Tag Archives: solar-passive

My better sun mirrors

Posted in Indoor Climate, Manilla NSW by
By 11.30 sun mirrors fill the patio with reflected light.

By 11.30 reflected sunlight floods into the patio.

In my blog post “Mirrors to reflect the sun“, I described sun mirrors I put up to reflect winter sunlight to warm my house in NSW, Australia. They were just sheets of cooking foil taped to a north-facing courtyard wall, and I had to remove them each summer.
Now I have better and stronger mirrors: hinged panels that function winter and summer. In winter they reflect sunlight, and in summer they give shade.
These simple hinged mirror panels should improve the indoor climate due to my “Heat Control Courtyard“. Compared to heliostats (see links in a Note below) they are cheaper and will not set the house on fire!

This post is also available as a PDF file My better sun mirrors.

Materials

The mirror panels

I bought the mirror panels from builders supplies as “FoilBoard insulation panels”, 2440 mm X 1220 mm X 20 mm.

These are “aluminium composite bonded panels (ACP)” of rigid cellular expanded polystyrene (EPS) (20 mm) bonded between two layers of aluminium (less than 0.5 mm). One aluminium surface has 97% reflectance; the other is pre-finished in shades of green using a fluoropolymer resin paint system. [Cost of five panels: $230.]

Framing

The fragile FoilBoard insulation panels had to be stiffened with frames of aluminium angle, corner brackets, and braces of aluminium strip. [Cost: $380.]

Hinges

I had the panels mounted on ten “hinges” that allow them to be held in two positions:

(A) flush against the courtyard wall to reflect the sun to the house in winter, or

(B) raised above horizontal to provide shade in summer.

These are standard hardware items called “Whitco Window Stays”. [Cost for ten: $430.] Here, they operate as hinges, using friction to secure the mirror panels at any angle. [I must thank my builder, Keith Freeman, for selecting and using them in this way.]

Schedule

Work on the new sun mirror panels began on 1 December 2019 and ended on 24 January 2020. Labour cost about $1800, while materials (given above) cost about $1050.

As soon as the work was done, I set the mirrors to provide summer shade until the end of February 2020. Then I re-set them to reflect winter sunshine until now (2 September 2020).

The finished mirror panels

Photo dates

Because the effect of the mirror panels depends on the seasonal path of the sun, I took separate sets of photos in June, to represent the eight winter months (March to October) when they acted as mirrors and in February, to represent the four summer months (November to February) when they acted as shades. Photos of hinge details were taken in February.

Hinge details

Whitco window stays that form hinges to support sun mirror panels in winter are set here to make the same panels give summer shade.

These window-stay hinges are set to support both panels to give summer shade.

Whitco window stays form hinges to support house-warming sun mirror panels to make them also summer shade panels.

These window-stay hinges are set to support panels for winter warmth on the left, and for summer shade on the right.

Continue reading →

Mirrors to reflect the sun

Posted in Indoor Climate, Manilla NSW by

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 (2017).

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.

Update in 2020

By 11.30 sun mirrors fill the patio with reflected light.

By 11.30 reflected sunlight floods into the patio.

I have now replaced these mirrors of cooking foil with much improved sun mirror panels.
See the new post “My Better Sun Mirrors”.

 

 

{Winter 2018.
The mirrors that were set up in March 2017 were taken down on 1 November 2017. On 5 May 2018, the same “temporary” set-up (as pictured above) was done again. The mirrors were removed on 3 November 2018. I continue to monitor temperatures and plot correlations.]

[Note added October 2019.
Winter 2019.
During 2019, I arranged to have new mirrors installed, made of aluminium-faced “Foil Board” insulating panels 20 mm thick. Mounted in frames, these would be more robust, and would have the advantage of providing shade in summer.
These new mirrors are not yet installed. Consequently, temperature data for winter 2019 is all in the category “without mirrors”.]

The first trial set-up: winter 2016.

Temporary aluminium mirrors to reflect sunlight

Sun Mirrors May-16

Last year, during April and May (2016), 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. On 6 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 in Melbourne, now re-named “Renew”. (I posted as “Catopsilia”, my first post being the 15th from the top.)

Solar-passive House Testimonials

Posted in Indoor Climate, Manilla NSW by
Photo of a birthday party in the solar-passive house

Birthday Group

Family members visited the solar-passive house in Monash Street, Manilla, NSW, in Mid-winter 2016. The date of their visit is shown on the graph in this earlier post. This photo shows us dressed for comfort at 17 degrees indoors.

Interviewer:
What do you think of Grandpa’s house in winter?

Grand-son (10):
I like Grandpa’s house. It’s nice. Except there’s no wifi. But apart from that, it’s good.

Grand-daughter (13):
Grandpa’s house? It’s cool. It’s interesting. Awesome curtains – I get a shock when they move because I’m not used to it. The garden is cool too – it’s pretty.

