Five year retrospective

Every so often I find myself chatting with someone about the performance of the house and I am caught out with not actually having looked at the numbers except on a month-by-month basis. So here is a bit of a look at 5 years of data. March 2020 - February 2025. Hard to believe that we have been living here for over 5 years, but we have been (actually longer than that, but the data are consistent back to mid-February 2020). For the record, I am using data spanning the 1st of March 2020 through 28th of February 2025.

A few things of note. In winter months, we aim for a house temperature at or above 18 °C inline with the WHO recommendations and a general happiness with sleeping / waking up to a house that is ~ 18 °C. Using the hourly averages, the outside temperature ranged from 0.2 to 42.4 °C with a median temperature of 17.1 °C. The inside temperature ranged from 17.6 to 26.6 °C with a median temperature of 22.2 °C.

Over the past 5 years, we have been in the Passive House temperature target band 94% of the hours and in the WHO band 99% of the hours. I consider this a substantial victory for the passive house modeling software, as I am 100% confident that we could have achieved the > 95% passive house target if we had tried to maintain a 20 °C winter minimum temperature rather than 18 °C over the past few years. In total we have recorded 13 hours with an average indoor temperature below 18 °C (0.03%), and we have recorded 500 hours with an average indoor temperature above 25 °C (1.1%).

The other thing that comes up from time to time is the variation of temperature inside the house given that the split system is on the first floor. How well does the HRV equilibrate the temperature inside the house? In this plot of hourly temperatures over the past 5 years you can see that the ground floor is a bit more variable than the first floor, but these differences tend to max out at an average of about 1.5 °C. Not surprisingly the first floor is a bit cooler in the winter than it is hotter in the summer. This can be a noticable difference walking up or downstairs, but it is very definitely a first world problem.

And just for a little bit of perspecive... The same plot, but with the y-axis expanded to show the outdoor temperature ranges. Very hard to see the differences between the floors in the house.

And a final note about energy consumption. It gets a bit tricky to make energy use sensible and/or comparable, but I will try. Passive House uses kilowatt hours per floor area per year (kWh/(m²a)), so I've used those units. We have used an average of 26.0 ± 0.5 kWh/(m²a) over the past 5 years. In more normal person speak we have averaged 12.76 kWh/day (over 179.3 m² of conditioned floor area), approximately half of that demand (6.2 kWh/day) was directly supplied by our own solar panels, about half of that (6.5 kWh/day) was imported from the grid which is matched by our average export of (6.8 kWh/day). (We don't have batteries.) Note: Andy tells me that the Passive House Planning Package predicted 26 kWh/(m²a), so another win for PHPP?

Popular posts from this blog

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