BACKGROUND

[0001 ] The thermal quality of a building can be characterised using a measure of thermal transmittance (or U-value). The U value provides a measure of the rate of transfer of heat through a given area of a structure at a particular location, divided by the difference in temperature across that region of the structure.

[0002] A low U-value indicates good thermal quality, typically stemming from good building insulation resulting in a low thermal transmittance. Conversely, regions with a high thermal transmittance will have a relatively higher U-value.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] Various features and advantages of certain examples will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example only, a number of features, and wherein:

[0004] Figure 1 is a schematic representation of a boundary in an environment, according to an example;

[0005] Figure 2 is a schematic representation of a processor linked to a memory, according to an example; and

[0006] Figure 3 is a representation of a screenshot according to an example.

[0007] Figure 4 is a representation of a screenshot of an environment according to an example.

[0008] Figure 5 is a representation of a screenshot according to an example.

DETAILED DESCRIPTION

[0009] In the following description, for purposes of explanation, numerous specific details of certain examples are set forth. Reference in the specification to "an example" or similar language means that a particular feature, structure, or characteristic described in connection with the example is included in at least that one example, but not necessarily in other examples.

[0010] The thermal quality of a building may be determined from the thermal transmittance value called the U-value. Thermal quality is also determined from the thermal resistance (R), which is given as the inverse of the U-value. A low U- value, and therefore high R-value indicates good thermal quality. Conversely a high U-value, and therefore low R-value indicates a less good thermal quality. Measurement of the thermal behaviour of a building can be performed using a heat flux meter (HFM) to determine a U-value. However, this non-invasive test can take at least 72h to execute, and the accuracy can be as low as 14-28%. It is also not reliable for non-homogeneous building elements. An alternative technique is based on infrared thermography (IRT). Although it is generally used for qualitative analysis, quantitative internal IRT methods can be adopted for in- situ measurement of the U-value.

[001 1 ] When used in this manner (for quantitative internal determinations), a process using IRT can proceed by obtaining multiple isolated measurements of part of a structure, which can then be used to provide an average value that enables a U-value for the part in question to be determined. For example, a wall in a building can have multiple temperature measurements taken using an IRT device in order to provide a U-value for the wall. The same process can be repeated over other discrete areas of a building where it is desired to understand the thermal quality.

[0012] According to an example, there is provided a method for generating an interactive three-dimensional thermal quality mapping of an environment. In an example, an environment can be a room inside a building a corridor, stairwell, or indeed any other internal part of a building. In another example, an environment can include part or all of the outside of a building or enclosure.

[0013] A three-dimensional representation of the environment can be generated, which comprises multiple surfaces defining respective boundaries of the environment. For example, an imaging module of user equipment, such as a smart phone for example, can be used to generate a real time image of the environment, or a portion thereof. A user can input data, using a data input device of the user equipment, such as a touchscreen, stylus, keyboard and so on, representing one or more datum positions of the environment. In an example, considering an indoor room, a datum position can comprise the corner of the room. The user can proceed to enter or otherwise indicate multiple such corners of the room in question until enough data (in the form of datum positions) is provided to enable a three-dimensional representation of the room to be generated. For example, as the user equipment is generating a real time image of the environment using an imaging module, comprising a camera for example, and presenting the image to a user using a display, the user can move the user equipment in order to alter the displayed image of the environment. Accordingly, the user can move the user equipment to show part of the environment that comprises a corner, such as a corner at the bottom of the environment where the floor meets two walls. The user can use the user input device to mark or otherwise indicate the position of this corner.

[0014] The user can then move the user equipment to display another corner of the environment. As they do so, the user equipment can be configured to display a line originating from the previously marked corner to a target position on the display that represents a cursor for example, which the user can use to point at another corner of the environment, such as the next corner where the floor meets two walls. This can be repeated until the user has marked all the bottom- (or top- ) most corners of the room. When the target or cursor comes within close proximity to the first such marked datum position, the user equipment can‘snap’ the cursor to that position in order to complete a portion of the three-dimensional representation of the environment. For example, considering the bottom-most corners of a room, once the user has marked the first three and proceeds to move the user equipment around to show the first point again (which will complete part of the three-dimensional representation representing the floor), the cursor can automatically snap to the first point and cause a rectangle to be formed and displayed to the user indicating an initial representation of the floor of the room.

