Tony99

Solar Gain and opening windows?

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Our build design will have several large unshaded south facing widows. I get the concept of solar gain and reading comments here it seems that it is often worse in Spring and Autumn when the sun is low and therefore the sunlight penetrates deeper into the room. Our house will, like many here, be built with a high level of insulation and airtightness (not passive standards)and MVHR  so I have always been a bit concerned about over heating.

My question-and I'm sure there is a simple answer (!): in the Spring and Autumn, when the air temp outside is lower than inside e.g. outside <20C, can't you simply open the windows to allow cold air in, circulate, and thus sort out over heating indoors?? 

Also-does anyone have any good 3G windows with built in or external blinds/shutters? Internorm windows seem to get a bit of a bad press on this forum!

Many thanks!

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Well I have MVHR and open windows in summer when it's hot inside and cooler inside. I also switch summer bypass on the MVHR to help. I also have integral blinds but in 2G glazing, not 3G. If I ordered again I would have electric blinds to the rooms I use the most (mine are all manual) although I notice that HMRC refused the VAT reclaim on electric blinds recently however these could have been separate blinds rather than integrated. 

 

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21 minutes ago, newhome said:

If I ordered again I would have electric blinds to the rooms I use the most (mine are all manual) although I notice that HMRC refused the VAT reclaim on electric blinds recently however these could have been separate blinds rather than integrated. 

 

 

I've had my external electric blinds done as supply and fit, zero rated as it's a new build. In fairness, there's a strong argument that they are part of the fabric of the building as part of the installation is done as a first fix item before the cladding.

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1 minute ago, vivienz said:

 

I've had my external electric blinds done as supply and fit, zero rated as it's a new build. In fairness, there's a strong argument that they are part of the fabric of the building as part of the installation is done as a first fix item before the cladding.

 

I don’t disagree but HMRC decided that electric blinds were not ‘ordinarily incorporated’ so refused the VAT on them. The first tier tribunal asked the appellant to provide evindence that they were ordinarily incorporated and he failed to do this. So sounds like supply and fit and thus zero rated is the way to go. 

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@Tony99 Yes you could open a couple of windows to create a draft running through the house to ventilate the incoming heat out. But what if no one is home when the sun pops out? Having to rely on windows open isnt ideal for security or noise or air quality.

 

When a well insulated house is heated up, say over the course of a sunny day through solar gain, opening a few windows in the evening will increase the air flow but it could take many hours for the fabric of the building to cool to an acceptable level.

 

Much better to design out over heating strategy whilst you still can.

 

 

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Blimey, that approach would discount most of the stuff that goes into a passive stsndard house, on the basis that it's not ordinarily incorporated into most UK houses.

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26 minutes ago, willbish said:

@Tony99

 

When a well insulated house is heated up, say over the course of a sunny day through solar gain, opening a few windows in the evening will increase the air flow but it could take many hours for the fabric of the building to cool to an acceptable level.

 

Yes-I presumed one of the issues is the fabric of the house being heated up rather than the air inside it....especially, if like many new builds, one has UFH which could keep the floor warm for several hours after the heating has been turned off. Thanks 

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1 hour ago, newhome said:

Well I have MVHR and open windows in summer when it's hot inside and cooler inside. I also switch summer bypass on the MVHR to help. I also have integral blinds but in 2G glazing, not 3G. If I ordered again I would have electric blinds to the rooms I use the most (mine are all manual) although I notice that HMRC refused the VAT reclaim on electric blinds recently however these could have been separate blinds rather than integrated. 

 

yes, I like the idea of electric blinds especially the ones that can be remotely controlled/timed. But, no doubt, more to go wrong with them!🙄

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Posted (edited)
30 minutes ago, Tony99 said:

Yes-I presumed one of the issues is the fabric of the house being heated up rather than the air inside it....especially, if like many new builds, one has UFH which could keep the floor warm for several hours after the heating has been turned off. Thanks 

so maybe a big thick slab is not the right answer /

I retro fitted ufh into my chipboard floor close to 20 years ago  and it does change temp very quickly even with it being tiled , cold to warm in under an hour and with in 20mins you can feel where the pipes are 

certainly it it were done from new with far superior insulation on the underside ,as I know mine is not perfect .

maybe that a way  to get round this problem ,yes the tiled floor does heat up form sun through windows ,but its only really the tiles that get warm  and then release it to the air.

so you just make heat when  you need it ?

Or maybe thin screed with pipe init  so its not a big --wait for it !! "thermal mass"  LOL

 why would you need a big heat store if heating requirements are very low anyway  and ASHP  works very quickly anyway ,

 yes you would need to run temp on ashp higher maybe 40c , but it won,t be on for long and if its not an open plan then room stat will shut it off where not needed.

no more over heating from sun through windows maybe?

