Responsible for a whopping 39 percent of US carbon emissions, buildings are silent contributors to climate change.

Surprisingly, researchers think the solution to these emissions lies in the ocean.

A new study funded by the Ministry of Economy and Competitiveness of the Spanish Government found that the tuna’s metabolism could serve as a model for how the layout of modern buildings can disperse human body heat in more efficient ways, decreasing fossil fuel use. The “tuna model” is an example of biomimicry, the design of systems and materials based on examples found in nature.

Conducted by researchers and architects as part of the Redesign of the Integration of Building Energy from Metabolisms of Animals (RIMA), the study modeled the annual heat generation, heat loss, and total energy use of two different floor plans within the same building—the Gamesa Headquarters in Pamplona, Spain – in three different climates. Simulations found that the rearrangement of office building floor plans in favor of the tuna model can save 16-39% of building’s annual energy demand. That’s huge.

Why does the tuna model reduce energy demand? Some species of tuna can regulate their interior temperature so efficiently that their bodies can be warmer than the water around them — often by 10 degrees Celsius. It is unusual for fish to be so warm because their heat usually escapes through the gills before the rest of the body can be warmed.

The anatomy of a tuna. The dark muscle encircles the spine.
Credit: http://www.fao.org/fishery/topic/16082/en

However, a tuna avoids this heat loss through a process know as “countercurrent heat exchange”. The tuna’s heat is generated within dark muscle, a long strip of red muscle that runs along both sides of the spinal column.

This muscle has a complex vascular system where blood flows in arteries and veins that are in close proximity and are parallel to each other. The heat generated by the muscle warms the blood, and its excess heat is transferred to the cooler blood returning to the muscle before the warmer blood reaches the gills. Thus, this process allows heat to be efficiently transferred and retained within the tuna’s body rather than be lost to the exterior environment.

Illustration of countercurrent heat exchange process.
Credit: RIMA study

How can this help us design more efficient buildings? In the study, enclosed spaces like offices or meeting rooms functioned as a building’s “dark muscle”; the more people that are in a room, the more heat is generated. That heat, especially when combined with heat given off by lighting fixtures and building machinery, can add up. Tapping into the natural heat generation of the human body decreases the building’s demand for external heat (often generated by fossil fuels) and the building’s total energy footprint.

What the tuna teaches us is that the key to maximizing body heat retention in buildings lies with the placement of these enclosed spaces.

In most office buildings, private offices and meeting rooms are located along the perimeter of a floor, near the windows. This layout, while desirable for its office views, is energetically problematic because the valuable body heat generated within them is likely to escape through the window before it can heat other areas of the floor – just like heat escapes through a fish’s gills.

The two floor plans modeled in the simulation. The tuna model (a) features closed office spaces placed together in the central ring, and the average office layout (b) features decentralized office spaces.
Credit: RIMA study

In the tuna model, however, the office spaces and meeting rooms are placed in a centralized ring around the interior core of elevators, just like tuna’s muscle wraps around its spine. Placing the offices in close proximity to each encourages a countercurrent heat exchange to take place. As expected, the tuna model resulted in more efficient use of the building’s internal heat, while the decentralized office layout exhibited greater demand for heat and total energy.

Using the metabolism of the tuna as a model for the energy systems of buildings has major implications for the way humans think about and interact with their built environment. While sustainable construction materials like living concrete and biomimetic building exteriors are important steps down the path towards a greener and cleaner city, they do not incorporate human services into the equation. With the tuna as our guide, perhaps we can swim against the tide of climate change and design cityscapes with both humans and nature in mind.