Sustainable House Day - 2024

Another successful Sustianable House Day. It was all quite civilised with 46 people across three sessions. Lots of great questions and interested people.

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Five year retrospective

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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 passivhaus temperature t...
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Batteries

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We did it. It is not clear that the batteries will save us money, although with the way electrical prices are going, they might, and it isn't clear that they won't save us money either. At some point, we wanted to be part of the solution, so the likely breakeven-ish economics were good enough. Call it an investment in the future stability and sustainability of the Australian electricity grid. In terms of economics. Relative to my last statement on the topic, back in 2021 , four years is a long time. Batteries have gotten better, the cost of electricity is up (and demand pricing has arrived), solar feed-in tariffs are down, and NSW has a battery rebate at the moment. The cost of electricity has become increasingly complicated, making modeling costs/savings more tedious as the costs vary by time of day with times of day changing seasonally. Which also means there are more ways that electricity costs will likely change in the future. Minimally, with the battery system, we shou...
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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...
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