WO2011128927A2

WO2011128927A2 - Measuring thermal parameters of a building envelope

Info

Publication number: WO2011128927A2
Application number: PCT/IT2011/000119
Authority: WO
Inventors: Ermanno Grinzato
Original assignee: Ermanno Grinzato
Priority date: 2010-04-16
Filing date: 2011-04-18
Publication date: 2011-10-20
Also published as: ITPD20100121A1; WO2011128927A3

Abstract

The method bases on the accurate detection of the difference of temperature between air and surface through thermographic measures, from which thermal parameters such as local thermal flux, quantitatively expressed in W/m2, are calculated. The surface heat exchange between the environment and surface, by convection and radiation, is also locally calculated and measured in separated way. The measure is remotely performed through an IR thermographic system, which completely and partially frames the surface to be tested and a grid, supporting a proper number of specific targets. The method also applies for calculating the thermal transmittance in situ. The measure of the thermal transmittance is got by integrating the detection of the thermal flux on the inner side, measured through this method, with the continuous recording of the external temperature of the surface and/or air obtained with traditional thermometric or thermograpich probes.

Description

METHOD FOR MEASURING THE THERMAL PARAMETERS OF A BUILDING ENVELOPE AND MEASURE EQUIPMENT SUITABLE TO IMPLEMENT SUCH A METHOD

The present invention relates to a method for measuring the thermal parameters of a building envelope, such as, for example, the surface heat exchange coefficients (or adduction coefficients), the heat flux per unit area running through such a building envelope and the thermal transmittance.

In other words, the invention relates to a method for measuring characteristic quantities which define the thermal performances of the envelope of the building.

Moreover, the invention relates to a measure equipment suitable to implement such a measure method.

The peculiarity of the method for measuring the thermal parameters of a building envelope hereinafter described is derived in particular from the fact of detecting the thermal performances over the whole inner surface of one or more rooms of a building, examined through an automatically calibrated thermographic system.

The measure method, which is the object of the invention, uses a specific measure equipment; the method allows the measure of thermal parameters such as typically the radiative heat exchange coefficient (in physics, symbol a_r), convective heat exchange coefficient (symbol α,), thermal transmittance (or overall heat exchange coefficient, symbol U) and heat flux (symbol Q) of the building detected on one or more inner surfaces of the building envelope.

Briefly, as known, thermography is a non-destructive diagnostic analysis technique which consists in the bidimensional display of the infrared (IR) radiation emitted by any body having a temperature above the absolute zero (-273.16°C); from the infrared radiation it is then possible to get the temperature of the surfaces of the rooms of a building. Such a technique uses a so-called IR thermal camera (IR) which operates non-invasively, without physically interfering with the body to be tested, unlike what happens with contact thermometers or the sensors so-called heat flux meters, positioned close to the body in order to measure the temperature thereof or the heat flux running through its surface. A heat flux meter consists of a calibrated plate to be applied in series to the wall whose thermal flux running through it has to be measured and however performs a local measure on a very limited area (in the order of 5÷10 cm²) of the wall itself.

The heat flux metres are not able to provide an accurate and representative estimate of the entire wall, because of the thermal contact resistance between sensor and wall and their time constant, unless placing them on the wall itself in a very large number and in any case unjustified in terms of costs and complexity of the installation.

Then, the heat flux meter should be carefully glued on the wall to be tested in order to avoid trapping between heat flux meter and the wall air which would provide an additional thermal resistance.

In practice, this is impossible and it can be often discovered that the coupling of heat flow meter with the wall to be tested is not optimal, therefore the value of the heat flux detected by it is inevitably little truthful.

Moreover, the final value of the average heat flux provided by heat flux meter derives from a cycle of measures, performed in period of time of several days, since the thermal conditions of the wall are not stationary.

In addition, also, the face of the heat flux meter oriented outwardly and in contact with the air is immediately disturbed by air temperature changes, while the opposite face, in contact with the wall, is affected late and to a lesser extent by these changes, thereby the heat flux meter returns a value with a significant or anyway not negligible error. Another significant source of error related to the use of heat flux meter is the different capacity to absorb the thermal radiations by the heat flux meter itself compared to the wall to be tested.

These drawbacks are at least partly overcome by the thermography technique which, by measuring the local thermal transmittance of an entire wall, consequently allows to know and assess the critical areas thereof, those ones where significant losses of thermal energy (so-called thermal bridges) occur.

