Climatic Design Information (CDI) is a set of data provided by ASHRAE that includes weather-related parameters such as temperature, humidity, and solar radiation for various locations worldwide. CDI is crucial for HVAC design as it helps engineers and designers to accurately size, select, and optimize HVAC equipment, ensuring that they can meet the specific cooling and heating demands of a building or application. By using CDI, designers can create more efficient and effective HVAC systems that reduce energy consumption and improve indoor air quality.