Glass type. I want more solar gain.

[ProDave]

Just musing about our sun room., that some time in the dim and distant future might get  completed. (unable to do much at all at the moment)

 

So we have Rationel windows and doors all tripple glazed. Of all the window quotes we had, these had the second best UW values, only beaten very slightly by Internorm.

 

Now good windows and good 3G glass units means not much heat loss. BUT it also seems not much solar gain either.  Given our colder climate than many parts of the UK I would LIKE a lot more solar gain please.

 

Now we can't do anything about the windows we have, but there is the "sun room" yet to be finished.  This will have a lot of glass on 3 sides but a solid roof (apparently it's an Orangery so I am told!!!)

 

The sun room is joined to the house with a pair of Rationel French doors. Because this is essentially in internal door, I didn't have this one aluminium clad and only chose  2G glass units with a slightly less good UW value.

 

Now my thinking, when we eventually get the doors and windows for the sun room, I want something that gives a LOT more solar gain.  I don't mind if we get too ,much solar gain in the summer, that's why windows open. If it's too hot or too cold it can be closed off from the house. It won't be heated and I won't go overboard with the air tightness detail.

 

So how can I make the sun room have a lot more solar gain. I want it to get hot on a sunny winters day so we can open the doors and let heat into the house.

 

I assume I want 2G glazing with no coating at all on the glass units?

[SteamyTea]

Do the sums for different radiative forcings i.e. 50, 100, 150, 200, 250 W.m^-2.K^-1

Then decide of you can actually shift that energy to the rest of the house.  You may find that you can suck more energy out between the roof tiles and a small gap under them.

 

One of the misunderstanding is that when stuff is heating up, that is all it is doing.  It isn't, it is also loosing energy at the same time and at a faster rate the relatively hotter it gets.

Just today, in my comic, there was this question answered.

Edited November 16, 2017 by SteamyTea

[ProDave]

All I know, is in out old house, on a cold but sunny winters day, you could turn the heating off (well the thermostat did that) and the house would heat up nicely from the sun.

 

Stand in front of a window on a sunny day at the new house and you barely notice any sense of heat from the sun.

 

Now I am sure overall that means on a dull grey wet cold day (or at night) , the new house is losing less heat out of the window than the old one,. so is overall beneficial.

 

BUT what I am trying to achieve is a means to get extra solar gain "on demand" and perhaps by fitting "poor" glazing in the sun room, we will get that extra solar gain and open the doors to let the heat into the house. On those cold grey days (and at night), keep the doors to the sun room shut and who cares if it is cold an uninviting in there?.

[Dudda]

The heat loss from a window is the u-value. The heat you get into the room from the sun is the g-value and a low g-value reduces the amount of solar gain. You want something with a low u-value (to reduce heat loss) and a higher g-value (to increase solar gain). The third figure is the Tv value which is the amount of light (think bright room) that gets in. With a lot of glazing this isn't an issue. It's a balancing act. Here are some examples (they will vary from company to company so using them as a guide only):

 

Glass type and designation	Structure	G	Ƭv	U
	(mm)	[mm]	[-]	[W/m2 K)]
Single glazing	4	0,87	0,90	5,8
Double glazing	4/ZR/4	0,78	0,82	2,7
Triple glazing	4/ZR/4/ZR/4	0,67	0,72	1,9
Double heat protection glass, coated	4/ZR-AR/b4	0,63	0,80	1,1
Triple heat protection glass, coated	4/ZR-AR/4/ZR-AR/b4	0,50	0,71	0,5
SOLAR + triple protection glass coating	4/ZR-AR/4/ZR-AR/b4	0,62	0,73	0,6

 

 

Looking at the above if you had standard double glazing you'd have a g-value of 0.78 which would be good for solar gain but that u-value is terrible. It would almost loose heat as fast as it gets it. For standard triple glazing you've a g-value of 0.67 but a poor u-value of only 1.9. The top spec triple glazing with a SOLAR layer has a g-value almost as close at 0.62 which will let almost as much heat enter via solar gain but a very low u-value of 0.6 reducing heat loss considerably.

 

In short I think you're far better off sticking with triple glazing but getting a high g-value (circa 0.6), low u-value (circa 0.6) and using the internal doors in summer to stop the house overheating.

[Jeremy Harris]

Our glass has a g value of 0.65, so we get a pretty high level of solar gain (too much in some areas) but a Uw of around 0.7 to 0.8 (varies a bit from one window to another).  This would work well for your sun room, although you may still need shading, even where you are, to reduce the solar gain sometimes.

