Solar power through the square window

In my last post I alluded to having some thoughts on whether my house was making the most of solar power, particularly in regard to how I was using it. Knowledge is power, and the knowledge I’ve gained in the past few of weeks of my solar power usage has been very interesting.

Understanding which appliances burn the most power, what the usage patterns are, and the effect of weather, are all critical to getting the most out of the investment. This ensures that I can achieve the ROI I want, and that I’m a responsible user of any fossil fuel energy I’m required to draw from the grid.

Though the weather today was pretty good.

In all my analyses, the ducted air conditioner keeps cropping up as the villain (and at some point I’ll reconcile myself to that).

Its a difficult issue to address, as ripping it out of the roof space and replacing it with something else would just cost a load of money, and may not practically address the issue of solar power for cooling on a bang-for-buck basis. I need to ensure I’ve investigated other ways to either offset its use, or reduce my reliance on it.

Air conditioning comes down to a simple premise: comfort. You use it because you have too much outdoors in your indoors, so to speak.

That’s not a bad thing in the world of modern convenience, where our cars, offices, and houses are all air conditioned. However, have you ever thought that air conditioning is just treating a symptom of the main problem, and not the root cause?

The root cause – intrusive heat in this case – is going unaddressed. Even if you have a really efficient unit with all the bells and whistles, you may be able to do even better through other, more practical means.

Beyond “don’t leave the door open!”, there are many factors affecting your use of air conditioning or heating, often reflected in the design and quality of your building. Do you have adequate insulation of suitable quality? When was the last time you had it checked? Gaps around the doors? What about covering the windows?

Windows are a general weak point for heat transfer into or out of a building, particularly in large parts of Australia, where we don’t suffer the kind of harsh winters that require central heating or double glazing.

As a design point, a lot of modern houses here open up windows far more, which often results in more energy usage. One design element I need to deal with in my house are the large, west-facing windows.

About 8 square metres of glass, pictured at 1PM Sydney time today, before the sun hit

Both windows are in the same room at the front of the house, are 1800mm (6 feet) high, with the one on the left nearly square and the other about 2700mm (9 feet) wide, getting hit by sun all afternoon. The internal venetian blinds, while slowing the direct heat down a little, aren’t stopping it from advancing into the room in the first place.

Simple science: the sun hits the glass, which heats up, subsequently transferring its heat to the cooler air inside that is right up against the glass. That air rises (because heat) and more cool air is drawn against the glass. Rinse and repeat for 4-5 hours on a hot Aussie summer day!

Some people also look at tinting their windows or installing double-glazing to assist with this, but I remain unconvinced about either option in terms of value-for-money in most parts of Australia.

Tinting provides an extremely thin buffer, so it is only going to slow things to a certain degree – better than nothing of course, and relatively cheap compared to other methods. The downside is that in winter its going to perform the same function, stopping heat from entering the house via those windows. As a side note, the privacy aspect of tinting is lost when the lights inside are brighter than the lights outside i.e. at night when you are using that space.

Double (or triple) glazing is the architectural method of choice for sound proofing and insulation of glass. While its overall effectiveness year-round as an insulator cannot be questioned, the expense often makes the average home owner hesitate. Double-glazing in summer is best used where you can keep the internal temperature cool, and therefore stabilise the buffer between glass panes at a temperature somewhere between the outside and the inside. Generally speaking, if you’re not keeping the room cool through e.g. air con, the buffer will heat up, and start transferring that heat into the room.

In my opinion, and that of several electricity companies, the best way to stop this kind of heat transfer is to stop the heat hitting the glass in the first place. In essence, you create an external buffer zone where the sun’s heat and UV rays can’t get to the glass in the first place.

There are several options available, from adjustable fabric awnings, metal shutters, louvres, window shades or fixed awnings.

Rather than run out and spend a pile of money on anything custom-made for those windows, I decided to experiment first on our north-facing garage window. In the garage I have a network cabinet* in which I have my network backbone with appropriate patch panel for all the points around the house. I don’t want that equipment to overheat, and shielding that window should help prevent that.

* on reflection, probably a mistake to put it there, but it wasn’t going anywhere inside the house, according to my wife. Its called “compromise” I think…

Window coverings

I went to Bunnings Warehouse and, for the princely sum of $297, bought a fabric awning (1800mm wide, 2100mm drop) to cover the garage window from the worst of the heat. That’s it on the right, and I put it up myself in about an hour.

The awning can quickly be retracted in case a storm blows up, or in winter when I want the sun to warm up that side of the house. Sydney winters may not be harsh with snow and such, but we tend to have low tolerance for cold as a result ?

I’m going to keep an eye on this for the next couple of weeks, as we move into cooler months, and see how it performs as the sun moves back north and puts more sun on this window.

Some (including my wife) may say that these kinds of awnings are a bit daggy, and yes you can buy them in stripy patterns if you want to be reminded of your grandparents’ post-war bungalow. However, if they do the job then I think for next summer I’ll be pushing to cover the rest of the problem glass on the north and west sides of the house.

It will be a battle royale between her Better Homes and Gardens and my New Scientist approach to this whole thing.

In the meantime, the best we can do is shut the problem room off during the heat of the day and let it become the buffer zone. My issue with that longer term is the electronic equipment in that room is under strain during that time from heat. And its the rumpus room for the kids, so now I have them in the main room watching my TV!

Garage door

The double garage door also faces west, and therefore gets a lot of heat in the afternoon. That was an issue from the day we moved in (late 2013), so after a bit of research I bought a roll of Green Insulation Reflecta-GDI which looks a bit like this once fitted.

Garage Door Insulation
Reflecta Garage Door Insulation
It definitely works – I can’t touch the bare metal of the door for more than a few seconds on a hot day like today (35oC / 95oF in the sun), while the insulation is merely warm , slowing the heat transfer into the space.

Measure your door panels before you order and, once fitted, you may need to recalibrate the garage door lifter to account for any weight change (it isn’t much but some units are sensitive). No adhesive required as it designed to fit most modern panel garage doors in Australia by sliding into the space at the correct width. That is actually a shot of it overhead – no issues whatsoever with staying in place in over two years.

While we’re on the topic of garage heat, DON’T close your garage door immediately in summer after you park the car in there. The heat you trap will radiate into the house through plasterboard before it will escape through brick or wall insulation. Leave the door up and get some air flowing through the place for at least half an hour.

Not so bad to trap that car heat in winter, but make sure the engine is off!

Solar Power Design – more than panels

If you’re in the process of building or renovating, you may have already made a lot of decisions around how you wants things to look. Some of those things may focus on solar power, while many more are about the right fittings, colours, and facade for your home.

Those with solar power aspirations will already know how important aspect is, though after discovering what I have about my own house, I believe it should be more than how many panels your roof can hold.

If you haven’t adequately considered the thermal efficiency of your home, you may not be capitalising on your investment properly.

Even if you’re not considering solar power for your house at this point, you might think about getting the place pre-wired while the build is occurring, as Jennian Homes in New Zealand is doing with all new builds.

Consider the design factors around your insulation (wall and ceiling) as well as windows and cooling or heating options. Sometimes these things can be lost when you’re focus is on the right marble bench top, or the right tapware.

The builder may promise the latest, you-beaut ducted AC, but it may end up costing you more over the longer term. Look instead at smaller, more efficient air conditioners (like split systems) to cool or heat the space you need. In either case, make sure you understand the energy requirements of these add-on extras and how they will affect your power usage.

A few little decisions now can save you hundreds or thousands in the future, particularly as prices rise (and they will) and governments feel pressure to adopt renewables standards across the world.

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