The Powers That Be (7): And The Heat Goes On
For the past 365 days I've logged the daily high and low temperatures and plotted it against my daily energy consumption. After much anticipation, the results are in: it costs more to run the heat pump or air conditioner than it does to NOT run the heat pump or air conditioner. If you're satisfied with that conclusion, you can stop reading. If you want to know the details, read on.
Below is a graph with 365 data points representing my energy consumption and the daily average temperature. I define the "average temperature" as the midpoint between the high and the low for the day.
While the "average temperature" is not a perfect measure of how hot or cold is was over the course of a day, it's a fairly predictable indicator of how much energy I'll use for the day. I'll consume the least amount of energy on a day when the average temperature is about 61 degrees (for example when the low is 50 degrees and the high is 72 degrees). On that day I would expect to use about 9 kwH, and a cost of about $0.10/kwH, that would cost me 90 cents.
On the hottest day in the summer I would likely use over 40 kwH for a daily cost of $4.00. On the other end of the curve, on the coldest winter day, I could use 70 kwH, costing $7.00. I'm surprised at how both sides of the curve have the same slope. I would have expected either cooling or heating to have a better efficiency than the other, but they're nearly the same. The only reason that winter costs are more than summer costs is because it often gets 35 degrees colder than ideal, while it rarely gets warmer than 20 degrees above ideal.
Now I'll draw some conclusions. My total energy consumption for the year was 9,010 kwH, or an average of 25 kwH/day. In the best weather conditions (i.e. when I don't run the heat pump or air conditioner), I still consume 9 kwH/day. Therefore, it's safe to deduce that 16 kwH (or, 64%) of my annual energy use is to heat or cool the house. Everything else that uses electricity -- TV, lights, computer, refrigerator, dishwasher, water heater, door bell -- accounts for only 36%.
I've never had a day where I used less than 7 kwH, even when I was out of town. Therefore, items such as TV, lights, and computer account for about 2 kwH (or, 8%) of my usage. Therefore, about 7 kwH (or, 27%) of my energy usage is for things that run all the time such as the refrigerator and water heater.
At 64% of my usage, the biggest opportunity I have for cutting energy costs is a more efficient HVAC system. That could mean anything from installing an 18 SEER system for thousands of dollars to planting a shade tree to keep the sun off the house in the summer. For now I'll do nothing except continue to document my usage.
If anyone has actually made it this far, I'll present two more graphs. One shows the correlation between my daily energy usage and the high temperature, and the other to the low temperature. The daily high temperature is a slightly better predictor of energy usage. It tracks more closely than the daily low temperature.
Or, you can always use these images as a pixelated version of a Rorschach Test.
Below is a graph with 365 data points representing my energy consumption and the daily average temperature. I define the "average temperature" as the midpoint between the high and the low for the day.
While the "average temperature" is not a perfect measure of how hot or cold is was over the course of a day, it's a fairly predictable indicator of how much energy I'll use for the day. I'll consume the least amount of energy on a day when the average temperature is about 61 degrees (for example when the low is 50 degrees and the high is 72 degrees). On that day I would expect to use about 9 kwH, and a cost of about $0.10/kwH, that would cost me 90 cents.
On the hottest day in the summer I would likely use over 40 kwH for a daily cost of $4.00. On the other end of the curve, on the coldest winter day, I could use 70 kwH, costing $7.00. I'm surprised at how both sides of the curve have the same slope. I would have expected either cooling or heating to have a better efficiency than the other, but they're nearly the same. The only reason that winter costs are more than summer costs is because it often gets 35 degrees colder than ideal, while it rarely gets warmer than 20 degrees above ideal.
Now I'll draw some conclusions. My total energy consumption for the year was 9,010 kwH, or an average of 25 kwH/day. In the best weather conditions (i.e. when I don't run the heat pump or air conditioner), I still consume 9 kwH/day. Therefore, it's safe to deduce that 16 kwH (or, 64%) of my annual energy use is to heat or cool the house. Everything else that uses electricity -- TV, lights, computer, refrigerator, dishwasher, water heater, door bell -- accounts for only 36%.
I've never had a day where I used less than 7 kwH, even when I was out of town. Therefore, items such as TV, lights, and computer account for about 2 kwH (or, 8%) of my usage. Therefore, about 7 kwH (or, 27%) of my energy usage is for things that run all the time such as the refrigerator and water heater.
At 64% of my usage, the biggest opportunity I have for cutting energy costs is a more efficient HVAC system. That could mean anything from installing an 18 SEER system for thousands of dollars to planting a shade tree to keep the sun off the house in the summer. For now I'll do nothing except continue to document my usage.
If anyone has actually made it this far, I'll present two more graphs. One shows the correlation between my daily energy usage and the high temperature, and the other to the low temperature. The daily high temperature is a slightly better predictor of energy usage. It tracks more closely than the daily low temperature.
Or, you can always use these images as a pixelated version of a Rorschach Test.
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