[0015] With this part of the three-dimensional representation of the environment complete, the user can then follow the same process with upper-most corners of the room. Initially, a line can be displayed stemming from the first (and also therefore the final) point representing the corner of the floor upwards towards the first corner at the ceiling of the room. As each such corner is marked, the user equipment can display a corresponding rectangle representing the surfaces or walls of the room in question, until the user returns to the first upper-most corner, at which point the cursor snaps into this position, in the same way as before, in order to provide an initial three-dimensional representation of the environment in question.

[0016] In an example, since the corners of the room may be obscured (e.g. by furniture and so on), the initial three-dimensional representation of the environment can be modified by the user in order to better represent the environment in question.

[0017] For example, the user can use a touchscreen of the user equipment to move the lines that are provided between the corners to modify the position of the corners. This can be easily done if at least some of the corners of the room between the floor and ceiling are visible and the user is therefore able to move a line representing such a corner into the correct position. That is, since the initial three-dimensional representation of the environment is provided as a line or box drawing overlaid on top of the real time image of the environment, the user can alter the position of the initial representation whilst having sight of the actual environment on the display that is being used to perform the modification.

[0018] According to an example, the user equipment includes a position sensor that enables the position and orientation of the user equipment relative to the environment to be determined. In this way, as the user equipment is moved (e.g. rotated, translated and so on), the position of the user equipment relative to a starting point can be determined, thereby enabling tracking with respect to the starting point. Accordingly, when the user indicates the first datum position within the environment, this can be used a starting point from which the relative position/orientation of the user equipment is determined so that it is possible to accurately define the datum positions with respect to the real time image of the environment.

[0019] A method according to an example effectively provides an augmented reality view of an environment in which the environment is overlaid with a schematic representation of the environment. That is, for example, the method enables a user to generate or draw a framework over the real time image that represents the environment.

[0020] According to an example, a thermal image representing a surface temperature at multiple points on respective ones of the surfaces of the environment within the three-dimensional representation is generated. For example, a thermal imaging module, such as a thermal camera for example, can be used to generate data representing temperature at multiple points. Each point may be a pixel on the display of the user equipment for example. Thus, the thermal imaging module can generate a data representing the temperature of the environment at multiple points, which can be displayed to the user on the display. As is typical, different temperatures can be represented using different displayed colours.

[0021 ] The thermal image of the environment can be obtained by scanning, translating or rotating the thermal imaging module around the environment in order to obtain temperature data. That is, similarly to the generation of a three- dimensional representation of the environment, the user equipment comprising the thermal imaging module can be used to capture image data of the environment by moving the user equipment in order to thermally image the environment. In an example, multiple thermal images can be stitched together using known image stitching techniques in order to provide an overall (e.g. 360 degree) thermal image of the environment.

[0022] In an example, the thermal image of the environment can be mapped to the three-dimensional representation of the environment. For example, using the position sensor of the user equipment, when generating the thermal image data, the position of the user equipment relative to the three-dimensional representation of the environment as the thermal image data is generated will be known. Accordingly, the thermal image data can be mapped to or overlaid to the three-dimensional representation of the environment, thereby providing a three- dimensional representation of the temperature of the environment at the time of capture which can be manipulated by the user to enable the provided view to of the temperature within the three-dimensional representation of the environment to be moved around, using a touchscreen of the user equipment for example.

[0023] In an example, the three-dimensional representation of the environment thus comprises multiple surfaces defining respective boundaries of the environment. Each of these surfaces can be provided with a corresponding visual representation of the thermal data for the surface.

[0024] Figure 1 is a schematic representation of a wall 100 of an environment according to an example. Figure 1 shows a cross section of a boundary of part of an environment, such as a room for example, that has an inside region 101 and an outside region 102, which may be classified as outside of the room in question but still inside a building, or outside to the open environment. The boundary, in this case a wall, comprises two air boundary layers 103. In an example, the thermal imaging module measures the temperature of the surface of the wall, Twall, from the inside. Tso is the outside wall surface temperature. The wall of figure 1 therefore represents a surface in an environment.