In this regard, it is stated precisely that a European standard exists explaining how to qualitatively apply IR thermography, not to measure the thermal transmittance of a wall of a building but to detect the thermal bridges.

Incidentally, it is reminded that the thermal transmittance (whose unit is [W/m²K]) defines the insulating capacity of a body: the lower is its value the greater the insulation of the body concerned is. The inverse of the thermal transmittance is the thermal resistance (symbol RG) that is the capacity of an object to oppose to the heat flow, so it is:

U = 1/R_G. In steady conditions, the equation linking thermal transmittance and heat flux through an object, such as the wall of a building, is the following:

where: S = tested surface area

Tj = air temperature of the environment T_e = air temperature of the environment U = thermal transmittance

Q = heat flux.

The thermal conductance (symbol K) is, instead, determined by the normalization of the heat flow on the surface temperature gradient between the two inner/outer sides of the building, rather than the air. Prior document WO2009/074783 describes a method of purely qualitative application of the thermography: the method described herein provides, indeed, performing outside the building, according to a proper angle of shot, of only one thermographic image at a given time, in order to not unduly disturb the tenants and detect the thermal bridges, so as to apply corrections to the calculation of the thermal transmittance obtained with mathematical models that use data on the sizes and thermo-physical properties of the materials, which are often not available and however little reliable.

The method of the aforesaid prior art document then considers a model of theoretical calculation (for example SAP2005), which can be carried out through a computer program, and uses the external detection obtained with the thermography in order to provide a correction to the value returned by such a method of calculation, correction deduced by tracing out in the map of distribution just quoted some isothermal lines related on problematic thermal areas.

Such a method does not detect the heat flux running through a wall but, more simply, it resolves to locate the critical areas in which significant heat losses occur: it has in any case some obvious drawbacks. The first drawback is due to the fact that a thermography performed in a single moment does not take into account the environmental temperature phase lags to which the wall is undergone as a result for example of the passage from the day to the night.

Another drawback of the method described in the document WO2009/074783 is given by the fact that it fails to correct from a geometric point of view the inevitably distorted thermographic images due to poor quality of the optics of the thermal camera with which the thermography is performed.

This prevents to assess the extent of those areas of the tested wall affected by the thermal bridges (such as the structural reinforcements), areas with low thermal resistance or high thermal transmittance, i.e. areas where heat finds a preferential path to spread into the environment.

Recent international publications on the subject prove that the accuracy of the thermography measures of the type described in WO2009/074783 is less than 50% (reference QIRT journal, year 2010, autor Vavilov).

In short, the method described in the document WO2009/074783 performs only approximate location of the thermally defective areas and not a true measure of the thermal parameters, such as heat flux, thermal transmittance and so on.

The present invention aims to overcome the drawbacks of the prior art in question just highlighted.

In detail, primary purpose of the invention is to provide a method for measuring the local thermal parameters of a building envelope, as well as a measure equipment suitable to implement such a method, which allow to optically measure the instantaneous value of these parameters in a way more accurate than equivalent methods and equipment of the known type.

Further purpose of the present invention is to develop a measuring method and automatic measure equipment of the thermal parameters, such as for example the heat flux crossing the building envelope of a building and the local and average thermal transmittance, getting rid of the need of contact measures typical of the prior art. It is a last but not least purpose of the invention to implement a method for measuring the thermal parameters of the building envelope which affects a large surface for an adequate and sufficiently long, therefore not instantaneous, period of time so as to adapt to the variability (or non- stationariness) of the environmental conditions and thus provide values more accurate and detailed than the methods used in the current state of the art.

These and other purposes are achieved by a method for measuring the thermal parameters of the building envelope as the attached claim 1 , as hereinafter referred for the sake of brevity. Further applicative features of detail of the method of the invention are highlighted in the related dependent claims.

Integral part of the present invention is also a measure equipment as the appended claim 16, as hereinafter again referred for the sake of brevity.

Advantageously, the measuring method of the invention is able to identify and quantify the possible insufficiency of the materials by determining the thermal properties of the building envelope of a building due to defects or lack of insulation materials, their bad installation or their aging.

Still advantageously, the innovation brought by the invention mainly but not exclusively consists in the total measure of large areas, performed with accuracy and speed largely greater than those ones of known measure systems based on thermography, besides optically and therefore without any contact with the surfaces themselves, as it usually happens, instead, in the known art using heat flux meters.

