A Rough Guide to Greening Your Home
Transcript of the "A Rough Guide to Greening Your Home" video
Philippa: It’s a basic human need to feel warm. That is why we started living in caves and then huts to keep out the cold winter nights and chill winds. Of course, over the years the structures that we’ve lived in have evolved but whatever the structure the basic compromise has always been there, even in the humble hut you create a space for light to come in and heat comes out.
And then down through the years from huts, to cottages, to castles the same basic compromise. You either have it really light but very cold or nice and warm but very dark.
Fast forward a few thousand years to the introduction of glass into our homes and we suddenly had the ability to create light and warm spaces. And with recent advances in glazing technology our living environments have become even lighter and warmer.
But it is now possible to put an end to losing any heat through our windows as we are about to find out.
The eternal compromise between keeping our homes light and warm has challenged scientists for years. But not anymore, todays most advanced windows can actually help heat the home by harvesting free energy in the form of sunlight and retaining heat, more heat than they actually lose.
And they do it with some remarkable changes to the basic components of the window, the glass.
To find out how I have come to one of the UK’s largest glass manufacturers and it is absolutely vast. But it is so automated that you barely see anyone around and I need to find someone to tell me how they make float glass.
Luckily this is Rachel Appleyard and she can talk is through the whole process. So what happens here then?
Rachel: Well this is the start of the process where we are adding sand as the raw material of glass. It is a continual process that happens 24/7, 365 days of the year.
Ok so here we are basically super heating the sand to melt it down to become molten liquid. It then flows out on to a bath of molten tin and it forms a perfectly flat, smooth bit of glass.
The glass now travels down the line a distance of just over half a kilometre and it is cooled slowly to prevent it from cracking and breaking into pieces
Philippa: So I’m imagining a river of glass inside here
Rachel: So yes, at this point the glass is solid but it is still at a very high temperature hence the reason that we need to continually keep that cooling process going down the line.
Here we are virtually at the end of the process. What we have got now is we are cutting before it is stacked and goes into the warehouse. What you will notice here is that the glass plate is continuously moving and therefore to ensure that we get a straight edge we cutting the glass on an angle.
Philippa: Ok so you’re not going to get a wonky line.
Rachel: Not at all, it will be completely straight
Philippa: And not a crack!
Rachel: No not a crack in sight
Philippa: It’s so perfect
Rachel: Perfect bit of glass
But not all the glass they make here is the same. As we mentioned the primary ingredient of glass is sand, and sand naturally contains tiny quantities of iron, just about 0.1%. You can’t actually see it with the naked eye when you look at a piece of glass like this. But when I twist it sideways like this and you look down lengthways through the glass you can see the green tinge. That is caused by iron. Now the big discovery was that if you use sand with less iron in it the glass becomes more transparent so you can harvest more energy from the sun in terms of light. There, again you can’t really see the difference but when I hold it up like that, the difference is really clear.
This discovery comes at a bit of a cost because you can only make low iron glass with low iron sand. And only two quarries in the UK produce sand with a suitably low enough iron content. Couple that with the fact that the transition required to switch in and out of the manufacture of low iron glass takes around 20 days, it is no wonder that it’s expensive to make!
But that is only half of the story. This machine solves the second half of the compromise, more light in means more energy in, but how do you stop the heat getting out?
Answer…they add a microscopically thin metallic coating which creates a reflective layer that actually bounces heat back into your room. To ensure the coating is perfectly even and transparent the glass travels along here through a vacuum. In zero atmosphere, ions of different metals are sputtered on to the surface. This creates a flawless layer which your eye can’t see.
The combination of one sheet of highly transparent, low iron glass and one sheet with an invisible reflective coating has done away with any compromise between getting in all the light you want and retaining the heat. But how do you know what to look for in a window if you literally can’t see any difference between the glass.
Simple, on every energy efficient or inefficient product nowadays you’ll find one of these energy labels to help you chose. Whether it is a freezer or a light bulb, the scale runs from inefficient G or F standards right up to an A rating. But with windows an A rating is not just a little bit better; A-rated marks a huge difference. It is the tipping point where a window moves from costing you money, to saving you money.
Anything less than A means the rating is letting you know just how much energy your house is going to lose. Whereas an A rating starts at zero and is rated in positive numbers which lets you know how much energy the window is going to give you.
It is a simple choice, how much your windows heat the outside, or how much they heat the inside. Let me show you using these two windows. Don’t be fooled by the fact that they look the same. This is a standard doubled glazed window with an F rating and an energy index of -70. That -70 is a measure of kilowatts of energy it would lose in a year. This is a 1kw electric fire, so for every square metre of window like this with a -70 energy index that is the equivalent of having one of these [electric fires] outside for 70 hours. You’d be literally heating the street as the average house has around 12m2 of windows like this. That would be the equivalent of heating the street with 840 of these fires for an hour.
Now this window although it looks the same is very different, this is an A rated window with an energy index of +1. It has one pane of glass with a low iron content to maximise the amount of light coming in and it has one pane of glass which is coated to maximise the amount of heat staying in. Now that +1 is the key because that is the equivalent of not having any of these [electric fires] out in the garden but having one inside switched on. And with 12m2 of windows that is the equivalent of having the heat from this fire inside for 12 hours. Where we used to measure windows by how much heat they did or didn’t leak, we now have windows measured by how much heat they add.
A window that actually heats our homes, now wouldn’t our ancestors have loved that.