How does weather affect energy usage? This presentation discusses the significance of weather data, and the powerful effects of weather on organization energy use. It also explains the degree day concept, and introduces a free online tool for obtaining a detailed historical weather data history for your location. This presentation has applications for energy management staff and other organization stakeholders who want to obtain and study historical weather data and gain understanding about the effects of weather on monthly utility expenses. -learn about the CBECS building benchmarking database. -discover the value of the degree day concept as an indicator of weather impact on building energy use. -find a free online tool for year-to-year weather comparisons. -view yearly cooling and heating trends. -hear why weather over-analysis can be unhelpful.

1. Why Energy Analysis Is
Cloudy Without Weather Data
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We all know the weather affects the
energy consumption of a building.
But how much? 90%? 50%? 10%?

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One way to get a quick idea is via the
U.S. Dept of Energy’s extensive CBECS
database, the result of surveys of tens
of thousands of buildings.
Our CBECS interface is free:
www.BuildingBenchmarks.com

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Cooling is 7% of
electricity usage

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Heating is 97%
of gas usage

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Overall, weather loads are 43%
(47 kbtu/sf) of the 110 kbtu/sf
annual total

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OK, 43% of the total energy bill.
How much can that vary year-to-year?
Enough to cause pain in my budget?

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Here’s the degree day report from free
www.WeatherDataDepot.com

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That’s bound to get someone’s attention!
The weather impact on building energy
usage is significant and can be analyzed
quite easily.
48% increase in degree days
x weather load of 43%
21% budget impact

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Degree Days is a weather metric
that’s only useful in the context of
building energy usage.

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How are degree days calculated?
1. Set a balance point temp, the outside
temp that divides heating and cooling.
2. Calculate the daily difference between
balance point and mean daily temp.
3. Track heating separately from cooling.

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Why bother with degree days?
Why not use the simpler concept of
average monthly or average annual
temperature?

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High Low Mean HDD CDD
San Diego
Day 1 65 55 60 0 0
Day 2 65 55 60 0 0
Average 60
Denver
Day 1 90 60 75 0 15
Day 2 60 30 45 15 0
Average 60
These cities had the same 60F average
temp for two days. Was building energy
usage the same?

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The average annual temperature in San Diego is 65F.
The average annual temperature in Dallas is 65F.
In Dallas, annual A/C usage is 160% more and annual
heating use is 350% of San Diego. How can that be?
The average annual temperature in Orlando is 72F.
The average annual temperature in Phoenix is 72F.
In Phoenix, annual A/C usage is 63% more and annual
heating use is 100% more than Orlando.
Huh?

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Conclusions:
Use Degree Days because this method
tracks heating and cooling needs separately
Average monthly or average annual
temperature doesn’t work–the warm and
cool days cancel each other out.

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What information does
WeatherDataDepot give me?

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1. Monthly Degree Day Comparison Report

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2. Cooling and Heating Cumulative Trends

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3. Monthly Trends

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4. Drill down to Daily Data

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5. Copy to Excel

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6. Degree Day Forecast, next 14 days

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7. Extensive FAQs

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8. Your Own Personalized Link

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9. Station Location and Excel File

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What about humidity, cloud cover,
wind velocity?
Huge increase in data cost and
computational complexity
Historical and current data for many
fewer sites
No significant analytical improvement

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