Posted By: TriassicIf I want a large window, surely I just increase the heat input with larger solar panels.

Only if you can store the heat till you need it. Which is pretty much impossible unless you have deep pockets.
Not the mean temperature you have to deal with here but the nigh time temperatures in the winter. Think we have just seen that 6 to 8 weeks of 10°C below the norm can play havoc with energy usage/supply. And just to rub it in, the cold time spell was March and April, so you are very limited in getting in Jan and Feb to last till then.

Could try some mirrors in the garden to focus more or what is available

I have seen an old rule of thumb used for not needing to calculate the excess heat loss from larger windows of 10% of the floor area and a different one for building regs saying 5% openable.

WAG: 2.5 m² of panel for every m² of window.

Heat loss say: 0.8 W/m²·K × 20 °C = 16 W/m²

Heat gain assuming panels work for equivalent of average ¾ hour per day at 20% efficiency (remember, actual exposure will be a lower light levels over a longer period) so 1000 W/m² × 0.75/24 × 0.2 = 6.25 W/m².

So panel area over window area = 16/6.25 ~= 2.5.

The start of it was a comment from fostertom asking if I could live with so little window area.

I have dug out my specs and my house has 27m² of glazing for a floor area of 215m² or approx. twice the Scottish guidelines so clearly perceptions differ (at least between the Scots and fostertom) as too how much glazing is required.

I certainly haven't any concerns about the house having enough light, you will see from the plans I posted in the other thread that the main living area downstairs has windows to both the south east and the south west so is brightly lit throughout the day, I would suggest that if you can incorporate dual aspect into the design of your main living area it's a good idea.

One thing I would say is that due to the thickness of the walls as the sun moves across the sky in the spring and autumn you can lose the direct sunlight quite rapidly. Flaring the reveals could help this but personally I don't like the appearance so didn't do it with our house.

The Peter Warm addon for PHPP clearly shows that it's the windows that are the biggest heat loss element in our design, so it is very much a balancing act to try and arrive at the optimum amount, our original design had two more windows and the windows to the south east all extended to the floor but I made changes to reduce costs and heat losses.

Take a house of roughly the shape of Crispy's but full two story. Say 13 m × 9 metres internally so total floor area 234 m². South face is 13 m × 2.4 × 2. 50% glazed would be 13 × 2.4 = 31.2 m². This is only about double the Scottish building regs minimum for the house (which would be 15.6 m²). Obviously you'd also have a bit more window on the other faces. Still, I don't think there's that big a difference between minimal glazing and what people feel is quite a lot. Even building regs minimum should be quite sufficient with careful design and decoration. No need to be miserable.

Priorities within your budget.

(1) adequate natural light (remembering that your vision *will* deteriorate as you get older)
(2) pleasant view (frame something attractive; don't expect to do birdwatching from the sofa)
(3) minimise heat loss (this is where you may have to resort to TG, shutters, heavy curtains etc)
(4) size and position windows for *useful* solar gain, i.e. solar gain during the heating season, and especially in the mornings when you want the house to warm up
(5) minimise unwanted solar gain. I think I can remember one or two years when this was an issue in England for people with windows - rather than glass walls.

Don't squander the natural light. Paint walls and ceilings in white or very light colours. Use light-coloured floor coverings too. Keep curtains well clear of the window opening. Keep windows clean.

Where can you get the reflective white paint used for road markings? Be good for window reveals. Only half joking.

Try 'natural' paints with no VOCs, but look for ones with a high Titanium DiOxide component.
This is the whitener used in most 'white' products.

Cheers

Better answer http://www.instructables.com/id/Paint-your-bike-bicycle-gear-reflective/

Hmm, yes, on second thoughts retro-reflective is not what you want as it'd just return the light back outside.

Indeed, but making good use of the August heat gain by the time you get to February is non-trivial. Some houses manage to stay just about warm enough in the UK using windows as their only solar collectors (e.g., the Hockerton houses) but I'd suggest that actually they'd do better with less window area and more of other forms of solar collectors (thermal or even PV).

Walls highly insulated but lots of 3G plastic (never again!) window area. The main glazed facade is turned 45o relative to the terrace's E-W orientation so it faces SE, with quite a low horizon, so gets whatever winter morning sun that's going.

In particular, the tiled floor was acceptably warm to bare feet, tho I'd been saying it wouldn't reach that state until a year or so on. The floor is basically uninsulated, in thermal contact with subsoil, within a perimeter insulation 'coffer dam' downstand (or rather, in this case, as we were on bedrock, a small downstand of EWI carried down, supplemented by a horizontal bed of Leca as 'wing' insulation 500 thick spreading 1200 wide). It's a suspended timber floor, without airspace below, but fully filled with Leca direct (with DPM) on the subsoil. So 18 chipboard + 170h joists + 35 Leca beneath their underside is about 225mm of material at 0.11W/m2.K (equiv to 75mm of white EPS). So in fact there's some modest insulation between interior and subsoil, but the insulation itself is moderately massive, compared to say EPS. About half that thickness would have been ideal, thermally (thinking of 8x2 or 8x3 joists laid flat edge-to-edge as combined floor boards + joists).

A pdf sheet setting out the rationale and justification for this ("they'll never let you") construction, to Bldg Control's satisfaction, is avail - email me (too big to post up).

So it seems the subsoil (bedrock in this case) has quickly absorbed internal heat and whatever solar heat there's been, to adopt a downward temp gradient, from room temp, down and outward by a long path to outside air temp. As it is a massive element, its temp should tend to stay stable, not only keeping the room warm in winter, but hopefully keeping it cool in summer. We shall see.

Yes, this one room extension - the rest of the 70s estate terrace house was freezing if not well central-heated. So yes we're getting heat thro the old back wall incl 1G french doors and 1G window now internal. But still, with all that lossy glass, the subject of this thread ...

<blockquote><cite>Posted By: Ed Davies</cite>Indeed, but making good use of the August heat gain by the time you get to February is non-trivial. Some houses manage to stay just about warm enough in the UK using windows as their only solar collectors (e.g., the Hockerton houses) but I'd suggest that actually they'd do better with less window area and more of other forms of solar collectors (thermal or even PV).</blockquote>

Of course - that's why I mentioned improving the loss rate or capturing and storing the energy inflow or both.

Big windows and thermal mass alone won't (usually) do the job.

trading window area for PV area or solar thermal area isn't a problem as generally you are using the electric or gas grids as the storage mechanism - ie they don't need to be part of the build.

It's the common approach on some so called zero carbon buildings - bung in a heat pump to low temp UF and then put in enough PV so you generate the whole annual electrical demand of the heat pump with PV. In reality you are usually importing or exporting and using the grid as "storage" but as long as the annual figures tally then it's carbon zero.

Of course that allows you to get away with poor practice on the passive aspects but the simple totals of heat energy used and PV energy generated never reveal that - innapropriate use of technolgy really

Regards

Barney

Posted By: barneyOf course that allows you to get away with poor practice on the passive aspects but the simple totals of heat energy used and PV energy generated never reveal that - innapropriate use of technolgy really

Exactly. You could easily have a “zero carbon” house which causes a lot more carbon emissions than one which doesn't export any energy. Totally bogus name.