I've interpreted the semiheated column in table 5.5-1 refering to the external walls of a semiheated space...as this table is much conserned with the envelope (the partition between the semiheated space and the heated space being irrelevant as it does not lay on the envelope.
It could, however, be interpreted as being the wall (partition) between the semiheated space and the conditioned space where if the semiheated space has external facing walls they will require the values of either the nonresidential or residential columns. This case is unconventional to me because the film co-eff. on either side of the semiheated partition are not really standardized and therefore the U-values don't make so much sence.
What is the correct interpretation.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
March 7, 2013 - 10:17 am
Refer to 5.5.2 and figure 5.5. To us it appears to be both the external walls and internal partitions to a conditioned space of a semi-heated space must meet the semi-heated column requirements.
The one that bugs me is the partition between conditioned and unconditioned but not ventilated space as only requiring the semi-heated levels of insulation.
Jean Marais
b.i.g. Bechtold DesignBuilder Expert832 thumbs up
March 7, 2013 - 10:57 am
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".
Jean Marais
b.i.g. Bechtold DesignBuilder Expert832 thumbs up
March 8, 2013 - 2:52 pm
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".
Jean Marais
b.i.g. Bechtold DesignBuilder Expert832 thumbs up
April 13, 2013 - 3:23 pm
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.
Jean Marais
b.i.g. Bechtold DesignBuilder Expert832 thumbs up
April 18, 2013 - 7:23 am
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).