Semiheated Walls

Thanks Markus. As it happens my figure is very badly visible in my eddition...I can't make out much. Maybe the logic is something like "two semiheated makes a whole".

Wow. Check out A9.4.1.1 and A9.4.1.2. It seems the second option is indeed the correct one. I would have called it a semi-exterior "partition".

Just a update after deeper investigation... Semiheated baseline requirements Semiheated spaces are defined in ASHRAE as spaces having cooling capacities less than 5 Btu/h•ft2 and have heating capacities that range from 3.4 Btu/h•ft2 up to the values in Table 3.1 (5 Btu/h•ft2 for climate zones 1 and 2, 10 Btu/h•ft2 for climate zone 3, 15 Btu/h•ft2 for climate zones 4 and 5, 20 Btu/h•ft2 for climate zones 6 and 7, and 25 Btu/h•ft2 for climate zone 8). Exterior surfaces for semiheated spaces should be modeled in the Baseline Case using the semi-conditioned values from Tables 5.5-1 to 5.5-8. Semi-exterior baseline requirements ASHRAE defines semi-exterior building envelope as: “The elements of a building that separate conditioned space from unconditioned space or that enclose semiheated spaces through which thermal energy may be transferred to or from the exterior, or to or from unconditioned spaces, or to or from conditioned spaces.” For example, a slab separating an unconditioned parking garage from the conditioned first floor of a building would be considered a semi-exterior element. Similarly, a wall separating a semiheated warehouse from a conditioned office space would be considered a semi-exterior element. As per the User's Guide, semi-exterior surface constructions should be modeled so as to adhere to the semiheated criteria from Tables 5.5-1 to 5.5-8 (even though they may not have anything to do with a semiheated space). However, one cannot use the same constructions for a semi-exterior wall of a semiheated space as that of the exterior wall of a semiheated space. The Max. Assembly U-Values listed in these tables under the semiheated criteria were calculated using the exterior air film R-Value co-efficients listed in section A9.4.1 NOT those of semi-exterior "partitions". This means that semi-exterior surfaces must adhere to the same criteria as the exterior surface, but due to the differing applicable air film resistances, should use different constructions to come to the required U-value. Lastly, as per the User's Manual, other interior partitions shall have the same build as those of the proposed design.

On a side note: external floors rated U-values are indeed calculated with an external air film resistance as that of a semi-exterior surface (probably because the underside doesn't experience the same wind as that of a roof or wall), meaning that in this case the semi-exterior surface floor element construction happens to be identical to that of the semiheated floor (for appendix G).