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


The two clear-story windows that open have fans mounted near them (See photo.). In the winter regimen these windows are kept closed to trap air that is warmed by bricks heated in the sun. The fans are directed downwards and operate on a thermostat (to the left of the fan in the photo) whenever the clear-story temperature goes over 26°. They spread warm air down through the house. Without the fans, the sunlit bricks would overheat, and later radiate heat out through the clear-story windows at night.

In the summer regimen, these two clear-story windows are kept open to allow warm air to escape. The fans are directed outwards and operate every night from 01:00 to 06:00, using timers. The fans add to the natural draught that is caused by the “stack effect” so as to purge warm air from the house at night.

Awnings

Canvas awnings on the wide western upstairs veranda (talar) and on the open back porch are re-arranged for each regimen. In winter these spaces are sun traps, and in summer they are shaded breeze-ways.

Note added 2017.
Seasonal use of the talar is described here, and my son-in-law gives an appreciation of it here.

Features needing attention frequently

Nearly every night during the summer regimen cool air must be let in to the house. This is done by opening some outside doors and windows while the air outside is cooler than that inside. Generally, this can be done by opening them up before going to bed and closing them on getting up. [But see “Note added 2016.”] These actions, with the fan-assisted ventilation through clear-story windows by the “stack effect”, achieve a “night purge” that replaces warm air by cool air. Finally, the night air cools the heat bank for longer-term cooling of the house.
From time to time, similar daily actions help to maintain warmth in the house from winter to spring. Because the heat bank warms more slowly than the air, the house can sometimes be too cool in these seasons. The day-time air temperature, however, is frequently warm enough (over 24°) for hours at a time. At such times, it is worth opening the doors and windows to admit warmer air to warm the heat bank, just as cool air is let in on summer nights.
The need for these actions could have been avoided if ventilation had played a larger role in the house design. Large louvers or vents, with covers to seal them closed, could have been built in the outer walls near the doors. Like the curtains and fans, they could have been controlled by timers or thermostats. Such vents are mentioned on p.28 and p.42 of “Warm House Cool House” by Nick Hollo.

Note added 2016.

Night purge air is now admitted through an automated louvre installed low down in a wall on the south side of the house. I have acted on the suggestion in the paragraph above. I no longer have to open doors to achieve night ventilation by the stack effect. See the post:“Louvre window for summer nights”.


Note.

The original ATA forum posts in the thread “Low Energy Houses” are here and here. These two posts were in answer to a question by Jeff Bloggs in the ATA forum thread “Highly insulated home with little or no thermal mass – thoughts anyone?” Jeff asked “How do you manage your thermal mass?” I realized that I had never explained how I do it.

The house was described earlier in the “Low Energy Houses” thread, and pictured here. (replacing a much earlier post, with a photo now removed from view by the image-hosting web-site “Photobucket”).

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