Temperature and energy use observations

As I continue sifting through our performance data, I’ve been focusing lately on outdoor temperatures and their relationship with our heating and cooling energy use. These are a few of my observations.

70 percent of time period was below 68 degrees

We have 9 months, 274 days, 6,576 hours of temperature data, from February 1 to October 31. Of those 6,576 hours, 4,635 outdoor temperature hours were below 68 degrees F.  Roughly 70% of the recorded time period has been below 68 degrees F.

Chart showing hours within degree F ranges

Breaking out the temperatures by 10 degree buckets you can see a rough bell curve. The majority of hours were in the 60-70 degree F range. The next three months of data will add more hours to the 60 degree and below buckets.

If we overlay air-source heat pump values on the same chart (below), we can see the power used for heating and cooling based on the temperature ranges. The  dip in the 50-60 degree range is likely to indicate our base building temperature.

Chart showing hours and kWh within each degree F range

The dip is where we shift from heating to cooling or dehumidification in our case. I really should plot the right side with interior humidity ranges rather than temperature ranges. I’m guessing the hottest days were more dry and less likely for us to use the AC.

Chart showing ASHP energy usage at different temperature ranges

We used the majority of our heat energy for temperatures below 54F degrees. This makes sense, but when I looked at the hours the heat was on in the two temperature ranges I saw something I didn’t expect.

Chart showing ASHP number of hours operated by temp ranges

The heat was only ON for for a small proportion of the hours that temperatures were below 54F degrees. It was off more than it was on. After I mulled this over it made sense too. A lot of spring, summer and fall nights can get quite cool, but the insulation and mass of the house keeps it warm through the night. Plus, we generally keep the heat turned off in the summer for obvious reasons.

Charts showing proportion of time heat was on or off in temp ranges

But it made me curious what types of temperature swings we were experiencing monthly.

Chart showing monthly temperature ranges, hi/lo

There is quite a range of temperatures throughout the months, March being the extreme due to a freakishly warm spell. The dotted line is 68F. This shows we’re getting some cool nights all through the summer.

That’s it for this week.

Notes

Number of kWh used for heating below 54F = 77.81 kWh

Number of kWh used for heating between 54F and 68F = 14.131 kWh

Number of hours heating was ON when temperatures were below 54F = 195 hrs

Number of hours heating was ON when temperatures were between 54F and 68F = 80 hrs

Number of hours heating was OFF when temperatures were below 54F = 1,351 hrs

Number of hours heating was OFF when temperatures were between 54F and 68F = 1,958 hrs

Heat was ON 6% of the total hours that temps were below 68F. In that time we used 91.941 kWh for heat, an average of 334 Wh/hr.

Heat was ON 14% of the total hours that temps were below 54F. In that time we used 77.81 kWh for heat. 82% of total heat usage, an average of 399 Wh/hr.

Heat was ON 4% of the total hours that temps were between 54F and 68F. In that time we used 14.131 kWh for heat. 18% of total heat usage, an average of 177 Wh/hr.

Temps were above 68F = 1,941 hrs

Temps were below 68F = 4,635 hrs

Temps were between 54F and 68F = 80 hrs

Hours temps were below 54F = 1,351 hrs

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