The case for office buildings with windows that open
Naturally ventilated facilities not only help cut air-conditioning usage, they are directly linked to improved employee productivity.
Over the past 20 years, offices around the world have changed from offering windows that open to air-tight spaces that are fully air conditioned.
Given the choice, most of us prefer greater control over our work environments. Because openable windows curb energy consumption, why don’t we design skyscrapers with windows that open? And what will it take to get a breath of fresh air during the workday without having to leave the office?
Here are six reasons why it’s assumed that openable windows in an office building are a bad idea:
- They allow conditioned air to escape and unfiltered air, noise, rain and insects to enter.
- They are more expensive.
- They make the owner liable should people fall out.
- Employees open the windows on a hot day, forcing the air conditioner to compensate.
- Openable windows are unfashionable as they disturb the lines of modern architecture.
- Ventilation is difficult to achieve with floor plans that pack in as many employees as possible.
Increasing productivity while saving energy
In actuality, well-designed, naturally ventilated buildings can cut the energy of air-conditioned buildings in half, as they don’t suffer from energy-intensive heating, ventilation and air-conditioning (HVAC) systems.
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 to the workforce. There’s also the satisfaction derived from the perception of control (PDF), as well as a connection to the outdoors.
In addition to well-being, employees in naturally ventilated buildings are healthier. One study shows workers in air-conditioned buildings have greater negative health impacts than those that work in naturally ventilated environments.
Throwing the windows wide open
Here are a few practical technologies that can be applied to almost any office building:
- Window switches — These inexpensive devices are integrated into the HVAC system, preventing wasted energy from employees opening windows at inopportune times. When the system senses a window is open, the cooling air supply to that zone turns off. Window switches can save on annual energy costs by 40 percent (PDF).
- Powered window actuators — We have them in cars, so why not in buildings? Taking measurements of various conditions, such as wind speed, dust and temperature levels, sensors are programmed to open vents automatically. They are cost effective, as a single sensor can control multiple vents.
- Night ventilation cooling — Because the outdoor temperature in the evening is generally lower, night ventilation uses outside air to cool down the heat accumulated in the exposed building structure. Windows can be left open manually or automated to provide nighttime cooling.
- Insect screens — Insect screens are desirable for windows in the tropics where illnesses are spread by insects. Smooth, rounded wires or threads forming the mesh of insect screens have non-linear resistance to airflow, with resistance higher at lower wind speeds.
- Slimmer plan depth — A ratio of greater surface to floor area will increase the capital expense related to an office but with significant potential for lower running costs and higher worker productivity. Narrow buildings with natural ventilation are less negatively impacted by times when ventilation systems are inactive (such as power outages), as they are not as dependent on daylight and artificial cooling.
- Ceiling fans — A study on the cooling effect and energy-saving potential of ceiling fans (PDF) shows that combining openable windows with ceiling fans delays resorting to air conditioning. For example, the Infosys office in Hyderabad, India has openable windows and ceiling fans (PDF download) that offer a perceived cooling effect of up to 5.6 degrees Celsius, enabling a temperature increase in the workspace while maintaining comfort.
In the quest for buildings to achieve better performance, a practice needs to emerge that blends mechanical and natural ventilation. These "mixed mode" buildings can pioneer a market shift, saving energy costs while responding to what occupants want most. And that ultimately means offering an option that we all crave — to get up from our desks and simply open the window.