A Cool Development

Summer here in the Washington DC metro area is often hot and humid; and this summer, at least so far, is no exception.  Of the 22 days in July so far, 11 have had daytime temperatures of 95 F (35 C) or higher, as measured at Dulles airport (IAD).   Local legend has it that, at one time, British diplomats assigned to Washington were given extra pay for living and working in tropical conditions.  So it’s probably good that a recent post on the “Babbage” technology blog at The Economist reminds us that things could be a lot worse.

It was just a bit more than 110 years ago, on July 17, 1902, that Willis Carrier, an employee of the Buffalo Forge Company,  finalized his design of the first modern air conditioner, to be installed at Sackett & Wilhelms,  a printing firm in Brooklyn NY.   The printers wanted it mainly for humidity control, not cooling; varying humidity levels can make a mess of paper, as anyone who has fetched in his or her daily newspaper on a rainy day will know.  The humidity-induced changes in the paper stock wrought havoc with color printing especially, since the same sheet needed to pass through the presses multiple times. The new device was a success, and other customers soon appeared.

A drug firm and a silk mill swiftly followed Sackett & Wilhelms in adopting Carrier’s device. A host of other companies in different industries, including Gillette’s safety-razor factory where humidity caused corrosion, converted soon after. In 1915 the Carrier Corporation was founded. It exists to this day as a division of United Technologies, an industrial conglomerate.

Carrier’s design incorporated the basic elements (evaporator, compressor, condenser) that are used today in air conditioners, refrigerators, and heat pumps.   (The Wikipedia article on “Heat Pump and Refrigeration Cycle” provides a good overview.)   One significant design choice is what to use as a refrigerant.

In early system, carbon dioxide (CO2) was often used, but fell out of favor because high pressure is required to liquefy it from a gas, requiring strong (and therefore expensive) plumbing.   New compounds were developed as substitutes, particularly chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), which have better thermodynamic properties.   (Freon is a DuPont trademark for a range of related refrigerants of this type.)  These refrigerants came under fire beginning in the 1970s, when it was discovered that they could act to deplete the ozone layer in the Earth’s atmosphere.  A new class of refrigerants, hydrofluorocarbons (HFCs), was developed and gradually adopted; however, although the HFCs do not attack the ozone layer, they are very potent greenhouse gases (~10,000 times as potent as carbon dioxide).

One of the effects of all this has been to re-examine an old choice: carbon dioxide as a refrigerant.  Modern manufacturing and construction techniques have made the construction of suitable high-pressure systems less problematic.  CO2 is non-toxic, and there is certainly plenty of it available.   Some commercial units are already using it.

John Mandyck, a vice-president of modern-day Carrier, says the company has already begun rolling out its first CO2-based products. They extract the gas from the air, making them carbon-neutral and easy to replenish in the event of a leak.

There are other methods being tried to improve the efficiency and environmental friendliness of air conditioning, of course.  Two look back to ideas that predate Carrier’s: using ice (made at night when power is cheap) to cool air, and using evaporative cooling.   With more steamy weather in the current forecast, I’m glad we have it, however it works.

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