[0025] A method according to an example determines the total thermal transmittance of a wall from inside the building envelope by determining the heat flow across the inside air boundary layer using measured temperature values and the calculated coefficients of heat transfer based on the physics models of radiation and convective heat transfer. According to Eq. (1 ), below, the radiation interchange q _r between the inner wall surface and its surroundings and the convection heat transfer q _c at the surface element must be obtained:

[0026] Where Uw denotes the measured U-value of the wall [W/(m2K)]; q [W/m2] is the specific heat flux through the building envelope including the specific heat flux by radiation q _r [W/m2] and the specific heat flux by convection q _c [W/m2]; T _in is the air temperature near the target from inside the building [K]; T _out is the outdoor air temperature near the target [K]; and T _in ^_ T _out is the temperature difference between inside and outside the building [K]

[0027] Radiation Heat Transfer (qr):

[0028] Heat transfer through radiation takes place in the form of electromagnetic waves, mainly in the infrared region. The radiation energy per unit of time from a blackbody can be expressed with the Stefan-Boltzmann Law. During the cold season, the surroundings radiate energy to a cooler object, such as an inner wall surface, which leads to a net radiation heat loss rate (Eq. 2). [0029] In Eqn. 2, q _r represents the specific heat flux by radiation [W/m2]; eWALL is the emissivity coefficient of the object (0 < < 1 , depending on the type of material and the temperature of the surface); s is Stefan-Boltzmann’s constant with a value of 5.67 x 10 ^{- 8} [W/m ² K ⁴ ]; T _REF denotes the reflected ambient temperature

[K]; and T is the wall surface temperature from inside the building [K]

[0030] Convective Heat Transfer (qc):

[0031 ] The heat energy transferred between a surface and a moving fluid at different temperatures is known as convection. Considering natural convection and laminar flow, the heat transfer per unit surface through convection (Eq. (3)) is known as Newton’s Law of Cooling. In the same way as in heat transfer by radiation, the cooler object is the wall to be tested.

[0032] q _c belongs to specific heat flux by convection [W/m2]; h _c is the convective heat transfer coefficient [W/m2K]; T _in denotes the air temperature near the target from inside the building [K] and T _wall is the wall surface temperature from inside the building [K] To determine the convective heat transfer coefficient, the Nusselt number (Eq. (4)) can be used as follows: N _u = (h _c -L)/k (4)

[0033] As mentioned above, h _c is the convective heat transfer coefficient [W/m2K] N _u is the Nusselt number [dimensionless] and L refers to the height of the wall [m] seen from inside the building k is the thermal conductivity of the fluid. Taking into account that the fluid is air, k is equal to 0.025W/m Kfor a temperature between 20°C and 25°C. For a surface which consists of a vertical plate such as a wall, the expression that describes the Nusselt number is the following (Eq. 5a for laminar flow (Ra < 10 ¹⁰ ) and Eq. 5b for turbulent flow (Ra > 10 ¹⁰ ): N _u = ( 0.68 + 0.67 x R _a ^1/4 )/(1 + (0.492/P _r ) ^9/16)4/9 (5a)

N _u = ( 0.825 + 0.387 x R _a ^1/6 )/(1 + (0.492/P _r ) ^9/16 ) ^8/27 ) ² (5b)

Gr = (g.b.( T _IN - T _WALL )L ³ )/n ² (6)

R _a =G _r Pr = Pr.(g.b.(T _IN _ T _WALL )L ³ )/v ² (7)

[0034] Where R _a and Pr are the Rayleigh and Prandtl numbers respectively. The Prandtl number for air is considered to be 0.73 for an air temperature between 20°C and 25°C. The Rayleigh number (Eq.(7)), which is the product of Grashof (Eq. (6)) and Prandtl numbers, should be 10 ⁴ < R _a < 10 ⁹ for a laminar flow. It should be noted that all of these parameters are dimensionless g refers to gravity (9.8 (m/s2 ). b is the volumetric temperature expansion coefficient [1/K], where all fluid properties should be evaluated at the film temperatures, so b = 1/Tm where T _m = (T _IN +T _WALL )/2. V is the air viscosity with a value of 1.5 x 10 ^{- 5} m2/s for an air temperature between 20°C and 25°C. Replacing the known values, the Rayleigh number (R _a ) can be expressed as a function (Eq. (8)) that depends on the inner air temperature [K], the inner wall surface temperature [K] and the height of the wall L [m]:

