This book is an advanced text for graduate students in ventilation and air-conditioning engineering, building technology, refrigeration technology etc. as well as a reference book for air conditioning professionals or building energy-conservation professionals. It deals with the building thermal process which is the fundamental of load calculation for air-conditioning system design and also the basics of building energy-conservation analysis and retrofittings. The analysis of building thermal process covers the dynamic heat transfer through the opaque building envelope, the heat transfer through the transparent envelope, the internal disturbances an well as the natural ventilation and artificially introduced outdoor air.