Optimising windows for solar gain & heat loss?

[Alan Ambrose]

I'm juggling with our windows, part O simple method & PHPP. I'll also go to TM59 if it'll help get what we want.

 

My objective (I think) is to get a set of windows that are OK for heat loss and make the best out of solar gain in the shoulder months while alleviating mid-summer gain. The windows are nearly all West & East with very few North & South.

 

So, I'm currently modelling automated external blinds & low G glass for protection against overheating but allowing us to benefit from positive solar gain when we can. My questions are:

 

+ is there a better way to optimise shoulder months by using brise soleil in addition to automated external blinds?

+ can I realistically reduce heat loss (in PHPP or real-life) by using automated internal thermal blinds as well?

+ is there are sensible way to include (in PHPP or real-life) a conservatory-type structure in all this?

[PNAmble]

We had to model and go TM59 in the end.  We could not get the simplified spreadsheet to work for the ventilation pass with windows we wanted.  We are having MVHR, external blinds, purging roof lights which never properly get taken into account in the simplified sheet.  We aren’t running PHPP although going passiv standards so the small cost of doing TM59 calc just went into the ‘excessive government required fee’ bucket of our build.  Lots of companies do it for a fixed price these days. 

[Alan Ambrose]

Interesting - have an indicative cost and/or a recommendation for TM59 supplier?

[Dan F]

On 03/12/2023 at 16:47, Alan Ambrose said:

+ is there a better way to optimise shoulder months by using brise soleil in addition to automated external blinds?

Correctly sizes overhangs. Automated external blinds are great and will mitigate the majority of the impact of not having overhangs.  Not sure why you'd want brise soleil and blinds.

 

On 03/12/2023 at 16:47, Alan Ambrose said:

+ can I realistically reduce heat loss (in PHPP or real-life) by using automated internal thermal blinds as well?

Why do you need external and internal blinds for overheating?

 

On 03/12/2023 at 16:47, Alan Ambrose said:

+ is there are sensible way to include (in PHPP or real-life) a conservatory-type structure in all this?

Not sure I understand this question.  You can add a building element to PHPP, but you'll need to look at the specifics of this area (due to the amount of glass in a conservatory) as PHPP mostly looks at things from a whole house perspective.

[Thorfun]

48 minutes ago, Dan F said:

Not sure why you'd want brise soleil and blinds.

+1

48 minutes ago, Dan F said:

Why do you need external and internal blinds for overheating?

I think the internal blinds are to reduce heat loss rather than overheating. 🤷‍♂️

[Alan Ambrose]

I’m imagining that brise soleil are most useful for midsummer S facing when the sun is high but allow useful solar gain for the other months when the sun is lower in the other 3 quarters. Outer blinds as an out-and-out sun block whenever needed. Internal blinds for thermal control in winter.

 

My train of thinking is - what’s to stop us having smartish window coverings that control solar gain and heat loss as and when we need it? ‘Windows don’t just have to be dumb bits of glass’.

 

The other thought I was persuing is - maybe we want to balance solar gain so we get useful gain in winter, not too much in summer i.e. there’s some optimum in the middle there somewhere.

[PNAmble]

2 hours ago, Alan Ambrose said:

Interesting - have an indicative cost and/or a recommendation for TM59 supplier?

We paid about £335 plus vat via easyEPC - only because they also did our as design SAP report, sent them dwgs, u values and window specs. They did the rest. 

Edited December 4, 2023 by PNAmble
Correction

[Dan F]

57 minutes ago, Alan Ambrose said:

I’m imagining that brise soleil are most useful for midsummer S facing when the sun is high but allow useful solar gain for the other months when the sun is lower in the other 3 quarters. Outer blinds as an out-and-out sun block whenever needed. Internal blinds for thermal control in winter.

 

With overhangs and blinds, don't see a need for Brise Soleil personally.   Outer blinds, if using the venetian style, can be used to keep the sun out but still allow room to be light and see allow view outside.

 

57 minutes ago, Alan Ambrose said:

 

My train of thinking is - what’s to stop us having smartish window coverings that control solar gain and heat loss as and when we need it? ‘Windows don’t just have to be dumb bits of glass’.

 

Internal window coverings aren't great for keeping solar gain out, external ones are much better.   Window coverings may help with heat loss, but there is nowhere to account for this in PHPP.

 

57 minutes ago, Alan Ambrose said:

The other thought I was persuing is - maybe we want to balance solar gain so we get useful gain in winter, not too much in summer i.e. there’s some optimum in the middle there somewhere.

 

Our solution to get the best of both was:

- High-g triple-glazed windows (higher solar gain)

- Overhangs modelled to keep the summer sun off of windows.

- External automated venetian blind.

 

[Thorfun]

1 hour ago, Alan Ambrose said:

I’m imagining that brise soleil are most useful for midsummer S facing when the sun is high but allow useful solar gain for the other months when the sun is lower in the other 3 quarters. Outer blinds as an out-and-out sun block whenever needed. Internal blinds for thermal control in winter.

 

My train of thinking is - what’s to stop us having smartish window coverings that control solar gain and heat loss as and when we need it? ‘Windows don’t just have to be dumb bits of glass’.

 

The other thought I was persuing is - maybe we want to balance solar gain so we get useful gain in winter, not too much in summer i.e. there’s some optimum in the middle there somewhere.

If you’re having external blinds then they will do the job of the brise soleil and shade the southerly sun in the summer. Although you would have to manually adjust them unless automating it. 
 

if you’re going the brise soleil route the get your SE/professional team involved early on as they will need to be designed in. 

[SteamyTea]

Have you done any manual calculation that include the solar elevation and azimuth?

 

https://www.sunearthtools.com/dp/tools/pos_sun.php

[Alan Ambrose]

>>> Have you done any manual calculation that include the solar elevation and azimuth?

 

@SteamyTea

 

You've done it again - how come you always have the right calculation at hand  - any books to recommenced? Thanks for the link, and no, let me try that though.

 

@Dan F re: Our solution to get the best of both was: - High-g triple-glazed windows (higher solar gain)

 

I'm guessing you mean low G and less gain - or were you deliberately allowing a lot of solar gain and heat through and then using the external blinds where necessary?

Also that means either ensuring the windows are closed before using the blinds, or using inward-opening blinds?

[Dan F]

3 minutes ago, Alan Ambrose said:

I'm guessing you mean low G and less gain - or were you deliberately allowing a lot of solar gain and heat through and then using the external blinds where necessary?

Exactly.  Combined with overhangs.  Our windows open inwards.

[SteamyTea]

3 minutes ago, Alan Ambrose said:

any books to recommenced

Not really.  All the 'solar houses' books I read 20 years ago when studying this area were all a bit flaky and 'it will be alright'.

Geometry and physics is really all that is needed. And a spreadsheet.