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Zone Pressure Diagnostics Tool User Guide

Zone Pressure Diagnostics
Red Calc Tool User Guide

What this tool can do for you

This tool allows you to easily achieve accurate Zone Pressure Diagnostics (ZPD) testing results. ZPD done with this tool will:

  • Determine the amount of air leakage between the house and an intermediate (or attached) zone such as an attic, basement, or garage.
  • Determine the amount of air leakage between an intermediate zone and outdoors.
  • Determine the portion of the whole-house leakage that is attributable to an intermediate zone.
  • Determine the effectiveness of air sealing by performing pre- and post-weatherization ZPD testing.
  • Estimate the amount of effective attic venting.
  • Appraise the connection between a zone with potentially bad air, such as an attached garage or a crawl space, and the living area.
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Attic as zone with interior and exterior pressure boundaries

Calculated values

  • Zone leakage ratio (zone-to-house : zone-to-outdoor) - the relative leakiness of the interior and exterior pressure boundaries of the zone.
    Note: This ratio only depends of the "House wrt outdoor" and "House wrt zone" ΔP values.
  • Zone-to-house leakage @ 50Pa - the airflow that would pass through the initial interior zone pressure boundary, at 50 pascals, if the exterior pressure boundary were completely removed. The + uncertainty value (95 percent confidence) is listed just after the airflow result.
  • Zone-to-house leakage area - the equivalent leakage area in the initial interior zone pressure boundary. The + uncertainty value (95 percent confidence) is listed just after the leakage area result.
  • Zone-to-outdoor leakage @ 50Pa - the airflow that would pass through the initial exterior zone pressure boundary, at 50 pascals, if the interior pressure boundary were completely removed. The + uncertainty value (95 percent confidence) is listed just after the airflow result.
  • Zone-to-outdoor leakage area - the equivalent leakage area in the initial exterior zone pressure boundary. The + uncertainty value (95 percent confidence) is listed just after the leakage area result.
  • Through-zone leakage at 50Pa - the airflow at 50 pascals through the zone, including both the initial interior and exterior pressure boundaries. This value represents the portion of the whole-house leakage that is attributable to the leakage though the zone. The + uncertainty value (95 percent confidence) is listed just after the airflow result.
  • Percent of whole-house leakage passing through the zone - this value being close to, or above, 100% is a good indication that you have entered some value incorrectly, or that you have made up a physically impossible example.

Tips

  • Clicking the label for any input or result will cause a popup help box to appear. This help box includes the allowed and normal values (for inputs). Read more.
  • We recommend you reset the tool before performing a new test. This will ensure that you don't mix inputs from one job with those of another. The Reset button is at the upper right corner of the tool.
  • ZPD zones can include attics, attached garages or sun porches, basements, and knee wall areas.
  • Zone Pressure Diagnostics is sometimes referred to as series-leakage testing. This is because the resistance imposed by the combination of interior and exterior pressure boundaries is analogous to an electrical circuit wired in series.
  • When opening (closing) a hole to reduce (increase) the resistance of a pressure boundary, it is not necessary to create the opening (closure) all in one place; you may open (close) more than one hole to achieve the recommended pressure shift.
  • We recommend the use of two manometers for zone pressure diagnostics testing. If you have two manometers and one has automatic pressure control (Cruise Control), use this manometer to control the blower door.
  • We recommend you use the automatic baseline feature for the house wrt outdoor pressure difference. If you have a second manometer, we recommend you use it for the zone pressure difference using its automatic baseline feature.
  • Be aware that connections between zones can effect single-zone ZPD results.
  • Use of manometers with WiFi capabilities makes zone pressure diagnostics easier to perform.