R _a = 3 18 x 10 ^b0 x b x (T _IN - T _WALL ) x L ³ (8)

[0035] In an example, flow can be considered to be turbulent when Ra > 10 ⁹ . Accordingly, from (4) and (5b) above, the convective heat transfer coefficient for turbulent flow becomes:

h _c [W/(m ² . K)] = ( 0.825 + ((0.387 x R _a ^1/6 )/(1 + (0.492/P _r ) ^9/16 ) ^8/7 ) ) ² x k/L (9)

[0036] Taking into account the value of the Prandtl number, Eq. (9) can be simplified to Eq. 10b: h _c [W/(m ² K)] = ( 0.825 + 0 325 x R _a ^1/62 x k/L

10(b) /Ld for laminar flow using 5a this becomes: h _c [W/(m ² . K )] = ( 0.68 + 0.56 x R _a ^1/4 ) ² x k/L (10a)

[0037] The instantaneous measured heat flow per unit area [W/m ² ] is denoted as q and can be calculated by (for turbulent flow): q[W/m ² ] = ( 0.825 + 0.325 x R _a ^1/6 ) ² x k/L x (T _IN - T _WALL ) + (ϵ _WALL x s x (T _REF ⁴ - TWALL ⁴ )) (Eqn. 1 1 b) and for laminar flow: q[W /m ² ] = and = ( 0.68 + 0.56 x R _a ^1/4 ) ² x k/L x ( T _IN— T _WALL ) + (ϵ _WALL x s x (T _REF 4 - T _WALL ⁴ )) (1 1a)

[0038] The total heat loss (Q _w [W]) through a wall will be the sum of these qi for each IR pixel or virtual pixel times the area of the pixel (A) on the wall measured over the whole wall:

Qw[w] = i=1S ⁱ⁼ⁿ q _i -A _i (12)

[0039] The cost of this heat loss is then given by Eq. 13:

Cost = Q _w / 1000 x Price per kW (13)

[0040] The instantaneous measured U-value of the building wall [WI(m2.K)\ is denoted as U and can be calculated by Eq. (14):

[0041 ] The averaged U _w [W/(m2.K)] value over the whole wall is then given by Eq. 15:

[0042] The wall emissivity e _WALL can be measured by comparing the IR temperature of a blackbody closely attached to the wall surface and the temperature of the wall surface TBB (e.g. thin matt black piece of card or tape) and is given by Eq. 16: ϵ _WALL = T _B / T _WALL ( 16

[0043] According to an example, user equipment comprising a thermal imaging module can be used to capture and display a three-dimensional representation of the environment, such as a room. An augmented reality representation of the environment can be provided in which the user equipment can capture and overlay an IR thermography image of the surfaces (walls, ceiling, floor etc. as desired) Twaii onto the three-dimensional representation of the environment. In an example, the thermal imaging module can provide a temperature measurement at each IR pixel. In an example, the ambient inside temperature is measured using a blackbody radiator (e.g. black cardboard positioned inside the room (typically several cm from the wall surface), to provide T _in.

[0044] The incident radiant temperature on each wall is measured using the temperature from a heat reflective structure, such as a portion of crumpled silver foil square attached to the wall, to provide T _ref. Using a thermal imaging module, a complete model of the temperatures of all the surfaces in the room is obtained. In some cases, a virtual IR camera may be“positioned” on each point of the wall that is currently being measured and a sum across all the surfaces by their solid angle to the point is obtained. This method may be used to determine the total infra-red radiation at the point using imaging ray-tracing from the point on the wall to all the other surfaces. In this way, a more accurate measurement of T _ref may be obtained.

[0045] In some cases, the blackbody radiator can comprise a structure defining an interior region adapted to minimise heat loss between the blackbody radiator and a surface of the environment, e.g. a surface adjacent to the black body radiator. For example, in some cases, the interior of the black body radiator can comprise a heat reflective surface or a solid insulating block.

