Six supposed reasons why openable windows are bad

By Prashant Kapoor of IFC*

We look at why offices are designed with windows that can’t open, and how we can work together towards changing this practice.

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Given the choice, most of us prefer greater control over our work environments. We want to have a breath of fresh air during the workday without having to leave the office. Since openable windows curb energy consumption, why don’t we design office buildings with windows that open?

Here are six reasons why it’s assumed that openable windows in an office building are a bad idea:

  1. They allow conditioned air to escape and unfiltered air, noise, rain and insects to enter.
  2. They are more expensive.
  3. They make the owner liable should people fall out.
  4. Employees open the windows on a hot day, forcing the air conditioner to compensate.
  5. Openable windows are unfashionable as they disturb the lines of modern architecture.
  6. Ventilation is difficult to achieve with floor plans that pack in as many employees as possible.

Increasing productivity while saving energy
Actually well-designed, naturally-ventilated buildings lead to profitability. They can cut the energy of air-conditioned buildings in half, as they don’t suffer from energy-intensive HVAC systems.

Access to fresh air also results in better employee outputs. Natural ventilation can increase productivity by up to 11%, 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, 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.

How much energy

In most Asian cities, openable windows with A/C shut-off can save 5-14% on energy consumption. The EDGE app shows that complementing openable windows with a simple passive design package can increase savings to 20-30%.

Throwing the windows wide open
Below are a few practical technologies that can be applied to almost any office building.

Window switch: This inexpensive device is 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%.

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: Since 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 night-time 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 capex of 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 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 that offer a perceived cooling effect of up to 5.6°C, 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.

About the author
Prashant Kapoor is the principal green building industry specialist for IFC, a member of the World Bank Group that focuses on private sector development and the inventor of EDGE certification.

 

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