Inputs and field measurements

  • Blower door test type - select "Depressurization" or "Pressurization".
  • Use Advanced Inputs (optional)
    • House temperature - the average temperature in the house during the test.
    • Outdoor temperature - the average temperature outdoors during the test.
    • Zone temperature - the average temperature in the zone during the test.
    • Zone is well vented to outdoors - checking this box changes the zone pressure exponent used for the calculation from 0.65 to 0.55. This is appropriate for a zone whose leakage to the outdoors is dominated by large holes.
    • Building pressure exponent - leave this at the default 0.65 unless you know the building pressure exponent as a result of performing a multi-point blower door test.
    • Baseline pressures (wrt outdoors) at 5 second intervals - these three baseline readings will indicate the degree of wind variation during your test and affect the assumed uncertainty of your pressure measurements. The greater the degree of wind variation (range of baseline pressures), the greater the uncertainty of your results.
  • Initial Zone Configuration
    • House wrt outdoor; BD off - the baseline pressure of the house. If you "Use Advanced Inputs", the average of the three "Baseline pressures (wrt outdoors) at 5 sec intervals [Pa]" may be used as this entry. This value is calculated for you as "Avg [Pa]". The sign of this value must be entered if it is negative. If you use the automatic baseline feature of your manometer, enter "0" in this input box.
    • House wrt outdoor; BD on - the house pressure with the blower door on. The sign of this value must be entered, for example, if you are depressurizing, a negative sign must be entered before this value. If you use the automatic baseline feature of your manometer, enter the resulting manometer house pressure in this input box, but make sure you enter "0" in the previous "House wrt outdoor" "BD off" box.
      Note: You do not need to get the house to 50 Pa pressure difference.
    • Zone pressure selection - choose "House wrt zone" or "Zone wrt outdoor" to indicate which of these pressures you are actually measuring. Measuring the smaller pressure (across the leakier pressure boundary) will generally yield the smallest through-zone uncertainty.
    • House wrt zone; BD off - the baseline pressure of the zone you are testing. If you are using a second manometer to measure the house-to-zone pressure, and you are using the automatic baseline feature, then enter "0" in this "House wrt zone" "BD off" box. Otherwise, enter the measured baseline value in the input box, making sure to enter the correct sign.
    • House wrt zone; BD on - the zone pressure with the blower door on. The sign of this value must be entered, for example, if you are depressurizing, a negative sign must be entered before this value. If you use the automatic baseline feature of a second manometer, enter the resulting manometer house pressure in this input box, but make sure you enter "0" in the previous "House wrt outdoor" "BD off" box.
    • Blower door flow adjusted to 50 Pa - the result of the whole-house blower door test for the initial zone configuration. Even though the house is not required to be at 50 Pa pressure difference, this flow must be adjusted to 50 Pa.
  • Modified Zone Configuration
    • Hole/door located between zone and "House" or zone and "Outdoors" - select the appropriate pressure boundary that will be modified for your test. This indicates which pressure boundary (interior or exterior) of the zone is modified so as to create as large a zone pressure shift as possible with the blower door running. The larger the shift in zone pressure between the initial and modified configurations, the more accurate the results.
    • Type of modification - select "Add a hole or open a door" or "Plug a hole or close a door". Most commonly a hole is added, or a door is opened, in the tighter of the two pressure boundaries. However, in some rare situations it may be easier to plug a hole, or close a door, in the leakier pressure boundary. This would most likely be covering existing vents in an attic or crawlspace.
    • House wrt outdoor; BD off - the baseline pressure of the house, in the modified configuration. The sign of this value must be entered if it is negative. If you use the automatic baseline feature of your manometer, enter "0" in this input box.
    • House wrt outdoor; BD on - the house pressure in the modified configuration. The sign of this value must be entered, for example, if you are depressurizing, a negative sign must be entered before this value. If you use the automatic baseline feature of your manometer, enter the resulting manometer house pressure in this input box, but make sure you enter "0" in the previous "House wrt outdoor" "BD off" box.
    • Zone pressure selection - choose "House wrt zone" or "Zone wrt outdoor" to indicate which of these pressures you are actually measuring. Measuring the smaller pressure (across the leakier pressure boundary) will generally yield the smallest through-zone uncertainty.
      Note: You are not required to make the same selection here as you did for the initial zone configuration.
    • House wrt zone; BD off - the baseline pressure of the zone you are testing, in the modified configuration. If you are using a second manometer to measure the house-to- zone pressure, and you are using the automatic baseline feature, then enter "0" in this "House wrt zone" "BD off" box. Otherwise, enter the measured baseline value in the box, making sure to enter the correct sign.
    • House wrt zone; BD on - the zone pressure for the modified configuration. The sign of this value must be entered, for example, if you are depressurizing, a negative sign must be entered before this value. If you use the automatic baseline feature of a second manometer, enter the resulting manometer house pressure in this input box, but make sure you enter "0" in the previous "House wrt outdoor" "BD off" box. The larger the shift in zone pressure between the initial and modified configurations, the more accurate the results.
    • Blower door flow adjusted to 50 Pa - the result of the whole-house blower door test during the modified zone configuration. Even though the house is not required to be at 50 Pa pressure difference, this flow must be adjusted to 50 Pa.

