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Heatwave: external blinds under test

Over the weekend Melbourne went through our biggest heatwave so far this summer, and the first real test of my external blinds, which were fitted to the house early this year.

Looking at the two nearest weather stations to me, yesterday the temperature at Melbourne (Olympic Park) peaked at 40.7 at 4:27pm. At Moorabbin Airport it peaked at 41.2 at 3:30pm. Happily by about 6:30pm the temperature had dropped about 10 degrees, but the lowest measurements overnight were in the high-20s.

I was away (in air-conditioned comfort for most of the day), but inside the house on Saturday it got to about 30 degrees. This compares to an inside peak of 33 degrees when I last measured it properly in 2014.

So on the face of it, the external blinds make about 3 degrees difference, which does take the edge off the heat, and combined with plenty of fans can make for a reasonable level of comfort. Fans all night have made sleep perfectly possible, and looking at our power consumption in daytime, keeping the house to 30 degrees while using fans, computers, TVs etc and still only burning 670 kW watts of power doesn’t seem too bad.

Window external blinds

Good roof insulation was installed some years ago, but seems to help more in winter than summer. Other options to explore would include wall insulation and double glazing. (One ceiling fan, suspected to be 15+ years old, also needs repair, as it’s stopped working.)

While they slow down the warming of the house, what the blinds and other passive measures don’t do is completely stop it getting hot, or cool things down. For that I would need actual air-conditioning or a split system, which I’ve tried to avoid, but is an idea I am slowly warming to. (Sorry x 2.) Perhaps to be installed with solar, to assuage guilt about increased energy consumption/emissions. Bear in mind of course the other measures have reduced what any cooling system would need to do.

By Daniel Bowen

Transport blogger / campaigner and spokesperson for the Public Transport Users Association / professional geek.
Bunurong land, Melbourne, Australia.
Opinions on this blog are all mine.

14 replies on “Heatwave: external blinds under test”

Good on you for installing outside blinds. Very unfashionable at the moment (we have them on our house, too) but saves energy and the need for air con.
A ceiling fan that works seems a good idea too.

I wouldn’t be too fussed about installing aircon. The most efficient now are very good, and the heating mode is probably cheaper to run than gas heating, if that’s your current.
Electricity network pricing is, perversely, already discriminating against you for not having aircon (you’re subsidising those who do) so if you can’t beat them….
Also – if you’re buying 100% greenpower – you’re helping stimulate renewable energy, and needn’t be overly concerned with emissions… : ) It’s a pretty easy/inexpensive move to make if you’ve also taken measures to improve energy efficiency.

I’m guessing you had the roof insulation installed during the politically infamous Pink Bats Scheme. I try to get the heat out my house and reduce the amount being produced within and entering the house. Also we’ve repainted certain outdoor walls to white to reflect the heat similar to our very tall fencing which helps.

Can I ask how old is this house in question. I know a few people who have quite (2010/2011ish) new homes without AC. It seems to bearable with blinds and other measures. How is air-flow in the house also Daniel since the better air-flow helps in terms of heat.

@Dave, thanks yeah good points.

@Ilham, no, I wasn’t eligible for the government-subsidised roof insulation, as I already had some (loose, ineffective) insulation in the roof. So I paid for an upgrade off my own bat. (Sorry, more puns).

The house is circa 1930, weatherboard, so it does heat up more than brick would. The external walls are mostly light yellow, so it does a pretty good job of reflecting light/heat. Air-flow is okay I think – when all the internal fans are going, the air does move around a bit.

That is a very nice window.

On the subject of air conditioning, it is now possible to buy a big enough solar power system (at a reasonable price) to power your entire air conditioner on a hot day. You can get plenty of cooling from an air conditioner that uses about 2500 watts, and a 3 kW solar power installation would probably cost about $3000 to install (after rebates, which I believe you can still get if you don’t have one yet). A system that big will produce enough to run the whole air conditioner on days when it’s needed. And on all the other days, it will pump so much power into the grid that you’ll probably end up making money (after you pay for it).

The shade will definitely help. You might want to consider evaporative cooling which is effective in hot and dry conditions and it uses very little electricity compared to a refrigerated system. My Australian made Convair Coolmaster portable evaporative cooler cools my entire apartment at only 200 watts on high speed. A smaller Convair Millenia only uses 85 watts on high (I know this because I sometimes find them by the curb and I repair them for friends and co workers).This past Saturday my Coolmaster was drawing in 41C degree outside air and blowing out 22C degree air into my apartment at about 78% humidity. It does drink several bucketfuls of water on a hot day. Whole house rooftop units (which you might consider installing) have the water piped in of course. The downside to evaporative cooling is that it puts out cool but humid air and it is not effective if the humidity goes above 50%. I have my unit set up and sealed to a window so that it only draws in hot dry outside air. I blocked off the open areas of the window with tape and some plastic panels called cornflute cut to size. I leave my bathroom and bedroom windows cracked open a few inches to let the air that the cooler blows in exhaust out. I found my portable unit by the curb and it only needed a good cleaning to get it working. If you want to buy a portable evaporative unit I recommend buying an Australian made Convair unit which are available in several sizes. They are a bit expensive new ($200-$300 ish) but sometimes Cash Converters has them much cheaper. The really cheap ones are not effective as I have also found them by the curb and tried them out too.

Have you ever considered evap coolers?

They hold up pretty well in Melbourne’s dry climate.

In last weekend’s heat, I kept the house at no more than 25 or 26 degrees celsius and I think my awnings do a poorer job than your blinds. Because of the extreme dryness outside, I did not seen humidity go above 65% indoors.

Remember that evaporative coolers use a LOT of water. They worked well in last week’s heat, but when you can get electricity from the sun to run a refrigerated unit, I’d forget evaporative.


That makes sense, but it depends on how much coverage you need for cooling.

For example, I have a 3kW solar system at home and a clunky old wall-type refrigerative cooling, and those bad boys suck up a lot of power that it exceeds my solar power generation.

The newer reverse cycle units are more efficient, and I’ve been told a bedroom-sized unit will draw about 0.5 – 1.5 kW. A living room type may draw up to 2 or even 3 kW.

If you need to cool multiple parts of the house at once, you can forget about having the solar system completely powering it up, even if you have a 5 kW system. However, it’s still better than no solar since it will cut down on the overall power cost.

During the weekend’s heatwave, my solar system did quite poorly as it was mostly cloudy. The higher temperatures too reduce the efficiency of the solar system. The most ideal condition would be a cooler (around 15-25 degrees celsius) but sunny cloudless day.

We have an evaporative system for a comparatively large house and it uses only about 1100W – a fraction of a refrigeration aircon unit’s energy usage. Our running costs are less than $2/day.

To the comment that they use a lot of water, this is trivial. Water is a natural, renewable, cheap and normally plentiful resource. Electricity is not, at least not when the sun is below the horizon.

There are fair arguments against evaporative aircon (e.g effectiveness in humid conditions), but environmentally they are easily the soundest aircon solution.

My parents have split system as it does get very hot in the summer at their place and it also gets very cold in the winter due to being further up in the hills SE of Melbourne. I only just moved in February to a new place in Carnegie. Not sure how it will go in the summer as I have a air conditioner in the bedroom and only a fan in the lounge room.

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