Using thermally massive elements as internal solar shading

[Y Claire Jenkins]

The current design of the passivish house I'm planning has a very tall south facing window next to the two storey stairwell to give light and a nice view to the stairs and landings plus desirable solar gain in winter. This is going to be difficult to shade against summer overheating as I don't fancy a louvre system in front of the window and the overhang at the top won't give any shade to the lower section.
As the stairs would be going to and fro across the window in half-storey flights, and could have a solid balustrade on the window side, they would shade the inside areas and, if thermally massive, could intercept quite a bit of summer heat. I'd planned to use the stairwell for night time purging anyway, with openable windows at the top.
Would that make sense? Or will I just have to accept reducing the size of the windows substantially?

[Mark Siddall]

Are you using PHPP to assess the design? This may help you to figure out the best option.

Mark

[Y Claire Jenkins]

Mark
Yes, we are using PHPP. It's currently showing about 17 kWh/m2a on a preliminary rough figures, and we're working out how we can modify the design to improve this without losing the things we like about it.
I didn't think PHPP would take account of the position of the thermal mass?
The shading of the window is a slightly different issue which our architect has raised and I wondered if using the staircase might help, even if PHPP wouldn't recognise it.
Thanks
Claire

[Mark Siddall]

Claire
PHPP does not take into account the position of thermal mass rather it takes into account the more generalised proprotion of thermal mass i.e. light, mid, heavy in Wh/m2K (as a specific heat capacity). The issue that you raise is perhaps to localised for PHPP at a whole house level but you could try developing a model that only considers the area that you are considering an all other parts of the house become adiabatic (no heat gain/loss). I've not tried this but it may offer some insight as to the value of shading vs. mass.

(I tend to think that you would benefit from some shading regardless of the mass within the space ....but night purge may also help achieve a suitable balance.)

Mark

[Christian Nialki]

Dear Claire,
In case you are still thinking about additional thermal mass for your project please have a look at our website www.ebb.im and under "projects" at "Steigerleiand 2.0". The latest news from last year's Summer was that it has been working very well. And like Mark Siddall mentioned, shading is very effective.
All the best,
Christian Nialki