Blower Door - AbsoluteAstronomy.com

A blower door is a piece of equipment primarily used to measure the airtightness of small to medium size buildings. It can also be used to measure airflow between building zones, to test duct

Duct

A duct may refer to:* Duct , various ducts in anatomy and physiology* Duct , for transfer of air between spaces in a structure* Duct tape, a kind of adhesive tape* Ducted fan, motor for aircraft...

work airtightness and to help physically locate air leakage sites in the building envelope

Building envelope

The building envelope is the physical separator between the interior and the exterior environments of a building. Another emerging term is "Building Enclosure". It serves as the outer shell to help maintain the indoor environment and facilitate its climate control...

.

There are three primary components to a blower door: (1) a calibrated, variable-speed fan

Centrifugal fan

A centrifugal fan is a mechanical device for moving air or other gases. It has a fan wheel composed of a number of fan blades, or ribs, mounted around a hub. As shown in Figure 1, the hub turns on a driveshaft that passes through the fan housing...

, capable of inducing a range of airflows sufficient to pressurize and depressurize a variety of building sizes, (2) a pressure measurement

Pressure measurement

Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure pressure are called pressure gauges or vacuum gauges....

instrument, called a manometer, to simultaneously measure the pressure differential induced across the face of the fan and across the building envelope, as a result of fan airflow, and (3) a mounting system, used to mount the fan in a building opening, such as a door or a window.

A variety of blower door airtightness metrics can be produced using the combination of building-to-outside pressure and fan airflow measurements. These metrics differ in their measurement methods, calculation and uses. Blower door tests are used by building researchers, weatherization

Weatherization

Weatherization or weatherproofing is the practice of protecting a building and its interior from the elements, particularly from sunlight, precipitation, and wind, and of modifying a building to reduce energy consumption and optimize energy efficiency.Weatherization is distinct from building...

crews, home performance contractors, and others in efforts to assess the construction quality of the building envelope, locate air leakage pathways, assess how much ventilation

Ventilation

Ventilation is movement of air in and out of an enclosed space, including a body. It is used in the following contexts:* Ventilation * Ventilation * Ventilation * Ventilation * Ventilation...

is supplied by the air leakage, assess the energy losses resulting from that air leakage, determine if the building too tight or too lose, determine if the building needs mechanical ventilation

Mechanical ventilation

In medicine, mechanical ventilation is a method to mechanically assist or replace spontaneous breathing. This may involve a machine called a ventilator or the breathing may be assisted by a physician, respiratory therapist or other suitable person compressing a bag or set of bellows...

and to assess compliance with building performance standards.

History of Blower Door Testing

Blower door technology was first used to measure building airtightness in Sweden around 1977. This earliest implementation used a fan mounted in a window, rather than a door. Similar window-mounted measurement techniques were being pursued by Caffey in Texas, and door-mounted test fans were being developed by Harrje, Blomsterberg and Persily at Princeton University to help them find and fix air leaks in homes in a Twin Rivers, New Jersey housing development. Harold Orr has also been identified as a member of a group in Saskatchewan, Canada who was pursuing similar testing methods .

These early research efforts demonstrated the potential power of blower door testing in revealing otherwise unaccounted for energy losses in homes. Previously, air leakage around doors, windows and electrical outlets was considered to be the primary leakage pathway in homes, but Harrje, Dutt and Beya used blower doors to identify “thermal bypasses”. These bypasses were air leakage sites, such as attic utility chases, that accounted for the vast percentage of air leakage energy losses in most homes. Use of blower doors in home energy retrofitting and weatherization efforts became known as “house doctoring” by researchers on the East and West coasts.

The blower door first became commercially available in the United States in 1980 under the name Gadsco. Harmax started to sell units in 1981, followed closely by the Energy Conservatory in 1982.

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

= Natural Air Changes per Hour

= Air Changes per Hour at 50 Pascal
Further physical modeling efforts allowed for the development and validation of an infiltration model by researchers at Lawrence Berkeley National Laboratory

Lawrence Berkeley National Laboratory

The Lawrence Berkeley National Laboratory , is a U.S. Department of Energy national laboratory conducting unclassified scientific research. It is located on the grounds of the University of California, Berkeley, in the Berkeley Hills above the central campus...

