Thermovision as a non – destructive method of technical condition assessment: case study in a smart building

Currently, more and more emphasis is placed on building energy-efficient buildings from the highest quality materials to keep heat and energy losses as low as possible. Relatively, such buildings are much more expensive than traditional buildings due to the technology that is used in them. This applies to HVAC systems, renewable energy sources and etc. This paper presents the correctness of the thermal insulation of the Energis intelligent building at the Kielce University of Technology with the use of a thermal imaging camera. Measurements and photos were taken outside and inside the building, in the winter, in the late afternoon. This research topic was undertaken because few works and articles offer thermal imaging studies of smart buildings. The analysis of the thermograms showed differences between the surface of the windows and the walls from the inside, and additionally a place in the room in which you can see how cold is trying to penetrate the interior. The study provided data on thermal insulation of the tested building, its assessment and correctness of execution.


Introduction
Non -destructive methods of measurements are an important tool for diagnostics and assessment of various elements in many areas of engineering and technology.In particular thermal imaging seems to be of considerable significance due to low cost and ease of use.This technique can be applied for machinery parts' assessment such as drum brakes [1], heat exchangers testing [2 -5] as well as building applications.In this case thermal bridges can be detected and analysed.Thermal bridges significantly affect the thermal conductivity of external partitions.They also contribute to building defects, such as mold formation, insulation defects and heat loss.
Aghasizadeh et al. [6] focused on assessing the impact of two thermal bridges for reinforced concrete and steel balconies.In their research, 33 different variants of balcony connections were made.In this way, they assessed the linear thermal transmittance of the tested elements and the influence of the temperature coefficient on the external surfaces.More and more often, research on the consumption of thermal energy in buildings is carried out.The use of good thermal insulation is the main aspect of saving thermal energy.On the other hand, other authors [7] performed a study of thermal bridges at the interface between window insulation.Two analyses were performed in the study to determine the thermal conductivity, numerical 2D and 3D.The results showed that the 3D numerical model is more accurate than the 2D model for assessing losses due to thermal bridges.Bergero et al. [8] performed a study on the correction of thermal bridges using a two-dimensional model.The research was carried out in order to check the average values of the heat transfer coefficient.Research on thermal bridges for energy-efficient buildings was also carried out by Cerneckiene et.al. [9].
The topic of air quality parameters, thermal comfort and energy consumption is still an interesting issue, which is linked with proper thermal insulation of buildings.Cakyova et al. [10] in their research focused on the analysis of carbon dioxide concentration in Tseri passive houses in Cyprus and the reduction of CO2 concentration.The authors showed that the maximum air-tightness of room partitions should be 0.6 air changes per hour.The authors also conducted research in passive houses [11].The study focused mainly on the assessment of thermal bridges and thermal properties of exterior wall materials.Misiopecki at al. [12] described the most favourable position of the windows in terms of reducing the effect of thermal bridges.Five wall structures and two windows were tested.The results showed that the positioning of the windows influences the amount of energy loss through thermal bridges.The article [13] discusses the assessment of the sustainable built environment and the progress in the sustainable energy industry.On the other hand, another author [14] carried out research on the modernized building using a thermal imaging camera.The results showed, among other things, a lot of irregularities resulting from inadequate thermal insulation of the balcony tides.
The application of infrared systems for the performance of thermal insulation has been successfully done by the authors [15] and other researchers [16] from Kielce University of Technology.During those tests proper settings of the thermal imaging systems have been determined.
The aim of the paper is to conduct a study on the assessment of the technical condition of the sustainable, smart and modern building "Energis" located in the Western part of the campus of Kielce University of Technology using a thermal imaging camera.The paper uses the existing methodology to assess the physical condition of thermal insulation of a smart building in Poland.Such thorough studies conducted in Polish climate conditions, on smart buildings erected according to Polish building regulations, national common practices at the building sites and know-how were not found in literature.Moreover, measurement peculiarities and errors are also discussed in the paper as well as the possibility of using thermovision for thermal resistance and heat flux determination.

