Floor heating and cooling - radiant fractions

[David_S]

We are evaluating thermal comfort (PPD & PMV as per ISO7730) in rooms with floor heating & cooling. The IES FAQ here: https://www.iesve.com/support/knowledgebase/faq/2100 lists several ways how to model this situation. Given the stage of the design and time constrains, we would like to use the first method as a starting point (even with awareness that the result will be approximate):

"The simplest way to do chilled slabs is to set a suitable radiant fraction for cooling in ApacheSim. The radiant fraction will depend on the position (floor or ceiling) and shape (chilled beams/chilled ceilings) of the cooling elements".

The question is what radiant fraction is suitable for floor cooling. Some radiant fractions (including surfaces facing up & down) are listed i.e. in apacheTables: https://help.iesve.com/ve2018/table_11_ ... 3D&mw=MjQw

Refering to this source, for horizontal surface facing up at 30C (heating), radiant fraction is 0.60. For 5C, it is 0.79. Building on the assumption that the relationship between temperatures and radiant fraction is linear (at least within the temperature range 5C - 30C), for cooling I would just interpolate the radiant fraction for may target surface temperature (lets say 20C). Does this make sense?

Or have you been using different values / approach altogether?

Thanks for any ideas and comments on this.

David