The perfect winter weather for a Passive Solar House like the Greeny Flat is when you have clear sunny days and cloudy nights. Sun during the day warms the Thermal Mass of the floor slab which stores the heat and keeps the house warm through the night. When it’s cloudy at night the outdoor air temperature tends to stay much warmer than when it’s clear. The clouds act like a blanket that helps to keep the earth warm, and when the outdoor air is warmer the house stays warmer inside.
This is exactly what we have NOT been having here over the last couple of weeks. If anything, it’s been tending towards the complete opposite with cloudy days followed by clear, cold nights. We’ve had a lot of frosty mornings which wouldn’t normally bother us but, because the days have been cloudy, the house has not had much chance to warm up during the day so it’s gradually been getting colder and colder. For example, on a nice sunny day, even if the outdoor temperature only gets up to say 14degC the interior will usually warm up to 21 or 22degC. Then it will drop down to maybe 15 or 16degC overnight even if it gets below zero outside.
Today, with only partial sunshine, we only managed to claw our way up to 17degC inside and it’s predicted to get down well below zero tonight. So lately we’ve been resorting to turning on a little fan heater from time to time to help take the chill off the air. Not that I’m complaining… after twenty years in Montana where it regularly got below minus twenty or colder during the winter, anything feels pretty good to me. I especially love the clear, crisp, frosty mornings that we’ve been having and, because our house is small, well insulated and fairly air-tight, it doesn’t take much additional heat to keep it comfortable, even on the coldest days.
In your ‘average’ inefficient home, the operational energy used for heating, cooling and hot water is often by-far the biggest portion of the overall environmental impact of the building over its life, especially in very hot or very cold places like Montana. But in an energy-positive house like the Greeny Flat, which actually makes more energy than it uses, the operational energy is no longer a factor and other things become bigger issues.
For example, the ‘embodied energy’ (i.e. the energy required to manufacture and transport the materials used to construct the building) becomes a much bigger portion of our environmental footprint. It would be possible to do a full ‘life-cycle analysis’ to quantify exactly what the various environmental effects of our choices might be over the life of the house (or any other product or system) but that is the stuff of phd’s. I haven’t done the calculations and I don’t care to, but we did make a concerted effort to limit the embodied energy in the materials chosen for the Greeny Flat. That is one of the reasons why we chose to use timber frames and plywood linings, because they have lower embodied energy than steel and gyprock.
Almost every decision is a compromise between competing priorities. For example, we could have used timber weatherboards for the exterior cladding which may have had a lower embodied energy than the galvanised steel that we used. However the goals of low-maintenance, durability and fire resistance took precedence in that case so we chose to use the steel. The most important thing that any of us can do to limit the embodied energy in a building is to Keep It Small and Simple (K.I.S.S.). A small, simple structure will generally have much less embodied energy than a large and complex one.
Our transportation choices also become a much larger factor in our overall environmental impact once we have limited our home energy use. Another huge issue is the energy and resources required to grow, process, transport, sell, and cook our food. That is the subject of an excellent book by Michael Mobbs called ‘Sustainable Food’ which I highly recommend (even though we still have a long way to go down that path ourselves). For today I would like to focus more on the transportation side of things.
More About Sustainable Transportation
In last week’s Newsletter I wrote about solar trains, planes and automobiles and regular readers of this Newsletter will know that we often highlight developments towards more sustainable transportation options. Before I go on, I want to make the very important point that the most sustainable forms of transportation are walking and biking. As such, the most important thing we can do as a society is to design our towns and cities in such a way that people can walk or bike to just about everything they need. On an individual level, we can choose to live (and to build) in a place that already allows for this to happen. For example, as we discuss in depth on this page of our website, the site for the Greeny Flat was deliberately chosen because it is within easy walking distance of Mittagong town centre, shops, recreation, parks, libraries, etc, etc… and importantly, a railway station so that, if we need to go further afield, we can hop on a train to get there. In all honesty, it would be quite easy to live here without a car if we needed to, as long as we could continue to work from home or find work nearby.
We took one step closer to that ideal recently when an unfortunate young gentleman accidentally rammed his ute into the back of Cintia’s car that was parked in the street outside. Even though the car was perfectly drivable, the damage was too expensive to fix and the car was written off by the insurance company. So we’re going to try living with just our feet, our two bikes, and my little van for a while and see how it goes. I’m thinking that it might be a good time to get an electric assisted bicycle like my friend Glenn’s. I love riding my bike but if I had to go to a meeting in Bowral I would be fairly soaked in sweat by the time I got over Mt Gibraltar. An electric assisted bike would get me there a lot quicker and smelling a lot nicer. I would also be able to charge the battery with some of our excess solar power during the day.
If it turns out that we really need a second car we will seriously consider getting a electric one… perhaps a second-hand Nissan Leaf or similar. A Tesla Model S would be quite nice but I can’t see the sense in owning a car that costs about twice as much as our house. So for now an electric boosted bike looks like a good option.