Davide Lanzoni

BUILDING THERMOGRAPHY(including blower door and heat flux meter)

BUILDING THERMOGRAPHY(including blower door and heat flux meter)

Copyright © 2014 Davide Lanzoni

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Table of contents

1. Foundations of Thermography

1.1 Heat and temperature

1.2 Heat transmission

1.2.1 Transmission of heat by conduction

1.2.2 Transmission of heat by convection

1.2.3 Transmission of heat by radiation

1.3 Infrared radiation and frequency spectrum

1.4 Planck's Law

1.5 Planck's curves and Wien's Law

1.6 Stefan Boltzmann's Law

1.7 Kirchoff's Law: emissivity, transmissivity, reflectivity

1.7.1 Emissivity

1.7.2 Transmissivity

1.7.3 Reflectivity and specular and diffuse surfaces

1.8 Aspects concerning the emissive and reflective characteristics of the construction

materials

1.9 Operation of a thermal imager and transposition in temperature

1.10 Characteristics and performance of thermal imagers

1.11 Possibilities offered by processing software

1.12 Obtaining a good thermographic image

2. Thermography applied to energy audits of buildings

2.1 Introduction

2.2 Technical references

2.3 Terms and definitions

2.4 Training requirements of a thermographer

2.4.1 The EN ISO 9712 standard

2.4.2 Knowledge required in the construction industry

2.5 Mechanisms that cause variations in the surface temperature

2.6 The EN 13187 standard on qualitative detection of thermal irregularities in the

construction industry

2.7 Interpretation of the thermal image and types of materials in the building industry

2.8 Environmental influences in surveys in construction

2.8.1 Influence of the wind

2.8.2 Solar radiation, colour and shading

2.8.3 Exchanges by irradiation with surrounding buildings and the sky

2.8.4 Rain and moisture

2.9 The RESNET technical standard

2.10 Quantitative criteria in thermographic analysis of the thermal insulation of buildings

2.10.1 Method of survey on thermal insulation on the basis of the fRsi factor

2.10.2 Method of survey on thermal insulation on the basis of the fTapp factor

2.10.3 Method of survey on thermal insulation on the basis of the difference in temperature between the inner dispersing and not dispersing surfaces