Said purposes and advantages will appear more from the description that follows relating to a preferred embodiment of the measure equipment according to the invention and the results obtained by implementing the measure method of the invention, given as illustrative and indicative, but not limited, way in relation to the attached tables of drawing, where:

- figure 1 is a provisional perspective view of the measure equipment of the invention in applicative conditions, close to the inner surface to be tested, of a room of a building, with the heat flux shown numerically and in false colours scale on such a surface;

- figure 1 a is an enlargement of a detail of figure 1 ;

- figure 2a is a schematic perspective view from the top of the room of figure 1 , with the map of the surface temperature shown on the inner surface at issue;

- figure 2b is a schematic and partial perspective view from the top of the room of figure 1 , with the map of the air temperature at 10 cm from the inner surface to be tested shown on the inner surface itself;

- figure 3 is the resulting map of the temperature gradient between air and surface, with the geometric horizontal and vertical scale in centimetres and the temperature in Kelvin degrees;

- figure 4 is the map of the specific local convective heat flux measured by the method of the invention and considering as a reference air temperature that one at 10 cm from the inner surface to be tested, with the geometric horizontal and vertical scale in centimetres and the specific convective heat flux in W/m²;

- figure 5 is the map of the specific local radiant heat flux measured by the method of the invention, with the geometric horizontal and vertical scale in centimetres and the specific radiant heat flux in W/m²;

- figure 6 is the map of the local specific heat flux q(x, y) in W/m², measured by the method of the invention using the local values of hj, calculated for example, with the reported algorithm, and Taj, with indicated values of the specific heat flux obtained in three points (5.03, 13.01 , 0106 W/m²), which are very different each other and thus show the importance of a local detection (in particular, the value 5.03 W/m² is close to the measure of heat flux meter);

- figure 7a is a perspective view from the outside of the building within which the method has been implemented and the measure equipment of the invention has been mounted, with the distribution of the geometrically correct surface temperature shown on the outer surface (the rectangular box highlights the tested inner surface);

- figure 7b is a front view of the outer surface of the building of figure 7a, with yellow points indicating insulation defects (higher thermal transmittance).

The measure equipment of the invention, globally numbered with 10, comprises the following elements, which are shown in the main figure 1 :

• a thermographic system, on the whole indicated with 1 , even of industrial type, mounted on a mechanical support having mainly a vertical development and provided with pan-tilt head 2, which allows to scan the inner surface to be tested A;

• a mechanical support and reference grid 6 arranged close to the inner surface to be tested A;

• a plurality of radiometric and geometric calibration targets 3, fixed to the mechanical support grid 6 according to a reticular pattern;

• a central processing and control unit 5 which implements an algorithm of computer vision of the targets 3, allows their recognition, identification of the specific areas and thermal and geometric measure of the examined surfaces.

The algorithm implemented by the central unit 5 exploits the particular layout and features of the elementary sub-areas which, as it will be explained shortly, form each of the radiometric and geometric calibration targets 3.

Moreover, the central processing and control unit 5 is able to record images, perform calculations in order to get the correct maps of temperature and display the results, even on a scale model of the building. The mechanical support and reference grid 6 is composed of a light mechanical support, which can be removed and adjusted to the shape and size of the surface A to be tested.

In particular, as figure 1 shows, the mechanical support and reference grid 6 is located close to said area A, for example 10 cm apart, in order to detect the thermodynamic conditions of the environment through the appropriate net of targets 3.

The mechanical support and reference grid 6 allows the correction of the prospective image errors and the images registration (merging, overlapping and rendering) on the draw of the room, expressed in metric units.

The geometric calibration (relative to the tested surface A) of all the measurement results, i.e. the various maps of temperature and fluxes detected, is achieved from the analysis of the thermographic images taken by thermographic system 1 so as to include for each thermogram a number of calibration targets 3 mounted on the mechanical grid 6 greater than three, since the geometry of the latter is known and its position in the room space is determined by automatic calculation.

The pan-tilt head 2 may be operated manually or automatically, for example by motors driven by the central processing and control unit 5. The radiometric and geometric calibration targets 3 are arranged in such a way as to form a network of known geometry with a density suitable for the optic of the thermographic system 1 : a detail of one of the targets 3 is enlarged in figure 1a.

