degreedaysystemet

Degreedaysystemet, or degree-day system, is a method used in energy analysis to estimate heating and cooling energy requirements from outdoor temperature data. The approach relies on the concept of degree days, which quantify how far daily temperatures are from a chosen reference temperature, known as the base temperature.

There are two main types: heating degree days (HDD) and cooling degree days (CDD). HDD measure the amount by which daily mean temperatures fall below the base temperature, indicating heating needs. CDD measure the amount by which daily mean temperatures exceed the base temperature, indicating cooling needs. A common formulation is HDD = max(0, baseTemp − Tmean) and CDD = max(0, Tmean − baseTemp), summed over a given period.

Base temperature selection is crucial and varies with climate, building characteristics, and comfort standards. A frequently used cooling base is around 22°C (72°F) and a heating base around 18°C (64°F), but many analyses adopt different values to reflect local conditions. Degree-day counts are often aggregated monthly or annually to compare weather-normalized energy usage between locations or over time.

Applications of the degreeday system include forecasting energy demand for heating and cooling, weather normalization of energy consumption data, capacity planning for utilities, and informing building design and retrofit decisions. They provide a simple, aggregate proxy for environmental impact on energy use, especially in initial assessments and policy studies.

Limitations include ignoring humidity, solar gains, heat storage, occupancy, equipment efficiency, and internal heat gains. As a result, degree days are best used for trend analysis and comparative studies rather than precise energy accounting.