Part III: Daily temperature cycles, east wing

This five-day period was a testing time for the unheated solar-passive house. Days were at their shortest, some nights were frosty, and overcast persisted for two days. It fell within a cold, wet, and cloudy winter.

This post is about the single-storied east wing of the house. It is the main part of the house, with most of the clearstory windows.

Back to Part I: Average temperature values.

Back to Part II: Daily temperature cycles, west wing

Forward to Part IV: Solar gain in the clear-story

Observations

In this wing, seen on the left in the photo, five thermometer stations define a profile in height. They are:

Subsoil in the heat bank beneath the house;
On the floor slab;
On the room wall;
In the clearstory space;
OUTDOORS, in a Gill Screen, 1.5 metres above the ground and eight metres from the house.

During the five days I made 84 observations at each station at intervals as shown. They define the daily temperature cycles. I observed the amount of cloud in Octas (eighths of the sky) at the same intervals.

This table lists for each thermometer station the five-day values of the average, maximum, and minimum temperatures, and the temperature range.

The daily cycles

Subsoil

The temperature in the heat bank 750 mm below the surface of the floor slab (green) did not cycle daily. It stayed near 19.2° the whole five days. That was the highest average of any thermometer station at this time.

Floor slab surface

The floor slab surface (magenta) began at 19.0°, but lost three degrees during two overcast days. In each of the following days of clear weather, it rose to 18.0° at 18:00, and fell to 16.5° at 08:00.

Room wall

The thermometer at 1500 mm on the wall (blue) shows that the room was 2° colder than the floor at 08:00 each morning, and all day on cloudy days. However, on three sunny afternoons it reached over 20° around 14:00. That is a comfortable temperature, never reached by rooms in the west wing at this time.

Clearstory space

In this photo, midwinter sun shines through the clearstory windows on to the double-brick thermal mass wall. The fan, angled to blow over-heated air downwards, is turned on by a thermostat (left) set at 26°. The clearstory temperature sensor is on the window-frame near the fan.

Plotted in black, the clearstory temperature was always colder than that in the room below, except between 09:00 and 21:00 on sunny days. Then it was 13.5° warmer than outdoors in the Gill Screen.
(Temperatures in the clearstory space matched a model described in Part IV.)

Outdoors in the Gill Screen

The cycle of temperature outdoors, as read in the Gill Screen, had a daily range of about 18° on sunny days. On such days, the cycle was as shown in textbooks:

Rapid increase from a minimum at sunrise (07:00);
Maximum increase about 10:00;
Peak temperature about 14:30;
Maximum decrease near sunset (17:00);
Rate of decrease getting slower through the night.

On overcast days the outdoor daily range was only about 5° with lower maximum values and higher minimum values.

Blower heater use.

Since the house very rarely gets as cold as this, I have only a few 1.5 kW electric blower heaters, which I run until I feel warm. In the five-day period I ran a heater for 16 hours, using 24 kWh at a cost of $6.00. As you see, the room thermometers scarcely responded.

Comment

This wing of the house performed very well, considering that the installed insulation would now be considered minimal. The mean room temperature of 16.6° was very little below the minimum of the Adaptive Comfort Zone. The minimum temperature, 14.1°, was not much cooler, and nearly 16° warmer than the frosty minimum outdoors.

The contrast with the much poorer performance of the 2-storied west wing suggests that the following features were effective:

The floor slab is large (11 m x 9 m) and has perimeter insulation.
Result: At midwinter, the subsoil under the slab was still as warm as 19.2°, which was 3.5° warmer than the subsoil in the garden.

Most of the thermal mass of internal brick walls (17 tonnes) is within this wing, and much of it receives solar radiation in winter.
Result: the average room temperature (16.6°) was higher than downstairs in the west wing (12.8°) and much higher than upstairs (11.7°).

North-facing windows, those of the clearstory in particular, are not much shaded by trees.
Result: The rooms receive most of the available solar heat on sunny days.

Part IV will show how closely the temperature in the clearstory space follows outdoor temperature and cloud cover.

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Key features of the house

This is a high-mass solar-passive house, built in Australian Building Code Zone 4 of hot dry summers and cool winters, as in Tamworth, Mildura and Kalgoorlie. It is stud-framed in cypress-pine on concrete slabs-on-ground with brick perimeter footings. There are internal brick walls for thermal mass. There is reflective foil insulation, and fibreglass batts that add R=2 in the walls and R=3 in the ceiling. Windows are double-glazed, and heavy pelmeted curtains operate on a timer daily.
The main east wing of the house is single-storied. It contains nearly all the brickwork thermal mass and most of the clearstory windows. There is insulation on the inside face of the perimeter footings.
The west wing of the house is two-storied, lacks those features, and is shaded by a large tree. Being tall and narrow, it loses a lot of heat.
There is detailed information with many photos in “My House Page”.