(LBNL). This model combined data derived from blower door tests with annual weather data to generate time-resolved ventilation rates for a given home in a specific location. This model has been incorporated into the ASHRAE Handbook of Fundamentals (1989), and it has been used in the development of ASHRAE Standards 119 and 136. Other infiltration models have been developed elsewhere, including one by Deru and Burns at the National Renewable Energy Laboratory

National Renewable Energy Laboratory

The National Renewable Energy Laboratory , located in Golden, Colorado, is the United States' primary laboratory for renewable energy and energy efficiency research and development. The National Renewable Energy Laboratory is a government-owned, contractor-operated facility; it is funded through...

(NREL), for use in whole building energy simulation

How blower-door tests work

A basic blower-door system includes three components: a calibrated fan, a door-panel system, and a pressure measurement device (manometer).

Test set-up

The blower-door fan is temporarily sealed into an exterior doorway using the door-panel system. All interior doors are opened, and all exterior doors and windows are closed. HVAC balancing dampers and registers are not to be adjusted, and fireplaces and other operable dampers should be closed. All mechanical exhaust devices in the home, such as bathroom exhaust, kitchen range hood or dryer, should be turned off. Pressure tubing is used to measure the fan pressure, and it is also run to the exterior of the building, so that the indoor-outdoor pressure differential can be measured. The exterior pressure sensor should be shielded from wind and direct sunlight. The test begins by sealing the face of the fan and measuring the baseline indoor-outdoor pressure differential. The average value is to be subtracted from all indoor-outdoor pressure differential measurements during the test.

Test procedure

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. This pressure difference forces air through all holes and penetrations in the building enclosure. The tighter the building (e.g. fewer holes), the less air is needed from the blower door fan to create a change in building pressure. Typically, only depressurization testing is performed, but both depressurization and pressurization are preferable. Different values for blower door metrics are to be expected for pressurizing and depressurizing, due to the building envelope's response to directional airflow. The smallest fan ring should be used, which still allows the fan to reach the maximum target indoor-outdoor pressure differential. A multi-point test can be performed either manually or using data acquisition and fan control software products. The manual test consists of adjusting the fan to maintain a series of indoor-outdoor pressure differentials and recording the resulting average fan and indoor-outdoor pressures. Alternatively, a single-point test can be performed, where the blower door fan is ramped up to a reference indoor-outdoor pressure differential, and the fan pressure is recorded. Oftentimes, the blower door hardware converts fan pressure measurements directly to fan airflow values.

Further details can be found in the blower door manual provided by the equipment manufacturer

Power law
Power law
A power law is a special kind of mathematical relationship between two quantities. When the frequency of an event varies as a power of some attribute of that event , the frequency is said to follow a power law. For instance, the number of cities having a certain population size is found to vary...

model of airflow for blower door testing

Building leakage is described by a power law equation of flow through an orifice. The orifice flow equation is typically expressed as

=Airflow (ft³/min or m³/sec)

= Air Leakage Coefficient

= Pressure Differential (Pa)

= Pressure Exponent
The C parameter reflects the size of the orifice, the ∆P is the pressure differential across the orifice, and the n parameter represents the characteristic shape of the orifice, with values ranging from 0.5 to 1, representing a perfect orifice and a very long, thin crack, respectively.

There are two airflows to be determined in blower door testing, airflow through the fan (Q_Fan) and airflow through the building envelope (Q_Building).

It is assumed in blower door analysis that mass is conserved, resulting in:

Which results in:

Fan airflow is determined using C_Fan and n_Fan values that are provided by the blower door manufacturer, and they are used to calculate Q_Fan. The multi-point blower door test procedure results in a series of known values of Q_{n, Fan} and ∆P_{n, Building}. Typical ∆P_{n, Building} values are ±5, 10, 20, 30, 40 and 50 Pascal. Ordinary least squares regression analysis is then used to calculate the leakage characteristics of the building envelope: C_Building and n_Building. These leakage characteristics of the building envelope can then be used to calculate how much airflow will be induced through the building envelope for a given pressure difference caused by wind, temperature difference or mechanical forces. 50 Pascal 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 Pascal, and then use an assumed pressure exponent, n_Building 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.