Best practices

  • If possible, seal obvious and significant leaks before performing zone pressure diagnostics on a house.
  • If you have a concern about insulation or other debris entering the living space, it is best to pressurize the house for ZPD testing.
  • Measuring the smaller of the two pressures (across the looser pressure boundary) will generally yield the smallest uncertainty for the through-zone leakage.
  • When opening a temporary hole needed for ZPD, it is best to reduce (shift) the pressure across the more resistant pressure boundary as much as possible. The greater the shift, the greater the accuracy (lower the uncertainty) of your results.
  • Conversely, if you choose to plug a hole, it is best to increase (shift) the pressure across the least resistant pressure boundary as much as possible. The greater the shift, the greater the accuracy (lower the uncertainty) of your results. Examples include temporarily plugging attic vents or closing a basement door.

RED ZPD tool error checking

Complex error-checking features have been added to this tool to help ensure that your input entries are valid. The items listed below will help you avoid error messages when using this tool.

  • All of the "BD on" (Blower Door on) pressure inputs MUST be the same mathematical sign; negative for a depressurization test and positive for a pressurization blower door test.
  • The house wrt zone ΔP values must be between 0 Pa and the corresponding house wrt outdoor ΔP value. For the initial configuration only, the house wrt zone &DeltaP value must also be at least 1 Pa away from 0 Pa and the initial house wrt outdoor ΔP value.
  • The direction of the shift in the house wrt zone ΔP values, from the initial to the modified zone configurations, must be consistent with the hole location and with whether the hole is being opened or closed.

A warning message will appear at the bottom of the tool if the calculated through-zone leakage @50 Pa plus the reported uncertainty is greater than the initial blower door flow rate (adjusted to 50 Pa).

History and background

The history and background below is excerpted from "An Investigation into Zone Pressure Diagnostic Protocols for Low Income Weatherization Crews". 2001. Energy Center of Wisconsin, page 1.
Note: See Related External Links below for a link to this document.

"Zone Pressure Diagnostics (ZPDs) has become an established tool for diagnosing indirect air leakage paths in houses since its introduction to the U.S. weatherization community around 1990. In cases where air must pass through at least two barriers to leak into or out of a house, ZPD is a way to use measured pressures to infer the location and size of air leakage paths."

"Michael Blasnik developed a set of ZPD techniques that are referred to as the Blasnik methods or “series leakage” measurements. These methods are known as the “Add a Hole”, “Open a Door”, and “Vents” methods or Methods 1, 2, and 3, respectively (Fitzgerald, 1994). These methods have become well established amongst weatherization crews, with hundreds of users across the country. Calculation procedures were developed by Blasnik (Energy Conservatory, 1998) and the uncertainty analysis was included in separate applications produced by Collin Olson based on ANSI/ASME PTC 19.1-1985 Part 1 "Measurement Uncertainty" for computing Method 1 and 2 results. In addition to these PC programs and published nomograms (Energy Conservatory, 1998), handheld calculator programs exist to perform the calculations."

"The methods are probably most widely used for prioritizing air sealing. By estimating the available air leakage reduction potential of various locations within a house, a crew can make informed decisions of where to best spend their time. Some groups within and outside of the low income weatherization field have also set performance specifications based on ZPDs. For example, the American Lung Association’s Health House program specifies a maximum amount of garage to house leakage, as determined using ZPDs (ALA, 2001). Also, the Metropolitan Airports Commission Minneapolis-St. Paul International Airport Part 150 Residential Sound Insulation Program (SIP) requires contractors to be able to perform Method 3 ZPDs and achieve a minimum level of air leakage in each attic zone (DJR Architecture, 2001)."

