This graph, for 2016, shows a winter pattern of indoor and outdoor temperatures that is typical for this house. Indoor temperatures vary much less than outdoor temperatures, they rise and fall with them, and they are higher nearly all the time.
While the outdoor temperatures shown go as low as minus three degrees, those indoors lie within the winter “comfort zone” from 17° to 24° (see this post) nearly all the time.
Weather this winter
This winter was harsh for a solar-passive house. Near-record rainfall (227 mm) came with the greatest number of cloudy days of any winter in the new century. There were 53 mornings with more than four octas of cloud, when the average is 33.
Because cloud limited the the solar gain, I had to use blower heaters far more than in previous winters. My records show that I used 320 kWh ($80) in these heaters this winter, when I normally use about 40 kWh ($10).
Heaters were also used by guests who were present on the six days shown. As well as being unused to the climate, the guests lived in the colder west wing of the house. They may have used 72 kWh ($18). Those guests have kindly written reviews of their visit.
Even using 400 kWh of electricity for personal heating in a winter could not make a detectable change in house temperature. I have found that blower heaters are surprisingly good at making a room in this house comfortable. As the radiant temperature of the walls is only 2° or 3° too low for comfort, it can be compensated by making the air temperature only slightly higher.
The pattern in detail
While cloudy days are not plotted here (Cloud observations for this winter are plotted elsewhere.), cloudy days can be recognised on the graph. In this climate, days with low maximum temperature and high minimum temperature are always due to cloud. Only in fine weather are days warm and nights frosty. The graph shows how the weather goes through a cycle every week or two: sunny days get warmer, then rain sets in. As it clears, the air gets even colder, before warming up again.
Indoor temperatures follow the same cycle, but there are differences. There may be a delay of up to a day, and sometimes longer.
I did scatter plots comparing all the variables shown in the first graph and I fitted linear regressions. I present the four scatter-plots that had the highest coefficients of determination (“R-squared”). Continue reading →
This graph is a log of indoor and outdoor 7-day meantemperatures at my low-energy solar-passive house at Manilla, NSW. Indoor mean temperatures are in red, and outdoor mean temperatures in black. Both logs show the same cycles of temperature with a period of two to three weeks. Indoor cycles have a much smaller amplitude.
This scatter-plot shows only daily maximum temperatures, indoors and outdoors, and displays the average values. The Manilla average outdoor maximum of 25.5° is already comfortable, if a little on the warm side. The average indoor maximum of 23.8° is closer to the ideal.
While this solar-passive house scarcely changes the average maximum daily temperature, it drastically reduces the extremes. The slope of the linear regression line shows that indoor maxima vary only 38% as much as outdoor maxima. This results from effective insulation and daily and seasonal storage of heat and coolness in thermal mass material through the year. In addition, the house is well shaded in summer, and catches warmth from the sun mainly in winter.
This scatter-plot shows only daily minimum temperatures, indoors and outdoors, and displays the average values. The Manilla average outdoor minimum of 10.1° is far too cold for comfort. Solar-passive design has raised the indoor minimum by 10.6° without applied heating. The indoor average minimum of 20.7° is near the middle of the comfort zone.
The slope of the linear regression line shows that indoor minima vary only 34% as much as outdoor minima. This results from effective insulation, daily and seasonal heat storage in thermal mass material, and warmth from the sun captured in winter.
A dashed line in the lower right shows that nearly all points have indoor minima warmer than outdoor minima. This is a disadvantage only on nights warmer than about 20 deg.
A dashed line in the upper left shows that many cold nights have indoor minima nearly 20° warmer than outdoors. One morning (9/5/06) the indoor temperature was 21.8° warmer than outdoors. Could this be a record for an unheated house? Such large over-temperatures come with very dry air in autumnand early winter.
This is a scatter-plot of indoor and outdoor daily maximum and minimum temperatures for a solar-passive house in Monash Street, Manilla, NSW. The house is not heated or air-conditioned.
Data in this graph are taken from two thermometers; one in a Gill-type thermometer screen seven meters from the house (photo in Gallery), and one on a wall in a core room of the house. The data are for the first three years of good screen readings.
The graph shows that indoor temperatures vary only 42% as much as outdoor temperatures. The outdoor temperature range is 45.9° (from -4.4° to 41.5°), but the indoor temperature range is only 19.4° (from 13.4° to 32.8°). Most indoor temperatures are within the “adaptive comfort zone”. Average temperatures are 17.8° outdoors and 22.3° indoors. The house raises the indoor average by 4.5° to near the ideal for comfort.
There is a similar three-year scatter plot for a solar-passive house at Bonnyrigg, near Liverpool, Sydney in “Energy Efficient Housing for New South Wales” by Ballinger, Prasad and Cassell.
Very likely the data is in this paper by John Ballinger:
I think Ballinger’s scatter-plot for a house near Liverpool must include daily maxima and minima as mine does. His extreme outdoor points are 40° and +1° (range 39°) and extreme indoor points 32° and 12° (range 20°). In broad terms these two houses seem to yield similar levels of comfort, but the Manilla house does it in a more extreme climate. Manilla’s daily temperature range is 15.5°, while Prospect Reservoir, near Bonnyrigg, has only 10.9°.