Passive Cooling: It Can Be Done Without Air Conditioning

When the sun’s rays ‘ignite’ the earth and scorch everything on it for days, and heat waves raise temperatures several degrees higher than the usual maximum, apartments, houses, and business spaces can be cooled without air conditioning – through passive cooling. Passive cooling includes underfloor heating, heat pumps, ice storage, and modern systems for cooling and heating based on renewable energy sources, as well as smart construction from the design of new neighborhoods shaded by greenery to the use of new materials. Buildings around the world today consume one-third of the total energy used and emit 39 percent of carbon emissions, and given the increase in the world population, an increase in the share of buildings in energy consumption and carbon emissions is expected.

Air Conditioners Worsen

Scientist Alexandra Rempel from the Environmental Studies at the University of Oregon studies building design models with passive cooling without the use of air conditioning and claims that temperature can be lowered by the shade of trees, building materials, and ventilation, thereby reducing the load on the electrical grid and protecting even those without air conditioning from the heat. Additionally, passive cooling will reduce greenhouse gas emissions resulting from the burning of fossil fuels for electricity generation, which will help in the fight against climate change.

Rempel stated that it is very important to reduce dependence on air conditioning units because they, for example, consume six percent of the total electricity used in America and produce 117 million metric tons of carbon dioxide annually, and hydrofluorocarbons, the main refrigerants used in air conditioners, are among the strongest greenhouse gases.

– Cooling with air conditioning is merely an attempt to solve a worsening problem, Rempel stated, adding that passive cooling allows for heat management and does not endanger further temperature increases. She also emphasized that very high summer temperatures can be further exacerbated by the way cities are built, a phenomenon known as ‘urban heat island‘.

Tall buildings create canyons that trap heat close to the ground, and dark surfaces like asphalt absorb solar energy and radiate it back into the environment, maintaining high temperatures even at night, while activities such as manufacturing in factories, driving cars, and even operating air conditioners generate waste heat that exacerbates the problem.

Welcome Draft

Buildings heat up during the day as sunlight penetrates through windows, roofs, and walls, and at night, energy is released from asphalt, concrete, and all other surfaces that have absorbed sunlight all day. Passive cooling refers to the effective management of these radiation sources, achieved through smart construction, new materials, and green environments.

Vegetation around the building can prevent wall heating because trees not only create shade, they can lower the temperature of the surrounding air through photosynthesis. According to the U.S. Environmental Protection Agency, vegetation can lower roof temperatures by 30 to 40 degrees, and ‘cool’ roofs also contribute to cooling because covering a building with light, highly reflective materials prevents the absorption of solar heat.

If the amount of solar heat that buildings absorb during the day is limited, there will be less heat radiation from the environment at night, which is achieved through a ventilation system that starts by opening windows and creating a draft. This last point is not a new invention, but it is extremely important for high-rise buildings. The external cool night air lowers the temperature of the indoor air and cools the materials from which the building is constructed.

Invisible Players

Certain materials, such as tiles and drywall, are particularly good for this because they have high thermal capacity and require a lot of energy to raise their temperature by just one degree, which is why tiled bathroom floors are always cool, even when the rest of the apartment is warm.

– Materials are an invisible player in all of this; they can remain quite cool and be a cold barrier after heating begins again, Rempel stated.

Spaces can also be cooled with underfloor heating, a system that can cool and heat, ensuring that the temperature is always comfortable, but only with the help of a reversible heat pump that can heat and cool water in the system. There are different types of heat pumps: air/water heat pump, hybrid heat pump, ground/water heat pump, and water/water heat pump.

For example, the air/water heat pump uses external air or ventilation air as an energy source and converts energy into cold or hot, which cools or heats the water in the underfloor system. The other mentioned pumps work in a similar way. However, if the underfloor heating is connected to a central heating boiler and is not used with heat pumps, cooling is not possible because the temperature of the cooling fluid must be lower than the ambient temperature. For instance, if the apartment is at 30 degrees, the temperature of the water in the central heating system is also 30 degrees and cannot be used for cooling.

The Great Return of Ice

Ice storage systems also provide significant advantages in reducing cooling costs. A comprehensive thermodynamic and economic analysis was conducted in a commercial building in Istanbul, Turkey, to assess their effectiveness, where the cooling bill was reduced by about fifty thousand euros annually.

The return on investment for the integrated ice storage system is expected in four and a half years, and its use over ten years can save 270 thousand euros. According to this data, the ice storage system has great potential for use in heat pumps as an energy source. Additionally, it is more environmentally friendly as it does not require fossil fuels.

Studies show that passive cooling can be very effective in reducing the need for air conditioning, as confirmed by an analysis conducted in the American city of Albany, which showed that these techniques reduced energy consumption for cooling by 50 percent, thereby reducing the load on the energy grid during heat waves.

For those without access to air conditioning, passive cooling can prevent their homes from becoming uncomfortable to live in, and improved regulation can also ensure that passive cooling is available to everyone. For example, the state of Oregon requires that rental property owners must provide heat in winter, but they are not required to ensure that it is cool in summer.

Therefore, David Hondula, a professor at the Center for Urban Climate Research at Arizona State University, argues that the lack of air conditioning will negatively affect those who cannot afford it, and it is essential to increase parks and greenery in public spaces in cities, especially in heat island neighborhoods, to ensure passive cooling during hot summer days.

European Strategy

Reducing heat stress is increasingly being addressed in Europe, where temperatures are constantly rising, urbanization is increasing, and the population is aging and more health-sensitive, leading to a growing need for cooling spaces. If appropriate measures are not taken, this will lead to uncontrolled increases in the use of cooling systems and electricity consumption, as research shows that Europeans spend up to 90 percent of their time indoors.

Therefore, energy renovation of the housing stock is necessary to improve the resilience of buildings and reduce energy consumption for cooling as well as greenhouse gas emissions. Thus, key elements of the European Union’s sustainable cooling strategy include adapting to the local context, promoting urban cooling solutions, prioritizing investment in passive cooling techniques, rational and moderate use of active cooling systems, and developing low-energy cooling systems adapted to climate change.

One of the sustainability challenges facing the EU is adapting the building stock to protect the population from the effects of rising temperatures without compromising the EU’s goals for addressing energy efficiency, energy independence, and climate neutrality in a socially just manner. However, in addition to residential and commercial spaces, some have begun to cool streets as well. Vienna is a city where this is happening, and it currently has eighteen temporary and four permanent cool streets cooled by mist sprayers.

They are not traffic streets, cars do not stop or park on them, they resemble an outdoor living room, and they are cooled by the Austrian company Tech, specialized in mist technology and mist cooling, using rainwater for this purpose. High-pressure mist systems can, for example, lower the outdoor temperature by up to 10 degrees Celsius on sunny hotel and restaurant terraces or in private gardens.