2.11 Thermographic survey of thermal bridges

2.12 Thermographic survey of the insulation defects in hollow walls

2.13 Thermographic survey of doors, windows and blinds

2.14 Thermographic survey of air infiltration

2.15 Influence of moisture on thermal insulation and its relief thermographic survey

2.15.1 General information on the thermal effects of the presence of moisture

2.15.2 Not destructive instruments for the qualitative detection of moisture

2.15.3 Combination between thermography and moisture detection

2.15.4 Thermographic survey of moisture in roofs

2.16 Thermographic diagnosis of mold formation for insulation defects

2.17 Thermographic surveys on external insulation

2.18 Use of thermal transients

2.19 Thermographic surveys during summer

2.20 The use of thermography in thermal comfort assessment

2.21 Thermographic detection of heating systems

2.21.1 Thermographic inspection of under-floor heating systems

2.21.2 Thermographic Inspection of remote heating systems

2.21.3 Thermographic inspection of heating systems

2.22 Thermographic inspection of photovoltaic systems

2.23 Thermographic inspection of air treatment systems

2.24 Example of a field survey operating instruction according to EN 13187

2.25 Emissivities of the main construction materials

3. Fundamentals of the air permeability of buildings

3.1 Introduction

3.2 Technical references

3.3 Terms and definitions

3.4 The EN 13829 standard and determination of the air flow infiltration

3.4.1 Measurement conditions

3.4.2 Preparation of the test area

3.4.3 Procedural stages

3.4.4 Reference values and determination of the flow of air infiltration

3.4.5 Derived quantities

3.4.6 Appendices B and C (outline)

3.5 Dynamics of air infiltration in buildings

3.5.1 Chimney effect

3.5.2 Wind pressure

3.5.3 The Beaufort wind scale

3.5.4 Typical entry routes of air into buildings

3.5.5 Effects of the imbalance of mechanical ventilation systems

3.6 Importance of air permeability for energy performance and comfort

3.7 Interstitial and surface condensation

3.8 Overview on controlled mechanical ventilation systems

3.9 Regulations with reference to the performance of air permeability

3.9.1 European standards

3.9.2 Legislation for the Province of Bolzano (KlimaHaus© - CasaClima)

3.9.3 Certification protocol GBC Home of Green Building Council Italy

3.10 Air-tightness and thermal bypass

3.11 Overview of the design and execution of the airtightness of buildings

4. Air permeability blower door test of buildings

4.1 Instrumentation for execution of an air permeability blower door test

4.2 Preparation of the building for execution of a blower door test

4.3 Execution of a blower door test

4.4 Execution of the blower door test with software

4.5 Search for air infiltrations during a blower door test

4.5.1 Methods for the detection of air leaks in buildings

4.5.2 Thermographic method

4.5.3 Method with thermography and anemometer

4.5.4 Method with smoke generator

4.6 Different behaviour of buildings under pressure and at negative pressure

4.7 Content of a test report according to EN 13829

4.8 Overview on the execution of the test through the ventilation system of the building

4.9 Study cases: air-tightness of wooden buildings and wooden roofs

4.10 Study case: air-tightness of windows in operation

5. The heat flow meter and the measurement of transmittance in situ

5.1 Introduction

5.2 Technical references

5.3 Terms and definitions

5.4 The ISO 9869 standard and the determination of active transmittance

5.4.1 Determination of transmittance

5.4.2 External surfaces

5.5 Operating principle for a heat flow meter and thermocouples

5.5.1 The heat flow meter

5.5.2 Temperature sensors

5.6 Heat flow meter measurement according to ISO 9869

5.6.1 Installation and positioning of the measuring

5.6.2 Data capture

5.6.3 Data processing

5.6.3.1 The averaging method (or cumulative average)

5.6.3.2 The dynamic method

5.6.4 Interpretation of results

5.6.5 Comparison between calculated and measured values

5.6.6 Accuracy and errors in the measurement

5.7 Contents of the measurement report in accordance with ISO 9869

5.8 Case studies: measurements of active transmittance

5.8.1 Measurement of a solid wall

5.8.2 Measurement of a light wall

1. Foundations of Thermography

For an offer for purchasing a thermal imager, a blower door, other instrumentation, software or thermography training courses, you may fill our form at link:

http://www.saige.it/e-book_en.aspx

1.3 Infrared radiation and frequency spectrum

All bodies emit electromagnetic radiation that propagate at the speed of light and are characterised by the wavelength (λ) , understood as the necessary length for the wave to complete a cycle and the frequency (ν) that indicates the number of cycles per time unit.

Fig. 1.3: the electromagnetic spectrum

Beyond the visible band is infrared radiation that is between 0.75 µm and 1000 µm.

Thermal imagers for the building industry are usually sensitive in the spectral band from 8 to 14 µm (long IR waves or long wave - fig. 1.3). The spectral band between 8 and 14 microns is chosen for thermal imagers because the infrared radiation detected by the thermal imager propagates through the atmosphere that behaves in a selective manner: it absorbs some of the frequencies and transmits others, determining the transmissivity "windows" (called "atmospheric windows") in wavelengths between 3 and 5 µm (shortwave "window" or short wave - SW) and 8 and 14 µm (long wave "window" or LW). Figure 1.4 below shows the values of the atmospheric transmissivity depending on the wavelength: it is seen that in the band between 8 and 14 microns, which corresponds to the spectral bandwidth used by thermal imagers for inspections in the construction industry, atmospheric transmissivity is maximum (approximately 100% if the path of radiation is short) as the absorption of the atmosphere is negligible and the energy captured by the thermal imager is at maximum, with obvious benefits for measurement.

