AWN+ Degree Days Explained: The Key to Better Yields and Lower Energy Bills

For anyone working in agriculture or managing building energy systems, Cooling Degree Days (CDD), Heating Degree Days (HDD), and Growing Degree Days (GDD) offer clear, temperature-based insights into seasonal patterns and performance. These metrics are essential for planning ahead, improving efficiency, and supporting more sustainable decision-making. You can now access degree day data directly on your AWN dashboard by subscribing to AWN+.

What Are Growing Degree Days (GDD)?

Growing Degree Days (GDD) are used to estimate the rate of development for plants and insects throughout the growing season. The concept is based on the idea that growth only occurs when temperatures rise above a specific threshold, known as the base temperature (TBASE). This threshold differs depending on the species and is determined through research and observation. (for example, corn vs. tomatoes vs. turfgrass).

How GDD Is Calculated:

1. Find the Mean Temperature for the Day: The mean temperature is found by adding the high and low temperatures and dividing by two.
2. Calculate Daily GDD: If the mean temperature is at or below TBASE, then the Growing Degree Day value is zero. If the mean temperature is above TBASE, then the Growing Degree Day amount equals the mean temperature minus TBASE. For example, if the mean temperature was 75°F, then the GDD amount equals 10 for a TBASE of 65°F.

   GDD = ((max temperature °F + min temperature °F) ÷ 2) – base temperature °F

Sum for the Period: Sum the daily GDD values over a specific period to get the total GDD for that period.

What Are Cooling Degree Days (CDD)?

Cooling Degree Days (CDD) is a metric used to estimate the energy demand for cooling during warmer months. The idea is that when outdoor temperatures exceed a certain baseline—typically 65°F—buildings require more air conditioning to maintain a comfortable indoor climate.

How CDD Is Calculated:

1. Determine the Base Temperature: Typically, the base temperature is set at 65°F (18°C), which is considered a comfortable indoor temperature without the need for heating or cooling.
2. Calculate Daily CDD: For each day, subtract the base temperature from the average daily temperature (the mean of the highest and lowest temperatures of the day). If the result is positive, it represents the cooling-degree days for that day.
   CDD = TMEAN – TBASE, where TMEAN is the mean temperature and TBASE is 65°F
3. Sum for the Period: Sum the daily CDD values over a specific period (such as a month or a season) to get the total CDD for that period.

What Are Heating Degree Days (HDD)?

Heating Degree Days (HDD) work in the opposite way to Cooling Degree Days (CDD). While CDD tracks energy needed to cool spaces, HDD measures how much heating is required when outdoor temperatures fall below a base temperature, typically 65°F. The colder it gets, the more energy is needed to maintain a comfortable indoor environment. This metric helps estimate how much heating a building will need during cooler seasons.

How is HDD Calculated?

1. Determine the Base Temperature: Similar to CDD, the base temperature for HDD is usually set at 65°F (18°C).
2. Calculate Daily HDD: For each day, subtract the average daily temperature from the base temperature. If the result is positive, it represents the heating degree days for that day.
   HDD = 65°F - MDT, where MDT is the mean daily temperature. To calculate the MDT, add the high and low temperatures for the day and divide by two.
3. Sum for the Period: Sum the daily HDD values over a specific period to get the total HDD for that period.

Real-World Uses for GDD, CDD, and HDD

For Energy Efficiency:

• Utilities use degree day data to forecast demand and manage grid loads
• Facility managers monitor building efficiency and adjust HVAC schedules
• Homeowners can track seasonal usage patterns and reduce energy bills

For Agriculture and Gardening:

• Farmers use GDD to plan planting and harvesting timelines
• Pest Control is easier with GDD-based models that track insect emergence
• Gardeners use GDD to anticipate blooming, fruiting, or turf development

Now Available in AWN+: Degree Day Tiles

With AWN+, you can now view GDD, CDD, and HDD metrics right on your personalized dashboard. These new tiles make it easy to:

• Monitor degree days in your exact location
• Compare trends across multiple stations
• Use historical data to plan for the weeks ahead

Whether you're managing a building, garden, or greenhouse, these insights help you make better, data-informed decisions.

Upgrade to AWN+ today and take the guesswork out of energy and environment management.

References

• U.S. Environmental Protection Agency. (2024). Degree Days. Retrieved from EPA Degree Days Overview
• National Oceanic and Atmospheric Administration. (2024). Degree Days Explanation. Retrieved from NOAA Degree Days Explanation
• American Society of Heating, Refrigerating and Air-Conditioning Engineers. (2024). Degree Days Information. Retrieved from ASHRAE
• Energy Information Administration. (2024). Degree Days Data. Retrieved from EIA Degree Days Data
• Purdue University. (2024). Growing Degree Days (GDD). Retrieved from Purdue GDD Info