Lowering the Carbon Footprint of Air Conditioning

A year ago, I wrote a story about Stan Cox’s book Losing Our Cool: Uncomfortable Truths About Our Air-Conditioned World. Cox is worried that as the planet continues to warm, more and more people will begin to use air conditioning and they will use it more often than ever. In a sense, this could become another positive feedback loop, not unlike the melting of the Arctic permafrost or the reduction in albedo due to melting sea ice. According to Cox, at the rate things are going, by 2050, we could end up using ten times as much energy for cooling as we use today.

In the year that has passed, some encouraging developments have occurred.

For one thing, there has been the advent of free cooling, as demonstrated by Schneider Electric at the Cogeco Managed Services data center in Barrie, Ontario. This novel approach takes advantage of natural cooling when it is available, combining fresh air heat exchangers in cooler weather, evaporative cooling in dry weather, and mechanical refrigeration the rest of the time.

According to Joe Capes, Cooling Business Development Director for Schneider Electric Americas, a system like this can reduce energy consumption by 36 percent when compared with traditional data centers.

Then there are the solar CHP systems, like this one, based on technology recently developed by IBM for cooling chips in their supercomputers. The high rate of heat extraction not only lets the PV cells run more efficiently, but also provides a great deal of useful heat, some of which, when paired with absorption chillers, can provide air conditioning at the hottest part of the day. In this application, the heat will also be used to drive a desalination plant to provide fresh water in certain parts of the world.

Last month, I spoke with Carrier’s Chief Sustainability Officer John Mandyck, about some impressive new developments. On the day we spoke it was a sizzling 93 degrees in upstate NY. It was also the 111th anniversary of the invention of air conditioning. Willis Carrier had come up with the idea as a way to help a printer in Brooklyn to reduce  paper jams in his printing presses due to the swelling of paper in hot humid summer air. Using water from a deep well beneath the plant, Carrier was able to provide cool dry air to help maintain production levels.

All of Carrier’s early applications were developed to advance commerce. After printing came candy-making, then munitions, department stores, and then, of course, movie theaters from which it spread into homes.

The product really took off with the invention of CFCs in the 1930s.  These new refrigerants were safer than their predecessors (e.g. ammonia, sulphur, etc.) which had been used in refrigerators until then. Their impact on the ozone layer was not discovered until decades later.

Carrier’s most recent breakthrough is its NaturaLINE marine container refrigeration system. The market for this product is the 175,000 refrigerated container ships that ply the ocean cooling roughly $6 billion worth of cargo every year.

NAturaLINE has enlisted the troublesome CO2 gas, for use as a refrigerant. It turns out that carbon dioxide, when used under high pressure, is well-suited for a variety of commercial applications involving low-temperature cooling.

The result is a refrigeration system that reduces the carbon footprint by 35 percent compared to its predecessor, primarily due its higher energy efficiency. Its carbon footprint also shrinks due to the fact that CO2 is a far less potent greenhouse gas (GHG) than its CFC-based predecessor, (a descendant of Freon). NaturaLINE systems also recycle CO2 that has been pulled out of the environment, making them carbon neutral in this regard. The amount of refrigerant used in each system is relatively small, so this does not represent a substantial opportunity for carbon sequestration. Still, no new CO2 is being made, and when a system is decommissioned the refrigerant is collected and reused as it is with conventional refrigerants.

This was a technical challenge for Carrier, since the use of CO2 as a refrigerant requires high pressures, which typically involves a good deal of power consumption. Carbon dioxide is unusual because it cannot exist in a liquid form under ambient conditions but instead goes directly from a solid to a gas through a process called sublimation. That is what you observe when a piece of dry ice is exposed to room temperature. Engineers at Carrier have found a way to compress the CO2 gas to the point where it becomes a liquid (a critical step in the refrigeration cycle) using relatively little energy. In fact, the efficiency of NaturaLINE matches the best in its class.

Mandyck told me that Carrier developed a system for supermarket refrigeration called CoolTech that is widely used in Europe (over 500 stores have it). In some instances they also use the condenser loop to heat water in a synergistic application they call CoolHeat, which provides even greater energy savings. They utilized a similar approach for heating water in a combined application to heat the swimming pools at the Beijing Olympics.

All refrigerants have an ideal range of operating temperatures for which they are best suited and carbon dioxide works best at low temperatures that are effective for storage of frozen and refrigerated food. If the system were to be run at the higher temperatures needed for air conditioning or residential heat pumps, it would operate less efficiently.

Carrier is also investigating the use of this technology for refrigerated trucks, as well as data centers servers as potential applications of this technology.

[Image credit: Wikimedia commons]

 

RP Siegel, PE, is an inventor, consultant and author. He co-wrote the eco-thriller Vapor Trails, the first in a series covering the human side of various sustainability issues including energy, food, and water in an exciting and entertaining romp that is currently being adapted for the big screen. Now available on Kindle.

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