JB
Member
Just wondering, how much more energy efficient is a non thermally broken Aluminium double glazed door & frame compared to a Timber single glazed door and frame.
Door is 2340x820 and both doors have a 100mm frame.
I'm in Melbourne, this is for a laundry door that won't get much direct sunlight. I'm more concerned about winter than summer.
I understand it won't be an exact calculation.
JB
Member
Aluminum door doesn't have a WERS rating. Plus I dont know the WERS rating of timber door 
However unlike a window, alumium door and frame has smaller ratio of glass compared to windows.
I'm also thinking it won't make much difference changing from timber to aluminium because as you said it has a second door (with draught stopper) into hallway.
Francis
Member
http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html
Thermal Conductivity W/(m K)
Material Temperature
25 oC 125 oC 225 oC
Aluminum 205 215 250
Glass, window 0.96
Glass, wool Insulation 0.04
Hardwoods 0.16
Polystyrene 0.03
Material R-Value thickness 100mm at 25 oC
Aluminium 0.00049
Glass, window 0.10417 (0.00521 at 5mm)
Glass, wool Insulation 2.50000
Hardwood 0.62500
Polystyrene 3.33333
Note your glass isn't going to be 100mm thick and neither is your door, only the jamb will be and it isn't solid aluminium but an extruded profile. The area of aluminium will end up being a radiator to the outdoors sucking heat from your building.
JB
Member
I didn't mean the door frame is 100mm thick. Usually 35 or 40mm.
The border of the door is 100mm wide. The rest glass.
Anyway I found a new old stock double glazed 1 lite timber door from ebay. $150 delivered so I was happy. Disappointingly the air gap is only 6mm but better than single glzed.
Now I have my laundry will have 3 glass doors. One leads outside, one to the garage and one into the house.
So I have 1 double glazed door and 2 singe glazed doors. I plan using draft stoppers on all doors. Should I use the double glazed door between the laundry and house or laundry and outside?
I'm using all 1 lite glass doors to gain natural light.
From general experience, the double glazed Al will have an R-value around 0.23-0.26, the single glazed timber roughly 0.15. So it's an improvement, but not a huge one. Good thermally broken double-glazing with low-e has R-value 0.35-0.45. Low-e coating adds about 0.08, so maybe you should go single glazed timber with low-e coating if it's significantly cheaper, and since Melbourne is cold but rarely extreme.
And yes, I'm using R-values rather than U-values even though windows are quoted in U-values. Everything else is in buildings uses R-values, and I think in R-values. R=1/U for those unsure about the conversion.
JB
Member
Thanks Ruffy, I understand the relationship between R and U value, but I believe that you shouldn't use R value for materials that conduct heat/cold, i.e. aluminium, glass etc.
Anyway, I have a double glazed timber door. Disappointingly the air gap is only 6mm. Anyway at $100 it's cheap.
JB, R-value are used for products that primarily address conduction. For example, bulk insulation and wall systems are always quoted in R-values, and their effect is mostly to reduce conduction.
I know what you are saying - that sometimes they quote R-values for radiant barriers, but usually they are directional (eg. sarking is "R1.5 upwards" - what they are really saying is that it's a radiant barrier that does virtually no conductive insulating downward or inward).
This confusing state of affairs is a systemic shortcoming. The system should use separate units for conductive vs radiant barriers since they do entirely different jobs.