Air density corrections

In order to increase the accuracy of blower door test results, air density corrections should be applied to all airflow data. This must be done prior to the derivation of building air leakage coefficients (

) and pressure exponents (

). The following methods are used to correct blower door data to standard conditions.

For depressurization testing, the following equation should be used:

= Airflow corrected to actual air density

= Airflow derived using

and

= Air density inside the building, during testing

= Air density outside the building, during testing
For pressurization testing, the following equation should be used:

The values

and

are referred to as air density correction factors in product literature. They are often tabulated in easy to use tables in product literature, where a factor can be determined from outside and inside temperatures. If such tables are not used, the following equations will be required to calculate air densities.

can be calculated in IP

- Computing :* Internet Protocol, the most commonly-used set of rules for dispatching data across a large computer network* IP address, a computer's address under the Internet Protocol, above...

units using the following equation:

= Air density inside the building, during testing

= Elevation above sea level (ft)

= Indoor Temperature (F)

can be calculated in IP

- Computing :* Internet Protocol, the most commonly-used set of rules for dispatching data across a large computer network* IP address, a computer's address under the Internet Protocol, above...

units using the following equation:

= Air density outside the building, during testing

= Elevation above sea level (ft)

= Outdoor Temperature (F)
In order to translate the airflow values derived using

and

from the blower door manufacturer to the actual volumetric airflow through the fan, use the following :

= Actual volumetric airflow through the fan

= Volumetric airflow calculated using manufacturer's coefficients or software

= Reference air density (typically 0.075 for lb/ft³ and 1.204 for Kg/m³)

= Actual density of air going through the fan

for depressurization and

for pressurization

Blower door metrics

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. Some of the most common metrics and their variations are discussed below.

Airflow at a specified building pressure

Probably the most common blower door metric is to measure airflow at a given building-to-outside reference pressure, typically at 50 Pascal (Q₅₀). This standardized single-point test allows for comparison between homes measured at the same reference pressure. A suitably high pressure, such as 50 Pascal, is chosen so that the effects of stack-induced airflow and wind-driven airflow are minimized. This increases the repeatability of the measurement, essentially controlling for the different temperature and wind conditions under which a building can be tested. Buildings of different sizes and similar envelope quality will have different results in this test.

Airflow per unit surface area or floor area

Oftentimes, an effort is made to control for building size and layout by normalizing the airflow at a specified building pressure to either the building’s floor area or to its total surface area. These values are generated by taking the airflow rate through the fan and dividing by the area. These metrics are most used to assess construction and building envelope quality, because they normalize the total building leakage area to the total amount of area through which that leakage could occur. In other words, how much leakage occurs per unit area of wall, floor, ceiling, etc.

Air changes per hour at a specified building pressure

Another very common metric is the air changes per hour at a specified building pressure, again, typically at 50 Pascal (ACH₅₀).

= Air changes per hour at 50 Pascal (hr^-1)

= Airflow at 50 Pascal (ft³/minute)

= Building volume (ft³)
This normalizes the airflow at a specified building pressure by the building’s volume, which allows for more direct comparison of homes of different sizes and layouts. This metric indicates the rate at which the air in a building is replaced with outside air, and as a result, is an important metric in determinations of indoor air quality.

