jamiecta
01-13-2010, 09:42 PM
I'm working on a project at the moment that has really thick concrete walls. Just some for example:
36" thick - 420 lb/ft2 weight
72" thick - 840 lb/ft2 weight
(architectural gave me the thickness and the density (140lb/ft3) and I just multiplied through by the thickness in feet for those weights)
For a reference, if you're using the CLTD method, the thickest wall-type group is ASHRAE Group A. These ASHRAE wall-types work fine for 99% of normal projects. As you know, if you are using CLTD, even if you're wall doesn't match up exactly, you can find something close enough. However, the thickest concrete this covers is 12" @ 156 lb/ft2 weight.
The U-Value portion of these walls is not a problem. Obviously I found the closest concrete construction type and used the resistance per inch to figure out the U-Value. The problem relates to the mass and weight of these walls. The ASHRAE wall types, as I'm sure you know, are primarily chosen because the mass of the building construction plays into the thermal transfer of heat through the wall into the building which affects what time of day the building will peak etc. Obviously a thin metal wall will see the heat inside sooner than a concrete wall, even if the U-Values are the same.
Have any of you dealt with construction this extreme? (ie this is for a nuclear power plant). If so how did you accommodate for this? With both CLTD and RTS, manually or using programs I have had to choose a wall type/mass value and it is significantly lower than what I am dealing with. As far as I know, HAP doesn't deal with walls this thick either and TRACE 700 seems to have problems as well (per someone I'm working with who messed around with the demo).
I am just not sure how to go about this. I've considered using the thickest wall group and just using the U-Value for 72", I'm just concerned that the difference in the mass is significant enough to cause an incorrect answer.
It might be a good enough approximation, but I'm not really sure. I don't have any data to test it against. As I stated, the thickest wall in the ASHRAE groups gets to only 12" of concrete and 156 lb/ft2. I am not sure if this was done because after that the difference is negligible or what.
But as far as I understand it, the thicker the wall and the more mass it has, the slower the release of the heat will be into the inside space. With super thick walls I am assuming that there is a huge difference in 72" vs 12" on the peak load hour in the space. I could very well be wrong though. But seeing as that 72" is 6x as thick as 12", I can compare and say that using 2" of concrete in a load calculation is not a good approximation for using 12" of concrete.
36" thick - 420 lb/ft2 weight
72" thick - 840 lb/ft2 weight
(architectural gave me the thickness and the density (140lb/ft3) and I just multiplied through by the thickness in feet for those weights)
For a reference, if you're using the CLTD method, the thickest wall-type group is ASHRAE Group A. These ASHRAE wall-types work fine for 99% of normal projects. As you know, if you are using CLTD, even if you're wall doesn't match up exactly, you can find something close enough. However, the thickest concrete this covers is 12" @ 156 lb/ft2 weight.
The U-Value portion of these walls is not a problem. Obviously I found the closest concrete construction type and used the resistance per inch to figure out the U-Value. The problem relates to the mass and weight of these walls. The ASHRAE wall types, as I'm sure you know, are primarily chosen because the mass of the building construction plays into the thermal transfer of heat through the wall into the building which affects what time of day the building will peak etc. Obviously a thin metal wall will see the heat inside sooner than a concrete wall, even if the U-Values are the same.
Have any of you dealt with construction this extreme? (ie this is for a nuclear power plant). If so how did you accommodate for this? With both CLTD and RTS, manually or using programs I have had to choose a wall type/mass value and it is significantly lower than what I am dealing with. As far as I know, HAP doesn't deal with walls this thick either and TRACE 700 seems to have problems as well (per someone I'm working with who messed around with the demo).
I am just not sure how to go about this. I've considered using the thickest wall group and just using the U-Value for 72", I'm just concerned that the difference in the mass is significant enough to cause an incorrect answer.
It might be a good enough approximation, but I'm not really sure. I don't have any data to test it against. As I stated, the thickest wall in the ASHRAE groups gets to only 12" of concrete and 156 lb/ft2. I am not sure if this was done because after that the difference is negligible or what.
But as far as I understand it, the thicker the wall and the more mass it has, the slower the release of the heat will be into the inside space. With super thick walls I am assuming that there is a huge difference in 72" vs 12" on the peak load hour in the space. I could very well be wrong though. But seeing as that 72" is 6x as thick as 12", I can compare and say that using 2" of concrete in a load calculation is not a good approximation for using 12" of concrete.