 

The key is in understanding that the anti-long wavelength IR reflective coatings (the low e coating) are one way, in effect.  They are sputtered on to the inner faces of the inner panes, (so the inner face of the outer pane and the inner face of the centre pane) and they control the emissivity at those surfaces, reflecting long wavelength IR inwards through the interstitial gap between the panes, but allowing long wavelength IR from outside to come in with only a slight reduction.  They are a bit like one way mirrors, that allow light (in this case long wavelength IR) to flow in, with little attenuation, but reflect back in long wavelength IR that is trying to get out.

Edited November 16, 2017 by JSHarris

[ProDave]

When I was buying the windows, nobody, and I mean not one of the window suppliers mentioned anything other than the Uw and Ug values.

 

Clearly I need more information from the suppliers when I buy the windows for the sun room and need to ask more questions.

 

So I still want a good Ug value but a "poor"G value then.

 

I really don't think summer overheating will be an issue. We have these things called trees that grow leaves ans shade us in the summer.  It is only now the leaves are falling that we can hope for enough sun to get some siolar gain.

 

The exception is the West facing windows but even there, stand in front of a window on a sunny day and you feel little heat.

[SteamyTea]

I just did a quick and dirty spreadsheet.  For a solar input of 100 W.m^-2, a solar azimuth of 45°, an altitude of 20°, with a temperature difference of 15°C.

Using a U-Value of 0.5 and a G-Value of 0.5, I make it 62.7 W.m^-2 (1m² window).  That is the basic triple glazing from the chart above.

An old light bulb would give you that I think.

 

When I change it to a U-Vale of 2.7 and a G-Vale of 0.78, I get 34.9 W.m^-2. That is a basic double glaze from the chart above.

 

(always a chance that my spreadsheet is wrong)

Edited November 16, 2017 by SteamyTea

[ProDave]

From here http://www.rationel.co.uk/energy/5-energy-guidelines/

 

Quote

South

The most important role of South-facing façades is to utilize the available solar energy to heat up the house. Choose modern double or triple-glazed energy windows with a lower U-value and a high g-value, to make use of the free solar heat. Naturally, as South-facing façades receive the most sun light there is a possibility of overheating, particularly in Summer months. This is easily avoided by using solar shading such as external sun blinds and roller blinds.

 

 

 

And from here http://www.rationel.co.uk/windows-doors/product-series/rationel-auraauraplus/

 

Energy efficient triple glazing

AURA and AURAPLUS are in the forefront of modern energy-optimised windows and doors.

With high performance 52mm triple-glazing provided as standard, AURA and AURAPLUS windows achieve U values as low as 0.79, which is ideal for low energy buildings and Passive House construction.

All triple-glazed units are constructed with argon gas insulation between the panes and a warm edge spacer or ‘thermal break’, which reduces heat loss round the perimeter of the window.

In fact, our energy-optimised glazing can let in more free solar heat than is lost through the window, which significantly reduces the energy consumption required to heat your home during the winter.

With AURA and AURAPLUS you can be certain to enjoy a more comfortable living environment with no drafts or cold spots.

All Rationel glazing been approved according to the EN 1279.

 

So that's what I have

 

Given that I was never offered a choice (other than 2G or 3G) does this mean I already have a low U value and a high G value?

 

I must fire off a question to them to find out for sure.

 

But why don't I feel the warmth of the sun if I stand in front of a window?

[MikeSharp01]

32 minutes ago, SteamyTea said:

  For a solar input of 100 W.m^-2, a solar azimuth of 45°, an altitude of 20°, with a temperature difference of 15°C.

Using a U-Value of 0.5 and a G-Value of 0.5, I make it 62.7 W.m^-2 (1m² window).  That is the basic triple glazing from the chart above.

An old light bulb would give you that I think.

What is the core equation that enables you to work this out, PHPP does something similar, but yours might help people here particularly if the coatings fiddle factors could also be worked up. I also wonder about the internal surfaces / materials and their ability to 'manage' the heat / radiation / convection flows driven by light in all its constituent parts. PS are you back this side of the pond or do they have better comics the other side?

 

[SteamyTea]

I worked the U-Value out as normal, so W.m^-2.K^-1 . m² . (T₁ - T₀)

 

For the radiation I multiplied the G-Value by the area, product of the cosine of the azimuth and Altitude angles and the solar power.

 

Something like (excel is a bit different as it uses radians):

 

G-Value (decimal fraction) . T-Value (decimal fraction) . Window Area (m²) . Cos(azimuth angle) . Cos(altitude angle) . Solar Power (W.m^-2).