Effective leakage area

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. Each gap and crack in the building envelope contributes a certain amount of area to the total leakage area of the building. The Effective Leakage Area assumes that all of the individual leakage areas in the building are combined into a single idealized orifice or hole. This value is typically described to building owners as the area of a window that is open 24/7, 365 in their building. The ELA will change depending on the reference pressure used to calculate it. 4 pa is typically used in the US, whereas a reference pressure of 10 pa is used in Canada. It is calculated as follows:

= Effective Leakage Area (in² or m²)

= Building air leakage coefficient

= Air density (lb/in³ or Kg/m³), typically a standard density is used

= Reference Pressure (lb_Force/in² or Pa), typically 4 Pa in US and 10 Pa in Canada

= Building pressure exponent
It is essential that units are carefully conserved in these calculations. C_Building and n_Building should be calculated using SI

Si, si, or SI may refer to :- Measurement, mathematics and science :* International System of Units , the modern international standard version of the metric system...

units, and ρ and ∆P_Reference should be Kg/m³ and Pascal, respectively. Alternatively, C_Building and n_Building can be calculated using Imperial units, with ρ and ∆P_Reference being lb/ft³ and lb_Force/in², respectively.

The ELA can be used, along with the Specific Infiltration Rate (s) derived using the LBNL infiltration model, to determine airflow rate through the building envelope throughout the year.

Leakage area per unit floor or surface area

Leakage area estimates can also be normalized for the size of the enclosure being tested, For example, the LEED Green Building Rating System has set an airtightness standard for multifamily dwelling units of 1.25 square inches (8.1 cm²) of leakage area per 100 square feet (9.3 m²) of enclosure area, to control tobacco

Tobacco

Tobacco is an agricultural product processed from the leaves of plants in the genus Nicotiana. It can be consumed, used as a pesticide and, in the form of nicotine tartrate, used in some medicines...

smoke

Smoke

Smoke is a collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-product of fires , but may also be used for pest...

between units. This is equal to 0.868 cm²/m².

Normalized leakage

Normalized leakage is a measure of the tightness of a building envelope relative to the building size and number of stories. Normalized Leakage is defined in ASHRAE Standard 119 as:

= Normalized leakage

= Effective Leakage Area (in² or m²)

= Building floor area (in² or m²)

= Building Height (inches or meters)

= Reference height (98.425 inches or 2.5 meters)

Uses of blower-door testing

Blower doors can be used in a variety of types of testing. These include (but are not limited to):

Testing residential and commercial buildings for air tightness
Testing buildings for compliance with standards for energy efficiency, such as the IECC
International Energy Conservation Code
The International Energy Conservation Code is a building code created by the International Code Council in 2000. It is a model code adopted by many state and municipal governments in the United States for the establishment of minimum design and construction requirements for energy...

and ASHRAE.
Testing building envelopes and window frames for water tightness and rain penetration
NFPA
National Fire Protection Association
The National Fire Protection Association is a United States trade association that creates and maintains private, copywrited, standards and codes for usage and adoption by local governments...

Clean Agent Retention testing (this type of testing is usually described as a door fan test rather than a blower door test)
Duct leakage testing
Duct leakage testing
A duct leakage tester is a diagnostic tool designed to measure the airtightness of forced air heating, ventilating and air-conditioning ductwork. A duct leakage tester consists of a calibrated fan for measuring an air flow rate and a pressure sensing device to measure the pressure created by the...

of forced air heating/cooling systems - both supply (vents) ducts and return ducts can be tested to determine if and how much they leak air.

NFPA Enclosure Integrity Testing

NFPA enclosure integrity testing is a specialized type of testing that typically measures the tightness of rooms within buildings (though testing entire buildings require testing on occasion) that are protected by clean agent fire suppression systems. These types of enclosures are typically server rooms containing large amounts of computer and electronic hardware.

NFPA standards for equipment calibration are more rigorous than other types of testing, but any modern blower door equipment is sufficiently accurate to perform NFPA enclosure integrity testing.

The NFPA standard requires that the blower door operator be trained, but does not specify the nature or source of this training. There is no official NFPA training available for enclosure integrity testing methodology at this time.

An NFPA enclosure integrity test result is typically reported in the form of an agent retention time which represents the duration for which the room will retain the agent at sufficient concentration to suppress a fire. This retention time varies based on the leakage area of the room, the location of the leaks and the particular clean agent being used.

Blower Door Manufacturing Companies

External links

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