The gases most responsible for the absorption of infrared radiation by the atmosphere are carbon dioxide and water vapour.

Figure 1.4: transmittance of the atmosphere for 1 m, at 32°C and at 75% relative humidity - Courtesy Fluke - www.fluke.it

The spectrum frequency is non other than the energy density of the radiation with varying of the wavelength.

Any body that is above the temperature of absolute zero emits electromagnetic radiation. The temperature of a body depends on the average speed of elementary particles that constitute it, while at a temperature of 0 K, every motion of the particles is cancelled. As the temperature rises, the radiation starts to become detectable first in the region of the radio waves and then in that of the infrared. When the temperature of the body exceeds 450°C, it starts to become light in the spectrum where it is perceptible to the human eye: first with a deep reddish light, then with the increase in temperature, it moves to red-orange, yellow, white and white-blue. As the temperature varies therefore, the body changes colour to the human eye: for this reason it is referred to as "colour temperature".

To have a standard reference to define the emission, reference is made to a black body that is an idealisation. To be more precise in physics, black body is meant to refer to a body that absorbs all the incident electromagnetic radiation for each wavelength, and emits it with the maximum efficiency, according to Planck's law. The black body is in perfect thermal equilibrium for radiation: the radiated energy is equal to that absorbed.

The light emitted by a black body is called black body radiation and the density of the energy radiated, black body spectrum. The radiation emitted by the black body follows the Planck's law and Planck's curves.

1.4 Planck's Law

Planck's law allows the solution of two paradoxical consequences of classical physics: black body radiation and the collapse of electrons in the atomic nucleus. Classical physics stated that a mass radiates the same amount of energy over the entire spectrum of frequencies irrespective of the frequency itself and, since the frequency can increase indefinitely, this meant that a body had an infinite energy to radiate.Planck overcame this paradox by assuming that electromagnetic radiation is quantised, i.e. multiple of a minimum amount linked to the frequency itself, showing that identical particles if they vibrate at different frequencies have a minimal amount of different energy.The energy associated with electromagnetic radiation is transmitted in indivisible packets called quanti , each of which is associated with a single photon. The size (E) of a quantum depends on the frequency (ν ) of the radiation, according to the formula

where h is Planck's constant [joule⋅s].

1.5 Planck's curves and Wien's Law

Connected to the black body theory are Planck's curves, Wien's law and Stefan-Boltzmann's law.

For the black body at a given temperature, the distribution of the emitted radiation throughout the frequency spectrum is represented by a graphic that assumes the name of Planck's curve. A curve thus corresponds at each temperature, espressed in K, which has for equation:

where:

• I(ν)dν is the irradiance, i.e. the amount of energy per surface unit, per unit of time and per unit of solid angle, emitted in the range of frequencies ν÷ ν+δν

• h is Planck's constant• C is the speed of light• K is Boltzmann's constant

The function above results in Planck's curves.

Figure 1.5 Representation of Planck's curves - Courtesy Fluke - www.fluke.it

From fig. 1.5 it can be seen that:

• each curve referring to a greater temperature is above those at a lower temperature• the curves never intersect• as the temperature increases, the peaks correspond to shorter wavelengths

Wien's displacement law allows identification of the wavelength at which the intensity of the radiation emitted from the body black is at maximum.

According to Wien's law, the more the temperature of the object increases, the shorter the wavelength at which it will emit more radiation. The curves above explain the concept of colour temperature: as the temperature of the body varies, the wavelength at which the maximum emission energy varies and thus the colour.

