The coronavirus pandemic has exposed a major weakness in contemporary building design: Conventional heating, ventilation and air conditioning (HVAC) systems require airtight buildings, which can contribute to the spread of respiratory disease. But throwing open the windows (according to public health recommendations) is difficult in very hot or very cold weather – or requires enormous amounts of energy to keep the air temperature in the comfort zone.
An international team of researchers offers a way out of this conundrum: a newly designed radiation cooling system, consisting of tubes embedded in a specialized membrane to prevent water condensation in hot and humid climates. They demonstrate the problem with conventional HVAC and the new system’s potential to solve it in a new study published in the journal Applied energy.
“We propose a different paradigm whereby energy savings and more fresh air go hand in hand,” says study team member Dorit Aviv, assistant professor of architecture and director of the Thermal Architecture Lab at Princeton University in New Jersey.
First, Aviv and her colleagues quantified the problem by modeling the energy consumption of conventional cooling systems in six American cities: Miami, Phoenix, Duluth, Chicago, Washington, DC, and San Francisco.
“Our analysis shows that increasing the outdoor air supply to meet COVID-19 guidelines in standard HVAC systems can double cooling energy costs,” said Aviv. The exact increase depends on location, with cities in mild climates like San Francisco doing best and cities in hot and humid climates like Miami doing worst.
They then analyzed climate data from 60 of the most populous cities around the world to determine cooling needs. They found that the radiant system combined with natural ventilation could keep things comfortable 80 to 100% of the time, again depending on the location.
This suggests that the new refrigeration system is a viable alternative to conventional HVAC. Many of the locations where the system has the most potential are in South and Southeast Asia, the researchers say.
In addition, the radiation system is much more energy efficient. The team’s calculations suggest that their cooling panels can reduce energy costs by 10 to 45% compared to conventional HVAC. This figure depends not only on the location, but also on how much fresh air is brought into the HVAC system. So the more external ventilation is used to reduce the risk of coronavirus transmission, the better the radiant cooling system looks.
Radiant systems can also provide effective heating while leaving windows open for ventilation, although in very cold climates, a mechanical ventilation system may be needed as a backup for part of the year, Aviv says.
And pandemic aside, the radiant system is useful because it avoids the overcooling of air often required to achieve dehumidification with conventional HVAC systems in humid climates.
“Rising temperatures due to climate change mean that more regions will experience extreme heat, making cooling systems even more important for many parts of the world,” said Aviv. “We need to approach cooling in a more energy-efficient way to stop the vicious circle of ongoing climate change with more emissions related to the energy consumption of building systems.”
Source: Aviv D. et al. “A fresh (air) view on ventilation for COVID-19: estimating the global energy saving potential by linking natural ventilation to new radiant cooling strategies. ” Applied energy 2021.
Image: Based on a photo of Preconscious Eye via Flickr.
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