The lowest cost method to reduce utility bills is almost always to improve the operation of existing equipment. After the first five years nearly all HVAC systems slip in efficiency, resulting in the need to measure and analyze performance, and then to make necessary adjustments and retrofits. This manual is designed to provide guidelines for engineers and technicians for correctly interpreting their readings of field measurements in order to accurately pinpoint system deficiencies, and then to prescribe the most effective strategies for correction. This manual goes beyond the usual manufacturer's operation and maintenance manual, showing you solutions for making parts of different makes work effectively together. Case studies and test data sheets are included.