At 298 K, or at room temperature, most of the energy is radiated at λ max = 2898/298 ≈ 10 micron or on infrared wavelengths (for this reason the use of LW thermal imagers is appropriate for applications in the building industry: the emission peak at room temperatures is centred on their spectral range that is between 8 and 14 micron), while at 5800 K, surface temperature of the sun, the maximum falls precisely within the region of the visible at approximately 0.5 microns. A bulb has a light filament

with a slightly lower temperature, which results in a yellow light emission, while an object that is located at "red heat" is cooler.In an incandescent lamp, light is emitted by the internal filament which is brought to approximately 2500 K through the Joule effect by the current that passes through it. Only 5% of the energy consumed is converted into visible light (range between 0.4 and 0.76 microns); the rest is dissipated into heat. In addition, the emission peak falls to 1.16 microns in the SW band of the infrared. Thus not only does the total amount of energy radiated by an object increase as its temperature increases but it tends to focus more towards the shorter wavelength (that is it tends to the values of wavelength of the visible spectrum). From all of the above, it can be deduced that the surface temperature of an object can be detected without contact by measuring the infrared radiation; furthermore, an infrared instrument sensitive only to the shorter wavelengths is more suitable for the measurement of high temperature surfaces, while for the lowest or ambient temperatures, an instrument sensitive to longer wavelengths is preferable.

1.8 Aspects concerning the emissive and reflective characteristics of the construction materials

We have seen that an opaque material can have a high or low emissivity, and that its reflectivity, in addition to being a number that is complementary to emissivity and hence greater the lower the latter, may also be diffuse or specular. The materials can therefore be divided into 4 categories discussed in the following and illustrated with examples.

1: Materials with high emissivity and low reflection that are diffuse in nature

Many of these materials are found the building industry: examples are concrete, wood, rustic or painted plaster, brick, tiles (if not painted or polished). The thermographic interpretation of the images relating to these materials is simple because the high emissivity and diffuse reflectivity allow the effect of reflections to be disregarded without major errors, and thus to easily pass from the apparent temperature (which is displayed directly by the infrared camera) to the true temperature (paragraph 2.7 ). In the case of inspections during the heating season for correct evaluation of insulations defects and surface temperatures, the survey conditions provided by EN 13187 (paragraph 2.6) must always be complied with and, in order to classify anomalies such as defects, the factors that affect the surface temperatures examined in paragraph 2.8 must also be taken into account.

Fig. 1.15 - plaster and stone are diffuse materials with high emissivity and low reflectivity; glass has good emissivity but specular reflectivity

The image above shows a portion of plastered outer façade on the first floor of a house: the blue zone that thermographically appears colder is actually colder, and it is possible to go directly to thermal analysis of the cause, that in this particular case consisted of additional insulation created by the owner in the room from the inside. This is not the case for the windows, that at ground floor appears hotter and at first floor colder than walls.

2: Materials with good emissivity (ε ≥ 0.7) and specular reflection

Due to the specular reflectivity, the apparent temperature of these materials is influenced by the environmental context in a way that varies according to the camera angle. The influence can be greater or less, depending on the reflected radiation, and this can lead both to defects of interpretation of the image, and to regarding them erroneously as very low emissivity materials. A classic example is

glass, which has emissivity equal to 0.86 ± 0.87 in LW but which is often thought to be a material of low emissivity. A typical error in interpretation consists of considering the glass as cold (image to the left) when it is instead reflecting the cold radiation from the sky; to read the true temperature correctly, it should be shot from above (image to the right) or from the inside. If from the outside, it is possible to set an apparent reflected temperature value that matches the actual one (very difficult to determine) it is seen that the temperatures calculated from the thermal imager are almost identical for the 2 images; this processing requires a software that allows the setting of different types of emissivity as well as reflected temperatures on several points in the image, e.g. Fluke SmartView®. For the meaning of “reflected temperature” see paragraph 1.9: it is the input value that takes in account the reflected radiation measured by the thermal imager, for eliminating it from the measurement and giving the true object’s temperature.

Fig. 1.16 - The glass (area A0) has a good emissivity but specular reflectivity, and in the picture to the left, where it reflects the sky, it appears colder than the plaster

For this class of materials, it is not possible to move immediately from the apparent temperature to the true temperature, the first being influenced by the view factor with which the surface reflects the radiations coming from the surrounding environment.

