Passively Cooled Building Inspired by Termite Mounds
Image: Aftab Uzzaman / Flickr / CC BY SA – Creative Commons Attribution + ShareAlike
Protect From Temperature
Many living systems function best within specific temperature ranges. Temperatures higher or lower than that range can negatively impact a living system’s physiological or chemical processes, and damage its exterior or interior. Living systems must manage high or low temperatures using minimal energy, which often requires controlling responses along incremental temperature changes. To do so, living systems use a variety of strategies, such as avoiding high or low temperatures, removing excess heat, and holding heat in. Insulation is a well‑known example of managing low temperatures by retaining heat using thick layers of hair, fur, or feathers to hold warm air next to the skin.
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Sense Temperature Cues From the Environment
Some living systems use their ability to perceive temperature to find prey or avoid predators, or as a way to gain information about their environment, such as whether they are near a warm or cold place. Temperature gradients can be subtle and modulate as they travel through water, air, or solids. Living organisms must therefore have a variety of thermal sensors appropriate to a given medium (liquid, gas, solid). Some even have a way to “visualize” a signal’s source. For example, the rattlesnake has heat sensors with thousands of nerve endings located in pit‑shaped holes on each side of its face. The sensitivity of the pits overlaps, giving the snake a bifocal image of the heat’s source.
The Eastgate Center designed by Mick Pearce uses passive and energy‑efficient mechanisms of climate control to cool residents.
- Reduced costs
- Energy saving
- Passive cooling
- Commercial and residential buildings
UN Sustainable Development Goals Addressed
Goal 11: Sustainable Cities & Communities
The climate of Harare, Zimbabwe usually requires buildings to be cooled year-round. This means the purchase, installation, and maintenance of a traditional air-conditioning system for a building has immediate and long-term costs. The challenge was to create a self-regulating ventilation system that would keep a building at temperatures that are comfortable for workers and residents.
The Eastgate Centre is a shopping center and office building located in Harare, Zimbabwe. Rather than using a traditional fuel-based air-conditioning system to regulate temperature within the building, the Eastgate Centre is designed to exploit more passive and energy-efficient mechanisms of climate control. The building’s construction materials have a high thermal capacity, which enables it to store and release heat gained from the surrounding environment. This process is facilitated by fans that operate on a cycle timed to enhance heat storage during the warm daytime and heat release during the cool nighttime. Internal heat generated by the building’s occupants and appliances also help to drive airflow within the building’s large, internal open spaces, as it rises from offices and shops on lower floors toward open rooftop chimneys. Various openings throughout the building further enable passive internal airflow driven by outside winds. These design features work together to reduce temperature changes within the building interior as temperatures outside fluctuate. The $35 million building saved 10% on costs up-front by not purchasing an air-conditioning system. Rents are less expensive in this building compared to nearby buildings because of the savings in energy costs.
At the time of the building’s design, researchers had proposed that termite mounds maintained stable internal climates by having a physical structure that enables passive internal airflow. While subsequent research on termite mounds has altered our understanding of the function of mound structures, the Eastgate Centre still achieves a controlled internal climate with the help of cost-effective and energy-efficient mechanisms originally inspired by termite mounds.
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A schematic showing the natural ventilation used in the Eastgate building in Harare.
It was previously thought that termite mounds functioned to continuously maintain the nest’s internal temperature within a narrow range in the face of extreme outside temperature fluctuations. However, the most recent published research on termite mounds suggests that they function much like mammalian lungs and act as accessory organs for gas exchange in the underground nests. During the day, changes in internal nest temperature are less extreme than changes in outside temperature, but over the course of a year, nest temperature does vary and closely follows the temperature of the surrounding soil.