*2.3. Measurements Method*

For investigating and monitoring the drying process, a dedicated data acquisition system was developed. The schematics of the system are presented in Figure 6. The main element of the system was the programmable logic controller (PLC) controller (XV 303 by Eaton Industries GmbH) equipped with a 10" screen. The PLC controller collected data from all sensors, saved them on the internal memory and allowed for remote contact via LTE GSM modem. The following sensors were used by the data acquisition system:


The whole system and sensors were checked for possible interaction. Test measurements were carried out for each sensor working separately and for all sensors working together. During these tests, the drying device was turned off and on. The only detected possible interference problem was between TDR probes. However, measurements applying these sensors were carried out in sequence, so the interferences were eliminated.

*Energies* **2020**, *13*, x FOR PEER REVIEW 9 of 13

*Energies* **2020**, *13*, x FOR PEER REVIEW 9 of 13

**Figure 6.** Schematics of the data acquisition system. **Figure 6.** Schematics of the data acquisition system. between TDR probes. However, measurements applying these sensors were carried out in sequence,

#### The whole system and sensors were checked for possible interaction. Test measurements were **3. Results and Discussion**

so the interferences were eliminated.

carried out for each sensor working separately and for all sensors working together. During these tests, the drying device was turned off and on. The only detected possible interference problem was between TDR probes. However, measurements applying these sensors were carried out in sequence, so the interferences were eliminated. **3. Results and Discussion**  The drying process using the drying device and data acquisition and control system described above was carried out in the basement of the considered building. The renovation works were conducted in August 2020. In this paper, only the results of in situ monitoring of the process for one 5-m-long part of the external masonry wall are presented. The wall had a thickness of 80 cm and a structure shown in Figure 3b. For the other masonry walls, similar behavior was observed. The process begun without heating, with fans switched on and set at the second speed. This stage lasted The drying process using the drying device and data acquisition and control system described above was carried out in the basement of the considered building. The renovation works were conducted in August 2020. In this paper, only the results of in situ monitoring of the process for one 5-m-long part of the external masonry wall are presented. The wall had a thickness of 80 cm and a structure shown in Figure 3b. For the other masonry walls, similar behavior was observed. The process begun without heating, with fans switched on and set at the second speed. This stage lasted 24 h and was characterized by quite stable air temperatures, presented in Figure 7a. The slight decrease of the absolute air humidity shown in Figure 7b was a combined effect of moisture gained from the wet wall and moisture captured by the dehumidifier. In the first stage of drying, moisture was removed mainly from the surface of the wall as well as surfaces of drillings and their surroundings. The temperature drop of the wall seen in Figure 8a in the first hours was connected to achieving the local saturation temperature of the wall. **3. Results and Discussion**  The drying process using the drying device and data acquisition and control system described above was carried out in the basement of the considered building. The renovation works were conducted in August 2020. In this paper, only the results of in situ monitoring of the process for one 5-m-long part of the external masonry wall are presented. The wall had a thickness of 80 cm and a structure shown in Figure 3b. For the other masonry walls, similar behavior was observed. The process begun without heating, with fans switched on and set at the second speed. This stage lasted 24 h and was characterized by quite stable air temperatures, presented in Figure 7a. The slight decrease of the absolute air humidity shown in Figure 7b was a combined effect of moisture gained from the wet wall and moisture captured by the dehumidifier. In the first stage of drying, moisture was removed mainly from the surface of the wall as well as surfaces of drillings and their surroundings. The temperature drop of the wall seen in Figure 8a in the first hours was connected to achieving the local saturation temperature of the wall.

24 h and was characterized by quite stable air temperatures, presented in Figure 7a. The slight

**Figure 7.** Air parameters during the drying process. (**a**) Temperature, (**b**) absolute humidity. **Figure 7.** Air parameters during the drying process. (**a**) Temperature, (**b**) absolute humidity.

The second period of drying started after 24 h when heating was turned on and the fan was operated without changes. This affected both the air and wall temperature, which started to increase—see Figures 7a and 8a. Differences between temperature variations for different points shown in Figure 8a resulted from different distances from sensors to heating holes and differences in the wall structure—it was very difficult to precisely drill the holes for probes and sensors. The highest temperature observed for point T2 in Figure 8a was a result of an accidental connection during the drilling of slots for the drying probe and temperature sensor. This sensor showed a temperature that was very close to the temperature of the heating probe. As the process progressed, the wall temperature stabilized. Differences in the behavior of moisture content in the wall, presented in Figure 8b, were connected to the variation in the local content of the water in the wall as well as with the material which surrounded the slots. The TDRs 3–5 were in locations surrounded by a much higher amount of mortar than TDR 1, 2 and 6, which were in locations surrounded by ceramic brick. In the first stage of drying, the reduction of moisture content was rapid even without heating; after 24 h, additional heating was necessary to maintain the drying rate. Finally, after 144 h of drying, TDR probes 1–6 indicated a moisture content inside the wall of 2%, 3.6%, 4.8%, 5.9%, 3.4% and 3% vol., respectively. shown in Figure 8a resulted from different distances from sensors to heating holes and differences in the wall structure—it was very difficult to precisely drill the holes for probes and sensors. The highest temperature observed for point T2 in Figure 8a was a result of an accidental connection during the drilling of slots for the drying probe and temperature sensor. This sensor showed a temperature that was very close to the temperature of the heating probe. As the process progressed, the wall temperature stabilized. Differences in the behavior of moisture content in the wall, presented in Figure 8b, were connected to the variation in the local content of the water in the wall as well as with the material which surrounded the slots. The TDRs 3–5 were in locations surrounded by a much higher amount of mortar than TDR 1, 2 and 6, which were in locations surrounded by ceramic brick. In the first stage of drying, the reduction of moisture content was rapid even without heating; after 24 h, additional heating was necessary to maintain the drying rate. Finally, after 144 h of drying, TDR probes 1–6 indicated a moisture content inside the wall of 2%, 3.6%, 4.8%, 5.9%, 3.4% and 3% vol., respectively.