It should be noted that certain materials have a specular reflectivity both in the infrared and in the visible spectrum, while some materials have a diffuse reflectivity in the visible but mirrored in the infrared, and thus their behaviour involves a more difficult interpretation. This is the case for certain treated metals: it can be seen from the images below how the apparent temperature varies on the metal under the windows depending on the angle of the image, due to different reflected radiation, while in the visible spectrum no reflections were detectable in the green metal.

Fig. 1.17 - Some of the treated metals have diffused reflectivity in the visible spectrum but it is specular in the infrared

3: Materials with low-emissivity and specular type reflection

This category includes raw metals that are untreated: in the construction industry the most common ones are copper and zinc, used most often for roofing and drainpipes. Although thermal imagers theoretically allow calculation of the actual temperature of each surface by inserting the correct values of emissivity and reflected temperature, correct determination of the surface temperature of materials such as these is not possible in practice in the field because of the spatial variation of the reflections and their great importance due to the low emissivity of the material.

4: Materials with low emissivity and diffuse-type reflection

Examples of these materials from among those used in the construction industry are not known. Such a material would provide an apparent temperature similar to that of the mean temperature of the surroundings (the so-called reflected temperature) and it is for this reason that, for measurement of the reflected temperature an attempt is made to "create" a similar material by making a specular reflector diffuse such as a sheet of aluminium (ε = 0.02 ): making it ball shaped and thus spreading it, the many facets reflect the radiation coming from all directions, thus making it suitable for measuring the reflected radiation, i.e. apparent reflected temperature, setting the emissivity equal to 1 in the thermal

imager: since their reflectivity is almost equal to 1 they show, as diffuse reflectors, an average of the radiation coming from the environment.

Fig. 1.18 - taking a material with very low emissivity and thus very high reflectivity and giving it

many facets makes it an almost perfect diffuse reflector

2. Thermography applied to energy audits of buildings

For an offer for purchasing a thermal imager, a blower door, other instrumentation, software or thermography training courses, you may fill our form at link:

http://www.saige.it/e-book_en.aspx

2.8 Environmental influences in surveys in construction

Environmental influences are mainly linked to outdoor surveys and can be summarised in the following table:

2.8.2 Solar radiation, colour and shading

Solar radiation prevents display of the thermal losses in winter: during the day, the surface temperature appears homogeneous because the solar radiation has "saturated" the exposed façades (figure 2.12), while during the thermal transients (heating and cooling phases), the different heat capacity of materials causes the non contemporaneous release of the absorbed energy, making it impossible to display a superficial thermal distribution comparable with the steady state. The image to the left (fig. 2.13) was taken in winter before dawn and is a good approximation of the stationary state; in the image to the right the building was still in transition and the thermal bridges appear colder due to their lower heat capacity.

Fig. 2.12 - Saturation of the surface temperature due to solar absorption

Fig. 2.13 - Influence of the sun in the winter period

The different thermal capacities along with the different superficial solar absorbencies affect the superficial radiometric temperature measurements.The solar radiation that reaches the earth is composed of approximately 3% of ultraviolet (UV), 55%

of infrared (IR) and 42% of visible light. These three components of radiation each correspond to a wavelength range. Ultraviolet extends from 0.28 to 0.38 microns, visible from 0.38 to 0.78 microns and infrared (in the band relating to solar radiation) from 0.78 to 2.5 microns. The curve shown below illustrates the energy distribution of global solar radiation for a surface perpendicular to this radiation.

Solar radiation spectrum according to EN 410

Solar absorption varies according to the colour of surfaces: the darker colours absorb much more radiation while the lighter ones reflect much more of it. The absorption of solar radiation causes an increase in the surface temperature, which may then differ according to the different colours of the building.Once the radiation has been absorbed, it is radiated in the thermal infrared; on the infrared LW band, but the different colours do not affect the values of emissivity, like the other surface conditions (see paragraph 1.7.1).