For the sake of completeness and clarity, it is stated precisely that the radiometry is that branch of optics which deals with the study of the measure of the electromagnetic radiation and, thus, implicitly provides information on the environmental physic quantities such as temperature: typical radiometric quantities are the radiant energy (measured in Joule), the radiant flux (measured in Watt), the radiant emittance (measured in W/m²) and the radiance (measured in W/m²).

More in detail, in preferred but not exclusive way, the targets 3 are spaced apart each other of 70 cm along a vertical direction and 100 cm along a horizontal direction in such a way that four targets 3, two by two lying on two vertical or horizontal directions mutually parallel and separated, are arranged according to the vertexes of a rectangle. Advantageously, each targets 3 is composed of a plurality of elementary sub-areas made of materials and surface treatments suitable to ensure specific thermal and radiometric features.

Preferably but not necessarily, the elementary sub-areas of each of the targets 3 are four in number, as specified below:

- a first elementary sub-area Si dedicated to the measure of the temperature of the environment air;

- a second elementary sub-area S₂ suitable to the evaluation of the radiant flow included in the band of the visible and the near infrared

(NIR) incident on the inner surface to be tested A;

- a third elementary sub-area S3 faceted and reflecting in a widespread way suited to determine the infrared (IR) radiation incident on the inner surface to be tested A and reflected by it;

- a fourth elementary sub-area S4 dedicated to the location of the targets 3 and designed to handle the automatic pan-tilt head 2.

More specifically, the elementary sub-areas Si and S₂ are used for detecting the temperature of the air of the room where the measure equipment 10 of the invention is set, especially the elementary area Si made, for example, of material plastic.

The first sub-area Si is white and quickly (with a few seconds) enters in equilibrium with the surrounding air: therefore, in the electromagnetic band of the visible, the first sub-area Si does not absorb radiations, but, in the infrared range, it is similar to a black body which answers only in function of the temperature.

The second sub-area S₂ is, instead, black and in the infrared range is still seen as a black body: it is used to evaluate which part of a given radiation belonging to the visible range is present in the environment.

The third sub-area S3 measures the electromagnetic radiations in the thermal infrared band that reach the inner surface to be tested A but which are emitted by the surrounding surfaces, depending on their temperature.

Actually:

- firstly, the third sub-area S3 is a kind of mirror useful to evaluate the radiation affecting it;

- secondly, the third sub-area S3 is randomly faceted, that is it represents a diffuse reflector, thus able to reflect by itself as the radiations coming from all the directions and emitted by all the surrounding bodies.

Through adequate integration of all the radiations reflected by the third area S3 the radiative heat exchange coefficient (symbol a_r) is obtained.

As it will be better shown hereinafter, the convective heat exchange coefficient in surface running (symbol α,), is in turn calculated, by one of the appropriate algorithms available in literature, considering the temperature difference between the tested surface A and the air temperature in surface running.

Incidentally, it is reminded that the sum of the radiative heat exchange coefficient and convective heat exchange coefficient provides the surface heat exchange coefficient (symbol h) or its inverse, that is the surface thermal resistance (symbol 1/h), wherefore:

1/h = 1/(α_Γ + αι).

The fourth sub-area S₄ consists of a special lint or hydrophilic fabric suitable to absorb by capillarity water present in a small tank underneath it, placed at the bottom of the sub-area S and filled with demineralised water which dampens and by evaporating cools the hydrophilic lint in such a way that between the inner surface to be tested A and the sub-area S of the targets 3 there is an appreciable difference in temperature, in the order of a few degrees and not of tenths of degree as it is normally for the other sub-areas Si , S2 and S3.

This allows to the thermal camera of the thermographic system 1 to autonomously operate, without lighting and at night, for a predetermined but in any case extended period of time, in the order of some days, returning reliable average values of thermal transmittance.

The elementary sub-areas Si, S₂, S3, S₄ of each target 3 are known in shape and size; the reflection coefficient (symbol p) and emissivity (symbol ε) that are mutually linked as complement to unity (ε = 1 - p) are also known, given their opacity (null transmission coefficient) in the respective spectral components.

It is also reminded that the emissivity of a body is given by the ratio of the energy radiated by that body in respect of the energy radiated by a black body at equal temperature: basically, the emissivity is an optical property of the surfaces and measures the effectiveness of a body to irradiate energy.