"The widespread use of ZPDs is an indication that the methods are generally thought to be a cost effective tool for air sealing houses and useful metrics for building air leakage resistance. However, there are substantial differences in the ways that field personnel use the techniques and there are many questions about how to decide when to use them, which method to use, and exactly how to make the best measurements. Everyone who has used these methods has seen instances where results have not made sense, indicating the need to consider the accuracy of the ZPD estimates."

Related tools

  • Air Leakage Metrics: Determine up to eight air leakage metrics, including ACH50, equivalent leakage area (EqLA), effective leakage area (ELA), specific leakage area (SLA), and more.
  • Design Infiltration with AIM-2: This tool calculates the stack-induced, the wind-induced, and the combined infiltration for given indoor/outdoor temperatures and wind speed. The primary use case is determining the design infiltration rate that can be used in a heating or cooling load calculation for system sizing.
  • Advanced Infiltration with AIM-2: This tool calculates the hourly (low, average, and high) stack, wind, and combined infiltration for a selected date range (one day to one year); and the infiltration load on a heating and/or cooling system for the same date range. Additionally, daily average infiltration rates (stack, wind, and combined) and daily infiltration load on heating and cooling systems are displayed on separate charts for a selected TMY3 weather station location and the selected date range.

Related external resources

  • Bohac, Dave. Zone Pressure Diagnostics: A new protocol shows how to make a valuable diagnostic test even more useful. Home Energy magazine, May 2002. http://www.homeenergy.org/show/article/nav/auditing/id/267
    Comment: An overview of the Energy Center of Wisconsin studies (listed below) and an introduction to zone pressure diagnostics.
  • Energy Center of Wisconsin. An Investigation into Zone Pressure Diagnostic Protocols for Low Income Weatherization Crews. Report 208-1. December 2001. Energy Center of Wisconsin. http://www.ecw.org/prod/208-1.pdf
    Comment: This is the first of two papers documenting the most in-depth research done on the topic of zone pressure diagnostics. This paper is likely to be of more interest to the general reader than the second paper, listed below.
  • Energy Center of Wisconsin. An Investigation into Zone Pressure Diagnostic Protocols for Low Income Weatherization Crews: Phase I and Phase II Final Report Appendices. Report 208-2. December 2001. Energy Center of Wisconsin. http://www.ecw.org/prod/208-2.pdf
    Comment: This is the first of two papers documenting the most in-depth research done on the topic of zone pressure diagnostics. This paper is likely to be of more interest to the general reader than the second paper, listed below.
  • Fitzgerald, J., Nevitt, R., Blasnik, M. User-Friendly Pressure Diagnostics. Home Energy magazine, September/October 1994. http://www.homeenergy.org/show/article/page/3/nav/blowerdoor/id/1074
    Comment: As far as we know, this is the first published article about zone pressure diagnostics. Good overview and introduction to the basic ideas behind the testing.
  • Karg, Rick. Zone Pressure Diagnostics: When Needed? What to Do?. Slide presentation. Affordable Comfort New England Conference. 2010. http://acinewengland.org/sites/default/files/session/79242/tech3rkcompatibilitymode.pdf
    Comment: Slide presentation on topic of ZPD. Balanced presentation including illustrations and text. Includes discussion of primary and secondary zone testing.
  • Morin, Paul. Zone Pressure Diagnostics (ZPD) for Optimal Air Sealing and Insulation. Slide presentation. The Energy Conservatory. http://www.energyconservatory.com/sites/default/files/documents/ZPD_Basics.pdf
    Comment: Slide presentation on topic of ZPD. Made up primarily of photos without much text. Good photos and if you have a pretty good idea of ZPD, you will understand what the photos refer to.
  • The Energy Conservatory. Zone Pressure Diagnostics (ZPD) Trainer. Software User's Guide. http://www.energyconservatory.com/sites/default/files/documents/zpd_trainer_manual.pdf.
    Comment: The Energy Conservatory also offers free software for this trainer's version.
  • The Energy Conservatory. ZPD Calculation Utility. Software for PCs. http://www.energyconservatory.com/software-download-registration.
    Comment: Free software using advanced zone pressure diagnostics procedures based on the Energy Center of Wisconsin documents listed above in this section. This software is more complex than the RED Calc Free Zone Pressure Diagnostics tool in that it reports connections between zones and allows for different hole types.

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