why energy analysis is cloudy without weather data

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 daysx 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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