Why Energy Analysis is Cloudy Without Weather Data
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Transcript of Why Energy Analysis is Cloudy Without Weather Data
Why Energy Analysis Is Cloudy Without Weather Data
©2014 EnergyCAP, Inc. ▪ @energycap ▪ #energyleader ▪ www.EnergyCAP.com
©2014 EnergyCAP, Inc. ▪ @energycap ▪ #energyleader ▪ www.EnergyCAP.com
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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©2014 EnergyCAP, Inc. ▪ @energycap ▪ #energyleader ▪ www.EnergyCAP.com
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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Presented by EnergyCAP, Inc.EnergyCAP is used by organizations that receive many utility bills for bill processing, energy reporting and analytics
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