Why were pneumatic thermostats commonly installed in buildings?

Question

According to Wikipedia, pneumatic thermostats were invented after electric thermostats.

Yet this article claims that "at least 25 percent of U.S. commercial buildings are served by pneumatic controls, according to the U.S. Department of Energy". I would guess that they were even more popular in the past.

This seems surprising. Why set up an air compressor system and run pneumatic tubes through the walls? Wouldn't an electric system be easier to set up and maintain?

What were the factors that made pneumatic thermostats so popular?

Answer 1

In the 1940's and 50's, dynamic system controllers were invented which used air pressure to work. It was possible in fact to design and build not only analog control mechanisms but also binary logic devices that ran on compressed air and which could perform simple switching functions. These devices were less expensive and more durable than electronic logic based on vacuum tubes and relays and were popular all the way up into the early 1970's. They were called "pneumatic logic" or "air control" and they disappeared quickly when solid state logic became cheap.