Porch Awnings in Summer and Winter
This porch, which is a sun-trap in winter, is converted simply to a shaded breezeway for summer.
The porch is an upstairs outdoor room, open on three sides, at the west end of my house. With a Tallowwood deck and steel balustrade, it could be called a verandah or a balcony. I like to call it a talar, although it is not as grand as the talar of the Ali Qapu Palace, Isfahan.
For the colder part of the year, from March to October, the talar awnings are arranged as in the right photo. I fasten down the canvas awning on the south side to stop drafts, and I roll up the awning on the west side so I can enjoy the views. On sunny winter afternoons it is pleasant to have a late lunch there, with temperatures in the high twenties, several degrees warmer than the maximum in the thermometer screen.
For the warmer part of the year, from November to February, the awnings are arranged as in the left photo. The awning on the west side is fastened down against the intolerable heat of the afternoon sun. That also keeps the heat off the west wall of the house. The south awning is raised, to allow air to flow through, from south to north. When there is a breeze, it can be comfortable to sit on this porch even on very hot days.
By the use of cheap canvas awnings, this porch can make outdoor living pleasant in months when the climate here is too cold or too hot for it.
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.)
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
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.
Strafford Street solar-passive house: plan
Length, East-West: 18.28 m
Width, North-South: 9.45 m
Ceiling height: 2.70 m
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
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
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
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.
Dashed lines to the left and right show how the indoor temperature on the hottest days is reduced by up to 10 degrees, while on the coldest days it is increased by up to 8 degrees.
This post is one of a set of four back-dated to June 2010:
Indoor versus Outdoor Temperatures (1096 days)
Indoor versus Outdoor Minima (1096 days)
Indoor versus Outdoor Maxima (1096 days) (This post.)
Indoor/Outdoor Regressions for Maxima and Minima
This article was originally posted in the weatherzone forum thread “Indoor Climate” on 7th June 2010. It is backdated here to 19th June 2010.