*Energies* **2020**, *13*, x FOR PEER REVIEW 10 of 13

increase—see Figures 7a and 8a. Differences between temperature variations for different points

The second period of drying started after 24 h when heating was turned on and the fan was

**Figure 8.** Wet wall parameters. (**a**) Temperature and (**b**) volumetric moisture content. **Figure 8.** Wet wall parameters. (**a**) Temperature and (**b**) volumetric moisture content.

Figure 9 presents the results of the infrared image of the surrounding of two heating slots for the end of the drying process. The surface temperature of the wall between the heating probes oscillated around approximately 43 °C, while the surface temperature close to the heating probes reached approximately 53 °C. The thermogram clearly shows the drying and heating area, which was a strip of approximately 12 cm width. Figure 9 presents the results of the infrared image of the surrounding of two heating slots for the end of the drying process. The surface temperature of the wall between the heating probes oscillated around approximately 43 ◦C, while the surface temperature close to the heating probes reached approximately 53 ◦C. The thermogram clearly shows the drying and heating area, which was a strip of approximately 12 cm width. *Energies* **2020**, *13*, x FOR PEER REVIEW 11 of 13

**Figure 9.** Thermogram of two drying probes and their surrounding at end of drying process. **Figure 9.** Thermogram of two drying probes and their surrounding at end of drying process.

new parameter, i.e., the specific energy consumption, was introduced to express the relation between the energy consumption and the amount of moisture removed from the wall. The specific energy consumption during the drying process was defined as the energy consumption divided by the mean volumetric moisture content (MC) difference between the initial and final state in the wall and by the length of the dried wall section. For the considered wall, it was equal to 11.08 kWh/MC%/m. This value is considered as satisfactory. The reactive power consume by the device was capacitive, which was due to the installed DC power supplies. When heaters were turned on, the power factor was high, so the device did not need reactive power compensation. Detailed energy parameters measured

**Table 1.** Energy parameters during the drying process.

Specific energy consumption kWh/MC%/m 11.08 Mean moisture content reduction % vol. (% wt.) 3.77 (2.35) Energy consumption kWh 208.6

Mean active power without heaters W 241 Mean apparent power without heaters VA 405 Mean reactive power without heaters VAr −325 Mean power factor without heaters - 0.595 Mean active power with heaters W 1 688 Mean apparent power with heaters VA 1 725 Mean reactive power with heaters VAr −356 Mean power factor with heaters - 0.978

During the six days of the drying process, the moisture content of the wall decreased to a value allowing for effective infiltration of the wall by the hydrophobic silicone micro-emulsion, i.e., to a mean level of 3.76% vol. (2.35% wt.). The increased temperature of the wall not only facilitated moisture removal but also had a positive effect on the impregnation process, i.e., high wall

**Parameter Unit Value** 

during the drying process are shown in Table 1.

During the 6 days of the drying process, the drying device consumed 208.6 kWh of energy with

During the 6 days of the drying process, the drying device consumed 208.6 kWh of energy with a mean active power of 241 W and 1688 W for the drying stage without and with heaters, respectively. At the same time, a 3.77% vol. moisture content reduction was observed on average in the wall. The new parameter, i.e., the specific energy consumption, was introduced to express the relation between the energy consumption and the amount of moisture removed from the wall. The specific energy consumption during the drying process was defined as the energy consumption divided by the mean volumetric moisture content (MC) difference between the initial and final state in the wall and by the length of the dried wall section. For the considered wall, it was equal to 11.08 kWh/MC%/m. This value is considered as satisfactory. The reactive power consume by the device was capacitive, which was due to the installed DC power supplies. When heaters were turned on, the power factor was high, so the device did not need reactive power compensation. Detailed energy parameters measured during the drying process are shown in Table 1.


**Table 1.** Energy parameters during the drying process.

During the six days of the drying process, the moisture content of the wall decreased to a value allowing for effective infiltration of the wall by the hydrophobic silicone micro-emulsion, i.e., to a mean level of 3.76% vol. (2.35% wt.). The increased temperature of the wall not only facilitated moisture removal but also had a positive effect on the impregnation process, i.e., high wall temperature decreased the viscosity of the micro-emulsion, which encouraged its depth infiltration and generation of waterproof membrane.
