How does IES calculates the U-value for ground-contact floor

[SakuraOno]

Hi,

Does anyone know how IES calculates the adjusted U-value for a ground-contact floor?
Does IES use the methods specified in CIBSE Guide A (section 3.5?) Because the the adjusted U-Value calculated by IES is slightly different from the one calculated using the equations specified in CIBSE. Also, after applying the U-value adjustment, the construction thickness is also adjusted. However, this is NOT the same as the "equivalent thickness", how does IES calculates this adjusted thickness?

Thanks!

[PCully]

Hi,

The U-value adjustment can be calculated using either EN ISO 13370 or F-Factor methods. There's a bit more info that you may find useful in the VE 6.1.1 New Features document http://www2.iesve.com/content/kb/ve/ve6 ... atures.pdf.

Again sorry the user guides are not updated to give more detail on this feature but hopefully this can help you.

Phil

[SakuraOno]

Hi,

The U-value adjustment can be calculated using either EN ISO 13370 or F-Factor methods. There's a bit more info that you may find useful in the VE 6.1.1 New Features document http://www2.iesve.com/content/kb/ve/ve6 ... atures.pdf.

Again sorry the user guides are not updated to give more detail on this feature but hopefully this can help you.

Phil

Thank you for the document. So it seems that IES does NOT use CIBSE's method for calculation. The document doesn't really say why though, any thoughts? And why would one choose one calculation method over the other? (does IES provide any guidance on the situation when one should pick one or the other?)

thanks!

[PCully]

Sorry, I don't have an answer to when each is appropriate. I believe these tools were added due to a requirement for the PRM application but were made available to all users as they can be useful rather than having to do the calcs manually, I guess if you have already done it using CIBSE method then you are free to modify the Construction yourself.

I mean to say in my previous note that's the defn of "ground contact" and "external" here, ground contact if it touches the ground/earth and external if it is adjacent to air (e.g. the floor of a room that overhangs the building so it has air below it rather than another room or the ground)

Phil

[SakuraOno]

Sorry, I don't have an answer to when each is appropriate. I believe these tools were added due to a requirement for the PRM application but were made available to all users as they can be useful rather than having to do the calcs manually, I guess if you have already done it using CIBSE method then you are free to modify the Construction yourself.

I mean to say in my previous note that's the defn of "ground contact" and "external" here, ground contact if it touches the ground/earth and external if it is adjacent to air (e.g. the floor of a room that overhangs the building so it has air below it rather than another room or the ground)

Phil

Thanks Phil.
For the record, CIBSE method generates similar U-value (adjusted), although the CIBSE value tend to be lower.

[byme_guy]

You also have to take into consideration the temperature you have to use for the ground, because if not IES will just use the outside temperature you have specified in APlocate. I am still don't know though what is the use of characteristic dimension. If you are using F-factor Method, isn't it that we have to use the perimeter of the building?

[Ben]

Hi there,
I'm wanting to apply the ground-contact u-value adjustment
Can someone please define:
Characteristic dimension (m):
Floor depth (m):
External wall dimension (m):

If you have a drawing (image) of the arrangment, this would be helpful to understand the arrangement
Thanks in advance,
Ben