The thermal inertia of the materials forming the elementary sub- areas Si , S2, S3, S4 is low enough in order to follow the dynamics of the measured quantities, but suitable to act as a low-pass filter against the frequencies of noises typical of the measured quantities, but low enough so as to follow the dynamics of the quantities measured.

In practice, the dynamic response of the measuring system can be adapted to the various cases of interest, obtaining a filtered signal from disturbs.

According to the preferred embodiment described herein of the invention, the measure equipment 10 also includes an accessory measure and recording unit of the air temperature, indicated with 4 in figure 1 , with which one of the targets 3 is provided. Such an accessory measure and recording unit 4 of the inside air temperature typically consists of a calibrated thermometer provided with a recorder (so-called "data-logger") and measures the air temperature inside the building envelope at such a target 3, independently from the thermal camera of the thermographic system 1.

The auxiliary measure of the inside air temperature performed by the accessory measure and recording unit 4 allows to eliminate the systematic errors affecting every measure and then even the infrared ones, thus obtaining the thermal calibration of the system.

This operative arrangement allows to achieve an accuracy in the order of the tenth of degree on the thermal differentials, desirable though not essential for the implementation of the measuring method of the invention described below.

In another embodiment of the invention, not shown in the accompanying drawings, the measure equipment could also include an additional accessory unit of measure and recording of the air temperature outside the building envelope, useful for calculating the thermal transmittance, using the mathematical formula previously introduced.

The measuring method according to the invention, also object of claim by the present invention, preferably provides the following steps:

- thermographic scanning of the outside of the building;

- assembly and arrangement of the mechanical support and reference grid 6 close to the inner surface to be tested A, as well as of the radiometric and geometric calibration targets 3, placed at a known mutual distance according to a reticular pattern extending over the entire surface;

activation of the calibrated thermometer 4, equipped with recorder, to measuring air temperature, placed near a target 3, for the thermal calibration;

- activation of the air thermometer, equipped with recorder and placed near the surface to be tested A, in order to measure the outside air temperature;

- positioning on the inner surface to be tested A of an adhesive material of high and known emissivity in the infrared bands (for instance ε = 0.97) and reflection coefficient similar to that one of the inner surface A in the visual band;

periodic scanning of the mechanical grid 6, usually from a central position, with the thermographic system 1 , whose thermal camera simultaneously frames in its field of view at least three targets 3, and subsequent recording of the individual thermograms; the pan-tilt head is automatically moved after having determined the spatial correspondence between the mechanical grid 6 and a virtual image plane (through homography);

- activation of the automatic calculation procedure of the control system.

The results of the measures are computed, displayed and recorded automatically by the central processing and control unit 5 or manually and provide the following steps:

- locating the targets 3 through the analysis of the images with manual or automatic recognition of the elementary sub-areas Si, S₂, S3, S₄ having different thermal behaviour; in particular, it is possible to identify in the thermograms the boundary between the sub-areas Si, S₂, S₃, S4 thanks to their high thermal contrast;

- detecting the radiant temperature on every third elementary sub-area S₃ present in the targets 3;

- calculating the emissivity of said inner surface to be tested A;

performing thermal and geometric calibration, through homography, of the thermograms;

- calculating the temperature (T_w) of the inner surface to be tested A.

Figure 2a shows the map of the temperature of the surface A thus calculated;

- calculating the air temperature (T_a) obtained by interpolating the values measured on the first sub-area Si of each target 3, when the latter is in thermal equilibrium with the surrounding air. Figure 2b shows the map of the air temperature thus calculated;

- calculating the temperature difference (T_a - T_w) = ATaWj [K] between air and inner surface A, as difference between the map of the air temperature and the map of the surface temperature obtained by the mosaic composition of the individual thermograms, automatically registered with the aid of the mechanical support and reference grid 6. Figure 3 shows the resulting map of the temperature gradient between air and surface A in correct (calibrated) geometric scale;

calculating the convective heat flux, through the following formula q^c = Oj (T_a - T_w) = QiATaWj, exchanged between air and surface A at each point, obtained using the map ATawj, multiplied by the convective heat exchange coefficient (α,) determined for each point with an algorithm selected from among those tested ones available in literature, such as for example the following one:

Qj = 1 ,594 (ATaWi)^{0 22}, or specifically developed. Figure 4 shows the map of the convective heat flux thus calculated;

calculation of radiative heat flux exchanged between adjacent surfaces and surface to be tested, through the following formula: q^r = O E (T_r ⁴ - T_w ⁴) where: σ = Stefan-Boltzman's constant

(σ = 5,6704 x 10^"8 Kg/s³K⁴)

ε = surface emissivity.

