Anticipating solar gain / overheating in a new extension

[Radian]

1 hour ago, SteamyTea said:

Pretty good really.  Makes me wonder why we don't fit a glass panel over 'daylight' walls and pump the thermal energy around the house.  A posh trombe wall, but not using the wall as storage so much.

I wish I had put in some trunking and ports to shift air from the top of our 'glass box' garden room into the rest of the house. Today it warmed the connecting kitchen and hallway from 17^oC to 21^oC just through natural convection although it was you who pointed out how feeble the SHC of air is. However, with 4 to 5 hours of constant  solar input today, it would have easily saved the 40kWh that the boiler used to bring the rest of the house from 17^oC to 19^oC.

 

On 02/04/2023 at 14:08, Brix said:

My architects are proposing a relatively large area of glass roof on a new kitchen extension (something between 35-45%).

If you are fitting solar PV to the build (and you really should if you haven't already) then the A2A mini split already suggested is a no-brainer. The coincidence of powerful Sun and plenty of free electricity is a match made in heaven. For 1kW of electricity you can readily get 4-5kW of guilt-free cooling in the summmer and similar for instant heating in the winter.

[SteamyTea]

10 minutes ago, Radian said:

I wish I had put in some trunking and ports to shift air from the top of our 'glass box' garden room into the rest of the house. Today it warmed the connecting kitchen and hallway from 17^oC to 21^oC just through natural convection although it was you who pointed out how feeble the SHC of air is.

It could be integrated into the MVHR.  There is an argument to have the MVHR pipework double the usual diameter.  I am not sure why it is so small really, probably ease of fitting/retrofitting.

Larger pipework would reduce airflow speeds, and therefore noise, shift a lot more energy around the place, and possibly, due to lower back pressure, use not much more power.

 

13 minutes ago, Radian said:

On 02/04/2023 at 14:08, Brix said:

My architects are proposing a relatively large area of glass roof on a new kitchen extension (something between 35-45%).

If you are fitting solar PV to the build (and you really should if you haven't already) then the A2A mini split already suggested is a no-brainer. The coincidence of powerful Sun and plenty of free electricity is a match made in heaven.

Yes.  But architects should not be designing in overheating.  They are paid to be the experts, or at least be able to employ the experts to get the design right.

My parents last house had a large, all glass, proboscis on it.  Even though the glass was heavily blue tinted, the overheating was dreadful.  Then freezing during the winter.

Thinking about it, maybe the blue tint was not the best colour.  Means it was absorbing the reds.

They moved after 5 summers in it.

[Radian]

4 hours ago, Iceverge said:

However at night or in winter it'll require a lot of heating to stay hot. 

 

Let's assume you have an outdoor temp of 5 Deg and want 20 deg inside. You spec really really top class windows with an installed U value of 1w/m2K. 

 

Now let's say the extension has a glass area of 50m2 and a floor of say 16m2 at a U value of 0.15 w/m2K. 

 

Heat loss floor is

 

16m2 X 0.1w/m2K X (20deg-5deg) = 36w

 

Heat loss glass box is

 

50m2 X 1W/m2K X (20deg-5deg) = 750w.  

 

For context this about half the heat load of our entire 185m² passive house for your 16m². 

 

 

Ok in California or the Mediterranean with warm temps all year around. Elsewhere its costly to run. 

 

 

 

I've run all the numbers like that on our garden room as well, although the glazed are is only 30m^₂ and you're right - it does look pretty terrifying. But the one thing missing from your calculation is the annual heat gain available. When this is taken into account, the added amenity of having large areas of glazing (if the plot suits it) can make it very much worth it IMO. While it's easy to do the heat loss calculation, in practice it seems a lot more difficult to work out the overall figure when offsetting by the gains. Empirically, taken over the full year, I can't even say it's obvious that a nett loss is involved (although it probably is). The potential for overheating seems considerably greater, but if the orientation and other things that can be done to manage the issue are in place, I don't think the option to use large amounts of glazing should be automatically discounted. Just as overhangs and Brise Soleil can play a part in keeping the space cool in Summer, so thermal blinds or curtains can reduce losses in the winter. Both are desirable for optical reasons as well.

