insects, unpredictability and safety of the users of the building. These “mixed mode” buildings can pioneer a market shift, wringing all of the advantages from natural ventilation while responding to what occupants want and need most. And that ultimately means offering an option that we all crave – the opportunity to get up from our desks and simply open the window.