Figure 5 shows the map of the radiant heat flux thus calculated;

calculation of the total specific heat flux, exchanged from the tested surface, by adding the radiant one with the convective one (q = q^r + q^c). Figure 6 shows the map of the specific heat flow (normalized to the surface), expressed in W/m² thus calculated.

Assuming that, in steady conditions, all the heat flux crossing the wall comes out from the tested surface A, the specific heat flux q (q = Q/S) calculated above and exchanged by convection and irradiation by such a surface tested A with the inner environment is equal to the specific heat flux exchanged by conduction running through the building envelope involved by the inner surface A.

Furthermore, considering the value of heat flow obtained with the aforesaid method of the invention averaged on the overall surface tested A, it is thus possible to determine the overall thermal transmittance U of the wall by the following formula:

U = q/(Taj - Ta₀) = hi ATaWj/(Tai - Ta₀) where: hi = surface heat exchange coefficient calculated as average on the tested surface A in accordance with the present method of measure of the heat flux running through the wall, by the following formula:

Ta, = average of the air temperature calculated inside the building measured according to the present method;

Ta₀ = average of the external air temperature calculated for a significant period of time in order to get a constant condition (in accordance with the current standard). In this regard, a thermometer equipped with data logger for measuring the air temperature near the outer side of the building, for the duration of the test and before it, is provided.

The measuring method of the invention provides to pre-set the position of the radiometric and geometric calibration targets 3 into the central processing and control unit 5, i.e. before starting the measure operations.

The homography by which the thermographic measures are geometrically related in space consists, as known, in making a correspondence between points of two different spaces, straightening or correcting in this case a distorted image, as soon as it is captured by the thermal camera of the thermographic system 1 , into a geometric reality.

Therefore, the measuring method of the invention optically determines thermal parameters, such as for example the heat flux crossing the building envelope, by performing a measure from the inside of the building on one or more entire inner surfaces having 20 m² area for a sufficiently long time.

One of the innovations brought by the method herein exposed is, indeed, the very high density of measure points produced, necessary for a correct and accurate evaluation of the local and average heat flux of defective areas (spatial resolution of 1cm² as indicative value).

For example, the measure method of the invention accurately detects the local value of the heat flux running through an extended portion or the whole of the wall, obtained through the analysis of a plurality of thermograms merging each other into a mosaic composition, after correction of the perspective and radiometric distortions. The scanning of the inner surface to be tested can be automatically performed by a thermographic system driven by a computer vision software with automatic recognition of the targets.

An innovation of the method described is the possibility of quantifying the local flux values and therefore the real impact of the thermal bridges or lack of homogeneity of the heat flow.

In confirmation of this, indeed, the very different values which are got in three points of the tested surface A are shown in figure 6 (5.03, 13.01 , 0.106 W/m²).

Another innovation of the current invention consists in the great accuracy of the measure performed by the method described, which is mostly obtained thanks to the use of only one detector for measuring the spatial distribution of the temperature gradient air-inner surface (ATaw,).

In addition, the thermographic measurement of the temperatures is correct on the basis of the best practice described by the technical literature, for the so-called radiant temperature (T_r), which is precisely detected in many points by means of the third elementary reflecting sub-area S3 of each target 3.

Finally, the possible common mode error on the thermographic measure is drastically reduced by comparing the value of temperature read by the calibrated air thermometer (0.1 K recommended accuracy) and the thermographic measure obtained on the first elementary sub-area Si of the corresponding target 3. The algebraic value of this difference is added to all the thermographic measures.

According to the present measuring method it is also possible to perform a non-destructive control of areas subjected to defective materials or their improper laying and quantify the weight of the defects or thermal bridges on the thermal dispersions of the building.

Figures 7a and 7b show an example of this control, with the areas corresponding to a defective insulation (shown in yellow). The previous figures refer to the tested room which, in this case, as the rectangle of figure 7a highlights, is located at the first floor of the building.

