Some of us can’t live without air conditioner. Aside of being not environment-friendly, ACs recirculate indoor air, which is not good during the pandemic.  

Circulating outdoor air inside is a better solution. Unfortunately, it’s not cost-effective so far. 

Probably this new technology by Purdue University engineers can change that soon. They’ve proposed a system that combines new membrane technology with the latest HVAC (heating, ventilating, and air conditioning) systems. 

It makes 100% outdoor air system more energy-efficient and not as expensive, especially in warm, humid climates. Oh, wouldn’t that be great for tropical countries like where I live? 

But anyways, the engineers say that their system could save up to 66% in energy costs for large buildings that choose to use the safer outdoor air. 

Previously, Purdue researchers found that HVAC systems are a key factor in spreading airborne diseases like COVID. That particularly happens in indoor environments like office buildings, restaurants and airplanes. 

Purdue Herrick Professor James E. Braun said, “Most people don’t realize the complexity of a modern HVAC system.  

“There’s a specific sweet spot for humidity in an indoor environment—between 40% and 60%. Any drier than that, and people aren’t comfortable; any more humid, and you’re at risk for mold and other problems.” 

Therefore, opening windows and turning off the AC is not a solution. 

“If you introduce outdoor air, the humidity levels of a building can fluctuate wildly. It’s an incredible challenge to maintain the right balance between temperature, humidity, human comfort and overall cost,” said Braun. 

According to Braun, a typical HVAC system uses 40% of the energy to dehumidify the air. That makes the heating or cooling of outdoor air even more energy-intensive and costly. 

Solving the problem using specialized membranes 

Braun teamed up with David Warsinger, an assistant professor of mechanical engineering who specializes in using membranes for water filtration and desalination. 

Together, they’ve proposed a system called the Active Membrane Energy Exchanger. It integrates specialized membranes into the HVAC system to reduce the energy required to dehumidify the outside air. 

With this, large buildings like hospitals could reduce their energy costs up to 66% with such a system, compared to current fully-outdoor air systems. 

Lead author Andrew Fix said, “The membrane is the key. We use membranes that are vapor selective, meaning they only allow water vapor to pass through when a pressure difference is applied but block air. 

“By passing the air over these membranes, we can pull water vapor out of the air, reducing the load on the motors and compressors that run the refrigeration cooling cycle.” 

To measure the system’s effectiveness, the team used computer models created by Pacific Northwest National Laboratory of hospitals in different climate conditions. 

They chose hospitals because they’re ideal test beds due to their indoor size. Additionally, buildings like hospitals often require a higher percentage outdoor air in their HVAC systems for safety purposes. 

The models showed an overall reduction in energy usage for all locations using the Active Membrane system. The more hot and humid locations (in this case Tampa, Houston and New Orleans) showed the greatest energy savings. 

Fix said, “The more hot and humid it gets, the better our system works. 

“This is a key finding, because as the climate continues to warm around the world, locations that want to use 100% outdoor air will now be able to economically afford it.” 

Making a prototype 

The researchers, whose work has been published in Applied Energy, are currently working toward building a physical prototype to validate their computer models. 

Now, instead of trying to save energy, they also have an additional matter at hand: the pandemic. 

“I think COVID was a wake-up call for all of us. Heating and cooling our buildings is not just a matter of temperature and humidity, but it can actually be a matter of life and death.  

“Hopefully, this work will help to make all of our indoor spaces safer,” Fix said. 

 

 

Another long-term solution 

Reducing the use of AC is still a wise move in order to save energy and save our planet in the long run. There are, of course, many innovations for that already, but let me show you this new one. 

Scientists at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) has made a breakthrough.  

They’ve developed a next-gen thermochromic window that not only reduces the need for air conditioning but simultaneously generates electricity. 

Indoor heat usually comes from sunlight shining through windows, and that brings the need for cooling systems and ACs in buildings. 

In US only, residential and commercial buildings use 74% of all electricity and 39% of all energy. Therefore, the shading effect from tinting windows helps buildings use less energy. 

Called “thermochromic photovoltaic”, this technology allows the window to change color to block glare and reduce unwanted solar heating when the glass gets warm on a hot, sunny day. 

This color change also leads to the formation of a functioning solar cell that generates on-board power.  

Buildings that have windows with this technology can utilize them to be energy generators, increasing their contribution to the broader energy grid’s needs. 

And now, the thermochromic photovoltaic has a lot of colors and a broader range of temperatures that drive the color switch. 

With this, it increases design flexibility for improving energy efficiency as well as control over building aesthetics. The windows will be highly desirable for both architects. 

 

 

The thermochromic windows 

Previously the NREL has made similar research/work and they’ve applied it to a thermochromic window that darkened as the sun heated its surface.  

As the window shifted from transparent to tinted, perovskites embedded within the material generated electricity. Perovskites are a crystalline structure shown to have remarkable efficiency at harnessing sunlight. 

Lead author Bryan Rosales said, “”A prototype window using the technology could be developed within a year. Reversible Multicolor Chromism in Layered Formamidinium Metal Halide Perovskites” 

Before, first-gen solar windows were able to switch back and forth between transparent and a reddish-brown color, requiring temperatures between 150 degrees and 175 degrees F (65.5 to 79.4 C) to trigger the transformation. 

However, this technology allows more choice of colors and it works at 95 degrees to 115 degrees Fahrenheit (35 to 46 C). On a hot day, temperature on glass can achieve that easily. 

Using a different chemical composition and materials allowed the researchers to be able to rapidly speed up the color transformation. 

It used to take three minutes during the proof-of-concept thermochromic photovoltaic window demonstrated in 2017. Now, the researchers were able to reduce the time about seven seconds. 

They’ve achieved that through sandwiching a thin perovskite film between two layers of glass and injected vapor. 

The vapor triggers a reaction that causes the perovskite to arrange itself into different shapes, from a chain to a sheet to a cube. 

Then, the colors emerge with the changing shapes. Lowering the humidity returns the perovskite to its normal transparent state. 

 

Sources

https://techxplore.com/news/2021-06-outdoors-energy-efficient-method-outdoor-air.html 

https://www.sciencedaily.com/releases/2020/10/201020131401.htm