Selected measurement peculiarities and errors
Thermovision is currently a very common method of temperature determination.It bacame quite cheap and accassible to ordinary users.However, the knowledge of the errors and measurement limitations is quite limited.Conequently, many operators of the thermal systems might not produce correct results of thermal maps that they generate during the measurements.
In order to generate proper temperature readings a lot of parameters need to be input into the camera (or the software).These parameters typically include: emissivity of the observed object, temperature of the air, temperature of the surrounding elements, relative humidity and distance between the camera and the observed object.Proper determination of these parameters enables to obtain correct temperature readings during the tests.However, the most important parameter that requires particular attention is the emissivity value.It ranges from 0 to 1 and should typically be determined with the help of contact temperature measurement systems.Naturally, emissivity of various substances (surfaces) can be found it textbooks, but it is recommended to make individual measurements of the observed element (e.g.concrete wall), because there might be significant differences between the literature data of emissivity and real measurement results.
An example of the importance of proper setting of the emissivity value has been presented in Figure 1.Two cases have been considered: measurements inside of the "Energis" building (with the air and surroundings' temperature of 20 o C, relative humidity of 40%, distance between the wall and the camera of 15 m) and outside (with the air and surroundings' temperature of 5 o C, relative humidity of 80%, distance between the wall and the camera of 100 m).The temperature readings from the infrared system have been obtained for difference values of emissivity -ranging from 0.51 to 0.99 (the correct value was 0.95).As can been seen the improper values of emissivity lead to significant errors in temperature determination -of a few degrees in the analysed range of emissivity changes.What is worth noticing is that in the case of the measurements taken inside the building, the temperature readings decrease with increasing emissivity (from about 31 o C to about 26 o C).The opposite is true when the measurements are taken outside (at a long distance from the building, at low temperatures and high relative humidity values).In this case the temperature readings obtained with an infrared camera increase as emissivity rises.

Infrared measurements of building elements
Thermovision uses the detection of infrared radiation emitted by every object (naturally, the object's temperature should be above zero Kelvin).The generated thermal map carries a lot of information and data regarding the condition of the surface which undergoes observation.However, care is needed when thermal images are analyzed.This is related not only to the proper determination of input parameters (as presented in section 2), but also to the various phenomena that can affect the readings and lead to misinterpretation of the thermal maps (such as radiation reflection on smooth surfaces, absorption by water vapour and carbon dioxide).Therefore, a thermal analysis of the Energis intelligent building inside and outside during the winter period was undertaken and discussed.The building was completed in 2012 and has a total floor area of 6289 m 2 and cubature of 21211 m 3 , while the U-value of the external wall amounts to 0.17 W/m 2 K.The construction material of the external walls was a 25 cm ceramic hollow brick.There are 2 underground and 5 aboveground storeys.The building is equipped with mechanical ventilation with cooling and heat recovery.All the building services are controlled by the Building Management System (BMS).
Accurate emissivity values were introduced into the measuring device, so as to obtain reliable thermal images (of proper temperature values).The entire Energis building has been presented in Figure 2 -as infrared and digital images.Comparing the two thermal images, it can be seen that the building is well insulated.In spite of the fact that it was built about 10 years ago, no defects in its thermal insulation could be detected.There are no thermal bridges, and thus energy losses are not increased.Below in Figure 3 there are photos of the interior of the selected classroom from the inside (room number 3.15 on the third floor).Basing on Figure 2 and analyzing the data from Figure 3, it is confirmed that the building has been properly insulated without generating heat and energy losses.No colder spots can occur between the windows, while cooler spots are above the windows closer to the ceiling (Fig. 3 a).This place can be a place where cold air wants to penetrate inside the hall.Figure 4 shows room 3.15 from the outside.When analyzing the above thermovision image, no construction shortcomings were noticed between the surfaces of the examined windows.Referring to Figure 3, the proper insulation performance of this building is confirmed.However, to further confirm this belief, a photo of the corridor was taken, showing the heat flow in the underfloor heating and a huge window on both sides of the corridor being tested, as shown in Figure 5. Here, it is also worth noting that thermovision cameras could detect any leakage from the underfloor heating, but here there are no defects of the heating system.Corridor's thermograph with underfloor heating.Figure 5 shows the arrangement of heating pipes used for underfloor heating.However, attention should be paid to the huge window with a very large surface.The temperature between it and the wall is significantly different from each other.The reason for such a difference may be the emissivity of each of these elements and the fact that the wall has a much greater thermal resistance than the window.When someone comes close to the window they usually feel cool there, and warmth from the wall.
As seen in Figure 5 thermal imaging can be used for the analysis of the heating systems within the building.In case of any defects (for example in the underfloor heating), the leakage can be easily detected.Figure 6 presents the images (both infrared and digital ones) of the radiator located in a lecture room on the first floor of the "Energis" building.The thermovision technology also enables to determine the hot air movement patterns from the radiators and/or other sources as can be observed in Figure 6a.The general and common application of thermovision as a building diagnostic tool is the early detection of thermal bridges and other defect sites.However, it can also be used to help assess thermal resistance of walls (if it is unknown) as well as heat flux dissipated to the surroundings.It can be done through a determination of surface temperature with an infrared camera supported by additional measurements of air temperature with traditional thermometers.Simple heat transfer equations involving thermal conduction (according to the Fourier's law) through walls of known thickness and thermal conductivity value as well as convection on both sides of the walls (according to the Newton's law) can help determine the unknown parameters.
As mentioned earlier in section 2, there are various sources of errors that can influence the readings.Figure 6b illustrates the phenomenon of reflection of thermal radiation emitted from the hot radiators and reflected from a shiny floor and received by the thermovision camera.The floor seems to be hot, but it is just an illusion.This phenomenon should also be taken into account when performing thermovision tests.
Another issue, which is of significant importance, is the influence of thermal performance of walls' thermal insulation on thermal comfort of room users in the buildings.It is mostly related to radiation heat transfer losses from people to the surroundings.The problem of thermal comfort analysis has been considered by the authors (e.g.[17][18]) and might be analysed in the future in conjunction with the thermovision measurements.

