Posted By: ringiMost solar gain is in the summer were no houses in the UK needs heating, let’s discount this.

The next highest months of solar gain are in the spring and autumn.

Even a house build to Part L standards is unlikely to benefit from much solar gain at the start of the autumn, as it is gaining more energy from the people living there and electrical items, then it is losing.

As we get closer to passive home level, the house does not need solar gain in the autumn, it also does not need solar gain towards the end of the spring. There is very limited solar gain to be had in winter, due to the lengths of days and how little sun light gets to the earth even in the day time.

Hence energy modelling needs to be done on “day by day” bases using data from a few years, not looking at average heat requirements and solar gains.

I agree about the lack of need for solar gain in the summer, or at least that the house will get enough*. In our case this year that was until approximately the start of November. But the solar gain on sunny days in autumn, winter and spring is extremely important. More than what season it is, what matters is whether a day is sunny or cloudy.

So yes, the actual heat demand each year will vary depending how many sunny days there are, but I think designing using monthly averages for demand, plus worst case figures for load design, is probably about as good a way as any.

* In fact the major reason for not having too much south-facing window area is overheating in summer. It's easy to reduce the overall heat demand of a house by increasing the south-facing glazing, but then you need to deal with too much solar gain in the summer.

Only one pic came thro ST

Any idea what's difference in what I see from Google results suncalc.net vs suncalc.org?

Let’s come back to normal homes being built for normal people in towns….

Just how much control is there over the window locations once practical issue of the site is taken into account? Shading is also a issue when the sun is low in the sky.

My wife expect any window that someone my see in to have blinds…..

Most people are only at home at this time of year for 2 days a week when the sun is out…

Most towns are a radial design, so there is often a lot of choice.
Villages are different as they usually only have two main roads.

Maybe a quick letter to the Daily Mail pointing out that widows can let in light, and this may kill some people will get a few responses.

Posted By: ringiLet’s come back to normal homes being built for normal people in towns….

Just how much control is there over the window locations once practical issue of the site is taken into account?

There's usually a lot more than you might think. Zedfactory comes to mind as having a set of plans that can be adapted to any orientation.

The problem tends to be a refusal by the developers and designers to even consider it. I know of a recent case where our local councillor got nowhere when he suggested solar orientation be considered for a big development.

Shading is also a issue when the sun is low in the sky.

My wife expect any window that someone my see in to have blinds…..

Most people are only at home at this time of year for 2 days a week when the sun is out…

Agreed that shading is a much bigger issue in winter. Fortunately, the type of blinds preferred by wives are typically inside, so any heat they absorb is inside the building, though I agree it's better to let the sunlight strike some absorber deeper in the room. People not being at home seems like a feature, since you can leave the blinds open.

Posted By: SteamyTea

Posted By: djhI'm not sure what point you're trying to make.

Geometry is the point I am making.
It is not just the 'arc' (really called azimuth) but also the altitude of the sun.
In the summer, the altitude may be high enough to not affect the SE and SW windows too badly.

I think you'll find that east and west exposure are problematic, as compared to southern exposure, precisely because they ARE affected to a considerably greater extent by low altitude sun. And that sun is more difficult to screen effectively. If you think you know something different, I'd appreciate a link to a reputable source.

It really comes down to what you are trying to achieve.
But just saying 'I will have lots of south facing windows to help with solar gain' is a bit simplistic and really misses the point of good design.

I think we're agreed about that.

Posted By: Ed DaviesIs there actually a net gain for south facing windows in December or January? I think I calculated that there was, just, and somewhat to my surprise.

Yes, there is.

Is that net gain actually greater than the gain you'd get from building more wall or roof and less window area and spending the money saved on PV? Again, my recollection was that it wasn't.

I don't know but your conclusion wouldn't surprise me.

I think you should build the windows you need for a nice view, summer ventilation, escape, and so on then get any further solar gain via solar panels

Don't forget the primary reason for windows - daylighting! The 'nice view' argument is frequently overdone and is a common cause of windows that are too large. Better design can achieve nice views with more reasonably sized windows.

because, though they're less efficient they:

1) work one way - they don't have the losses that windows do on cloudy days and at night and

2) allow you to direct where the heat goes (into a thermal store) whereas gain through a window directly heats the room and so is awkward to store - you have to overheat the room to push the heat into a store at a useful temperature.

Agreed. I think that's part of the rationale for the substitution of PER for PE in PHPP and I think there's a move to allow active cooling, as long as it is renewably powered.

edit: grammar.

