**4. Results**

#### *4.1. Surface Thermal Resistances on Both Sides of Tested Walls*

In the case of the computational method, the surface thermal resistances *Rsi* and *Rse* for the tested building enclosure should be assumed in accordance with Table 1. While the value of 0.13 m2K/W assumed as surface resistance, *Rsi*, on the warm chamber side did not raise any doubts, the authors had doubts regarding the value of *Rse* to be assumed on the cold chamber side. By assumption, this chamber mimics the external environment, but it was found that the air movement velocity measured there was several times lower (see the next paragraph) than the one assumed in ISO 6946 (*ν<sup>e</sup>* = 4 m/s) for the given *Rse* values. Therefore, for further analyses on the cold chamber side, *Rsi* = 0.13 m2K/W was assumed as for a horizontal heat flow, but for a space within the building envelope (e.g., for an unheated space).

During one of the measurement sessions in the climate chambers, in which air temperatures θ<sup>i</sup> = +20 ◦C and θ<sup>e</sup> = −10 ◦C were maintained in respectively the warm chamber and the cold chamber, the air movement velocities measured by the anemometers on average amounted to:


Assuming that no surface temperature could be measured in this case (no surface temperature sensor is available), the mean thermodynamic temperatures of the two surfaces in Formulas (14) and (15) were set as the air temperatures in climate chambers, so Tmi = 293.15 K and Tme = 263.15 K. After that, the above air velocities were introduced into Formulas (12) and (13) and the surface thermal resistances were calculated from Formulas (10) and (11). Then, during measurements of the heat flux density and the air and surface temperatures for each tested wall, the actual surface resistances on both sides of the enclosure were determined from Formulas (16) and (17). All of the *Rsi* and *Rse* values are presented in Table 3. The clear differences between the calculated surface resistances and the measured ones are due to the measurement conditions that differed from the real building enclosure service conditions. Additionally, the specific way in which air with set temperature is blown into climate chambers (different chamber designs), how closely the temperature sensors adhere to the analyzed wall surface and the heat flux density contribute to the differences.


**Table 3.** Surface thermal resistances of tested partitions depending on method of determining them.

#### *4.2. Air Temperatures in Chambers and Wall Surface Temperatures*

4.2.1. Measurements with Thermocouples

Diagrams of the internal (warm) surface temperature and external (cold) surface temperature of the walls measured with thermocouples and air temperatures in the warm chamber and in the cold chamber during the measurements are shown in Figure 4 for the walls without insulation and in Figure 5 for the insulated walls.

From the start of the test (switching on the chambers), the temperature values began to approach the target temperature settings, i.e., θ<sup>i</sup> = +20 ◦C and θ<sup>e</sup> = −10 ◦C. The temperature values given below are the average of the temperatures in the 72 h time window (marked with a double-headed arrow in the diagrams) selected from the period of stabilized temperatures. In the case of wall A (Figure 4a), one can notice that the time in which the planned temperature settings were reached amounted to about 24 h, whereby the surface temperatures also stabilized. The latter on average was θsi = +17.8 ◦C and θse = −6.8 ◦C. In the case of wall B (Figure 4b), the time in which the planned temperature settings were reached was similar (about 36 h), but the surface temperatures stabilized after about 96 h from the start, ranging on average to θsi = +10.7 ◦C and θse = −0.6 ◦C. In the case of wall C (Figure 4c), the time in which the planned settings were reached amounted to about 36 h and the surface temperatures stabilized after 90 h, on average amounting to θsi = +9.7 ◦C and θse = +0.4 ◦C. Then, the walls above were insulated with expanded polystyrene and tested again in the climate chambers. The temperature diagrams for insulated wall A are shown in Figure 5a. In this case, the time in which the planned temperature settings were reached was much shorter, slightly more than 6 h. The surface temperatures stabilized after less than 24 h, but probably due to the fact that the door to the warm chamber had been accidentally left open there are visible fluctuations in air temperature in the third 24 h of measurements. Therefore, it was decided to average the temperatures measured from the 72nd hour onwards, whereby θsi = +19.5 ◦C and θse = −7.8 ◦C were obtained. The temperature diagrams for insulated wall B are shown in Figure 5b. In this case, the time to reach the planned temperature settings was disturbed by the abnormal operation of the cold chamber, in which the temperature stabilized as late as after 48 h. The surface temperatures averaged from the 84th hour onwards amounted to θsi = +18.3 ◦C and θse = −8.1 ◦C. In the case of insulated wall C (Figure 5c), the time in which the planned temperature settings were reached was slightly longer, amounting to about 12 h. The surface temperatures stabilized relatively quickly (after less than 24 h), but for averaging purposes, the measurements from the 84th hour onwards were taken, whereby θsi = +18.8 ◦C and θse = −7.5 ◦C were obtained.

**Figure 4.** Air temperatures and temperatures of two surfaces of tested walls in their uninsulated version: (**a**) wall A made of aerated concrete, (**b**) wall B made of solid ceramic bricks, (**c**) wall C made of concrete blocks.

**Figure 5.** Air temperatures and temperatures of two surfaces of tested building partitions in their insulated version: (**a**) wall A made of aerated concrete, (**b**) wall B made of solid ceramic bricks, (**c**) wall C made of concrete blocks.

#### 4.2.2. Thermograms of Tested Walls

While the walls were tested in the climate chambers, they were also observed by means of an infrared camera, which recorded data at certain intervals (usually at every 10 min) during the measurement period. The selected thermograms in Figure 6 show temperature field distributions in the period of stabilized temperatures (72 h period shown in Figures 4 and 5) for the analyzed walls in their uninsulated version (Figure 6a,c,e) and insulated version (Figure 6b,d,f). Table 4 contains measured values for points SP01, SP02 and SP03, and area AR01 for all three randomly chosen thermograms.

On the thermograms basis it can be, in addition, concluded that:



**Table 4.** Air and surface temperatures for tested walls by means of infrared camera measurements for all three randomly selected thermograms.
