Avoid a high-energy cold crunch with more efficient cooling

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As temperatures are expected to rise worldwide, power grids can be overwhelmed by inefficient cooling systems. PNNL researchers developed a more efficient cooling technology that reduces energy consumption. Image by Wang An Qi | news
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Texas Frontier Business

By Kelsey Adkisson

Newswise – When the temperatures rise, the air conditioners turn on. Cooling costs a lot of energy – this puts a strain on the power grid and drives up emissions in countries that are still dependent on fossil fuels.

Almost 20% of the electricity consumed worldwide is used to cool buildings. Unchecked, this number could triple by 2035. One solution: develop technologies to make cooling more efficient.

Researchers at the Pacific Northwest National Laboratory (PNNL) are developing an alternative cooling technology that uses adsorption (with a “d”) – the attachment and release of refrigerant compounds by an adsorbent material. In search of various nanoporous materials as adsorbents, researchers turned to covalent organic polymers (COPs). COPs can absorb three times more refrigerant than the best available alternatives, resulting in more efficient cooling.

But the story of how this latest discovery came about is somewhat unexpected. Small defects in the material increased the adsorption in a completely imperfect way.

“It was unusual – you know? We knew something inexplicable was happening with our results, but we didn’t know exactly why, ”said Radha Motkuri, a PNNL chemical engineer who led the study, which was selected as a HOT article and featured in the top 10 publications in applied Chemistry.

Future demand for electricity is expected to increase, and air conditioning is already consuming a lot of energy. image by Demian Cher | news
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More efficient cooling … accidentally

Some of the world’s great discoveries were made by chance, such as nylon, the invention of the microwave, or even shatterproof glass. When it came to cooling, a few small glitches led to great insights.

For the past decade, Pete McGrail, a PNNL Laboratory Fellow, and Motkuri and their team have studied materials that are more efficient at adsorbing common refrigerants used in their adsorption cooling technology. You have made great strides in developing various types of porous materials that contain refrigerants. However, they thought there might be unexplored potential in other nanoporous materials, including COPs.

“As the climate problem continues to grow, it is imperative to find ways to reduce energy consumption, for example through alternative and more efficient cooling,” said McGrail. “This research builds on our cooling technology that won the R&D 100 Award in 2017.”

Polymers are used in all walks of life, from shampoos to spacesuits. They can be combined with other elements for different purposes – in combination with carbon, for example, they can be processed into polyester and nylon.

The team tested 23 different COPs to determine their potential for adsorption chilling or chilling. Most had a plateau with low adsorption capacities, which means that they could no longer adsorb and were maxed out. But two not – the adsorption increased. And kept climbing.

“We thought there was something wrong with the device when we tested the adsorption capacities. The rates were much higher than we expected, ”said Motkuri.

So they tried again. They got the same results. Two compounds, named COP-2 and COP-3, had sky-high adsorption capacities. They were so high that they exceeded the researchers’ expectations. So Motkuri turned to a colleague in France, Guillaume Maurin of the University of Montpellier, who has experience in molecular simulations, to predict the adsorption of these two polymers.

Like a slinky, COP-2 and COP-3 are chemical rings made of carbon and nitrogen, all stacked on top of each other. They had to unpack each layer to see how this affected adsorption.

Oddly enough, the simulated COP-2 and COP-3 structural models did not result in the adsorption values ​​they saw on the bench. In the simulations there was an adsorption plateau. In the lab, however, it climbed exponentially.

“That’s when we noticed that something else was going on,” said Motkuri. “And our team had an idea.” Based on previous work, the researchers knew that small defects play an interesting role in adsorption. “What if we added defects to these COP structural models in the simulation?”

Defects that are anything but defective

Maurin and his team used simulations to create tiny holes or defects in the material by removing some of the chemical features from the rings.

“That’s when we saw something magical happen,” said Motkuri. The adsorption increased and the adsorption for the severely defective polymers agreed with the laboratory results.

They found that strategic defects increase adsorption in COPs, which explains the increased rates they saw in the laboratory.

“Two of the COPs that we tested in the laboratory had defects initially,” said Maurin. “Sometimes it works, even if something unexpected happens.”

Why is efficient cooling so important for the climate?

Cooling is not only used for comfort on hot summer days. Extreme heat is a deadly health hazard. As global temperatures rise, some populated regions may become too hot to be habitable at certain times of the year.

In addition, it is expected that future electricity demand will increase and that air conditioning will already consume a lot of energy. In 2019, 8.5% of US electricity consumption was from air conditioning, according to the International Energy Agency. Electricity grids around the world can become overloaded as the number of cooling systems increases, populations grow and incomes rise, so more people can afford air conditioning.

This becomes especially important in areas where energy does not come from green sources. Air conditioning is expected to increase significantly in countries where it is currently less common, such as Indonesia or India.

Powerful air conditioning systems could cut the energy required for cooling in half. Developing technologies for more efficient cooling is an important goal, especially as the amount of energy required for cooling is expected to triple over the next three decades. Developing technology for more efficient cooling can help alleviate the challenges of a rapidly warming world.

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