Before revision: Early radiant cooling systems were installed in the late 1930's and 40's in Europe and the US, and became more common in Europe by the 1990's, with over 800,000 m (over 8.6 million square feet) of radiant cooling systems installed in Germany alone by 1994.
After revision: Early radiant cooling systems were installed in by the 1950's in late 1930's and 40's in Europe and the US, and became more common in Europe by the 1990's, with over 800,000 m (over 8.6 million square feet) of radiant cooling systems installed in Germany alone by 1994.