An Investigation Into Zone Pressure Diagnostic Protocols For Low Income Weatherization Crews

Zone pressure diagnostics (ZPDs) have become an established tool for low-income weatherization programs in diagnosing indirect air leakage paths in houses.  Other programs, such as the American Lung Association’s Health House, use ZPDs to establish performance specifications.  Despite widespread use, there are substantial differences in the way field personnel decide when to use ZPDs, which of the three methods to use, and how to make the best measurements.  A project team comprised of staff from the Center for Energy and Environment, Michael Blasnik & Associates, and the Energy Conservatory developed and tested protocols for ZPDs used by weatherization crews and developed methods for determining the accuracy of ZPDs. 

ZPDs are used to identify and measure series leaks or leaks that pass through several zones of the house.  For example, air leaking through the attic roof must first move from the living space into the attic through the attic floor.  ZPDs measure the pressure difference between the living space and the bordering zone (the attic) and the bordering zone and the outdoors.  The techniques rely on the principle that the ratio of the pressure difference across the interior and exterior boundaries of a series leak is a direct function of their leakage area.   Field personnel can choose from three different ZPD methods: (1) Hole Method (add-a-hole to the zone), (2) Flow Method (open a door to the zone), and (3) Vent Method (estimate zone venting).  Algorithms are available to compute the results for all three methods but there has been little consensus on the “best practice” for performing the measurements and application of ZPD techniques in the weatherization process. 

In order to establish a protocol for using ZPDs and determine their accuracy, the project team: 

  • Surveyed state weatherization agency staff and weatherization crews to determine how ZPDs are used currently 
  • Established test protocols and computation algorithms for all three ZPD methods 
  • Developed an additional (Hybrid) method for ZPDs 
  • Conducted laboratory tests to measure the relationship between the physical and effective area of different types of openings used in the Hole Method 
  • Conducted tests on two houses to assess the short-term repeatability of the different methods and compare results from the Hole Method and the Flow Method 
  • Analyzed data from air leakage tests conducted on houses in the Sound Insulation Program in Minneapolis, Minnesota 
  • Conducted extensive ZPD tests on weatherization program houses to provide information on the frequency of occurrence of zone conditions, to investigate the reliability of the different ZPD methods, and to compare the air leakage reduction measured by the different ZPD methods and whole-house air leakage tests 
  • Performed simulations to study the impact of stack effect baseline pressures, to develop a simplified approach for calculating ZPD method errors, and to investigate the effect of various errors on the Hole and Flow Methods. 

Phase I and Phase II Final Report Appendices

Full Report (PDF)
An Investigation Into Zone Pressure Diagnostic Protocols for Low Income Weatherization Crews