Posted By: GreenfishSadly no, all PD removed, can't even have a garden shed without permission :(

Same here.
I think it is a Cornish thing. What the rest of the country calls a shed, we call a Chalet and can rent them out at £600/week in the summer.

When an old industrial, dirty, run down, polluting and bankrupt mining area is allowed to become a World Heritage site, you know that something has gone seriously wrong in people's heads.

Posted By: Greenfish

Posted By: ringiWhat about filling the gaps with tall, fast growing, thick and dense hedging...

I am surrounded by gorse at it is, nature will do that left uninterrupted. But not sure how that mitigates the energy loss down to the shape of the house?

A hedge that is higher then your roof will trap air and hence could provide some insulation benefit.

Posted By: Ed Daviesthough they're less efficient they:

1) work one way - they don't have the losses that windows do on cloudy days and at night and

2) allow you to direct where the heat goes (into a thermal store) whereas gain through a window directly heats the room and so is awkward to store - you have to overheat the room to push the heat into a store at a useful temperature.

Concisely put Dave [Edit - sorry - Ed] - I'm remembering how many years it's taken to get it that clear, even on GBF. And many other similar understandings, which have come from almost nowhere (speak for myself) during the years I've frequented this forum. We have made progress!

Posted By: fostertomConcisely put Dave

It was Ed wot said it, actually.

Whilst I agree with what he said, I would also add something he didn't say.

Having restrained your window sizes and saved some money, one option is to spend the savings on PV to get solar gain another way. But another option is to save the money and buy the power from the grid. Which may leave some cash to put into more efficient schemes like big turbines.

Posted By: Ed Davieswhy wouldn't I be with storing it in the community's Tesla Powerpack for the same period? It's not obvious.

Because everyone else will be doing the same and the storage is not increased as part of your build, but why can't yo invest some of your build fund in better stoves for the 3rd world that use less wood then an open fire...... (I don't find there is a better way to save CO2 based on cost.)

Posted By: Ed DaviesIs there actually a net gain for south facing windows in December or January? I think I calculated that there was, just, and somewhat to my surprise.

Ignoring the re-allocation of resources to wall or PV, are we talking in all cases here or only for certain ratios or values of U and G? Is it just that in a [heat] leaky house there is still a net gain, just that it's lost pretty soon after the sun goes down?

Posted By: gravelld…are we talking in all cases here or only for certain ratios or values of U and G? Is it just that in a [heat] leaky house there is still a net gain, just that it's lost pretty soon after the sun goes down?

Sorry, I don't remember the details but the calculations were for a specific house in Northern Ireland with large windows facing somewhat off south with a clear horizon (overlooking a loch). Can't remember, either, if the discussion was on here or another forum. I used PVGIS to get the insolation on to the windows and HDD data for heat loss.

(I was setting out to show that there wasn't a net gain so was a bit surprised by the result. “He who refuses to do arithmetic is doomed to talk nonsense.” [¹])

Yes, the U and G values will be relevant, of course. These were new windows but not particularly highly specced (good double glazing, I think) so I think it's probably reasonably generally true that you get a net gain as long as you're sensible. I doubt there was a net gain in the big single glazed window in the static caravan I was in last winter, for example.

In a way a leaky house ought to have a higher net gain as, presumably, indoor temperatures will be lower if the heating is off overnight or when unoccupied so losses through the window will be less. On the other hand, if it's unoccupied during many days the gains in the daytime will be less useful.

[¹] https://en.wikiquote.org/wiki/John_McCarthy_(computer_scientist)#1990s

OK, I'm provoked. Looking at the square versions and assuming a 2.7 m storey height:

2 storey: roof and floors both 62.5 m², walls 170.64 m² (total 295.64 m²).
1 storey: roof and floors both 125 m², walls 120.96 m² (total 370.96 m²),

Assuming ceilings and floors are the same cost to insulate and walls are a factor w times more then for the two forms to match on price:

(2 × 62.5) + 170.64w = (2 × 125) + 120.96w
49.68w = 125
w ~= 2.5

Even assuming walls are a bit more expensive to insulate I doubt they're two and half times as much.

Also, with the single storey version parts of rooms are further from the edges so to get decent natural lighting you'll need more window area which is a) expensive and b) needs better insulation to compensate for its losses. Also, you'll need them all round making any bias towards putting them on the south harder to achieve.