By performing the external thermographs of a building, the conditions of solar radiation of the façade or of particular areas of the façade should be borne in mind before the inspection. For example, if the examination is conducted shortly after sunset, and the façade was previously exposed to the sun, this can lead to different thermal aspects of particular areas which were subject to different insolation conditions, even during winter. The thermographic image in fig.14 , taken in December an hour after sunset, would seem to indicate that the different areas of the façade, for example the band of visible surface brick to the right, due to defects of insulation or internal concentrated thermal loads (such as radiators) are hotter than other areas in identical material. The analysis of solar insolation conditions present 1 hour prior to sunset reveal the reasons for the different thermal appearance of the visible surface: the areas at a higher temperature were subject to previous insolation while the area at the height of the balcony was shaded and thus has a lower temperature.

Fig. 2.14 - Ratio between the position of the shaded part and thermal appearance after sunset

For this reason, a photographic and thermographic survey should be performed both from within and externally. The photographic survey is a reminder as to where the shady areas were and to relate the effects with the thermal aspects of the thermographs.In the photo in fig. 2.15 to the left, it is obvious that the lower area of the wall is warmer because, unlike the upper region, it is not shaded.For those indoors, the reason for the different thermal appearance of the lower part (fig. 2.15 to the right) is less obvious, especially when thick walls are being analysed several hours after sunset.Before diagnosing an insulation defect, the question must always be posed: where was the sun a few hours before?The phenomenon of the displacement of the thermal wave is more pronounced the thicker the walls.

Fig. 2.15: thermographic appearance of a sunny wall from the outside and from within

The calculation of non stationary internal temperature of environments during the summer in the absence of an air conditioning system based on the method of thermal admittances, leads to writing of the thermal load of the environment in which, among other aspects, the heat flow appears that crosses an opaque component Φop,t at the time t, given by:

where:

U [W/m2K]: thermal transmittance of the wall; A [m2]: area of the wall; θe,t – φa [°C]: external surface temperature calculated at time (t -φa);

θem [°C]: external air temperature daily average;

φa [h]: phase displacement of the thermal wave; fa [-]: attenuation factor of the thermal flow

The external temperature θe,t, also called "sol-air temperatures", corresponds to the surface temperature below the liminal layer of air due to the combined effect of the external air temperature and the solar radiation. Its value is given by:

where:θe,t [°C]: external air temperature at time t;

α [-]: coefficient of absorption of solar radiation incident on the outer surface; It [W/m2]: solar irradiance incident on the outer surface of the wall in question, at time t; he [W/m2K] surface coefficient of external heat exchange. The formula includes the corrective coefficient α that depends on the colour of the irradiated surface tabulated in the following manner:

If you consider the wall having the stratigraphy shown in Tab. 1 (the stratigraphy obviously does not affect the temperature of the air or the surface, however, it is necessary for the calculation of U, φa, fa

that appear in (1) to obtain Φ op,t) which is assumed has a southern exposure, assuming the values of solar radiation (It) and external mean air temperature (θ ae,t) typical of Brescia in the month of June at 12; the values of θe,t depending on α are shown in Tab. 2.

From the tabulated values it is evident how the external surface temperature and the heat flow undergo significant increases with increase of the coefficient α that thus assumes a significant role in the context of calculation of the internal summer temperature of a building. The indication of the technical standards does not however provide an objective criterion on perception, leaving it to the subjective and arbitrary judgement of the designer to decide whether a colour is light, medium or dark.

We would like to thank Prof. Alberto Arenghi from the University of Brescia and eng. Isaac Scaramella for having released part of their article "The influence of colour" (published in NEU-EUBIOS,ANIT magazine, issue 32 of 2010, downloadable from www.anit.it); the article contains a method for the calculation of the absorptivity of any colour tone.

The wall subjected to the most severe weather conditions is the one oriented to the west, since the peak of solar radiation occurs upon this during the same hours as the temperature of the external air is also at its highest.

