What does a cooling degree day (CDD) measure?

A cooling degree day (CDD) is a measurement used to quantify the demand for cooling in a particular area during warmer months. It is determined by calculating the difference between the actual air temperature and a predetermined base temperature, typically set at 65 degrees Fahrenheit. When the air temperature exceeds this base, each degree of temperature above 65 degrees contributes to the CDD count for that day. This metric helps in understanding energy consumption for cooling purposes, predicting energy loads, and aiding in the design and implementation of HVAC systems.

The other choices do not accurately describe what CDD measures. Temperature differences between two cities would involve specific comparisons and not the cumulative degree days based on a single base temperature. Average outdoor and indoor temperature differences do not reflect the concept of cooling degree days, which is focused solely on external air temperatures. Lastly, daily temperature fluctuations throughout the year do not capture the purpose of CDD, which is to create a consistent measure based specifically on days exceeding the cooling threshold rather than the total range of temperature changes.