Greener air conditioning for a warmer world

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Jul 28, 2022

(News from Nanowerk) When the summer heat arrives, air conditioners turn on and demand for energy skyrockets, putting a strain on the grid. In a warmer world, more efficient cooling options will play an important role in curbing rising energy demands related to cooling. This will be especially true for the nearly 80% of the world’s population living in countries around the equator, where even small increases in temperature could be life-threatening.

New research from Pacific Northwest National Laboratory (PNNL) provides a roadmap outlining how more efficient cooling systems are achievable with industry development and support. The guest research study was published in the journal, Chemical research accounts (“Manipulation of pore topology and functionality to promote fluorocarbon-based adsorption cooling”).

A warmer world means increasing reliance on energy demands related to air conditioning and cooling. Researchers at Pacific Northwest National Laboratory are studying the many facets of adsorption cooling, which offers a more energy-efficient option for cooling systems. (Image by Shannon Colson | Pacific Northwest National Laboratory)

“Right now it’s basic science. However, it could be a game-changer for the industry,” said Radha Motkuri, PNNL chemical engineer and corresponding author.

The chemistry of cool

Motkuri and the research team looked at an approach that could offer significant energy savings: adsorption cooling. These systems can operate with small amounts of waste heat from a building or industrial plant to power reactions between a vaporous refrigerant and a solid material.

“Once we got the power in the first time, that’s it,” Motkuri explained. “Then the system continues to cycle – adsorption, desorption, adsorption, desorption – with very little energy.”

This is in direct contrast to conventional cooling systems which use a compressor and require regular inputs of energy.

cooling systems In adsorption cooling systems, vapor refrigerant molecules (the guest) are adsorbed into the nanopores of a solid material (the host). Motkuri and co-workers investigated how changing nanopore geometry (pore engineering) and the rate of host-guest chemical interactions affect the cooling capacity and energy efficiency of adsorption cooling systems. (Image by Rose Perry | Pacific Northwest National Laboratory)

Tuning an adsorption cooling system to achieve ideal cooling capacity and energy efficiency requires understanding the complex chemistry between the system’s vapor refrigerant, called the guest, and the solid absorbent material, called the host. Motkuri and his collaborators delved into these details — adjusting the pore geometry of the solid sorbent, the rate of chemical interactions, and even the impact of tiny defects in the solid material — to understand how they affect the whole system. Recently, the team was asked to compile their work into an effective package that can help developers in the cooling industry try to meet the demand for more energy-efficient options.

“Refrigerant-based adsorption cooling eliminates key cost, efficiency and reliability issues that have limited the adoption of current water-based adsorption cooling systems in commercial and residential buildings,” said Pete McGrail, lab researcher and chemical engineer who led PNNL’s adsorption cooling effort. for several years. “This journal article represents a summary of years of research into new sorbent-refrigerant pairs that have significantly advanced adsorption cooling technology.”

Environmentally friendly components

With increasing global heat waves and cooling energy demands expected to triple by 2050, there is a push for cooling systems with smaller environmental footprints. In addition to more energy-efficient systems, this includes changing standards for refrigerants.

Commonly used hydrofluorocarbon refrigerants will be phased out over the next few years in favor of more environmentally friendly hydrofluoroolefins (HFOs). HFOs have a global warming potential close to zero, which means that HFO emissions trap much less relative heat in the atmosphere than hydrofluorocarbon refrigerant emissions.

Aware of this transition, Motkuri and his collaborators conducted their tests using the cheap and readily available hydrofluorocarbon refrigerant, R-134a. This hydrofluorocarbon refrigerant has a high global warming potential, but similar chemical behavior to HFOs, making it a suitable alternative for studying the molecular interactions of adsorption cooling systems that will use HFOs in the future. Researchers are eager to incorporate HFOs into future adsorption cooling research as the next step in green cooling systems.

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