Shadow of a flag on the façade of a building in winter

4. Air permeability blower door test of buildings

For a special offer for purchasing a thermal imager, a blower door, other instrumentation, software or thermography training courses, you may fill our form at link:

http://www.saige.it/e-book_en.aspx

This chapter addresses the method for evaluation of air changes in a building by the blower door test.In the absence of site inspections and final inspections by specialised professional figures for testing of the project, there may be a devaluation of the role of the energy certifier. The latter then becomes a simple producer of reports, with detrimental effects that will subsequently be difficult to repair, both because the mode of construction, if it changes, will do so too slowly, and due to the absence of perception of the importance of the objective to be achieved.The blower door test, if combined with thermography, allows checking of the correct execution of the envelope and identification of its weak points.

4.1 Instrumentation for execution of an air permeability blower door test

Ascertainment of the number of air changes to a building is not only important to estimate the thermal losses of ventilation (caused by an excessively high value of n50), but also to assess the possible need for mechanical ventilation necessary to ensure good quality of interior air, increasingly frequent, even if ignored, in modern buildings that often have excellent sealing characteristics, or to understand if the air-tightness of a building already equipped with ventilation systems allows the system itself full efficiency.The objective of the survey, in addition to estimation of of the n50 value, is to understand the various components of the building envelope (structural joints, areas of discontinuity between different materials, windows, window boxes, window frames, the glass of these same windows) which are much weaker.A blower door test carried out according to EN 13829 measures the air changes with Δp significantly greater than those normally present and caused by natural phenomena (wind, "chimney effect"): they are performed at high pressure differences Δ p in order to be repeatable and to be less prone to large variations in the external conditions (e.g., wind speed and direction). In addition, during a blower door test, all parts of the envelope are subject approximately to the same pressure.For execution of the blower door test is installed, on a door or a window in the outer envelope, a metal frame with adjustable width and height. The frame consists of 4 perimeter elements and by a transverse bracing element. Retrotec company offers a model with blind modular panels (fig. 4.2 .central image).

Fig. 4.1: elements of the blower door system - Source: www.retrotec.com

Each element is telescopically extendible up to a maximum length that allows coverage of most of the dimensions of the doors, while a system of screws and cams allows the fixing into position of the various elements once they have been adjusted. The frame firmly holds in place, on the chosen opening, a sturdy nylon sheet, in which are made:

• one or several large round holes, with sturdy elastic, for the insertion of one or a number of fans• small holes for the insertion, with a perfect seal, of small diameter silicone pipes, for the

measurement of outside pressure

Fig. 4.2: Installation of a single fan - Source: www.retrotec.com

Once the frame with the sheet has been installed on the door (or window), the next step to insert the pipes for control of the pressures and the fan (see photo). A pipe is inserted into the connection present on the outer side of the sheet, unrolled until just a few meters from the fan in such a way that measurement of the external pressure is not altered by vortices generated from operation of the fan or by the wind, and arranged so that it will not be influenced by sunshine.At the connection of the external pressure on the inner side of the sheet there is a fitting for another silicone pipe on the internal side, in order to create by-pass of the sheet, and to allow, while maintaining tightness, external pressure within the building being tested (figure below).

Operating digram of the configuration - Source: www.retrotec.com

The pressure gauge system also has identical pipes for:- measurement of the pressure inside the building- measurement of the pressure inside the fanas required from EN 13829 standard.

The fan is provided with various closures to reduce its flow (fig 4.3); for the different types of closure it was calibrated in the laboratory in order to ascertain, depending on the pressure within, the corresponding flows.

Fig. 4.3 : different calibrated sections - Source: www.retrotec.com

The pressure gauge (figure 4.4) also integrates a transducer which converts the pressures measured by every single channel into a digital signal that can be analysed by the PC to which it is connected by a cable. In this way, all the pressure data measured is transmitted in real time to the PC, displayed within it and stored by the software supplied with the equipment, and then processed to obtain the values required by the standard, once the dimensional data of the specific building and the environmental parameters present during the test have been set. Certain advanced models, such as the Retrotec, are fitted with devices that allow setting of the parameters without the need for connection to a PC.