Before the installation of the measure equipment inside the room to be tested and after the conclusion of the inner measures, the operator could perform a thermographic scanning from the outside according to the best current practice, in order to provide the infrared images to be used to identify defective areas of the masonry which are located near to the outer surface. These data could be also used to support calculations models of the thermal dispersions, available in literature, according to the current standard.

Finally, according to the present method it is also possible to perform the measure of the conditions of environmental comfort to the international rules.

Indeed, the measuring method of the invention, through mathematical tested models or algorithms available in literature which process the values obtained by the local environmental detections, allows to detect through thermography quantities such as the radiant temperature, air temperature, relative humidity and air speed.

On the basis of what just exposed, it is, therefore, understood that the method for measuring the thermal parameters of a building envelope and the measure equipment suitable to implement said method, both object of the current invention, reach the purposes and achieve the advantages previously mentioned.

In case of very wide surfaces (greater than 20 m²), the measuring method of the invention could be repeated after having displaced the thermographic system to an adjacent area, till the complete covering of the surface to be tested.

It is, finally, clear that many other variations may be made to the measure method and equipment in question, without departing from the principle of novelty intrinsic in the inventive idea expressed here, as it is clear that, in the practical implementation of the invention, materials, shapes and sizes of the illustrated details can be changed, as needed, and replaced with others technically equivalent.

Where the constructive features and techniques mentioned in the following claims are followed by reference numbers or signs, those reference signs have been introduced with the sole objective of increasing the intelligibility of the claims themselves and therefore they have no limiting effect on the interpretation of each element identified, by way of example only, by these reference signs.

Claims

1. Method for measuring the thermal parameters (q, q^c, q^r, α,, hi, U) of a building envelope, characterized in that it comprises the following operations:

- arranging a mechanical support and reference grid (6) at a close distance from the inner surface to be tested (A) of an environment delimited by said building envelope;

positioning a plurality of radiometric and geometric calibration targets (3) on said mechanical support and reference grid (6);

- positioning in said environment of said envelope a thermographic system (1) pointed toward said mechanical grid (6) and surface to be tested (A);

- measuring the emissivity of said inner surface to be tested (A);

- orienting the thermal camera of said thermographic system (1) in such a way as to include in the field of view of said thermal camera at least three of said targets (3);

- scanning the whole surface to be tested (A) taking from time to time in said view field of said thermal camera at least three of said targets (3); measuring through thermal camera the difference of temperature between air and said inner surface (A);

- automatically calculating the local and global convective heat exchange coefficient (α,) and/or the local and global radiative heat exchange coefficient (a_r) exchanged between said inner surface (A) and said environment.

2. Method as claim 1) characterized in that it includes the operation of overlapping, rendering and geometrically correcting said temperature difference displaying it in a two or three dimensions diagram of the building, performed after said operation of optically measuring said temperature difference between said air and surface (A) through said thermal camera of said thermographic system (1).

3. Method as claim 2) characterized in that said operation of rendering said difference of temperature is performed through homography.

4. Method as any of the preceding claims characterized in that it comprises the operation of calculating through mathematical formula the specific heat flux (per area unit), local and global, exchanged by irradiation (q^r) and/or the specific heat flux (for area unit), local and global, exchanged by convection (q^c), performed after having measured said convective heat exchange coefficient (aj), local and global, and/or said radiative heat exchange coefficient (a_r), local and global.

5. Method as claim 4) characterized in that it comprises the operation of adding said specific heat flux, local and global, exchanged by radiation (q^r) and said specific heat flux, local and global, exchanged by convection (q^c) in order to get in steady conditions the specific conduction heat flow (q), local and global, across said envelope at said surface to be tested (A).

6. Method as claim 4) characterized in that it includes the operation of calculating the total radiative heat flux and total convective heat flux by multiplying the area (S) of said inner surface (A) respectively by said specific radiative heat flux (q^r) and said specific convective heat flux (q°).

7. Method as claim 6) characterized in that it includes the operation of adding said total radiative heat flux and said total convective heat flow in order to obtain the total heat flux and the subsequent operation of calculating the surface heat exchange coefficient (hj) by dividing said total heat flux by the temperature difference between said inner surface (A) and said air by said total heat flow.

8. Method as any of the preceding claims characterized in that said air temperature is optically measured by processing through interpolation the data supplied by a first elementary sub-area (Si), having white colour and in equilibrium with the air of said environment, of each of said targets (3) from time to time involved in said field of view of said thermal camera of said thermographic system (1).

