4 ms·

Thermal mass is usually not a factor you're looking at when choosing windows; thermal resistance is. In a nutshell, stone, concrete, metal, and glass are very

by maratc 4y ago

Thermal mass is usually not a factor you're looking at when choosing windows; thermal resistance is. In a nutshell, stone, concrete, metal, and glass are very good at transmitting heat, so the inside of your house will quickly be as hot (or as cold) as the outside. Plastic, wood, and especially air are very bad at transmitting heat (or good resisting to heat transmission) and this is what you want for your house. Back to windows, multiple sheets of glass are only desirable because they have an air chamber inside. Three layers of glass mean two air chambers, each at its own temperature.

dan-robertson 4y ago
I know how double glazing works but if you put a window somewhere then you aren’t putting a wall there. So I’m wondering if having a much higher % window (is less wall and more glass) will cause the building to have an importantly lower thermal mass. But I don’t really know if modern buildings would want a large or small thermal mass. I’m confused by what you write about stone and concrete being good at transmitting heat. I thought the point was that (a) they act as an accumulator regulating the temperature because they take a lot of energy to heat up and (b) they conduct heat poorly (or worse than a window would be mm of thickness but they are much thicker) which is insulating. Looking up random values from the web, it seems a the low numbers for a thin concrete wall (single wythe means no cavity insulation) are about 2.5x those of a coated double glazed window. A wall which is thicker or has insulation will perform much better. And this doesn’t count any insulation from plaster or cladding or whatever. Concrete: 0.8 W/m^2K for 10cm solid dense concrete. https://ncma.org/resource/rvalues-ufactors-of-single-wythe-concrete-masonry-walls/ https://ncma.org/resource/rvalues-ufactors-of-single-wythe-c... Window: 2.1 W/m^2K for a coated especially insulating window. https://www.justrite.com.au/products-and-services/double-glazing-canberra-double-glazed-windows-and-doors-in-upvc-and-aluminium-for-new-homes-extensions-or-renovations/thermal-properties-of-double-glazed-units/ https://www.justrite.com.au/products-and-services/double-gla... I wrote about conductivity here because that’s what your comment seemed to be about. Maybe I misunderstood your comment because it seemed to me that you were implying that windows transmit less heat than eg concrete walls (reading carefully, you don’t write that) and I thought it was a given that they transmit more heat. But my question isn’t about adding windows making a building require more heating but about adding windows making a building’s temperature harder to maintain because there are not a load of big (eg) concrete blocks in the wall releasing their heat into the air after you open the door and let a load of cold air in.
- maratc 4y ago
  > But I don’t really know if modern buildings would want a large or small thermal mass. This depends on climate. When the outside temperature changes, the building will eventually get itself to the outside temperature (thermodynamics laws). How fast that change would happen exactly — depends on thermal resistance and thermal mass. Thermal resistance acts as an amplifier (or rather diminisher) of that changing force: the higher the resistance, the lower is the force, and so more time for the change to take effect. Thermal mass acts as a momentum against that changing force: the higher the mass, the more time for the change to take effect. In some climates (e.g. south Europe) the outside temperature is only a problem on winter nights and on summer days. You are only fighting the outside weather for hours on end. And you can effectively make that fight with large thermal mass alone. In other climates (e.g. north Europe) the low temperatures at winter can come for months, so you want mass, resistance, and inside heating.

by maratc 4y ago

dan-robertson 4y ago

I know how double glazing works but if you put a window somewhere then you aren’t putting a wall there. So I’m wondering if having a much higher % window (is less wall and more glass) will cause the building to have an importantly lower thermal mass. But I don’t really know if modern buildings would want a large or small thermal mass. I’m confused by what you write about stone and concrete being good at transmitting heat. I thought the point was that (a) they act as an accumulator regulating the temperature because they take a lot of energy to heat up and (b) they conduct heat poorly (or worse than a window would be mm of thickness but they are much thicker) which is insulating. Looking up random values from the web, it seems a the low numbers for a thin concrete wall (single wythe means no cavity insulation) are about 2.5x those of a coated double glazed window. A wall which is thicker or has insulation will perform much better. And this doesn’t count any insulation from plaster or cladding or whatever. Concrete: 0.8 W/m^2K for 10cm solid dense concrete. https://ncma.org/resource/rvalues-ufactors-of-single-wythe-concrete-masonry-walls/ https://ncma.org/resource/rvalues-ufactors-of-single-wythe-c... Window: 2.1 W/m^2K for a coated especially insulating window. https://www.justrite.com.au/products-and-services/double-glazing-canberra-double-glazed-windows-and-doors-in-upvc-and-aluminium-for-new-homes-extensions-or-renovations/thermal-properties-of-double-glazed-units/ https://www.justrite.com.au/products-and-services/double-gla... I wrote about conductivity here because that’s what your comment seemed to be about. Maybe I misunderstood your comment because it seemed to me that you were implying that windows transmit less heat than eg concrete walls (reading carefully, you don’t write that) and I thought it was a given that they transmit more heat. But my question isn’t about adding windows making a building require more heating but about adding windows making a building’s temperature harder to maintain because there are not a load of big (eg) concrete blocks in the wall releasing their heat into the air after you open the door and let a load of cold air in.

maratc 4y ago
> But I don’t really know if modern buildings would want a large or small thermal mass. This depends on climate. When the outside temperature changes, the building will eventually get itself to the outside temperature (thermodynamics laws). How fast that change would happen exactly — depends on thermal resistance and thermal mass. Thermal resistance acts as an amplifier (or rather diminisher) of that changing force: the higher the resistance, the lower is the force, and so more time for the change to take effect. Thermal mass acts as a momentum against that changing force: the higher the mass, the more time for the change to take effect. In some climates (e.g. south Europe) the outside temperature is only a problem on winter nights and on summer days. You are only fighting the outside weather for hours on end. And you can effectively make that fight with large thermal mass alone. In other climates (e.g. north Europe) the low temperatures at winter can come for months, so you want mass, resistance, and inside heating.