Bifolds : Solar gain vs heat loss

[Benjseb]

We have a largish kitchen (50sqm) which stays quite cool all year round due to lots of stone and insulation

 

its lovely in the summer and rarely goes about 20c. It’s south, north and west facing!

 

However in the shoulder months we tend to have to extend the heating to take the edge off as there’s only small windows. whereas other more glazed rooms are warmer. 

 

We were here considering knocking a small window/wall into a bifold door. This would be south facing so give some decent solar gain hopefully. 

 

How can we balance this so it works well and doesn’t lead to a cold room in winter. I’m thinking triple glazed, is that enough, I’m not really sure how they perform as never had bifolds. 

 

Thanks

 

ben

[nod]

I’ve fitted bifold door to our south facing kitchen D glazed 

We wanted to be able to open that area up completely in summer 

Others wise we would have fitted sliders which I’m pretty sure would be more airtight 

Bifolds can be problematic so many opt for sliders instead I personally wouldn’t have triple glazing in a bifold as I think it would add unnecessary weight to the pivot points on each door 

[joth]

If the overarching goal is to reduce energy use, you're probably better not making any changes to the windows as the winter losses are likely greater than the shoulder season gains, just because of the difference in temperature is that much higher in winter.  Instead add some solar (PV or thermal) to capture shoulder season radiation and reduce cost of the internal heating.

 

So I'd say only consider adding glazed doors if they will add  aesthetic and utility value as well as solar gain increases. And then as you say it's about maximizing desirable gains Vs reducing undesirable gains and losses:

 

1/ unwanted winter heat loss

All windows leak heat through the frames just as much as the glazing, especially once you're at triple glazed levels

Bifolds are a particular issue as having a higher ratio of frame to glass, they also struggle to get such a good seal due to their shape. In terms of energy efficiency the preference order is approximately single door, french door, lift and slide door, fold and slide door, bifold door. So If you're looking for the whole wall of glass/bring the outside in Kevin McCloud moment, I think a big slider or fold and slide doors maybe best choice. 

Even so, the winter losses will always be higher than a solid insulated wall.

 

2/ unwanted solar gains

The sun is higher in the sky in the summer so many solutions work on the angles, e.g. recessing the glass in the reveal, pulling the eves low over the windows, or install external awning or brise soleil to throw shade over the glass in summer, but in the shoulder season the lower sun can get in under it. Assuming there's a patio out there, a big retractable awning could work well and serve multiple uses. 

Else there's shutters or smart glass tinting but they have drawbacks (limit size of door, cost).

 

If still undecided a detailed energy survey could help with all this. 

 

Edited August 28, 2019 by joth

[Ferdinand]

6 minutes ago, joth said:

single door, french door, lift and slide door, fold and slide door, bifold door.

 

Just to check - fold and slide are where they are on a track, but each door is separate?

 

So the action of closing them all is like dealing cards from a shoe in a casino, rather than say like opening a concertina-folded set of 10 postcards of Skegness?

 

F

[Jeremy Harris]

In general terms, what @joth says is right, but I'd add that of all the possible ways to gain light into a room, bifolds are almost certainly the least thermally efficient.  The seals will gradually lose their effectiveness with time, just due to the geometry and the very light sealing forces that are available to try to maintain compression on them. 

 

For a house that stays cool, even in summer, adding glass will make it colder in winter.  Solar gain in the coldest months of the year is negligible, and I strongly suspect that the reason this room is colder than others has everything to do with factors other than solar gain.  Does it have more than one external wall, for example?  Corner rooms lose more heat than those in the centre of the house, as do single storey rooms, or worse still, single storey rooms with three external walls.

[Ferdinand]

@Benjseb

 

Welcome to the forum.

 

I think we need context on how well insulated your house is etc, before we can comment on whether that amount of solar gain would make much difference.

 

My suspicion is that potentially the extra problems in weather like the present may not be an overall benefit.

 

F

[joth]

7 minutes ago, Ferdinand said:

 

Just to check - fold and slide are where they are on a track, but each door is separate?

 

So the action of closing them all is like dealing cards from a shoe in a casino, rather than say like opening a concertina-folded set of 10 postcards of Skegness?

 

F

 

Exactly: Vegas vs Skegness.

I should add this is a massive generalisation, a good bifold could (initially) outperform a bad slide and fold etc, but it's what I understood to be the preference order for best-in-class performance

 

9 minutes ago, JSHarris said:

The seals will gradually lose their effectiveness with time, just due to the geometry and the very light sealing forces that are available to try to maintain compression on them. 

 

Thanks, yes - this must be what I was recalling  when I mentioned "they also struggle to get such a good seal due to their shape"

[Benjseb]

Thanks guys

 

So to give a bit more info, the house is 'long and thin' - most rooms are the depth of the house, so have two external walls, both north and south facing. On the ends the rooms have three external walls. 2 storey,

 

The kitchen is an end room, so West/South/North facing

 

42sqm. 60W/m2 heat loss

 

Stone built. Brick inner leaf.  Insulated internally. There are some fairly large half-glazed doors on the north wall, plus a small double glazed window and small door on the south facing wall.

 

We're not interested in insulating it further, as it would be too disruptive, and it's not "cold" by any stretch, it just sits at say 17c most of the year unheated so feels like a little extra solar gain and light would make a difference, like it does in the other rooms.

 

 

Ben

 

 

[Benjseb]

Any further suggestions based upon the extra info above?

 

Thanks all. 

[Jeremy Harris]

As stated earlier, increasing the area of glazing will increase the heat loss in cool/cold weather, and increase solar gain in summer.  If you want the room to be warmer in summer and cooler in winter, then more glazing would fit the bill.  Also, as mentioned earlier, bifolds are almost certainly the worst way of adding additional glazing area, as they will end up being draughty after a while, when the seals stop sealing, as they will.  

 

There are better thermal/airtightness options for adding glazing, either lift and slide or maybe fixed glazing panels with French windows.  Be prepared for that room feeling cooler in winter, though, as even the very best glazing available provides much less insulation than even a pretty poor wall.

[SteamyTea]

9 hours ago, JSHarris said:

even the very best glazing available provides much less insulation than even a pretty poor wall.

May be worth improving the walls with some extra insulation it it is possible.