 

Then took the Thermal losses away from the solar gain.

 

Try it, but change the extension from txt to xlsx.  I may have made an error.  Just don't input anything in the last 3 cells, they are the answers (B14, B15 B16)

 

Solar Gain Calculator1.txt

Edited November 19, 2017 by SteamyTea
Edited to include T-Value in spreadsheet

[SteamyTea]

So I am just playing about with some local weather data and at noon today, I could have got, with a south facing 1 m² window, 177W with double glazing and 188W with triple.

At 15:00 I would have got -1.8 W with double and 12.5 W with triple.

At 9:00 it would have been 5.8W or 22.4W

At best, with the solar power at 368W, I would have got either 298W or 309W, for 5 minutes or so.

 

Go for the triple.

Edited November 16, 2017 by SteamyTea

[Nickfromwales]

4 hours ago, ProDave said:

It won't be heated

Why not put Ufh pipes in so the room can be used year round? With the ashp and less than £100 worth of pipe it seems a no brainer ? 

[Dee J]

We took the unheated, high light level, high solar gain, high heat loss route on the sun-room of our current ancient house. Unframed 10mm single-glazed office partition glass 2.5 m high and 5.4 m long (6x0.9mm panels with silicone joins). Excellent system... a bright warm room when ever there is the slightest hint of sunshine. Open the doors and window to the house when heat transfer is needed. Open the skylights to ditch excess heat. Close it all up when it's dark or cold.

Wish we'd built it earlier, and its one thing that we are afraid we'll miss in our new-build.

[coconutsaregood]

On 16/11/2017 at 19:11, Dudda said:

The heat loss from a window is the u-value. The heat you get into the room from the sun is the g-value and a low g-value reduces the amount of solar gain. You want something with a low u-value (to reduce heat loss) and a higher g-value (to increase solar gain). The third figure is the Tv value which is the amount of light (think bright room) that gets in. With a lot of glazing this isn't an issue. It's a balancing act. Here are some examples (they will vary from company to company so using them as a guide only):

 

Glass type and designation	Structure	G	Ƭv	U
	(mm)	[mm]	[-]	[W/m2 K)]
Single glazing	4	0,87	0,90	5,8
Double glazing	4/ZR/4	0,78	0,82	2,7
Triple glazing	4/ZR/4/ZR/4	0,67	0,72	1,9
Double heat protection glass, coated	4/ZR-AR/b4	0,63	0,80	1,1
Triple heat protection glass, coated	4/ZR-AR/4/ZR-AR/b4	0,50	0,71	0,5
SOLAR + triple protection glass coating	4/ZR-AR/4/ZR-AR/b4	0,62	0,73	0,6

 

 

Looking at the above if you had standard double glazing you'd have a g-value of 0.78 which would be good for solar gain but that u-value is terrible. It would almost loose heat as fast as it gets it. For standard triple glazing you've a g-value of 0.67 but a poor u-value of only 1.9. The top spec triple glazing with a SOLAR layer has a g-value almost as close at 0.62 which will let almost as much heat enter via solar gain but a very low u-value of 0.6 reducing heat loss considerably.

 

In short I think you're far better off sticking with triple glazing but getting a high g-value (circa 0.6), low u-value (circa 0.6) and using the internal doors in summer to stop the house overheating.

Good  summary. To enhance it is there anyone able to price it and  do a Life Cycle benefit for say 30 years?

[joe90]

So @ProDave what did you end up with?, my glazing is double (with coatings) as is my conservatory (not orangry), but the coatings on the conservatory are to limit the sun as everyone said it would overheat badly. 
 

On 16/11/2017 at 22:01, Nickfromwales said:

Why not put Ufh pipes in so the room can be used year round? With the ashp and less than £100 worth of pipe it seems a no brainer ? 

we use ours all year round without UFH, the solar gain is sufficient, the floor is insulated and tiles are black. ?

Edited September 8, 2021 by joe90

[ProDave]

Yes I had forgotten about this thread.

 

I ended up with Rationel 2G alu clad windows in the sun room.  Too early to tell if I get much solar gain as this time of year the sun room is in so much shade from the trees.  Winter and Spring will be the time to tell how much solar gain I get on a sunny day when the leaves are gone.

 

The sun room has certainly not over heated yet.

[joe90]

3 minutes ago, ProDave said:

The sun room has certainly not over heated yet.

But with a  Solid roof you will not get the solar gain a conservatory does, I did consider growing deciduous trees to give it summer shading, saves me driving to the south of France to get my fix of “heat” ?‍♂️