Heating and Cooling Degree Days Calculator

Degree Days Formulas:

\[ HDD = \sum (65°F - Avg\,T) \quad \text{if} \quad Avg\,T < 65°F \] \[ CDD = \sum (Avg\,T - 65°F) \quad \text{if} \quad Avg\,T > 65°F \]

Heating Degree Days (HDD):

Cooling Degree Days (CDD):

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1. What are Heating and Cooling Degree Days?

Definition: Degree days measure how much (in degrees) and for how long (in days) the outside air temperature is above or below a certain level (base temperature).

Purpose: HDD and CDD are used in energy consumption calculations, particularly for estimating heating and cooling requirements for buildings.

2. How Does the Calculator Work?

The calculator uses these formulas:

\[ HDD = \sum (Base\,Temp - Avg\,T) \quad \text{if} \quad Avg\,T < Base\,Temp \] \[ CDD = \sum (Avg\,T - Base\,Temp) \quad \text{if} \quad Avg\,T > Base\,Temp \]

Where:

\( HDD \) — Heating Degree Days
\( CDD \) — Cooling Degree Days
\( Base\,Temp \) — Reference temperature (typically 65°F)
\( Avg\,T \) — Daily average temperature

Explanation: For each day, the difference between the average temperature and base temperature is calculated and summed over the period.

3. Importance of Degree Days

Details: Degree days help in:

Estimating energy requirements for HVAC systems
Comparing energy usage between different periods
Designing heating and cooling systems
Energy performance benchmarking

4. Using the Calculator

Tips:

Enter one daily average temperature per line
The default base temperature is 65°F (common standard)
Negative values are acceptable for temperatures

5. Frequently Asked Questions (FAQ)

Q1: Why is 65°F commonly used as base temperature?
A: 65°F (18.3°C) was historically considered the temperature below which buildings needed heating. It remains the standard for consistency in comparisons.

Q2: How do I calculate daily average temperature?
A: Typically (Max Temp + Min Temp) / 2, but more accurate methods may use hourly readings.

Q3: Can I use different base temperatures?
A: Yes, adjust the base temperature field to match your specific requirements or building characteristics.

Q4: What's the difference between HDD and CDD?
A: HDD measures coldness (heating needs) while CDD measures warmth (cooling needs) relative to the base temperature.

Q5: How are degree days used in energy bills?
A: Utility companies often normalize energy consumption by dividing usage by degree days to compare efficiency across different weather conditions.