Managing my low-energy house: II. Features needing attention

Photo of clear-story area with winter sun and a fan

Clear-story fan set for winter

This post, and the companion post I. Features needing no attention were posted originally to a forum of the Alternative Technology Association (See Note below.)

My low-energy house at Manilla, NSW, maintains year-round comfort in a climate of daily and seasonal extremes. In the climate classification of the Building Code of Australia, it is in Zone 4: “Hot dry summer, cool winter”, along with Tamworth, Mildura and Kalgoorlie.
This house differs from most houses in relying on the design of the house to achieve comfort, with hardly any energy needed for heaters or coolers.
There is little artificial control: the “home automation system” consists only of timers set twice a year. Some of the comfort features call for daily action in certain seasons. However, these simple daily chores could have been avoided by small changes in the design. [But see “Note added 2016.”]

The success of the house in maintaining comfort in all seasons is shown by scatter-plots of daily indoor and outdoor maximum and minimum temperatures over a period of three years.

Features re-set twice a year

Dates for re-sets

For part of each year, the Manilla climate is too hot for comfort, and for the rest it is too cold. Some house features are re-set twice a year, making a “winter regimen” and a “summer regimen”. At first, I set the change-over dates near the equinoxes, 20th March and 22nd September. For simplicity I changed on 1st April and on 1st October. Later, I found it better to change on 1st March and 1st November, because the time when the climate is too hot is shorter than the time when it is too cold.

Motorized curtains

Curtains fitted to five north-facing windows, and a shutter fitted to a sun-porch window, should be opened to admit winter sun and closed at night to trap the heat. In summer they should be closed by day to keep out radiant heat and opened at night to allow heat to radiate out. The curtains and the shutter have motors controlled by a programmable timer (at lower right in the photo). In autumn (1st March), the timer is set to open at 07:40 and close at 17:20 daily. In spring (1st November) the timer is set to open at 18:00 and close at 06:00 (Standard Time).

Clear-story windows and fans

Continue reading

Managing my low-energy house: I. Features needing no attention

Photo of sunlit house interior

July sun heats the house

This post, and the companion post “II. Features needing attention” were posted originally to a forum of the Alternative Technology Association (See Note below.)

My low-energy house at Manilla, NSW, maintains year-round comfort in a climate of daily and seasonal extremes. In the climate classification of the Building Code of Australia, it is in Zone 4: “Hot dry summer, cool winter”, along with Tamworth, Mildura and Kalgoorlie.
This house differs from most houses in relying on the design of the house to achieve comfort, with hardly any energy needed for heaters or coolers.
There is little artificial control: the “home automation system” consists only of timers set twice a year. Some of the comfort features call for daily action in certain seasons. However, these simple daily chores could have been avoided by small changes in the design. [See “Note added 2016” below.]

The success of the house in maintaining comfort in all seasons is shown by scatter-plots of daily indoor and outdoor maximum and minimum temperatures over a period of three years.

I. Features needing no attention

Heat transfer to and from the heat bank

The mass of concrete, bricks and rubble under the concrete floor slab is edge-insulated with foam to a depth of half a metre to prevent heat leaking sideways to and from the surrounding soil and subsoil. This 150 tonne edge-insulated under-floor mass is a “heat bank” which absorbs and yields heat so slowly that it holds the same temperature (at 750 mm depth) within a degree for weeks at a time.
Double-brick walls (17 tonnes) inside the house, and the floor slab itself (28 tonnes), are also parts of the heat bank. Their exposed surfaces (See photo.) absorb heat from sunshine (and yield heat to cool flows of air) so as to spread heat (or coolness) around the rooms. Within each day they conduct heat to and from the rooms of the house, and from room to room. They then conduct heat slowly to and from the under-floor mass.
In the absence of the house, the under-floor mass would have the same temperature as the subsoil of the area. A thermometer at 750 mm in the subsoil near the house shows a 14.6° yearly temperature range, from 12.9° to 27.5°. Even an ordinary light-weight, poorly-insulated house built on a concrete slab on the ground here would be made more comfortable by these stable subsoil temperatures. Midsummer and midwinter temperatures in such a house (next door) are plotted here and here.
It is clear that temperatures in that conventional house vary much less than outdoor temperatures, and remain close to that of the subsoil. The heat bank under my solar-passive house has an even more stable temperature than that of the surrounding subsoil. (There is a graph showing one year of heat bank and subsoil temperatures here.)