[Radian]

19 minutes ago, SteamyTea said:

It could be integrated into the MVHR.  There is an argument to have the MVHR pipework double the usual diameter.  I am not sure why it is so small really, probably ease of fitting/retrofitting.

Larger pipework would reduce airflow speeds, and therefore noise, shift a lot more energy around the place, and possibly, due to lower back pressure, use not much more power.

I stood our Dyson AM03 fan (450mm diameter although it only has a piddly little fan in the base driving the air multiplier) in the doorway between garden room and kitchen on the hottest day last Summer and it did disappointingly little to balance things out. I got a feeling something like a 1m diameter industrial fan would be needed to make an impact. What I'm working on right now is independent control for the UFH and radiator circulating pumps to see if I can spread the heat from the floor (which is the biggest surface are bathed in sunlight) into the house for a tiny lift in the shoulder months on days like today. It'll probably be a flop but I only need to add one relay to override the CH pump and a couple of lines of code to try it out.

 

In terms of similar surface area and orientation, I estimate that the 20kWh from our solar PV (today) translates into anything up to 80kWh hitting our garden room SE elevation. Between 4% to 8% of that bounces off each of the two panes but given the 50kWh of gas that went into raising the rest of the house by 2^oC and the 4^oC temperature rise at the garden room end, I can readily believe that over 50kWh might have been gained from direct Solar radiation.

[Brix]

2 hours ago, Radian said:

If you are fitting solar PV to the build (and you really should if you haven't already) then the A2A mini split already suggested is a no-brainer. The coincidence of powerful Sun and plenty of free electricity is a match made in heaven. For 1kW of electricity you can readily get 4-5kW of guilt-free cooling in the summmer and similar for instant heating in the winter.

Believe me that if there were scope to install PV here I would have done so - I have two 4kw arrays elsewhere. Listed building, conservation area, awkward roof and mostly shady garden... 🙄

[SteamyTea]

12 minutes ago, Radian said:

I stood our Dyson AM03 fan (450mm diameter although it only has a piddly little fan in the base driving the air multiplier)

Were you thinking that the Might James Dyson had fooled nature.

Of cause it did nothing, the motor is tiny.

 

There was a report about a new wind turbine on Moneybox the other day.

Wind hits the vertical pipe, gets forced up to the turbine by vanes and generates power.

Better than a traditional turbine.

My arse it is. Why don't the BBC, who do reality checks, check with one of the many physicists they employ to show them the error of their ways.

[Radian]

3 hours ago, SteamyTea said:

Were you thinking that the Might James Dyson had fooled nature.

 

No, it's the only fan I had to hand. I think some credit is due (a tiny amount) for sticking a brushless DC motor and Li-ion battery in a small hand-held vacuum cleaner. But nothing else they make is quite as inspired.

[Iceverge]

6 hours ago, Radian said:

 

I've run all the numbers like that on our garden room as well, although the glazed are is only 30m^₂ and you're right - it does look pretty terrifying. But the one thing missing from your calculation is the annual heat gain available. When this is taken into account, the added amenity of having large areas of glazing (if the plot suits it) can make it very much worth it IMO. While it's easy to do the heat loss calculation, in practice it seems a lot more difficult to work out the overall figure when offsetting by the gains. Empirically, taken over the full year, I can't even say it's obvious that a nett loss is involved (although it probably is). 

 

 

From our own PHPP

 

 

Losses are indeed offset by gains but we have pretty good windows. 

 

However without the South facing glazing it would be a loss. 

 

 

6 hours ago, Radian said:

I don't think the option to use large amounts of glazing should be automatically discounted. Just as overhangs and Brise Soleil can play a part in keeping the space cool in Summer, so thermal blinds or curtains can reduce losses in the winter. Both are desirable for optical reasons as well.

 

Sadly with this it's lightly that it'll loose the simple beautiful glass boxiness of the design as there'll be too many add ons. You may end up at a place where aesthetically you'd be better off with less glazing. 

 

 

@Radian is your garden room above inside the heated envelope? 

 

I think there's a place for a highly glazed room outside the main body of the house to be used as a solar air heater amongst other things like below.  