 

Edited by scottishjohn

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56 minutes ago, vivienz said:

Blimey, that approach would discount most of the stuff that goes into a passive standard house, on the basis that it's not ordinarily incorporated into most UK houses.

 

HMRC fixated on the electric blinds because there had already been a case at the Upper Tribunal whereby Taylor Wimpey tried to zero rate all kitchen electric appliances such as washing machines etc. and they lost the case. 

 

Taylor Wimpey vs HMRC

 

In the electric blinds case, HMRC tried to suggest that the eco home in question wasn't any different from the 4 bedroom Taylor Wimpey homes in the case referred to above. Luckily the tribunal disagreed and stated that an eco home is a distinct category of building. That has more significance than the electric blinds really as if eco / passive / sustainable homes had been judged the same as a bog standard 4 bed developer built house then who knows what HMRC would be refusing in the future! Had the appellant actually provided any proof that electric blinds were ordinarily incorportated into an 'eco' home I think he may have won his case but after the 90 days he was given to provide the information he hadn't come forward with anything so he lost the case.

 

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If you are still in time to get external blinds then go for them you can get supply and fit zero rated but even if you had to pay the vat it will still be worth it. I was too late for blinds - by the time everyone acknowledged the problem  it would have meant major works to retrofit and no one on site wanted to go there...the carpenter quailed at the idea of removing his beautiful cladding to get cable runs behind. Blinds inside the glazing are not as effective nor are internal blinds.  I have an overheating problem with a house built to passive standards of insulation and airtightness with mvhr as per but solar gain not properly taken into account (thats another story).  I always said I would have issues due to amount of glazing on south and west but was told it would be fine.....it was not.

 

I have had solar film fitted to see if this will help but it was only done last October so this summer will give it a test.  A bris soleil would help but design of house and roof and exposed location make this tricky.

 

Internorm windows... I have them.....the windows are beautiful.  The installers are the problem.  Be aware of that if you do choose Internorm, the bad press on here is well deserved.

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Gaulhofer do external blinds.  I have specced them on our south facing windows, mostly for managing the solar gain, but the optional extra privacy will be good too. We are considering shutters for the 3 veluxes & will probably put the infrastructure in so that they can be added later if required. 

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Posted (edited)

Whilst at the design stage shouldn’t the OP be considering specifying coatings on the glass to reduce the effects of the sun?

 

 

Edited by Triassic
Typo
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1 hour ago, Triassic said:

Whilst at the design stage shouldn’t the OP be considering specifying coatings on the glass to reduce the effects of the sun?

 

 

They would probably welcome solar gain from November to January and coatings that reflect the heat in the summer would also do so in the winter. Coatings work well if you never want solar gain, as I have on my bathroom roof window.

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So, to mitigate against overheating you can make south facing windows smaller, provide external shading, use low g glass etc.

But the more you reduce summer overheating, the more you need winter heating.

If you have solar PV to provide electricity is it better to design a house that overheats in the summer and use free electricity to cool the house via a cooling heat pump, than to pay for grid electricity to heat the house in the winter when the PV doesn't work so well?

Where does the balance lie in a well insulated, fairly airtight house??

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1 minute ago, Grendel said:

But the more you reduce summer overheating, the more you need winter heating.

Not quite the case as a brise soleil works by cutting higher summer suns and does not so much interfere with low winter suns. 

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For us, winter heating is virtually negligible, less than £100.  The electricity we use for cooling is easily three or four times that we use for winter heating, even though most of it comes from the PV system.

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But that 3-4 times summer electricity is free off your solar PV??

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14 minutes ago, Grendel said:

But that 3-4 times summer electricity is free off your solar PV??

 

Most of it, but not all, and that's with solar reflective film on the outside of the windows (which also cuts down winter solar gain a lot).  In terms of money spent, we probably still spend more on cooling than heating.

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I know you must all think I'm on some commission deal (I'm not), but SageGlass really is (imho) the most elegant and least intrusive option if your budget will stretch to it.

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Posted (edited)

Due to location and orientation we have no South facing windows as all. We are situated on an East facing hillside with East facing valley views which are really "the view" that makes the house. The West facing windows are shaded by trees and the hill itself from around 3 pm in the winter and 6pm in the summer.

We have an upside down config to the house with 26mtriple glazed glass running the entire Eastern side. We are already aware we will require aircon but are planning a cross flow series of windows on the West side for natural ventilation when conditions permit. We will have PV & MVHR to assist but some times the view is the whole reason for the property in the first place.

I have been quite concerned about overheating and looking into various shading options for the East side but as the sun hits the windows from sunrise it was 26c at 5.30 in the morning already in the East facing room, the shade above window option will make no difference until the about midday. Blocking the view is the only physical way to prevent the rays penetrating deep into the building.

I still like the look of these and wish the kit form was available in the UK. Still dragging myself to France to collect these wont be that painfull!

brochure_sam-2015---bilp_23.pdf

Edited by EverHopefull
bad english!

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