The document discusses air conditioning systems. It describes how air conditioners work using a refrigerant chemical to transfer heat from inside to outside. There are three main parts: a compressor, condenser, and evaporator. Air conditioning systems can be individual units, unitary packaged systems serving multiple rooms, or central hydronic systems with air handling units, water systems, and a central plant. Properly sizing and installing air conditioners can improve energy efficiency. The goal of AC system design is to have an effective, efficient, and cost-effective system that meets requirements.