Blower door

The General Services Administration (GSA) requires testing of new US federal government buildings.

[2] A variety of blower door air tightness metrics can be produced using the combination of building-to-outside pressure and fan airflow measurements.

[4] By 1979, similar window-mounted measurement techniques were being pursued in Texas, and door-mounted test fans were being developed by a team at Princeton University to help them find and fix air leaks in homes in a Twin Rivers, New Jersey housing development.

[7] In Canada, a team at the National Research Council of Canada's Division of Building Research (NRC/DBR) in Saskatchewan, advanced the published work of Tamura in 1975 and went from a blower window to a blower door concept used in the construction of the Saskatchewan Conservation House in 1977.

These early research efforts demonstrated the potential power of blower door testing in revealing otherwise unaccounted for energy losses in homes.

[9] Use of blower doors in home energy retrofitting and weatherization efforts became known as "house doctoring" by researchers on the east and west United States coasts.

[13] While these blower door-testing efforts were useful in identifying leakage pathways and in accounting for otherwise inexplicable energy losses, the results could not be used to determine real-time air exchange in buildings under natural conditions, or even to determine average annual air exchange levels.

Sherman attributes the first attempt at doing this to Persily and Kronvall, who estimated annual average air exchange by:[14]

[17][18] Other infiltration models have been developed elsewhere, including one by Deru and Burns at the National Renewable Energy Laboratory (NREL), for use in whole-building performance simulation.

The test begins by sealing the face of the fan and measuring the baseline indoor/outdoor pressure differential.

The blower door fan is used to blow air into or out of the building, creating either a positive or negative pressure differential between inside and outside.

Different values for blower door metrics are to be expected for pressurizing and depressurizing, due to the building envelope's response to directional airflow.

A multi-point test can be performed either manually or using data acquisition and fan control software products.

Fan airflow is determined using CFan and nFan values that are provided by the blower door manufacturer, and they are used to calculate QFan.

The multi-point blower door test procedure results in a series of known values of Qn, Fan and ∆Pn, Building.

Ordinary least squares regression analysis is then used to calculate the leakage characteristics of the building envelope: CBuilding and nBuilding.

50 Pa can be plugged into the orifice-flow equation, along with the derived building C and n values to calculate airflow at 50 pascal.

This same method can be used to calculate airflow at a variety of pressures, for use in creation of other blower door metrics.

An alternative approach to the multi-point procedure is to only measure fan airflow and building pressure differential at a single test point, such as 50 Pa, and then use an assumed pressure exponent, nBuilding in the analysis and generation of blower door metrics.

This method is preferred by some for two main reasons: (1) measuring and recording one data point is easier than recording multiple test points, and (2) the measurements are least reliable at very low building pressure differentials, due both to fan calibration and to wind effects.

In order to increase the accuracy of blower door test results, air density corrections should be applied to all airflow data.

They are often tabulated in easy to use tables in product literature, where a factor can be determined from outside and inside temperatures.

Depending on how a blower door test is performed, a wide variety of airtightness and building airflow metrics can be derived from the gathered data.

The airflow, (Imperial in Cubic Feet / minute; SI in liters / second) at a given building-to-outside pressure differential, 50 pascal (Q50).

[citation needed] Another common metric is the air changes per hour at a specified building pressure, again, typically at 50 Pa (ACH50).

[citation needed] In order to take values generated by fan pressurization and to use them in determining natural air exchange, the effective leakage area of a building must be calculated.

Specialized software or a tedious calculation must be provided to arrive at the hold time which is generally ten minutes.

An NFPA enclosure integrity test result is typically reported in the form of an agent hold time which represents the duration for which the room will retain at least 85% of the design concentration in order to suppress a fire and to ensure it does not reignite.

This retention time inversely proportion to the leakage area of the room which is the major factor.

Location of leaks, height being protected, the presence of continual mixing and clean agent being used will affect the hold time also.