Heating & power usage...

Heating - how much do we use / need in our house?

A simple question, but there are many ways to look at it. I've taken a fairly simplistic. I've used linear models to estimate the effect of temperature on energy usage. The graphical representation of the relation between temperature and energy usage is below... 
Some key take aways for people not used to reading graphs:
  1. The vertical (y-axis) is daily energy consumption in kilowatts.
  2. The horizontal (x-axis) is temperature (in this case it is the running mean operating temperature [RMOT] recorded by the HRV).
  3. The dots are 160 individual days - each with a corresponding RMOT and energy consumption reading.
  4. The black line is straight and declining - indicating that energy use decreases as temperature increases. In fact for every degree colder we use an extra 0.5kW (this is the slope of the black line).
  5. The grey area encompasses 95% of the variation and there is considerable variation. Temperature explains ~ 39% of the total variation in usage. I looked at using other temperature measurements including daily mean temperature but the RMOT explains more of the variation which makes sense since the house with have some thermal inertia as well.
  6. I added other things to the model like how much power we produced (electrical power production should be a good proxy for the amount of solar gain or passive solar heating), but none of these improved the model much. Power production only explains an extra ~ 1.5% of the variability.
  7. Statistically this relationship in the figure above is highly significant, and even more importantly this is quite a meaningful and intuitive result.
  8. While 39% of the total variance is not as much as one might want to predict, but it is worth considering the magnitude of the power usage - at 20 °C we use 11.3kW on average. 
    • About 4.5 kW of that is what I would consider as unavoidable base usage. That is the power between midnight and 5am extrapolated over 24 hours. That is the HRV, the refrigerator, clocks on the microwave/oven, router and all the other things that don't ever get turned off. 
    • We average about 2.5kW a day in hot water based on examining the change in power usage during the period when the hot water heating system is active. 
    • The rest of the power usage is complicated by people. Each time the dish washer runs is about 1.5kW, a load of clothes in a cold wash is barely even detectable. Cooking energy use is highly variable - with the oven being used more often on the weekends and in colder weather as well. 
    • So the an extra load of dishes or a meal in the oven - easily explains the variability in the consumed electricity.
  9. Below is the quarter hourly electricity consumption. The black line is the median usage, with increasing shades of grey from 95th, 75th, 50th, 25th, 5th, and 0th percentiles.


Popular posts from this blog

Temperature (Out vs. Old vs. New)

Image
I have fielded more than a few questions about the temperature of our passive house versus the temperature of the house that we lived in prior (on the same lot).  So I've used the data I had on hand which is temperature (°C) recorded every 5 minutes over since October 2012. For the sake of consistency I am only using the NetAtmo sensors that I have had for that entire period. So I only have one outside sensor and one inside sensor located in the the respective living room. The outside sensor moved around a bit, but it should be good enough.  I've converted those measurements to hourly averages.  This ends up being ~ 66,955 hours to play with (52,232 hours from the original house, 14,723 hours from the passive house). I've left the rental house out of this comparison, but it was disturbing like the original house despite being ~ 20 years old. The key take-home messages: The passive house a much less variation in temperature than the original house (or outside).  In the summe
Read more

Water wall...

... Currently a work in progress... Thermal Mass A material’s capacity to absorb, store and release heat. Thermal mass is typically used to moderate temperature extremes by releasing heat when the home is cool and absorbing heat when the home is warm. Specific heat capacity A material's capacity to store heat (measured per unit mass). Some materials are better at storing heat than others. Water can store 4× as much heat per kilogram as concrete. Density Mass per unit volume (mass / volume). Denser materials have more mass per volume so they can make up in density what they lack in specific heat capacity. Concrete has twice as much mass per m3 as water. Thermal conductivity The ease with which heat travels through a material. Ideally, thermal conductivity should be moderate so that the absorption and release of heat synchronises with the building's heating and cooling cycle. Both water and concrete are highly effective! In comparison, steel and water hold a similar a
Read more

international passive house open day...

We had ~49 people come through the house for one of the International Passive House open days of 2019. As the event is not as widely publicised as Sustainable house day when we had more than 200 people through. The visitors who came through for this open house tended to already know a fair bit about passive houses (with many dragging along family members who they were working to convince of the merits of passive house living). Lots of the visitors were already planning or working on projects that were including passive house principles.
Read more