Mirrors to reflect the sun

I have begun to warm the shady side of my house with reflected sunlight in winter.

Aluminium mirrors to reflect sun

Sun Mirrors Mar-17

This winter’s set-up.

The first photo shows the present temporary set-up, done on the 10th of March 2017. That is, soon after I had changed the house from its summer regimen (to keep cool) to its winter regimen (to keep warm).
As shown, I attached aluminium foil to the courtyard wall on the south boundary of my block. The foil forms mirrors that reflect winter sun onto the south wall of the house, the edge of the floor slab, the footings and some nearby concrete paths.
The mirrors are sheets of aluminium cooking foil (“Alfoil”) 300 mm wide, cut to 900 mm lengths. I attached the foil to the wall in vertical strips with double-sided tape. As the wall is 12.6 metres long, the total mirror area is 11.3 square metres.

Last winter’s set-up.

Temporary aluminium mirrors to reflect sunlight

Sun Mirrors May-16

Last year, during April and May, I attached only 17 strips of foil 700 mm long in the same way. The total area then was 3.6 square metres. In that winter, the wind did a little damage, which I taped over. Much worse damage was caused by a magpie-lark attacking his reflection. By October, they were torn as shown in the third photo.

Aluminium foil damaged by birds

Bird Damage Oct-16

I repaired some of that damage, too, using builders’ foil, which is stronger. Early in November 2016, I removed all the foil. By then I wanted shade. not sunlight.

Effect of the mirrors

The white-painted courtyard wall reflects nearly all the sunlight it receives. However, this is diffuse reflection, going equally in every direction. Only a small part of it goes to points likely to warm the house.

Sunlight that has been reflected towards the house.

Reflected Light May-16

The aluminium foil reflects in a specular (mirror-like) way, sending nearly all of the solar energy downward at the same angle that it arrived. Because the foil is wrinkled, these mirrors spread the beam of sunlight out to about twice the width of the mirror surface. It is still quite concentrated as can be seen in the last photo, which is lit mainly by reflection from the foil.

Light reflected from these aluminium mirrors is not aimed precisely at points where it would best warm the house. The mirrors are not mobile, and their location owes a lot to chance. Furthermore, the house shades the mirrors for parts of each day; different parts as the season changes.
However, I think the warming effect will be useful, and I hope to be able to measure it.

Related Topics

The mirrors are part of the Courtyard that I have described in posts and pages listed in “My House Page”.


I raised the question of mirrors to reflect sunlight in a thread titled “Reflective Film” on a forum of the Alternative Technology Association (Melbourne).

Porch is a Breezeway or a Sun-trap

Photos show awnings arraged for summer and for winter

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.

My Heat-control Courtyard

Photo of a small courtyard

A Heat-control Courtyard

I have added a courtyard to my high-mass solar-passive house to improve summer cooling and winter heating.

Photo of building materials

Courtyard Wall Panels and Gates

The courtyard extends 13 metres along the south wall of the house. It is completely enclosed by a wall of white-painted polystyrene sandwich panels 1.8 metres high, with two gates of the same material.

By September 2015 trenches had been dug for the courtyard foundation, and by December it was complete.

Photo of trenches dug for courtyard

Courtyard Trenches, West

Photo of trenches dug for courtyard

Courtyard Trenches, East

Operation

This house is in BCA Climate Zone 4: Hot dry summer, cool winter. For comfort, it must be made very much cooler in summer and very much warmer in winter. The courtyard was built to help to achieve both results without the use of heaters or coolers.
In summer, it should ensure a supply of very cool air at night. In this house, cool air is drawn in to replace warm air that flows out the clear-story windows by the stack effect, assisted by fans. By day, the courtyard walls also block some solar radiation.

Photo of courtyard from the west

The Courtyard Through The Western Gate

In winter, the white courtyard wall reflects sunshine north towards the house, and re-radiates heat lost from the house wall back towards it.

More

Much more detail is given in the page “A Heat-control Courtyard”. All photos on this topic are in a gallery in “House Photos – 2016”.


To invite discussion of how courtyards can affect indoor and outdoor climate of houses, I opened a thread “Courtyards for Climate Control” on the forum of the Alternative Technology Association (ATA) based in Melbourne.