This October has been very cold. That has kept indoor temperature
in this solar-passive house almost too cool for comfort. I wore warmer clothes and opened windows to admit warm air.

The climate this October

The graph shows (on the x-axis) how cold this October [in red] was: the coldest of the new century.
Here on the North-west Slopes of NSW, October warms and cools more from year to year than other months. It is the month most affected by climate cycles such as the El Nino-Southern Oscillation (ENSO). As shown, October warmed by one degree each year from 2011 to 2015, then cooled by nearly six degrees from 2015 to 2016.
ENSO followed almost the same pattern, but October 2012 was warmer than October 2013.
For five months, world temperature has also been down: much lower than it was in the record-breaking months of February and March 2016. (HadCRUT4 Global monthly near-surface data set (Column 2 in the linked table.))

Indoor climate this October

As shown on this graph beginning 2005, the indoor mean temperature in October months has varied with outdoor mean temperature. This coldest October outdoors (15.9 degrees) was also the coldest indoors (20.8 degrees). (But see Note below.)
October is the final month that I keep the house in its winter warming regimen. In 2014 and 2015 it had been almost ideally warm, but in 2016 it was just above the comfort minimum. Since this figure is just an average, there were times when the house was too cool for comfort, especially in the mornings.

Successive unfavourable months this year

As in other seasons, I intend the indoor climate to be comfortable through each spring season.
As I posted in “Hard Winter for Solar-passive” this very cloudy winter had reduced solar gain, making heaters needed much more than usual. However, the mean indoor temperature at winter’s end (August) was normal, although the heat bank was 0.7 degrees cooler than normal.
In September months, the warmth indoors still depends on solar gain through the north windows. This time,the sky continued very cloudy, and the daytime temperature was a record low value. As a result, the indoor temperature was 0.9 degrees down and the heat bank 0.7 degrees down.
By October, there is no solar gain through the north windows: warmth is gained from the surroundings in daytime by conduction, convection and radiation and retained by closed curtains at night. This time, both day and night temperatures were three degrees below normal, reducing daily heat gain and increasing nightly loss. As a result, the indoor temperature was 1.2 degrees down and the heat bank 0.9 degrees down.

What I did

As the October cold weather continued, I wore warm clothing in the evenings: 0.84 clo on average. I nearly always wore long trousers, flannel shirt, jumper, socks and slippers. In Octobers from 2012 to 2015, I had worn much less: only 0.35 clo on average. I nearly always wore a T-shirt and shorts then, but I usually wore socks and slippers because the floor was cool, barely reaching 22 degrees. Indoor temperatures this month were comfortable enough when I wore enough clothing.
I still felt I should warm the house more, if I could do it at no cost. I was concerned that having the heat bank 0,9 degrees lower than normal might keep the house uncomfortably cold in November. As I mentioned in the post “Managing my low-energy house: II. Features needing attention” and elsewhere, I can raise the house temperature in spring by opening doors and windows when the outdoor temperature is high enough. In this October I did this more than ever before, for a total of eighty hours. The admitted air was several degrees warmer. The effect at the time was pleasant, but I cannot judge the total warming over days or weeks.

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Note: October house management corrected in 2005

I have not included in this graph the first years, from 1999 to 2004. In those years, I had been opening the house for nocturnal purge ventilation from the 1st of October. I published an earlier graph in the ATA forum thread “low-energy Houses” on 29/10/2011.

The outdoor climate for 2016 was indeed the coolest for October since the house was built in 1999. However, the indoor climate was the coolest only since 2005. In every October month before that, the indoor climate had been cooler.

I modified the earlier graph in this “weatherzone” forum post.  I pointed out that a house management regimen with nocturnal purge makes the house much more vulnerable to a month of cold weather than one without it.