Building air-tightness that is below 0.6 air changes per hour at 50 pascals pressure (0.6ACH50) is a simple target that the Passive House Institute (PHI) requires for new building certification. (A retrofit may meet 1.0ACH50 for EnerPHit certification.) This is a measurement of air flow and not much input or calculations are required…. Just build a house tighter than that and you will comply. However PHI uses a European standard (EN13829) to measure this air flow. While very similar to ASTM E779, the protocol is different, and therefore it is useful to clarify the specifics in relationship to the following:
- calculation of the interior volume – V n50*
- test protocol with PHI additions
- properly reporting the test results
As defined by EN 13829 this internal volume is the:
deliberately heated, cooled or mechanically ventilated space within a building or part of a building subject to the measurement, generally not including the attic space, basement space and attached structures.
The volume (V n50). you use to determine the air-leakage per hour is different than the ventilation volume noted in the PHPP (which is TFA *2.5m) because the V n50 does include air above stairs and counts storage, mechanical rooms and spaces under slanted roofs 100%. The volume is calculated by multiplying the net floor area according to DIN 277 (in German) with the average floor height. In short:
- Volume of the intentionally conditioned space (no sunrooms, garages, etc), that is usable
- Net area is the TFA + 100% the circulation areas (stairs) + 100% mechanical areas + 100% conditioned storage areas
- Measure the rough dimensions of each room (length, width, height) from interior finish to interior finish. So from sheetrock to sheetrock.
- Spaces less than 5′ (1.5m) high do count as long as they are conditioned
- Multiply floor areas with their average ceiling heights.
- Window nooks are not included in this volume
Tester to independently verify the V n50 and report how these were determined by him. It should be noted on the report if the architect or consultant provided these calculations and the tester simply spot-checked a number of measurements – or if the tester has measured the volume herself.
During the construction phase, when the airtight layer is still accessible, a simple one point depressurization test will give you a clear indication of how many air-changes per hour (ACH) are leaking out of the house at that given pressure (50 pascals).
The final test should be done when construction is (almost entirely) complete; all finishes have been applied, and all services have been run into and out of the airtight layer. This so the chance of the airtight layer becoming compromised is slim to none (so make sure cable, phone wires are installed at this time). Make a note of all unfinished parts.
Final test for certification:
PHI has defined that Test method A of EN 13829 should be used, in this protocol the following is defined:
- The condition of the building envelope should represent its condition during the season in which heating or cooling systems are used.
- Close all intentional exterior openings of the building or part of the building to be tested (windows, doors, fireguard). For the purpose of method A (building in use) do not take any further measures to improve the airtightness.
- Exhaust and supply ducts of HRV systems shall be sealed. Other openings (natural ventilation, vents, exhaust, combustion air) shall be closed for purposes of method A…
In short this means:
- HRV ducts connected to the exterior can be sealed
- All exterior doors and windows are closed and locked
- Interior doors open if leading to conditioned space
- Closet doors can remain closed
- Dampers of intake/exhaust ducts for combustion air can be closed or leave as is – these openings cannot be purposefully sealed for the test.
According to EN13928 the following conditions should be met (verify them before and after running the test):
- Windspeed must be below 6 m/s (13.4mph) if measured – otherwise below 3 on the Beaufort scale (ie a gentle breeze).
- The result of multiplying the height of the building in feet * inside/outside delta T (F) should be below 85. (This is to assure proper measurements in high-rise buildings.)
- Baseline pressure should be below 5 Pa over a 30 second average (most automated test will do this for you).
EN13829 protocol + PHI specific test requirements:
- minimum of 5 target building pressures
- the maximum target building pressure must not be less than 50 Pa
- the interval between the 5 target building pressures must not exceed 10 Pa (ie 10,20,30,40,50 would comply with 3 requirements above)
- At least 5 readings per target pressure need to be recorded (automated test do 100 per target pressure)
- PHI requires both a depressurization test and a pressurization test – result will be the average of the two ACH values
- the lowest pressure point allowed is 10Pa, or at least 5 times the baseline pressure. So if your baseline was 3Pa – your lowest minimum pressure is 15Pa (and your highest will be at least 55Pa) – Tester to verify this himself, automated test might not catch this.
Conservation Energy TECTITE Express 4.0 or Retrotec’s FanTestic can perform and automated test conforming to EN13829 with the digital pressure/flow gauge is attached to a computer and comply with the following minimums:
Most testing software will prepare reports that contain most of this information. However tester should make sure all relevant information is included when making a report for certificate purposes. Comprehensive list of the items is:
- Identify the tested object: Address, construction date, architect
- Standard used (EN 13829 – method A)
- Which part of the building were tested (floors, areas included, excluded etc)
- Net floor area (TFA) and internal volume of the space (V n50)
- Documentation of verification of V n50 calculations
- Elevation of building, height of the building
- Status of all opening in the building enclosure (sealed, open, closed, locked)
- Description of temporary seals
- Make and model of blowerdoor, serial number – date of last calibration
- Baseline pressure differences
- Inside and outside temperatures (Celcius)
- Windspeed or beaufort scale
- Table of pressure differences and air flow rates (generated by software or derived in manual test)
- Air leakage graph
- Air change rate, n50, at 50Pa for pressurization, depressurization and mean value of the two.
- Test date
The tester reports the absolute flow rate (m3/hr @ 50Pa) as well a the air exchange rate (n50) in the report and notes who measured, calculated and verified the volume.
A longer English article regarding this protocol can be found in this PDF from Greenbuild.ie
* n50 is another abbreviation commonly used to reference the air exchange rate at 50 pascals pressure.