My winter sun reflectors
This is the story of how the living areas in my house were transformed from cold and dark in winter to warm and sunny. It’s a happy tale for a house in Canberra where summers are quite hot but winters are cold.
Like many houses built in Australia, the orientation of my house was far from perfect. While the bedrooms and utility rooms were very sunny on winter mornings, the living areas faced due south-west: cold and dark in winter, very hot in summer. My family room was so unpleasant and cold in winter that I had stopped using it altogether.
Also I wanted to achieve some significant results for the environment:
This article talks about:
The solution: retrofitting with winter sun reflectors
The solar architect Derek Wrigley drew detailed plans for large winter sun reflectors to be constructed on the south-west of my house. I first heard of Derek’s work a few years ago while I was researching a project for my Master of Landscape Architecture at the University of Canberra. Later, as a member of Nature and Society Forum, I attended one of Derek’s Open House days, bought his book Making Your Home Sustainable: A guide to retrofitting, joined See-Change, and then consulted Derek to see what he could do to improve my dark and dank family room. The orientation of my house was difficult for Derek to work with: the closer a house is to north-south orientation, the more effective winter sun reflectors will be.
Figure 1 shows the view of my winter sun reflectors from my back door with sky and trees reflected on the panels. Figure 2 shows the reflected sun on family room, kitchen and lounge room windows, and the darkness of the walls and windows where no sun is reflected. This was the normal dark state of the back of the house before the reflectors were installed.
What is a winter sun reflector?
A winter sun reflector is a panel of polished stainless steel installed on the southern side of a house. It reflects winter morning sun into cold, dark south-facing rooms. The precise location and size of the reflector panels have to be calculated carefully to take into account the exact orientation of the house, the slope of the roof and the location of windows, so as to maximise the entry of sun and minimise glare at eye level. The principles are outlined in Derek’s book (http://www.publish.csiro.au/pid/ 3990.htm). My reflectors were expertly constructed by Peter Culleine of Ratz Mobile Welding.
In March 2010 the morning sun started to creep across my family room floor for the first time ever (see Figures 3 and 4). My family room, like the whole back of my house, faces exactly south-west so it gets no direct sun at all between May and August.
What a difference my winter sun reflectors have made! The cheerfulness factor, as Derek calls it, is huge and I have regained a room for about a quarter the cost of extending the house. I now have the largest domestic winter sun reflectors in the world but they are clearly not an eyesore ‑ they reflect the sky and the surrounding trees (see Figures 1, 2 and 5).
In April 2010, Derek adjusted the angle of the reflectors slightly so that more sun would enter the house ‑ compare Figures 3 and 6. I later adjusted the angle down a notch because the sun was reflecting too high up the walls. It’s very easy to make adjustments ‑ three steps up the ladder, then undo, move and redo a couple of thumbscrews.
My now sunny house
My house is basically a simple rectangle with bedrooms at the front and lounge/dining room, kitchen/family and laundry at the back. It is also split-level with an open-plan design where the central hallway opens out to both the family room and the lounge/dining room. Figure 7 shows how the winter morning sun from the front and the reflected sun from the back can now penetrate right into the centre of the house along almost its full length. Figures 8 to 12 show the morning sun in most other rooms of the house.
Benefits already mentioned include:
During the cloudy and wet 2010 winter I experienced a temperature rise of about 3° in southern rooms. In summer the family room is about 5° cooler than the lounge/dining room because the panels shade the house from the afternoon sun.
Frequently asked questions
1. What happens in summer? Doesn’t the house get hotter?
In summer the reflectors are adjusted so the top is tilted slightly towards the house. Because summer sun is at a much steeper angle than winter sun, it hits the reflectors almost vertically and is reflected almost vertically to a fairly narrow band of light quite close to the reflectors, about 2 metres from the house.
Meanwhile the panels themselves shade the house from the afternoon sun. My family room is now about 5 degrees cooler than my lounge/dining because of this incidental benefit.
2. Does late afternoon sun reflect from the back of the panels and cause problems to back neighbours?
In winter there is no sun hitting the back of the panels. Last summer I had a small tree behind the panels (see Figure 5) which largely prevented afternoon sun reaching the panels. Sadly this tree has since died but its replacement will eventually help prevent afternoon sun reflecting off the panels. However, even without trees, the late afternoon sun will be reflected at an angle close to horizontal which is well above eye level but below airline flight paths. Also the frames on the back of the panels will mean that any reflection would be quite small (see Figures 2 and 5).
3. What impact do the reflectors have on neighbours’ amenity?
Side neighbours only see the reflectors from the side so their visual impact is slight. A side neighbour looking at the panels from their back garden, or a back neighbour, would mostly see a reflection of sky and trees.
Reflectors installed on houses on smaller blocks would still reflect mostly sky and trees. If a neighbour’s house was so large that there was no room for trees, they could hardly blame the reflectors if they have nothing attractive to look at.
4. Do the reflectors shade the garden?
Gardens on the south-west of a house get very little sun in winter. In general plants which are about 5 metres from the house will get winter sun from about 10am. The reflector panels do shade the garden to some extent but because the panels are almost vertical, the shade area is quite narrow and it is constantly moving.
5. Are plants under the reflectors killed by the reflected heat?
Plants close to the posts supporting the reflectors will probably be killed by reflected heat. Derek had some groundcovers which looked quite frizzled where the midday sun reflected on them in summer.
Reflector panels are usually placed on the outer edge of a pergola with paving underneath, about 2 metres from the house. Plants would probably survive the reflected heat if they were close to the house (but they would be exposed to a very wide range of winter temperatures ranging from –10° to about + 15° and they would be very hot and dry in summer so they may not survive anyway). A better solution for the south or south-west of a house is to grow plants in movable pots. Otherwise planting would be best kept to beyond the pergola.
6. Do the panels need cleaning?
Mostly the panels will be cleaned by rain but they may need an occasional hosedown if we have heavy dust storms or to remove bird poo.
7. Do I get glare from the reflector panels?
Yes sometimes, but it is lovely compared with the previous darkness! And the reflected glare is no stronger than any glare from the actual sun on the other side of the house.