Can we cool buildings without overheating the planet?

Before the proliferation of air-conditioners (ACs), a main task of architecture was to create enclosures that befit its specific climate.

In tropical regions, this translated to wide openings that invite breeze, coupled with overhanging roofs that could shelter against hot sun and rain; subtropical climates relied on thick walls that could keep out the cold during winter and prevent radiation during summer; desert buildings insulate the interiors to withstand extreme variations in temperature; and so on.

With the advent of air-conditioning, modern buildings around the world were able to take on many different forms and expressions that were no longer climate-specific. But climate change is about to disrupt this.

A double-edged problem

The latest severe heatwaves around the world have rendered ACs less effective; yet paradoxically, the more we use ACs, the more its refrigerants like hydrofluorocarbons (HFCs) and hydrochloroflourocarbons (HCFCs) will be released into the atmosphere and worsen the greenhouse effect.

The most commonly used split ACs that use an indoor and an outdoor air unit connected by pipes utilize HCFC-22 and HFC-410 as refrigerants, but both of them are characterized by a very high global warming potential score up to 2,256—meaning that they trap up to 2,256 times more heat than carbon dioxide over 100 years. Urged by the Kigali Amendment to the Montreal Protocol, manufacturers are looking for alternative refrigerants with lower global warming potential scores, such as HFC-32. However, with a global warming potential score of 771, HFC-32 still poses a significant climate hazard. High energy consumption is another problem, as ACs make up around one-tenth of all electricity usage—which is still reliant on fossil fuels in many parts of the world.

Extreme heat events are likely to increase in severity and frequency in years to come. Since the modern world is already populated by buildings that rely heavily on AC—with a predicted tripling of space-cooler demand by 2050—it is necessary to find solutions for more sustainable air conditioning, be it those that are energy-saving or have less impact on the atmosphere.

Can propane be a more sustainable cooling solution?

Many companies and industry associations are actively pushing for innovations to lower the energy consumption of ACs (read more in the full article of “The Sky as a Source of Cooling” in FuturArc 2Q 2022). On the refrigerant side, a new study has found that switching to propane as a refrigerant might lessen the global temperature increase from cooling.

Pallav Purohit, a researcher at the International Institute for Applied Systems Analysis (IIASA), in collaboration with researchers from the United Nations Environment Programme (UNEP) and the University of Leeds, showed that by switching to propane—an alternative low (<1) global warming potential refrigerant for space cooling—we could avoid a 0.09-degree Celsius increase in global temperature by the end of the century, thereby making a significant contribution towards keeping the global temperature rise below 1.5 degrees Celsius.

“Propane exhibits significant environmental advantages through good energy performance and a global warming potential of less than 1. In split ACs up to 7 kilowatts, propane can be classified as a technically valid alternative to HFC-driven split-ACs,” said Purohit.

In the study published in Proceedings of the National Academy of Sciences of the United States of America (PNAS), researchers used the IIASA Greenhouse Gas–Air Pollution Interactions and Synergies (GAINS) model to compare the baseline halogenated refrigerant emission scenarios with scenarios of switching to HFC-32 or propane. While the switch to HFC-32 also lessened the global temperature increase (0.03 degrees Celsius by the end of the century), propane proved to be the superior solution in terms of sustainability.

Energy-efficient split ACs that use propane are already available commercially in the Chinese and Indian markets. Despite performing similarly to split ACs using HFC-32, and even better than the currently widespread appliances using HFC-410A and HCFC-22, some national regulations prohibit their use, primarily due to standards and codes restricting the use of refrigerants with higher flammability, hindering their wider adoption.

“To achieve the ambitious 2050 climate neutrality targets, early and aggressive action is needed. In the short term, converting new air-conditioning systems to more environmentally-friendly refrigerants can reduce their climate impact significantly, underlining the urgency of updating standards for policymakers,” concluded Purohit.

For architects and built environment practitioners, selecting options with less impact on the climate—as well as continuing to implement passive measures to condition our thermal surroundings—may be the way to future-proof our current and upcoming buildings.

References:

Purohit, P., Höglund-Isaksson, L., Borgford-Parnell, N., Klimont, Z., Smith, C.J. (2022). The key role of propane in a sustainable cooling sector. Proceedings of the National Academy of Sciences (PNAS)  119 (34) e2206131119. DOI: 10.1073/pnas.2206131119 [pure.iiasa.ac.at/18153].

https://ag.arizona.edu/oals/ALN/aln36/Etzion.html

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