Posted By: Mike1when the sun goes away

Found some stats here - not sure how reliable: https://www.currentresults.com/Weather/United-Kingdom/average-sunshine-january.php

Headline: The UK as a whole has an average 48 hours of sun in January, which isn't many hours to try to keep a house warm through solar gain, even if approaching PH standard. Bearing in mind too that there may be an entire a week with zero sunshine.

Thanks again guys - think I'll aim at best-poss insulation apart from 0.25U floor, accept a smallest poss AAHP incl AC, shd still save much of the cost of an ASHP-powered wet system, but maybe have to spend that on a PHPP jockey. Don't know if any such can actually include or integrate with the MVHR, and assume a AAHP is no help at all with DHW.

Even the smallest £500 A-A HP you can buy, puts out 2500W which is twice what you need. You could have 2 or 3 of those for the price of a single 3G window, and then your heat budget goes up to 5 or 7.5kW. Then you don't need a PHPP consultant and extra thick polystyrene everywhere as 0.3U or 0.5U is plenty, so your embodied carbon goes down.

The 2030s design approach!


Do you have a target in mind for your RIBA/LETI embodied carbon band? You could be shooting for an A or A+ as you are starting with a reused floor and frame.


ETA hot water is going to be a big part of the energy use so for SAP purposes should defo look at some kind of heat pump, whether a standalone DHW heatpump or integrated with space heating. If the latter, the smallest practical heatpump is around 3.5kW so (given you'll have one for DHW) you could set that as the heating budget for the space heating and design the insulation to meet that.

Posted By: fostertomDon't know if any such can actually include or integrate with the MVHR

Zehnder sell an AAHP integrated with their MVHR. Others may too.

"Do south facing PH grade windows in the heating season absorb more (intermittent) solar heat in total, than they lose (more continually) by conduction/radiation?
If so, that beneficially alters the building's nett heat loss, doesn't it?"


Yes in principle that's true - it's the main justification for using 3G units, but in PHPP training you're generally warned off relying on Solar Gain to hit the annual target because of the monthly overheating risk (which you identify).


"But AFAIK, PHPP doesn't really embrace or expect full brise soleil, so concentrates on limiting window area."


Not strictly true, you can enter different shading types quite accurately in PHPP and there are plenty of precedent buildings which use this strategy for shading.

One of my favourite examples: https://www.karawitz.com/projects/maison-bambou/

Rather than paying a 'PHPP jockey', depending on your budget/enthusiasm you might want to try out the designPH plugin for sketchup yourself. The latest version (v3.0) has just been released for about £450. It gives you live dashboard feedback on your model and ultimately you can export the finalised results to a PHPP spreadsheet for full certification.

Check out the example image (with vertical brise soleil!): https://passivehouse.com/en/designph/designph-phpp/
NOTE: annoyingly the 'buy now' link is currently giving a 404 error, so you might not be able to purchase currently..!

Thanks especially D-T, incl bringing DesignPH to my attention. Apart from hating SketchUp, it could be a good-enough starter to explore geometry and results. When it says 'Ex­ports are saved as PPP files, which can be im­por­ted in­to PHPP for re­fine­ment', in the absence of PHPP, are results intelligible, even savable in raw .xls form or anything?

It seems the logic of 'south PH-grade 3G windows gain more than they lose' doesn't extend to say fully-glazed south walls, because diminishing returns set in:
1. the amount of powerful gain, when it happens so intermittently, that can be quickly stored into internal fabric, however massive (leading to dissipation by window-opening etc);
2. the in-between cold radiation from even PH-grade 3G, which has to be limited, to be tolerable;
3. summer overheating, which PHPP limits primarily by limiting window area.

Where 3. turns out to be the governing limitation on window area, envisaging exceptionally effective brise soleil as the enabler to go further with south glazing, it seems there is mileage in that.

About Bambou House - it looks marvellous, its layered screening a very 2020s look. However by brise soleil I didn't primarily mean that kind of vertical screening which partly obstructs windows, but overhead horizontal louvres which allow unobstructed horizontal view out (and beneficial low-angle winter sun in), while blocking all high-angle summer sun. Yes, that principle of partial-block vertical screening is almost the only alternative for eastish/westish glazing, but I was looking at southish glazing for which overhead louvred brise soleil is effective.

And for that, for the louvres, I'm looking into not the hitherto hefty structural fins of typically 150-300mm dimension, nor venetian-blind size fins, but the tiny blades 1.25mmx0.3mm of https://www.smartlouvre.com/metal-fabrics (unfortunately out of production - temporarily it's hoped) or specially-shaped expanded metal - both of whose slatted aerodynamics are certified intriguingly immune to storm and wind.

These are also ideal for the partial-block vertical screening alternative, being 'wide' in the plan (facing the sky) dimension that does the work, but extremely thin in the horizontal (view out/winter sun in) direction, even when all tilted down a bit (17o for Smartlouvre) from the horizontal. That's my comment on the Bambou House installation - being round 'blades', in order to get the plan width, they are also big vertically, thus blocking much more view out/winter sun in.

Master of none....

A bit I guess - even when it's slatted, with 50% open area? At that, it'll certainly slow air velocities, as in "slatted aerodynamics are certified intriguingly immune to storm and wind", like a hedge does, whereas a solid garden wall just creates eddy currents. It would feel 'sheltered' in that respect, and that slow-down should improve surface resistance at the glass. It'll interrupt sightline to a clear-night cold sky. Not sure about warmer space though except, when no wind, it may keep two sluggish air masses separate, to adopt intermediate temp - but one puff would start convection-mixing going. Gd idea tho, which I seem to be adopting.

Thanks v much Dominic - am away now, so early next wk.