[0046] In an example, a black body radiator can comprise a box-like structure, a cylinder, a semi-cylinder or other shape with a low thermal mass. Such a structure provides a high emissivity surface to the front face of the structure that is separated from a surface (e.g. a wall) of the environment. In an example, the separation distance of the high emissivity surface from the surface of the environment is such that the air temperature gradient therebetween is levelled out to that of the ambient temperature of the environment in question.

[0047] The thermal imaging module can be configured to generate a IR thermography image from a plurality of frames. In an example, each frame comprises multiple points representing a surface temperature on a surface of the environment.

[0048] In some examples, the thermal imaging module exhibits an instability. In an example, the measurement of surface temperatures between successive frames can introduce an error. This error can become large when measurements are taken across a whole wall surface. Herein this error is referred to as inter- frame drift.

[0049] According to examples, inter-frame drift can be accounted for by determining an overlap of surface temperature measurements between successive frames. An offset can be determined and used to modify the IR thermography image on account of the inter-frame drift between successive frames. Modifying the IR thermography image in this way can ensure a constant calibration of surface temperature measurements is maintained.

[0050] In one example, the difference between temperatures at pixels in an overlap region of a first frame and second frame are determined. The average difference is calculated to generate an offset between the first and second frames. The output image is modified based on the average difference. In a second example, the thermal imaging module is arranged to determine a correlation of pixel temperature distributions of the first and second frames to generate an offset. The output image is modified based on the offset determined according to the correlation.

[0051 ] Methods described herein may be used to determine when an infrared thermal imaging camera is stable for performing more accurate temperature measurements. According to examples, in some thermal imaging devices, a calibrated temperature jumps significantly after a calibration event. This may be particularly large on the first couple of calibrations after turning a device on. In particular, in some cases, it takes more than one calibration cycles to get a stable calibration. [0052] According to examples described the calibration status of the thermal imaging device may be monitored. A survey of the accuracy of the thermal imaging device is performed after two or more calibration cycles have occured. In this way, the stability of the thermal imaging calibration may be improved.

[0053] In an example, the blackbody radiator and heat reflective structures can include machine-readable representations of data, such as matrix codes for example. The machine-readable representations of data can encode information about the blackbody radiator and heat reflective structures. For example, they can encode information about one or more of: position of the blackbody radiator and heat reflective structures, size, identification number (e.g. each blackbody radiator and heat reflective structure can have a unique identifier to enable it to be disambiguated from others).

[0054] In an example, as the environment is scanned using the imaging module of the user equipment, in order to generate the three-dimensional representation of the environment for example, the machine-readable representations of data can be scanned and the data encoded thereon can be determined.

[0055] In one example, the outside temperature of the surface T _out can be measured using the thermal imaging module of the user equipment or by using a thermocouple. In an example, wall emissivity can be measured by comparing the IR temperature T _BB of a black piece of card closely attached to the wall surface and the temperature Twaii of the wall surface according to Eq. 16. The heat flow through an air boundary layer can then be calculated for all the points on each wall using Eq. 12, and a total and an average Heat Flow per square meter obtained and displayed to a user. A value for the cost per Kw of heat energy can be used to display the cost of the heat going through the wall (Eq. 13). The averaged U value of the wall can also be calculated using Eq. 15 and displayed.

[0056] In a further example, a temperature sensor, such as a Bluetooth ^® temperature sensor is used to provide alternate temperature measurements of T _BB . The measurement of T _BB using either a thermocouple or Bluetooth ^® temperature sensor can be used to determine an offset in the measurement of the thermal imaging module. The offset can be applied to the measurements from the thermal imaging module to correct for an inaccuracy in the measurements produced by the thermal imaging module. [0057] Examples in the present disclosure can be provided as methods, systems or machine-readable instructions, such as any combination of software, hardware, firmware or the like. Such machine-readable instructions may be included on a computer readable storage medium (including but not limited to disc storage, CD-ROM, optical storage, etc.) having computer readable program codes therein or thereon.

[0058] The present disclosure is described with reference to flow charts and/or block diagrams of the method, devices and systems according to examples of the present disclosure. Although the flow diagrams described above show a specific order of execution, the order of execution may differ from that which is depicted. Blocks described in relation to one flow chart may be combined with those of another flow chart. In some examples, some blocks of the flow diagrams may not be necessary and/or additional blocks may be added. It shall be understood that each flow and/or block in the flow charts and/or block diagrams, as well as combinations of the flows and/or diagrams in the flow charts and/or block diagrams can be realized by machine readable instructions.

