Rating System

LEED BD+C: New Construction, LEED BD+C: Schools, LEED BD+C: Retail, LEED ID+C: Retail, LEED BD+C: Healthcare, LEED BD+C: New Construction, LEED BD+C: Schools, LEED ID+C: Commercial Interiors, LEED ID+C: Commercial Interiors, LEED BD+C: Core and Shell, LEED O+M: Existing Buildings, LEED O+M: Existing Buildings, LEED BD+C: Core and Shell

Rating System Version

v3 - LEED 2009, v3 - LEED 2009, v3 - LEED 2009, v3 - LEED 2009, v3 - LEED 2009, v2 - LEED 2.2, v2 - Schools 2007, v2 - LEED 2.0, v3 - LEED 2009, v3 - LEED 2009, v3 - LEED 2008, v3 - LEED 2009, v2 - LEED 2.0

Inquiry

The project is an 80,000 sf K-12 school located in the pacific northwest. A majority of the building is being conditioned by "standard" mechanical means and can demonstrate compliance according to ASHRAE 55-2004 Figure 5.2.1.1., however there are portions of the building that will be thermally regulated by natural ventilation and with extensive radiant systems.\n\nThe purpose of this request is to determine whether the more passive, naturally ventilated portion of the building may be considered "naturally conditioned" with their thermal comfort criteria evaluated according to ASHRAE 55-2004 Figure 5.3 rather than being evaluated according to Figure 5.2.1.1.\n\nThe northwest climate is considered heating dominated with narrow diurnal temperature variations and as a consequence has limited cooling needs, especially during the school year. The need for cooling is isolated to only brief time periods at the beginning and end of the 9-month school year when potential thermal comfort concerns would arise. To mitigate thermal comfort concerns during these isolated times, the design incorporates occupant-controlled operable windows and ceiling fans to allow comfort control within the classrooms. In addition to the operable windows, the design also includes utilizing the thermal massing properties of the concrete floors to better modulate the release of cooling within the space(s). The cooling will be supplied by evaporatively-cooled water via hydronic loops in the floors during the nighttime periods when the building is unoccupied. The intent is pre-charge the thermal mass of the floors with enough cooling to offset the effects of internal heat gains and eliminate the need for active mechanical cooling during the day. Since the charging is taking place during the evenings, there will not be any ability for the occupants to directly call for additional cooling to be added to floor or space and the mass will in essence be allowed to release it cooling naturally trough out the day. Lastly, we are interpreting that this approach of pre-cooling the mass without the need of compressor-based mechanical cooling could be construed as a assisted passive approach, however it is unclear whether the USGBC will recognize these spaces as "naturally conditioned" for the purposes of IEQc7.1. \n\nASHRAE 55-2004, Section 5.3, states that "occupant-controlled naturally conditioned spaces are those spaces where the thermal conditions of the space are regulated primarily by the occupants through opening and closing of windows". We believe that the definition is still being satisfied with the mass pre-charging strategy described previously, since the regulation of the thermal conditions will still be controlled by the occupants through the opening and closing of windows.\n\nCan the thermal comfort criteria in these rooms be evaluated according to "naturally conditioned" rather than "typical" criteria and if so, is modeling an acceptable means of documenting compliance?\n