Insulation

Thermal insulation reduces the flow of heat in and out of the house. With sufficient insulation, the heat of the day is replaced by the cool of night before the house becomes too warm. Insulation improves comfort permanently. Continue reading

Geoff’s solar-passive house at Manilla

View of solar-passive house

Geoff’s solar-passive house

A second high-mass solar-passive house was built in 2009 in Strafford Street Manilla, within 300 metres of my house in Monash Street.
My friend Geoff designed his house and used the same builder that I did. Sadly, after five comfortable years in his house, Geoff has passed away. Thanks to his daughter, I can show you the features of the house.
Thermometers, and power bills show that its performance is similar to mine. That is to say, it is very successful!

In Manilla’s climate of daily and seasonal temperature extremes, Geoff rarely needed to use his low-powered reverse-cycle air conditioner.

Plan of solar-passive house

Strafford Street solar-passive house: plan

Specifications

Dimensions

Length, East-West:     18.28 m
Width, North-South:    9.45 m
Ceiling height:               2.70 m

Area

Room area, Living/Kit/Bed 1/Study:      115.9 m^2
Room area, Bed 2:                                    13.8 m^2
Room area, Bed 3:                                    14.1 m^2
Room area, Bathroom:                              8.6 m^2
Room area, Laundry/Darkroom:               7.7 m^2
Area of walls:                                             12.7 m^2
Total House Area (without patio):       172.8 m^2

Exterior walls

North wall: double brick
East, west, and south walls: 90 mm stud, including 9.61 m reverse brick veneer
Cladding of stud walls: custom orb (horizontal)
Cladding of gable ends: plain roofing panels with 50 mm foam

Interior walls

Single brick:    17.16 m
Stud wall:        11.66 m

Windows (and two glass doors)

All double-glazed 3/6/3 in uPVC frames
(North-facing window area is 16% of the floor area of the house.)
North-facing:           27.00 m^2 (76%)
East-facing:               3.84 m^2 (11%)
South-facing:            4.50 m^2 (13%)
West-facing:             0.00 m^2 (0%)
Total:                      35.34 m^2 (100%) Continue reading

House Thermal Mass Works in Summer Too

House temperature ranges diagram

My house at Manilla, NSW, is in a climate with temperatures that are extreme, but comfortable on the average. To reduce extreme temperatures indoors, the house contains more than a hundred tonnes of thermal mass within a shell of insulation.
The “thermal mass” is the materials, such as bricks, stones, concrete, earth or water, that have high thermal capacity (See Notes below): they take in and give out a lot of heat.
Many people, who can see that having thermal mass inside a house will help to keep it warm in winter, think that the thermal mass will make it hard to keep the house cool in summer. They see many brick and brick-veneer houses in which thermal mass is exposed to the intense heat of the summer sun. In that case, thermal mass material does no good.

In this graph, I have used my last twelve months of temperature data to show the benefit of well-insulated thermal mass in summer as well as in winter.
Outdoor temperature in this year went as low as minus 4.0° Celsius and as high as plus 43.7°: a range of 47.7°. Continue reading

January “Coolth” in a House without Air-Conditioning

I have now 15 years of January average temperature data for my house at Manilla, North-west Slopes, NSW. These graphs show how the house temperature relates to the outdoor (or ambient) maximum, mean, and minimum temperatures.Regression graphs of indoor on outdoor temp in the hottest month

The house is not too hot and not too cold

Solar-Passive House from the NE.

House at Monash St Manilla from NE

In January (the hottest month) the rooms* in this solar-passive house do not heat up much during the day, nor do they cool down much at night. Since the indoor temperature always rises and falls just one or two degrees from the mean, only the mean is shown. Green lines on the graphs, which are drawn to pass through the middle of each cloud of data points, show by how much (on the average) the indoor temperatures have differed from the outdoor maximum, mean, and minimum temperatures. On the middle graph the green line shows that the rooms have been 0.5° cooler than the mean temperature outdoors. The left graph shows that the rooms have been 8.2° cooler than the daily maximum outdoor temperatures. The right graph shows that the rooms have been 7.3° warmer than the daily minimum overnight temperatures.

The design of the house aimed to protect those living there from excessive summer heat. It may seem that reducing the mean temperature by only half a degree is a failure. Not so! The January mean temperature at this site (26.1°) is near the middle of the adaptive comfort zone for this month, and so is the indoor mean temperature (25.6°). The house succeeds in keeping the indoor temperature comfortable in the heat of the day, when that outdoors is an uncomfortable 34 degrees. The high thermal mass that achieves this has the unfortunate result that the minimum indoor temperature overnight (not shown) is some five degrees warmer than the outdoor minimum. However, on average, it is still a comfortable 23.5 degrees. (Curiously, no-one knows the best room temperature for sleep.) Continue reading