Summary and conclusions
The following conclusions can be drawn based on data and studies presented in the paper: x The correct temperature readings with the use of thermovision cameras require proper emissivity values.Otherwise, errors of a few degrees Celcius might occur.x Possible reflection phenomena should also be considered when analysing the obtained infrared data.
x Thermal imaging studies carried out on a smart building belonging to the Kielce University of Technology proved proper technical condition of the thermal insulation.x Infrared measurements can be effective in the assessment of thermal resistance of walls (if it is unknown) as well as heat flux dissipated to the surroundings in winter.x Thermal imaging tests can be an additional source of information, especially for designers to take into account the location of windows and the selection of an appropriate building material.

Figure 1 .
Figure 1.The temperature readings on the inside and outside walls of the Energis building for various emissivity values (winter conditions).

Figure 2 .
Figure 2. Thermal images of Energis: (a) front facade, (b) rear facade.Comparing the two thermal images, it can be seen that the building is well insulated.In spite of the fact that it was built about 10 years ago, no defects in its thermal insulation could be detected.There are no thermal bridges, and thus energy losses are not increased.Below in Figure3there are photos of the interior of the selected classroom from the inside (room number 3.15 on the third floor).

Figure 3 .
Figure 3. Classroom 3.15 in the Energis building, from the inside.

Figure 4 .
Figure 4. Classroom 3.15 from the outside of the building.

Figure 5 .
Figure 5. Corridor's thermograph with underfloor heating.Figure5shows the arrangement of heating pipes used for underfloor heating.However, attention should be paid to the huge window with a very large surface.The temperature between it and the wall is significantly different from each other.The reason for such a difference may be the emissivity of each of these elements and the fact that the wall has a much greater thermal resistance than the window.When someone comes close to the window they usually feel cool there, and warmth from the wall.As seen in Figure5thermal imaging can be used for the analysis of the heating systems within the building.In case of any defects (for example in the underfloor heating), the leakage can be easily detected.Figure6presents the images (both infrared and digital ones) of the radiator located in a lecture room on the first floor of the "Energis" building.The thermovision technology also enables to determine the hot air movement patterns from the radiators and/or other sources as can be observed in Figure6a.

Figure 6 .
Figure 6.Thermal imaging of the heating system elements in a lecture room in Energis.