This section is from the book "A Treatise On Architecture And Building Construction Vol4: Plumbing And Gas-Fitting, Heating And Ventilation, Painting And Decorating, Estimating And Calculating Quantities", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
259. In many cases the air supplied to public halls and other large buildings requires to be treated in various ways, to render it wholesome and prepare it for personal use with comfort. In summer time, it needs to be washed free from dust, and also to be dried and cooled. During the winter months, it is necessary not only to heat the air, but to increase its humidity also.