[0059] The machine-readable instructions may, for example, be executed by a general-purpose computer, a special purpose computer, an embedded processor or processors of other programmable data processing devices to realize the functions described in the description and diagrams. In particular, a processor or processing apparatus may execute the machine-readable instructions. Thus, modules of apparatus may be implemented by a processor executing machine readable instructions stored in a memory, or a processor operating in accordance with instructions embedded in logic circuitry. The term 'processor' is to be interpreted broadly to include a CPU, processing unit, ASIC, logic unit, or programmable gate set etc. The methods and modules may all be performed by a single processor or divided amongst several processors.

[0060] Such machine-readable instructions may also be stored in a computer readable storage that can guide the computer or other programmable data processing devices to operate in a specific mode.

[0061 ] For example, the instructions may be provided on a non-transitory computer readable storage medium encoded with instructions, executable by a processor. [0062] Figure 2 shows an example of a processor 150 associated with a memory 152. The memory 152 comprises computer readable instructions 154 which are executable by the processor 150. The instructions 154 comprise:

Instructions 156 to generate a three-dimensional representation of the environment, the representation comprising multiple surfaces defining respective boundaries of the environment;

Instruction 158 to generate a thermal image representing a surface temperature at multiple points on respective ones of the surfaces of the environment within the three-dimensional representation;

Instructions 162 to determine a measure for an ambient temperature within the environment; determine respective measures for incident radiant temperature of the surfaces; provide a measure of temperature outside of a surface; and

Instructions 164 to calculate, at each of the multiple points, a value for the instantaneous heat flow per unit area using the measures for surface temperature, ambient temperature within the environment and incident radiant temperature of the surfaces; and using the values for the instantaneous heat flow per unit area, and the measure of temperature outside of a surface, calculate respective measures for thermal transmittance at the multiple points.

[0063] Such machine-readable instructions may also be loaded onto a computer or other programmable data processing devices, so that the computer or other programmable data processing devices perform a series of operations to produce computer-implemented processing, thus the instructions executed on the computer or other programmable devices provide a operation for realizing functions specified by flow(s) in the flow charts and/or block(s) in the block diagrams.

[0064] Figure 3 is a screenshot of a portion of a room, according to an example. The screenshot of figure 3 shows measured U values (W/m ² K) and Heat flow (Q, in Watts) across a wall. The screenshot of figure is a screenshot of an image displayed to a user using user equipment, such as a smart phone for example.

[0065] As can be seen, a slider tool 301 is displayed/provided. The slider tool enables modification of a range of temperature values, which temperature values are to be excluded. That is, the slider tool can be used to exclude certain areas of an environment from consideration by way of modification of a range of considered temperature values.

[0066] The slider tool can be a passive visual representation or an active controller. For example, if the display upon which the slider tool is presented to a user is touch sensitive, the slider tool 301 can be manually adjusted on the display of the user equipment by a user. In the event that the slider tool is a passive representation, other means can be used to adjust

[0067] In an example, the slider tool enables a range of temperature values within an environment to be excluded. That is, the tool enables a user to quickly eliminate parts of a surface that they do not want to measure by setting minimum (303) and maximum (305) temperatures to use with the slide bar 301 , thus enabling a user to eliminate certain things in an environment such as radiators, sofas or windows and so on (e.g. with windows you are essentially looking at the outside temperature).

[0068] Accordingly, by adjusting the minimum (303) and maximum (305) temperatures with the slide bar 301 , a modified representation of the environment in question can be obtained. The modified representation of the environment can therefore include portions in which no U values and/or Heat flow is calculated and/or displayed. As depicted in figure 3, portions of the representation of the environment are simply greyed out areas, devoid of any information. An alternative is that the parts to be excluded are still displayed, but no calculations for those parts are performed, and/or they are displayed in the visible spectrum as opposed to the infra-red.

[0069] Thus, like heat sources (e g. radiators), obstructions (e.g. sofas) and IR transparent materials like glass (e.g. windows) can be excluded. Therefore, parts of a surface you do not want to measure can be eliminated or excluded by setting the minimum and maximum temperatures to use with the slide bar at the top of the screen.

