I thought there was another discussion on this somewhere but I can't find it...

Is it worth incorporating south facing glazing beyond that required for good day lighting? I'm in favour of using passive solar design principles in designing new houses (orientation, window positioning, thermal mass, internal layout etc) but I'm thinking the large expanses of south facing glass common in passivhaus and earthship design in sunny continental and north american climes might be a step too far in the dreary winters of the British Isles, i.e. you will lose more heat on the cloudy days and at night than you will gain on the infrequent sunny days.

I've seen guidance of 50% glazing on south facing facades for the UK which seems rather a lot to me. Any comments?

Mostly, in my neck of the woods, it is cloudy during the daytime during the heating season in the UK. Why should we suffer the heat losses during the cloudy days and nights just to get extra gain on the odd sunny day? You can't shut the shutters in the daytime.

I'm thinking perhaps we should be working out how much glazing we need for good day lighting and trying to put as much of that as possible on the southern facade, but going no further than this. Is the passive solar gain argument a convenient justification for what in reality is a purely aethestic choice?

You may have fewer sunny days in the UK, but you have warmer temperatures than eastern Canada & New England.
Here south-facing lowE high SHGC windows are a net heat gain. During the day, even when it is cloudy, lowE double-glazed windows are a net heat gain (based on measurements I did with outside temp of -15C & full cloud cover).
50% of your south wall glazed is higher than I'd go with. I suggest 20-25% with dark cladding for the wall.
The drawback to large amounts of glazing is an increase in peak heating load.
I suggest playing with LBNL therm.
http://windows.lbl.gov/software/therm/therm.html
Here's another good page about the net heat gain.
http://www.arkema-inc.com/pdf/additives/lowe_performance.pdf

-Ralph

Posted By: jonbased on measurements I did with outside temp of -15C & full cloud cover

I think you missed the minus fifteen Celsius part.

Posted By: fostertomralphd, I'm greatly appreciating your contributions.

if measuring gain under cloudy conditions - i.e. predominantly directionless diffuse radiation from the sky plus ditto from ground and external objects, then what difference which way the window faces? Surely, only clear(ish) sky radiation varies (yes, greatly) depending on orientation?

You are correct, it makes little difference on a cloudy day which way your window faces.

Posted By: ralphdeven when it is cloudy, lowE double-glazed windows are a net heat gain

In that case, why

Posted By: ralphd50% of your south wall glazed is higher than I'd go with. I suggest 20-25%

Posted By: ralphdThe drawback to large amounts of glazing is an increase in peak heating load

meaning, at night? but not so daytime, because the increased nett gain actually reduces or eliminates heating load?

Correct again. Glad to know people can make sense of what I'm saying.

Granted (?) that big S windows can be nett heat gainers even when cloudy, and hugely more so when clear, is the building mass so arranged as to be able to
a) absorb all of that heat as it arrives, especially the clear-sky gain
b) transmit or transport the heat away from the receiving surface (floor, internal walls) fast enough, as it arrives, to not overheat the surface, hence the room
c) transmit or transport the heat deep enough into the massive material (floor, internal wall) to allow storage of all the heat that's arriving
d) there store it for more than 36hrs without uncontrolled dissipation (which equals unwanted heat input to wherever it dissipates to), so as to make stored heat available not just overnight, but over several colder days/nights that may follow a clear-sky day
e) usefully release the stored heat in a controlled way, but only as reqd to maintain temp over those several colder days?

If it's just S windows with gain falling on 100-200 of dumb floor/ internal wall mass, then probably No to all the above - hence advice to limit glass to 25/40/50% of wall area.

What if massive internal walls were 300 thick, and floor was effectively 500, 1000, 1500, whatever thick, above u/floor insulation (if any)? My guess is, that wouldn't help much - the first 100-150 of those thicknesses would still be the active bit, and the greater thicknesses beyond be relatively ineffective.

Are there ways that the receiving surfaces could be 'cooled' by air or water flow, actively transporting heat away from the surface however fast it arrives, into deeper layers of the massiveness?
And then returning it to re-heat the surfaces as required?
Could this be done simply, almost passively but cunningly e.g. by convection, stratification etc? - in one direction at least.
Could the 'deeper layers of the massiveness' in fact be remote from the receiving surface?

Seems to me, there's a dividing line between current 'state-of-art' thinking i.e. Passivhaus, CSH 4+, BldgRegs 2010 etc - the only idea that the mainstream's got - and what I'm suggesting above.