9. Method as claim 8) characterized in that the value of the air temperature supplied by said first elementary sub-area (S^ of each of said targets (3) is processed by mathematically fitting and integrating the data optically detected by said thermal camera on a third elementary sub-area (S₃), having a surface reflecting in a widespread way, of each of these targets (3) from time to time involved in said field of view of said thermal camera, said third elementary sub-area (S3) measuring the electromagnetic radiations reflected on it but emitted by every surrounding body present in said environment.

10. Method as any of the preceding claims characterized in that said temperature of said surface to be tested (A) is calculated by interpolating and re-sampling, the radiometric calibration being performed, the various thermographic measures of said thermal camera of said thermographic system (1) relating to individual thermograms obtained with said thermal camera oriented towards at least three of said targets (3) and/or by mosaic composing, the geometric calibration being performed, the various individual thermograms.

11. Method as any of the preceding claims characterized in that it comprises an auxiliary operation of measuring of the internal air temperature of said environment, suitable to increase the accuracy of the measure, performed through an accessory measure and recording unit (4) placed at one of said targets (3) and coupled with said mechanical grid (6).

12. Method as any of the preceding claims characterized in that it comprises the operation of detecting the air temperature outside said building envelope, performed through an accessory measure and recording unit placed near said building envelope at said inner surface (A) for a prefixed period of time, before and during said operation of measuring said temperature difference between said air of said environment and said inner surface (A).

13. Method as claim 12) characterized in that said period of time is not less than three days if the heat capacity of said building envelope is less than 20 kg/m³ and not less than 72 hours if said heat capacity of said building envelope is greater than 20 kg/m³.

14. Method as claim 12) or 13) characterized in that it comprises the operation of calculating the thermal transmittance of the building envelope, performed after operation of detecting said air temperature outside said building envelope on the basis of the values of temperature obtained by it.

15. Method as any of the preceding claims characterized in that said close distance at which said mechanical grid is arranged (6) is not greater than 20 cm and said calibration targets (3) are placed on said mechanical grid (6) according to a reticular pattern.

16. Measure equipment (10) characterized in that it comprises:

- a thermographic system (1), mounted on a mechanical support mainly developing vertically and provided with pan-tilt head (2), suitable to scan an inner surface to be tested (A) of an environment delimited by a building envelope;

- a mechanical support and reference grid (6) placed in front of said inner surface to be tested (A);

- a plurality of radiometric and geometric calibration targets (3), fixed to said mechanical support grid (6) in such a way as to be directed towards said thermographic system (1 );

- a central processing and control unit (5) which implements an algorithm of computer vision of said radiometric and geometric calibration targets (3), suitable to allow the thermal and geometric measure of said inner surface to be tested (A).

17. Equipment (10) as claim 16) characterized in that said radiometric and geometric calibration targets (3) define a reticular pattern on said mechanical grid (6).

18. Equipment (10) as claim 16) or 17) characterized in that said radiometric and geometric calibration targets (3) are arranged on said mechanical grid (6) with a density of 70x100 cm².

19. Equipment (10) as any of the preceding claims characterized in that each of said radiometric and geometric calibration targets (3) includes:

- a first sub-area (Si) suitable to measure the air temperature of said environment;

- a second sub-area (S₂) suitable to evaluate the radiant flux included in the visible and infrared band incident on said inner surface to be tested (A);

- a third sub-area (S3) reflecting in a widespread way suitable to determine the infrared radiation incident on said inner surface to be tested (A) and reflected by it;

- a fourth sub-area (S₄) suitable to detect said targets (3) and allow the automatic management of said pan-tilt head (2).

20. Equipment (10) as any of the claims from 16) to 19) characterized in that it comprises an additional accessory measure and recording unit (4) of air temperature, with which one of said targets (3) is equipped, suitable to measure the air temperature inside said environment of said building envelope at said targets (3), independently from said thermal camera of said thermographic system (1).

21. Equipment as any of the claims from 16) to 20) characterized in that it comprises an additional accessory measure and recording unit of air temperature outside said building envelope, suitable to allow calculation of the thermal transmittance of said building envelope.

22. Equipment as any of the claims from 16) to 20) characterized in that said pan-tilt head (2) is operatively connected with driving means of manual or automatic type.