An analysis done by researchers at the National Renewable Energy Laboratory (NREL) in Jefferson County, Colorado found that on average, more than half of the energy consumed by residential air conditioning deals with the moisture in the air on a hot day. In other words, it’s the humidity that results in a/c unit’s energy consumption, not the heat.
The results also project that with climate change will come more hot days, and the energy consumption of humidity will become an even bigger challenge.
This summer, a/c systems were already challenged around the globe. Portland, Oklahoma City, and Denver reported some of their warmest Julys. Oregon health officials also reported an uptick in heat-related illness.
Humidity varies from region to region, according to Iain Campbell, senior fellow at RMI, a nonprofit organization working to accelerate the clean energy transition. While the removal of existing humidity will become a bigger issue in a lot of places such as Florida or other tropical states, in a state like Colorado with desert-like climate, it isn’t as pertinent.
A/C and Humidity
The Colorado Sun noted that it was humidity, not heat, that began the need for the window air conditioner, when an engineer experimented with humidity controls for a Brooklyn printing plant troubled by blurry prints and swelling pages in 1902.
Current a/c technology, though it requires additional energy usage, can effectively remove up to 60% relative humidity. Most a/c deals with humidity by cooling to the dew point, when the moisture in the air drops out as water. When the water is wrung out of the air, it releases additional heat that the a/c must handle.
To do the extra work, the a/c needs an extra 20-30% of capacity, said Eric Kozubal, a co-author of the study and an NREL researcher developing new cooling technologies.
The analysis divided the globe into 60-mile-by-60-mile boxes and within each box added population, a measure of economic activity, air conditioning ownership, and weather.
The study also looked at how much the electric grid depended on fossil fuels, since its goal was to estimate through computer modeling the greenhouse gas emissions from a/c.
The researchers calculated that almost 4% (1,950 million tons) of the world’s annual greenhouse gas emissions come from a/c. The bulk of that percentage was linked to the air conditioning working to cool and dehumidify.
According to the study, the rest of the emissions come from refrigerants leaking from units, and the releases associated with the manufacture and transportation of those units.
The study projects that greenhouse gas emissions for temperature and humidity loads will be five times larger by 2050 as more a/c units pop up in hot and humid places.
Researcher, National Renewable Energy Laboratory
Energy to Come
According to the Colorado Sun, RMI estimates that providing electricity to all the air conditioners running in 2050 will take 2,000 gigawatts of new electric generating capacity — equal to nearly 2,700 of Colorado’s largest power plant, Comanche 3, thus increasing the need for new and better technology.
Researchers and companies, including those at NREL, are searching for new a/c technologies that remove moisture and then cool the air in a two-step process.
Using a lithium chloride solution — 10 times saltier than the sea with a strong affinity to absorb water — an NREL team, led by Kozubal, and a start-up company 7AC developed a dehumidifying technology that was acquired by Emerson.
A system like this could save a substantial amount of energy — about 50%, said Kozubal. The expense of the system could be paid for by the energy savings. Blue Frontier, a startup backed by Bill Gates’ Breakthrough Energy Ventures, also uses NREL patented liquid desiccant technology, and reports it will deliver up to 80% energy savings.
Still, the days are getting hotter and heat waves are lasting longer.
The co-author of the study and senior research engineer at NREL, Jason Woods, projects that in the future, there will be places where it will be too hot and too humid to be outdoors.
“Right now, our grid is very stressed, even though renewables are going in. In the immediate future, more efficient air conditioning helps us save energy,” Kozubal said.