Our house, like many old houses in this part of Australia was not designed well for the local climate. In an area that is quite cool, the house was built with minimal windows facing the northern sun. Australian’s have a love affair with verandas and generally that’s ok because most of them live where it is usually hot. What is needed here is passive solar design.
We found we did not use the veranda often because it was either too hot, too cold, too windy, too many flies buzzing about, too many vicious mosquitoes or there was just too many other things to do. It was just a waste of space that required regular maintenance. We decided to convert it into a sunroom and become lovers of the sun.
I won’t go into too much detail about the build as I’m not a builder and this post is really about the benefits of passive solar design.
The build started with help from my father to replace the floor. Then I ordered a lot of windows and a glass door.
A massive hail storm hit the town before our windows were built. Many windows around town were smashed and repairing those was the top priority for glaziers so our windows were delayed until around the time our first baby was born. This added some extra pressure at a time when we didn’t really need it.
Once the windows and doors were in place I removed an existing window between the kitchen and the new sunroom and converted it into a doorway. Next job was fastening some plasterboard over the old weatherboards and hiring a plasterer to finish it off. We got an electrician to install lights and a power point and then we painted the walls and bought and carpet and had that installed. On the exterior we had to add a row of brickwork around below the windows and a small section of tiling at the front door.
All up it cost around $10 000. That was 15 years ago, so these prices are out of date. The windows and glass front door were the biggest cost at $7000. We needed 100 meters of fabric for the curtains and our family helped by sewing these. Even so, with curtain rods the total for that was around $1000. The final $2000 went on flooring, carpet, electrician, plasterer and paint.
How good is it?
Aesthetically it is ok. You won’t read about it in Home Beautiful. It’s not going to win any design awards. From a practical viewpoint it’s great. A lot of projects that I have done have not been successful, but this was more successful than I imagined it would be. It went from the least used area of the house to one of the most used. Visitors gravitate to it and are usually surprised at how warm it is inside.
Some people are surprised that a sunroom will significantly warm a house although they are not surprised at how hot the interior of a car can get parked in the sun and there really is not that much difference between the two. There is roughly 1KW energy per square metre from the sun, or so I beleive. About 14 square metres of sunshine enters through the front windows at midday in winter, so I think that we are getting about 14KW of energy. It doesn’t all get retained as heat as some is reflected back out, but it’s still substantial.
We have a wood heater that is very good, but it only outputs around 10KW of heat. We have a reverse cycle air conditioner as well and it is ok, but it only outputs around 6KW of heat. The sunroom makes a far bigger contribution to our heating than either of these. It only takes a cloudy day to be reminded of this, although even when it is cloudy there is often some warmth in the sunroom. It is now our main heating source with the wood heater only required on cold nights and the reverse cycle usually only on cool mornings when the wood heater has not been used overnight.
During the day it is often 10 – 15°C warmer inside the sunroom than it is outside. It’s not uncommon for it to get up to 28°C (82°F) inside when it is only 13°C (55°F) outside. We usually wear tee shirts in winter and still feel very warm. Parts of the house further away from the sunroom are not as hot as that, but generally they reach very pleasant temperatures.
It has changed our house from a cold old house into a warm, light and pleasant place. If you live in a cool climate and you get the opportunity to visit a house that uses passive solar heating then see what it’s like. Using “alternative” technology does not have to be inferior – it can be superior.
When you have as many single glazed regular glass windows as we do it doesn’t seem to matter if curtains have thermal backing or not, or even if you draw them closed or not, it is still going to get cold overnight. Maybe the temperature will not drop quite as quick but it seems to be just as cold by morning. We overcame this by shutting the sunroom off from the rest of the house at night.
Windows on the northern side (in the southern hemisphere) are good. The sun shines in during winter, but not in summer. Windows on the west or possibly the east are not as good. We place a temporary awning above the western windows during summer to reduce the sunshine entering the house otherwise the house would be unbearably hot.
A concrete floor with a high thermal mass should absorb and store heat during the day and release it during the night. That was too difficult for me to do, so we don’t get that benefit.
The sun is harsh on carpet, paint and furniture. We currently have three chairs. We deliberately use old ones. Only one was purchased new, one is second hand and the other came from our local dump shop. Covering them will lengthen their life, otherwise they will not last many years.
Cleaning the house windows became a big job.
To work well the room needs to receive plenty of sunshine. A cloudy climate of shading from trees and buildings will make a vast difference.
This is the second post about solar projects we have tried. I have already covered using waste heat from the roof to warm our house. Still to come is our experience with solar hot water heating and grid connect solar electricity systems.
This is the first post in a series I’m working on about our attempts at using solar energy for heating and electricity generation. Later posts will cover construction of a sunroom, a solar hot water heater and a 3kw grid connect PV electricity system.
