Part II: Daily temperature cycles, west wing
I report here on the thermal performance of a solar-passive house in Manilla, NSW, during five days at the winter solstice of 2016. The house is described briefly in a Note below.
This post is about the 2-storied west wing of the house, which is less successful. The more successful east wing will be considered later. An earlier post showed that average temperatures decreased with height. Go to Part I.
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.
In this wing, seen on the right in the photo, five thermometer stations define a profile in height. They are:
Subsoil in the garden near the house;
On the downstairs floor slab;
On the downstairs wall;
On the upstairs wall;
OUTDOORS, on the wall of the upstairs veranda.
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
The temperature 750 mm below the garden surface (green) did not cycle daily. It began at 16.3° and ended at 15.1° five days later.
Floor slab surface
The floor slab surface (magenta) averaged 13.9°, and was never as warm as the subsoil. On days with clear weather, it was only 1.0° cooler than the subsoil at 18:00, but was 2.5° cooler at 08:00. In cloudy weather it remained 2.0° cooler all the time.
This thermometer (blue) shows that the downstairs room was 2° colder than the floor at 08:00 each morning, and all day on cloudy days. However, on sunny afternoons the room reached over 16°.
Plotted in black, this room also reached over 16° at times. However, the walls and roof leaked so much heat that it got as cold as 9° in the mornings.
Both upstairs and downstairs rooms warmed rapidly until 10:00, but warmed no more until after 15:00 due to shading by a tree.
(See Note below on a temperature anomaly.)
A thermometer high on the wall of the upstairs veranda read much the same as the one in the Gill Screen used as the outdoor standard. At times when the house was warm, it read a little higher, due to heat leaking through the wall. There were sharp temperature peaks at 16:30 as the veranda trapped the late afternoon sun.
This wing of the house performed poorly under the stress of a cold wet winter. It has several deficiencies:
The slab is not insulated.
Result: the floor slab temperature was close to the subsoil temperature in the garden, rather than to that of the subsoil in the heat bank beneath the east wing. That made its temperature 3° colder and less stable.
The wing is narrow (4.8 m) and tall (5.5 m), and the upstairs room is only 4.6 m long.
Result: (i) the slab and under-slab is not wide enough to store much heat, even if it were insulated; (ii) the rooms have a large area of wall and roof losing heat.
It is shaded: in the morning by parts of the east wing, and in the afternoon by a large tree.
Result: the north-facing windows collect a reduced amount of solar radiation. As noted, this shows on the temperature record.
Part III will give results for the main east wing, which has a single-story with a clearstory. Go to Part III.
Note on a temperature anomaly
For a few hours, from 03:00 to 11:00 on the 27th, the upstairs temperature was near 12°, about 1° warmer than expected. Perhaps the door to the east wing was open, allowing warmer air (15°) to enter and flow up the stairwell.
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”.