[0070] In another example, it can be possible for a user to manually exclude certain regions of a surface by drawing around an object on a surface in the model to eliminate it from the calculations. In this connection, a touch screen of a smart device for example can be used to receive user input representing a bounding region for exclusion. The user could use their finger or a stylus and so on. [0071 ] Figure 4 is a screenshot of a portion 400 of an environment, according to an example. The screenshot in Figure 4, shows five box structures 410, which act as blackbody radiators with a high emissivity surface. The front faces of each box structure 410 are placed at a distance of approximately ten centimetres from the wall. At this distance the air temperature gradient is levelled out to that of the ambient temperature. The box structures 410 can be made out of a black cardboard or polypropylene sheet.

[0072] Figure 5 shows an interior region 500 of a box structure 510 similar to box structures 410 shown in Figure 4, according to an example. In the example shown in Figure 5, the interior 500 comprises reflective foil on the inner surfaces 520 to minimise radiative heat loss from the front surface of the structure 510 to the back surface when the box structure 510 is attached to a wall in the manner shown in Figure 4. In another example, the interior of the box structure 510 comprises solid polystyrene or foam.

[0073] As previously indicated measurement of the thermal behaviour of a building can also be performed using a heat flux meter (HFM) however this may take 72 hours or more and is inaccurate. If such a method is used the U value is an average U value where fluctuations due to external varying conditions are cancelled out. In contrast, if the methods described herein are used, the resultant U value measurements at any instant may differ significantly from the U value obtained from the HFM.

[0074] According to examples the methods described herein may also be used to determine an average U value where fluctuations due to external conditions are taken into account. In an example, a weighted or low pass filtered average of the history of the local external temperature over the last 24 to 48 hours leading up to an instantaneous measurement and an effective outside temperature T _ext-eff may be used in the calculation of the U-value according to Eq. 14 and 15.

[0075] According to an example, a weighted average of the external temperature may be determined as follows. An approximate value for the thermal time constant of a wall, based on information gathered about its age and construction, is used as a sigma, s of a standard distribution curve. The external temperatures are scaled by the normal distribution from 4s ago to the time a survey is carried out, with the peak of the distribution at 2s in the past. Such a weighting reflects the fact that the most recent external temperature fluctuations have little impact and the fluctuations in temperature from long ago will have decayed.

[0076] An internet weather service or a temperature sensor placed outside prior to the measurement may be used to record the external temperatures which can then be used according to the above to determine a value for T _ext-eff .

[0077] In further examples the methods and apparatus described herein may be used to determine how much forced convection is present in an environment. Forced convection may occur due to a hot fire or radiator on another wall or a large panoramic window transparent to infrared on an opposite wall of the environment. This allows a determination of the accuracy of Q and U value measurements based on whether there is likely to have been forced convection present in an environment. In another case, a model that incorporates the effects of forced convection in measurement of Q and U values may be obtained.

[0078] The teachings herein may be implemented in the form of a computer software product, the computer software product being stored in a storage medium and comprising a plurality of instructions for making a computer device implement the methods recited in the examples of the present disclosure.

[0079] While the method, apparatus and related aspects have been described with reference to certain examples, various modifications, changes, omissions, and substitutions can be made without departing from the spirit of the present disclosure. In particular, a feature or block from one example may be combined with or substituted by a feature/block of another example.

[0080] In an example, automatic collection and tagging of location for surveys can be provided using device location services. This can be extended to include automatic inference and logging of outside conditions from e g. internet weather services at the location in question.

[0081 ] In an example, multiple scans of the same room or surface can be taken or performed at different times and/or in different conditions. Corresponding surfaces within those scans can be identified and a report on the differences in temperature, heat flow, and U-value between those scans can be generated. In an example, a mechanism which allows repeated scanning of a room to be carried out without user intervention can be provided, using (e.g.) a mechanised pan/tilt head on a tripod. [0082] The word "comprising" does not exclude the presence of elements other than those listed in a claim, "a" or "an" does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the claims.

[0083] The features of any dependent claim may be combined with the features of any of the independent claims or other dependent claims.