Well May is nearly over and BOM data shows that Canberra's coldest May minimum of -4.5 degrees occurred last night and the coolest May maximum of just 11.7 degrees happened yesterday. So how are things going at Jenny's place without any heating other than a 600W infrared panel on the ceiling in each bathroom?

Zac, the solar passive pup, soaking up the warmth on the burnished concrete floor at 8:30am on 22 May after a 0.2 degree minimum earlier that morning.

Jenny's north-facing kitchen/dining/living area (green on the graph) peaked at 20.4 degrees yesterday (8.7 degrees higher than the external max) and dropped to 14.6 as it was hitting -4.5 outside (a whopping 19.1 degree difference). The southern bathroom, shown in black on the graph, reached 16 degrees yesterday (without assistance from the infrared ceiling panel) and then dropped to 13.2 overnight (still 17.7 degrees above the external temp). If you're wondering what the strange temp spikes are in the bathroom: 1. Jenny's partner had a very late shower last night (the midnight peak) and 2. Jenny turned on the infrared heater panel in the bathroom at 6:40am after scraping the -4.5 degree ice from her windscreen and ducking off to the gym. The infrared panel was switched off again at 8:45am.

Temperatures in Jenny's house over the 24 hour period that included Canberra's lowest maximum temp (11.7) and lowest minimum temp (-4.5) for the month of May, 2017. See floor plan with colour key below. It was 18.3 degrees in the dining/living area … — Temperatures in Jenny's house over the 24 hour period that included Canberra's lowest maximum temp (11.7) and lowest minimum temp (-4.5) for the month of May, 2017. See floor plan with colour key below. It was 18.3 degrees in the dining/living area at 10pm when it was about to hit 0 degrees outside.

HOW IS IT SO? The reason Jenny's house does so well is because it has been designed and optimised (through a combined architectural and scientific process) to soak up, and retain, free heat from the sun during cooler months. Despite the skinny, north-to-the-street block of land, the house takes clever advantage of low-angle, winter sun and maintains comfortable temperatures due to its thoroughly insulated and sealed building envelope (using standard construction methods). The teenage boys still get around in barefeet and the dog loves the cosy concrete! See pics below.

But what about overcast days? Well we had a few of those this month and nobody was shivering and cursing at Jenny's house. See the graph below showing the temperature in the dining/living area throughout the whole month - the overcast days are obvious from the graph (the days where the max internal temp didn't reach 19 degrees - 14, 19, 25, 26, 28 May). For those who want to compare to the BOM observations for the month of May I've also posted a screen shot of them below the graph.

Less than 15 sounds freezing! An important point: The radiant temperature of our environment and air movement dominates our sense of comfort, not air temperature. In winter our environment is “cold walls, floors and ceiling and chilly draughts” and in summer our environment is “hot walls, floors and ceiling”. Our bodies primarily react to this – emitting our own body heat out to the cold surfaces in winter, and absorbing heat energy from them in summer. In this house the internal surfaces of the well-insulated and sealed building envelope stay at comfortable temperatures. This combined with the lack of air leaks and draughts means the home still feels comfortable even when the air temperature drops below 15 degrees in some rooms.

The temperature in the Dining/Living area at Jenny's house throughout the month of May.

May minimums - the prelude to winter at Jenny's place!