Daughter:
I love winter. And I love visiting my Dad. He built this really great house in Manilla nearly twenty years ago. Prior to that, he was tenanted in an old office space above the newsagent. I loved visiting him back then as well, even if his flat was super hot in summer and not at all cosy in winter. The house he built is wonderful all year round.

Even if there are only a few hours of sun each day in the depths of a NSW winter, that is all you need to warm my dad’s house. You can find yourself a chair in the sun, sit for a while and imagine you’re on vacation in Hawaii. Only with much better coffee. As the sun goes down, the sound of noisy birds settling in for the night comes through from outside.

Kitchen view SW

Kitchen view SW

The kitchen is well-stocked for preparing dinner (especially after we restock it) and, once the stove is on, it’s toasty warm in there. There is a curtain that closes the kitchen off from the rest of the house, but cooking time is social time for us, so we leave it open – which also helps flood the house with the delicious smells of curry. The house finally gets coolish sometime after dinner. That’s when we don the cardies and fluffy slippers and pre-heat the beds. The electric blankets, even on low, manage to warm the bedrooms all night.

Next morning, on a strict schedule, the automatic curtains fly open to announce the new day. Not being an early-morning person, I make good use of the curtain override button. At least, until I get the first whiff of toast.

Son-in-law:
Having grown up in India, I find summer is a breeze and cold weather is a challenge. After a couple of decades in Canberra and almost a decade in Switzerland, I have finally realised that dealing with winter boils down to managing the environment in the house and wearing the right gear.

I have stayed in my father-in-law’s house in Manilla several times, in summer and in winter, most recently in the winter of 2016. The house is comfortable in both summer and winter. I remember feeling colder in winter when I first stayed there compared with now – I am not sure whether the house is warmer, or I have more layers of fat to protect me as I get older. Maybe I just dress more appropriately now for winter thanks to my time in Switzerland.

The place where we hang out the most is the kitchen, and around the kitchen table, over cups of coffee or improvised meals, catching up on left and right leaning newspapers. The kitchen is very cozy in winter, especially when there are multiple dishes cooking away on the stove.

A memorable feature of my father-in-law’s house is the automated curtains which felt space-age when I first experienced them, but now I am used to them. They are like a bell-less morning alarm. Being a morning person, I beat them to it, and am awake before they start moving and letting in light.

Photos of porch awnings adjusted for outdoor living in winter and in summerI love the balcony on the first floor. It is well protected and I can sit there for hours with a cup of coffee and a book, and listen to cockatoos and other birds, and watch the paragliders in the distance when they are out. In winters the mid to late afternoons are the most comfortable.

Photo of a path between trees

In the garden

As the trees and shrubs in the evolving garden have grown and the paths have become more structured it has become a wonderful place to walk around and to relax. The garden bench is particularly inviting. This man is as passionate about his garden as he is about his house. The guided tour of his garden is one of the highlights of our stay there.

Interviewer:
Thank you all for your answers.
Goodnight, everyone.

Recent photos of the house and garden are here.

Hard Winter for Solar-passive

Posted in Indoor Climate, Manilla NSW by

Graphical log of daily indoor and outdoor temperatures for winter 2016.

Temperature log: main features

This graph, for 2016, shows a winter pattern of indoor and outdoor temperatures that is typical for this house. Indoor temperatures vary much less than outdoor temperatures, they rise and fall with them, and they are higher nearly all the time.
While the outdoor temperatures shown go as low as minus three degrees, those indoors lie within the winter “comfort zone” from 17° to 24° (see this post) nearly all the time.

Weather this winter

This winter was harsh for a solar-passive house. Near-record rainfall (227 mm) came with the greatest number of cloudy days of any winter in the new century. There were 53 mornings with more than four octas of cloud, when the average is 33.

Heater use

Because cloud limited the the solar gain, I had to use blower heaters far more than in previous winters. My records show that I used 320 kWh ($80) in these heaters this winter, when I normally use about 40 kWh ($10).
Heaters were also used by guests who were present on the six days shown. As well as being unused to the climate, the guests lived in the colder west wing of the house. They may have used 72 kWh ($18). Those guests have kindly written reviews of their visit.
Even using 400 kWh of electricity for personal heating in a winter could not make a detectable change in house temperature. I have found that blower heaters are surprisingly good at making a room in this house comfortable. As the radiant temperature of the walls is only 2° or 3° too low for comfort, it can be compensated by making the air temperature only slightly higher.

The pattern in detail

While cloudy days are not plotted here (Cloud observations for this winter are plotted elsewhere.), cloudy days can be recognised on the graph. In this climate, days with low maximum temperature and high minimum temperature are always due to cloud. Only in fine weather are days warm and nights frosty. The graph shows how the weather goes through a cycle every week or two: sunny days get warmer, then rain sets in. As it clears, the air gets even colder, before warming up again.
Indoor temperatures follow the same cycle, but there are differences. There may be a delay of up to a day, and sometimes longer.

Correlations

I did scatter plots comparing all the variables shown in the first graph and I fitted linear regressions. I present the four scatter-plots that had the highest coefficients of determination (“R-squared”). Continue reading →