Pax FuturaCase Study: Published | Updated: | | Seattle | #1702901710
- Building Type
- Marsha Poon | City of Seattle Mechanical/ Energy reviewer
Geoff Belau | Building Plans Examiner
- Ratings & Awards
Targeting Built Green 4 Star
Net Zero Ready
The Pax Futura multifamily passive housing project is designed and built to achieve a near zero energy rating and aims to achieve passivhaus certification. Use of high thermal efficiency construction methods, solar thermal water heaters and a heat recovery ventilation system (HRV) help approach passive house for multi-unit dwelling. HVAC system required an engineering validation to demonstrate ample airflow to satisfy the code requirement.
To achieve the building performance desired, the building’s mechanical engineers installed joined exhaust ventilation for both kitchen and bathrooms. The HRV system was designed with minimal air circulation and exhaust specs did not meet current City of Seattle ventilation requirements. To achieve economic performance, one HRV was used for each six units and the exhaust of 27 cfm was well below the coded 45cfm. These numbers came from ASHRAE’s prescriptive pathways, and the the architects submitted a code modification to the City of Seattle Department of Construction and Inspections with alternate code modification, the current code requirements, the justification and a written analysis describing a reviewed building practice. Seeing this data and modification proposal, the Mechanical Reviewer on the project approved the building’s HRV-based ventilation system. Legislative code updates for high performance building are slowly adopted, and the ASHRAE recommended HRV performance metrics were recognized as an emerging best practice helping to earn the modification approval.ASHRAE standards suggest air flowing through the kitchen into the bathroom, giving both spaces an exhaust of 30 cfm. NK submitted a Code Modification or Alternate Request form to the City of Seattle Department of Construction citing minimum exhaust rates for private kitchen and toilet rooms by ASHRAE and citing SBC 104.4- code waivers for spirit of the code. The city of Seattle approved the code modification after determining adequate ventilation would be provided by this innovative system.