 

 

 

Edited April 3, 2023 by Iceverge

[Gill]

7 hours ago, Radian said:

wish I had put in some trunking and ports to shift air from the top of our 'glass box' garden room into the rest of the house. Today it warmed the connecting kitchen and hallway from 17^oC to 21^oC

Mirrors my experience. On a cold sunny day once the sun room temperature is above the lounge, the doors get opened and the lounge will generally climb up. Even on a cold day (5 degrees outside last week), the sun room hit 24 and that brought the lounge & kitchen up by 3 degrees. 

If only I could pipe that heat to the baltic north facing room. 

 

To avoid energy waste, we simply don't open up the sun room when it would leach heat from the house. It still benifits the rooms its build off as it's generally at worst 4 degrees warmer than outside temps. 

[joe90]

18 minutes ago, Gill said:

Mirrors my experience. On a cold sunny day once the sun room temperature is above the lounge, the doors get opened and the lounge will generally climb up. Even on a cold day (5 degrees outside last week), the sun room hit 24 and that brought the lounge & kitchen up by 3 degrees. 

If only I could pipe that heat to the baltic north facing room. 

 

To avoid energy waste, we simply don't open up the sun room when it would leach heat from the house. It still benifits the rooms its build off as it's generally at worst 4 degrees warmer than outside temps. 

Exactly my experience with my build. (I used to have a link to a glass house surrounding a house that had active vents into the house but can’t find it, anyone?)

Edited April 3, 2023 by joe90

[Radian]

20 hours ago, Iceverge said:

is your garden room above inside the heated envelope? 

A bit of both really. It's built as an extension on the back of the house and retains the original DG French Windows so we can close it off thermally - but it has a dedicated UFH zone that's fed from the gas boiler . I'm aware that this needs frost protection if we were to close it off but that's not how it's used.

 

20 hours ago, Iceverge said:

Losses are indeed offset by gains but we have pretty good windows. 

 

Your windows are much better than mine! But thanks for posting your PHPP figures. Do they not confirm my contention that "excess glazing" can be a benefit if managed correctly?

[Iceverge]

@joe90

 SOLAR CONSERVATORY PASSIVE HOUSE GLENGARIFFE IRELAND VIKING (cherrymortgages.com) this one?

 

 

3 hours ago, Radian said:

Do they not confirm my contention that "excess glazing" can be a benefit if managed correctly?

 

Yes, the issue becomes cold weather I think. There will be days that you have little sunshine and low temperatures so an over glazed heated envelope will need lots of heat input.  

 

A hypothetical house with no window's in the main body, just super insulated shutters opening onto a south facing conservatory could perform very well. Try selling that idea to a human however and they'll tell you where to shove it! 

[gc100]

@Brix I might stating the bleeding obvious, but why not plant a couple of trees to catch most of the direct sunlight In summer months? 

[Radian]

12 hours ago, Iceverge said:

Yes, the issue becomes cold weather I think. There will be days that you have little sunshine and low temperatures so an over glazed heated envelope will need lots of heat input.  

 

 

Yes, there are plenty of days like that! But surely what counts is the long-term energy performance, whether it be measured in terms of annual Carbon or energy costs?

Granted that the added amenity of having an extra feeling of space, light and (hopefully) pleasant views counts for little in terms of Carbon savings (although any replacement for natural light comes at a cost) but it seems to me that many people are ready to describing a space as 'over glazed' without doing a full and proper analysis. This apparent "negative bias" is what puzzles me.

[Brix]

On 05/04/2023 at 07:18, gc100 said:

@Brix I might stating the bleeding obvious, but why not plant a couple of trees to catch most of the direct sunlight In summer months? 

Cheers for the suggestion. The extension will be built up to the boundary which runs east west. So anything providing shade to the roof between about 10-4 would need to be in the neighbour's garden. Not going to happen!

[gc100]

On 06/04/2023 at 11:38, Brix said:

Cheers for the suggestion. The extension will be built up to the boundary which runs east west. So anything providing shade to the roof between about 10-4 would need to be in the neighbour's garden. Not going to happen!

But arn’t we discussing solar gain through the glass? Or does your glazing face your neighbours garden? The roof should be insulated correctly so won’t get any solar gain

[andyj007]

On 02/04/2023 at 14:30, Iceverge said:

 very scientifically skilled design. 

