Rockefeller Center was the site of many technological wonders when it first opened in the 1930s. Escalators were novel at the time, and the machinery that kept the ice rink frozen was also a new development. But right at the core of the buildings were just-minted heating and cooling systems designed by David Nelson Crosthwait Jr., whose achievements in HVAC design drove the field forward, and who broke racial barriers as an African American electrical and mechanical engineer in the early 20th century.

Crosthwait (1898-1976) was born in Nashville, where his father was a biology and chemistry teacher, and principal of the city's first black high school. The family moved to Kansas City, and then Crosthwait, having shown an early knack for inventing things, studied engineering on a full scholarship at Purdue Univeristy in Indiana, earning a bachelor of science and later a master's degree. The young engineer joined the C.A. Dunham Company (now Dunham-Bush), where he created new products to heat and ventilate buildings, and became director of the research department in the 1920s.

His most high-profile project was designing the steam system used to heat Radio City Music Hall, and the challenges involved must have been considerable. So while the hydraulics beneath the stage remain a source of fascination for tech buffs, it's Crosthwait's conception and execution of the mechanics to keep the magnificent space warm that ensured a packed house for the Christmas Spectacular.

As an inventor, Crosthwait obtained more than 39 U.S. patents (and 80 international), such as for refrigeration, auto turn signals, thermostat controls and vacuum pumps, and some of his research articles and industrial manuals have further documented his contributions. He continued to work at Dunham until 1969, and then taught at Purdue, where he received an honorary doctorate in 1975; he was made a fellow at the American Society of Heating, Refrigeration and Air Conditioning Engineers in 1971. A leader in engineering science, Crosthwait helped steer the course of technologies that the whole country still relies on every day — not least of which is his landmark work at Rockefeller Center.