A cool climate
Unlike many other places in Australia, winter here is cool as we live up in the tablelands at about 1000m altitude. Many nights during winter the thermometer drops down well below zero (32°F) and we wake up to glistening frost. It’s not just that the nights end up cold, it starts to cool down as soon as the sun sets. Often cars outside have a layer of ice crystals on them by 8:00 or 9:00 at night.
Days are often clear but the average maximum winter temperature is only around 13.5°C (56°F). Without external heating houses here get very cool.
All things are relative so people from really cold places like Alaska and Siberia are probably rolling their eyes at this point and thinking what a wimp I am, while most other Australians are nodding their heads and remembering a freezing cold night they spent here camped in a tent at the local caravan park. The thing is, houses here are not built that differently to those in more tropical parts of the country – put simply we are not really set up for the climate.
Our house is fairly old – maybe 80 to 100 years old and used to be quite cool and I don’t mean cool in an “awesome” sense. It used to get down to quite unpleasant temperatures inside in winter. Like many old houses in the area it has small windows and a verandah; in our case facing north (that’s towards the sun here in the southern hemisphere) and also to the west so it blocked precious sunlight entering the house. Like many houses in Australia, the house also has a corrugated iron roof.
It’s hot up there
While doing some maintenance in the roof cavity I noticed how hot it often was up in there on a sunny day even though it was quite cool outside. A traditional way of dealing with this heat is to add vents to get it out. There is a layer of fiberglass wool insulation bats on top of the ceiling but there is no layer of reflective insulation under the roofing iron that would normally be there. That could be useful if I wanted to do some experiments as I would not need to damage anything that was already there. I started thinking about ways to use some of this heat to warm the house and made a series of measurements.
I bought some 25 x 50mm (2” x 1”) pine timber, some reflective insulation, closed cell foam, some 15cm diameter fruit tins and a lot of duct tape and set about sealing off a section of the north facing roof. I had an old DIY heat transfer system that was designed to move warm air from one room to another. This system consisted of some flexible 15cm (6″) tubing wrapped with insulation, vents and a low wattage fan. I setup a vent in one corner of the house and had the fan between that and the heat collector. I ran some more of the flexible tubing down to the coldest room at the back of the house.
It was while doing the construction that I realised just how hot ifT gets up there. It was quite uncomfortable in protective gear and I was reminded again how much tougher builders must be than I am.
Unfortunately, I don’t have any pictures of the system, but I do have a picture taken before the build started. The reflective insulation was fastened to the underside of the rafters and held up with the pine timber. The ends were sealed with MDF that had holes with old fruit tins fitted into them for intake and exiting.
I had planned to use a thermostat to control the fan so that it would automatically come on when it was warmer at the roof than it was in the house.
So how did it go? Well not quite as good as I had hoped. The corrugated roofing iron is silver and I expect that a reasonable amount of heat is reflected off it. Also, as the iron gets quite hot I expect quite a bit of that heat rises up from it into the air above, rather than down below. Air blowing into the room did feel warm but the rooms temperature only increased by a few degrees. While it was warm up there when the fan was on heat may have been extracted faster than it was being collected so temperatures in the system dropped off.
I took a lot of steps to isolate the system so that glass fibers did not enter the house. I had set up the fan so that it was blowing air into the heat collector rather than sucking are out of it so if there was an air leak air would escape into the roof rather than suck air from the roof. Even so, I was never comfortable using it because of those fiberglass insulation bats in the ceiling. After all, the bags this insulation came in had a warning on them “Possible cancer hazard by inhalation”.
In the end we decided to convert our verandah into a sunroom and that made such an enormous difference that the ceiling system was abandoned.
Was it a complete failure?
It did give me a lot to think about. There is a lot of heat falling on most roofs and lots of houses need heating. There is roughly 1KW of energy in ever square metre of sunlight at midday, so even allowing for lower levels of energy at other times of the day and inefficiencies in the system there is still a lot of energy to be harnessed – at least in an area that has sufficient sunshine at cooler times. Another way of thinking about it is to imagine if half the roof was glass and the sun shone directly into the house, the house would be unbearably hot during the day even in winter. I don’t recommend creating your own system like I tried. There may well be health risks not just from insulation and dust but also from fumes from heated materials.
One of the benefits of a well designed system could be that it can be automated to switch off when the roof is cold and the insulated rooms below should remain warmer for longer. A problem with our sunroom is lots of heat is lost overnight through the glass windows but there is ways around that.
It is possible to buy solar air heating systems that can be retrofitted to a house, but I have not seen where this has been designed into the house so that it does not look like another thing bolted onto the roof.
Our verandah sunroom conversion will be the next post in this series.