 

 

 

 

 

lol..  since when did common sense become scientific..   if who ever is designing your extension home, is not clever enough to sort/design shading  as part of the package then perhaps they should not be undertaking such work..  its very simple.. the sun and how it tracks through the season is a known quantity..  you can even use google sketch  up to map the shadows..  ..  The key to a good liveable design  is not just how it looks  but design consideration  to how it works and will be lived in..  making use of the sun , making use of shade,  cross ventialtion , and natural ventilation via convection..   simple skils that cost little for the home owner..  if you have to instrall air con in the uk other than say a bedroom for a house to work..  then i agree with the poster above ..  the initial design is lacking 

 

Edited April 13, 2023 by andyj007

[Iceverge]

15 minutes ago, andyj007 said:

lol..  since when did common sense become scientific..   if who ever is designing your extension home, is not clever enough to sort/design shading  as part of the package then perhaps they should not be undertaking such work..  its very simple.. the sun and how it tracks through the season is a known quantity..  you can even use google sketch  up to map the shadows..  

 

 

 

 

The phrase "common sense" is a contentious one.

 

I've only seen it used when someone self deprecates their level o knowledge,experience and application or someone else who is just guessing wildly and hoping things will work out. 

 

A scientific method might be as simple as drawing freehand some summer sun angles on a bit of graph paper and counting the boxes. There needs to be measuring and consciousness to get consistent results. Hence science. 

 

Almost all houses built everywhere ever have insufficient passive heat protection. Most rely on ventilation, active cooling or active shading so yes, almost nobody designs buildings is competent really. 

 

When windows are as insulative as walls it'll be a doddle. Just shade out the unwanted heat as needed. However at the moment they're relatively thermally poor and annual losses need to be balance with gains.

 

 

Edited April 13, 2023 by Iceverge

[gc100]

I would have 100% designed in summer shading if the stupid planners/law would have allowed me. Being class q it was impossible so now I have a house that overheats in the summer and I have to use active cooling. 

[saveasteading]

16 minutes ago, gc100 said:

summer shading

Window blinds? External is best.

[gc100]

2 hours ago, saveasteading said:

Window blinds? External is best.

yeah I some plans to get around the issue when I get time. I used to live in south of France and shutters and brise soleils are the norm . 

[Brix]

On 12/04/2023 at 08:40, gc100 said:

But arn’t we discussing solar gain through the glass? Or does your glazing face your neighbours garden? The roof should be insulated correctly so won’t get any solar gain

Through the flat glass roof.

[saveasteading]

25 minutes ago, Brix said:

Through the flat glass roof.

The good thing about a glass roof in the UK is that the sun doesn't get very high, so we get lots of daylight and not too much direct sun.

 

I once put huge amounts into a school classroom with the clients blessing (and their accepting the risk) because it was an art studio.

Did it ever get too hot? Yes, for a few days per annum. Teachers hung assemblages resembling clouds to stop direct rays.

It wasn't as hot as we feared. They had windows. "The best art practicing  space I have ever known".

 

Vaguely relevant...again lots of windows and skylights in a big lounge for a nursing home. The building inspector claimed it failed regs on overheating.

We pointed out the french doors, that aircon was bad environentally  and hinted we would box the skylights in until signed off.

Then the client killed the subject by saying to the bco " if ever my residents get too hot, I will take one of their blankets off".

 

My point is that there are calculations and hunches, but individual preferences vary.

You can always add greenhouse shading or louvres ( or a sheet of ply) to a skylight, perhaps even only in extreme summers.

And when it is that hot, you can usually open doors and windows.

 

 

 

 

[joe90]

Yes, lots here said my South facing large conservatory would overheat, yes it may fir a couple of days a year but mostly  it’s a light airy warm area that actually heats the house via bifolds a lot of the year.

[ProDave]

This last week when it has been sunny but the air not very warm (cold east wind off the cold North Sea) our sun room warms up nicely and we just open the doors to let the warmer air into the house.

 

I did think about ducts and fans to automate this, but the sun room is outside the "air tight" envelope of the house and hence outside the scope of the MVHR system.  So any such duct would kill the air tightness of the house.