Fig. 4.4: pressure transducer, display, test settings in the same portable device - Source:

www.retrotec.com

The pressure transducer can also be provided, in current models such as the Retrotec, with a cable for connecting to the device that adjusts the fan rotation speed. With this solution the entire test can be performed automatically from the PC, which is particularly important for those tests conducted in accordance with EN 13829 which provide for a minimum of 5 points, as the software varies the speed of the fan thus adjusting it to obtain the differences in pressure set by the user, for all the necessary steps according to EN 13829.As the software is able to correctly process the results of the test, a barometer and a thermometer are also necessary to measure the external pressure, and the interior and exterior temperatures: the software automatically corrects the values derived from the calibration curve of the fan, which are related to standard conditions, to the actual conditions, with the differences in air density value. External absolute pressure measurement is generally not critical but is important to measuring temperatures. If you have an anemometer, you can also detect the speed and direction of the wind, but a qualitative estimation of the same on the basis of the Beaufort scale is sufficient. The uncertainty of the test is determined on the basis of these parameters.Once the fan begins to function, for example expelling air from the inside of the building and thus creating a depressurization condition in its interior, the exterior air tends to enter the gaps in the envelope (fig. 4.5).

Fig. 4.5 : the pressure variation generates infiltration - Source: www.retrotec.com

For the detection of infiltration and its quantification in terms of air speed, there are a number of ways, among which the most popular are thermal imagers and smoke generators for identification, and thermo anemometers for quantification.In summary, the instrumentation necessary to run a blower door test including identification and measurement of the speed of infiltration is the following:

1. a fan, with adjustable diaphragms section and system for adjusting the speed of the blades2. a system for measuring the rate of air flow with tolerance of ±7%, to be corrected on the basis of

the air density according to the specifications of the manufacturer

3. an adjustable frame in terms of height and width, adaptable to the most widely used size of door and window

4. a sturdy nylon sheet for insertion of the fan in the opening used for installation of the frame and therefore for its sealing during the test

5. sheet for sealing of the fan, necessary for measurement of the zero flow pressure difference6. a transducer device able to measure internal and external pressures (and thus the difference in

pressure), as well as the differences in pressure in the fan, preferably able to send real-time parameters measured to a PC for monitoring of the test and recording of the data. The accuracy of the pressures meter must be within ±2 Pa in the range between 0 and 100 Pa according to ISO 9972, or in the range between 0 and 60 Pa according to EN 13829

7. a thermometer for measuring the internal and external temperature, with an accuracy of ±1 K8. a barometer to measure the absolute external pressure9. an anemometer for measurement of the wind; this can be avoided if you proceed visually

according to the Beaufort scale10. a PC with dedicated software for the control, setting and programming of the test parameters and

data detected and its processing11. A thermal imager for locating air infiltration (fig 4.6 - in the presence of the sufficient

temperature difference between inside and outside), and/or a smoke generator12. A thermo anemometer, preferably with telescopic pole, for measurement of the rate of air

infiltration (fig 4.7)

The instrumentation from point 1 to point 8 represents the absolute minimum for execution of the test with determination of parameter n50 (or the parameters w50 or q50).Control via a PC with dedicated software greatly assists the operator in performance of the test and the data processing.The instrumentation from point 11 to 12 is fundamental in the search for critical points of the envelope and thus for improvement of its performance and/or for energy diagnostics.

In the USA, Germany and the United Kingdom, the execution of blower door test is widespread, and there are cases of testing on large volume properties, with the use of several fans in parallel (fig 4.8).

Fig. 4.8: installation of 15 fans to test a large building - Source: www.retrotec.com

The United Kingdom is the only country where the test is mandatory (for properties with surface area greater than 1000 square meters), and this has led to the creation of specialised companies for large volume testing, using large fans mounted on a motor vehicle.