For making use of/collecting/storing/using solar heat, the mainstream relies entirely on gain falling on 100-200 of dumb floor/internal wall mass, hence the tug-of-war between big or small S windows, the weirdness of housebuilders' attempts e.g. http://www.bdonline.co.uk/story.asp?sectioncode=426&storycode=3126408 http://www.bdonline.co.uk/story.asp?storycode=3127259&origin=BDweeklydigest and the anal concentration of Passivhaus etc on loss reduction at all cost, because not enough solar's being collected and stored. This is short-cycle solar.

There's also medium-cycle solar e.g. Drakes Landing, which despite its headlining in-ground storage, is predominantly an insulated-tank storage solution, an approach which at enormous expense typically struggles to store for more than 2-3 months, hence is still reliant on weak and intermittent spring/autumn insolation. Then there's full interseasonal (or continuous) storage, able to harvest and store through the winter easy, plentiful mid-summer insolation - the holy grail and only longterm runner - watch this space!

However, short of these, there's an intermediate - I dunno - improved short-cycle? which is what I'm suggesting above, giving 10-17 days (I'd hope) storage, enough to bridge over many winter cloudy spells, and reducing emergency-heating days to a minimum

Posted By: fostertomThere's also medium-cycle solar e.g. Drakes Landing, which despite its headlining in-ground storage, is predominantly an insulated-tank storage solution, an approach which at enormous expense typically struggles to store for more than 2-3 months, hence is still reliant on weak and intermittent spring/autumn insolation.

Where do you get the 2-3 months figures from? Also, only the "top of the tank" is insulated - the sides are certainly not. The design goal of the Drakes Landing system is that it will take several years to "charge up" that heat storage area. By then 90% of the annual heat requirements will be met from the storage system. And as for weak spring/autumn insolation, that's not the case at Drakes Landing as it is one of the sunniest locations in Canada with (if I recall correctly) more than 320 sunny days per year.

I'm also not sure of the "enormous expense" comment either. The solar panels work out at around Can$0.05 per kWh and the rest of the costs are distributed over the 52 houses - like a community heating system would be.

Paul in Montreal.

Posted By: ralphdTony apparently has something with UK climate data as he has posted charts of heat loss/gain including solar & internal gains. I suggest you ask him what software he uses.

I wrote a hot2000 model for Tony and used international climate data provided to me by Brian Bradley of Natural Resources Canada derived from ASHRAE CD "International Weather for Energy Calculations" v 1.1.

Paul in Montreal.

Posted By: Paul in Montreal

Posted By: ralphdTony apparently has something with UK climate data as he has posted charts of heat loss/gain including solar & internal gains. I suggest you ask him what software he uses.

I wrote a hot2000 model for Tony and used international climate data provided to me by Brian Bradley of Natural Resources Canada derived from ASHRAE CD "International Weather for Energy Calculations" v 1.1.

Paul in Montreal.

Ahh, another Hot2K user. And one that seems to have more pull with Brian than I do.
Time to start my first thread... on Hot2000.

Posted By: ralphdThat's what they modeled, but no actual measurements. No reports on performance for almost 2yrs now.

The also did some measurements: http://dlsc.ca/reports/EPD_March_April_2007.pdf - but you're right, it is disappointing that there's been no other reports since 2007.

Anyway, there are other more interesting developments, including some in Montreal that have net-zero energy consumption on an annualized basis. I'll let you do the search for these yourself as I have already posted the links in this forum.

Paul in Montreal.

We discussed this on http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1191&page=2#Item_20

To me a lot of glass = big heat losses especially in winter when it is dark.

All this talk about net -- net is no use over a whole year need it to over a few days.

My calcs were done by Mike George using TAS modeling software.

I think you missed the minus fifteen Celsius part.

Yes, but I would expect losses of perhaps 50-75 watts /sqm for this assuming a 35 differential whereas, in many parts of Canada, the maximum available midwinter daily insolation in the plane of a south window would not appear to exceed these daily losses except perhaps in summer in the far North: So it's very interesting that you've measured otherwise. Where in Canada are you?

Thanks Ralph

But, overall, don't your figures just show that even good windows are likely to make a net loss over the heating season and a net gain over the cooling season?

Are Thermotech a glazing supplier?

If all the daytime nett gain could be stored and released at the right moment, could it deal with the night time nett loss?

Posted By: jon"The total losses over a 24hr day no doubt exceed the total insolation during the same 24hrs on a cloudy day"
"No, lowE high SHGC open exposure south-facing windows are a net heat GAIN during the heating season (October-March)."

So, you're saying that there's no doubt it's a loss and also that there's no doubt it's a net heat gain?

I am confused.

You apparently missed the "cloudy day" part of the first sentence. The heating season has many days that are not coudy.