@shanefinn03 – Thank you for the info on weather temperature indexes. You inspired me to review my data.
I analyzed my home HVAC energy usage with the CDD index. I have a two-story house with two electric central HVAC units (with gas-fired heating). We live on the Texas Gulf Coast so we generally are always cooling the house. I did not run a ‘HDD comparison’ because we use gas for heating. I do not have an ECOBEE type of thermostat that allows me to gather any daily information on runtimes.
_“Cooling degree days”, or “CDD”, are a measure of how much (in degrees), and for how long (in days), outside air temperature was higher than a specific base temperature. They are used for calculations relating to the energy consumption required to cool buildings. Quoted from: https://www.degreedays.net/_
Setup Steps:
- I extracted the daily readings from the ‘SENSE V4.0 web version’
from 9/14/2017 through 8/27/2018. - I downloaded my local weather readings using 75 degF as the baseline for CDD from https://www.degreedays.net/
- I combined all of the .CSV files into a single Excel file for 2017 and 2018.
- I setup my calculations in Excel:
- Total KWh/day = AC1 + AC2 (I only have the compressor wattage readings from SENSE. SENSE has not discovered my blower fan motors for each HVAC unit.)
- I did not remove any bad data. I attempted to delete bad data and found the same correlation and trend.
Plotting Charts in Excel (Windows 10):
First, I plotted the SENSE values against the CDD values using a simple scatter graph. This allowed me to determine which days might be bad data. Then I plotted a linear regression.
Second, I also deleted what appeared to be bad data points and plotted a second chart.
If the R2 factor is 1.00, then the data points would be a perfect correlation. I am only posting the first chart showing ‘all data for all days’.
Observations:
Both charts had similar slopes and R2 values. There is a large scattering of data points away from the baseline. My correlation value (R2) was 0.835 I am not certain that I can find a 100% direct correlation between the outside temperature (CDD) and the amount of energy that is used to cool our house. I think our home energy usage for cooling the house is based upon several factors:
- Outside temperature.
- How humid is it outside / inside.
- The amount of stove top or oven cooking occurring.
- The number of times we enter or exit the house on a daily basis.
- The amount of laundry done for that day.
- Our personal preference for the thermostat set-point on that day.
- Whether we have family or guests visiting.
What I did notice is that ‘shanefinn3 R2 values’ were similar to my R2 values. I would be interested to see a similar type of charting that anyone has created and hear their thoughts.