Risk of Using Capillary Active Interior Insulation in a Cold Climate

Round 1

Reviewer 1 Report

The subject of the paper is interesting and its purpose complies with the journal’s aims and scope. The manuscript requires minor modification to be suitable for publication in Energies journal.

In greater detail the following should be corrected/added:

1. The abstract is too weak, it did not demonstrate a good brief about this study.
2. Introduction. The introduction is also very generalized. For example Line 41-42 Many different combinations of original wall and materials of a capillary active interior insulation have been investigated numerically [2, 4-7] and experimentally [2,3,7-11] - Describe exactly what kind of materials and walls systems. What the authors mean saying that numerically and experimentally?
3. Materials and Methods. Line 76-78 Each wall consists of the very same 12 cm thick layer of historic normal format bricks (from now on called the original wall) on a cold side - The authors must clarify what kind of bricks were used, dimensions? Line 87-88 Figure 1. The test walls consist of different internal thermal insulation on the hot side and brick 
   wall (original wall) on the cold side. Units are in cm - The units of measurement of the dimensions should be indicated in the figure. Line 106-107 Thus, they provide us with the information of the surface contact temperatures, namely Tin on the warm side of the insulation, and Tout on the cold side of the original wall, i. e. in the refrigerator. Line 99-100 The air temperature and relative humidity (RH) in the laboratory RHin and the refrigerator RHout. - Write correctly like in Line 122 The contact temperatures T_in, T_out, relative humidity R_Hin, RH_out. Line 90 For the simulation of the cold conditions - It is necessary to indicate the temperature. Line 99 The air temperature and relative humidity - Specify temperature and humidity.
4. Experimental section. The authors mentioned that: Line 131 the period of 8 days for three different interior insulations - The authors must clarify why the investigation was 8 days. Line 185 Table 1. The expected thermal conductivities (Literature ?) and the measured ones (Experimental) - How to understand (Literature ?) ? 
5. Discussion. Formulas (1), (2), (3) and (4) must be attached to the methodological part. 
    
   
   
   
   
   
   
   

Author Response

We are thankful to the Reviewer for a positive evaluation of our manuscript and constructive comments, as addressing these has resulted in significant further improvements of the manuscript.

We have tried to follow the comments/suggestions as much as possible. In particular:

1. The abstract is too weak, it did not demonstrate a good brief about this study.

We have tried to emphasize our results and the main message of the manuscript, i. e. the interior insulation without the vapour barrier is not suitable in cold climate, as much as possible. However, the limitation of the abstract’s length, prevent us to considerable change the abstract. The changes are denoted in the new version of the manuscript as “track changes” and new version is copied here:

 

Retrofitting for energy efficiency of cultural heritage buildings often require internal thermal insulation of external walls. Most of the in-situ studies of capillary active interior insulation were performed in mild oceanic climate regions and they showed an excellent performance. However, as a large part of Central-eastern Europe belongs to a continental climate with cold winters and long periods of temperatures below the freezing temperature, the applicability of the capillary active interior insulation in cold climate was studied. The hydrothermal behaviour of the three walls were determined, each consists of one of three different interior insulations and the original wall made of historic regular solid bricks. Two interior thermal insulations were capillary active (aerated cellular concrete, calcium silicate) and one vapour-tight (glass foam). A hot box – cold box experiment and a steady-state model were used to demonstrate an increase of the original wall mass due to the water condensation only when the capillary active interior insulation is used. The combination of the water condensation and the low sub zero temperature may lead to a risk of freeze-thaw damage to the original wall. The numerical simulation of the water vapour condensation for the considered walls for the Slovenian town Bled with sub-zero average winter temperatures was performed to obtain the whole temperature and moisture profile. It is shown good agreement between experimentally and numerically obtained amount of water condensation. The capillary active interior insulation proved to be unsuitable for improving the thermal insulation of buildings in cold continental climate and only a vapour-tight system can be recommended.

 

 

 

2. The introduction is also very generalized. For example Line 41-42 Many different combinations of original wall and materialsof a capillary active interior insulation have been investigated numerically [2, 4-7] and experimentally [2,3,7-11] - Describe exactly what kind of materials and walls systems. What the authors mean saying that numerically and experimentally?

 

We added few examples of insulation materials used in the literature, while the original wall was usually a brick wall. With numerically and experimentally we meant numerical simulations and laboratory or in-situ experiments. In order to clarify these points, we change the sentence to:

 

Many different combinations of original brick wall and materials of a capillary active interior insulation (for example calcium silicate, aerated concrete, polyurethane board with capillary active channels) have been investigated by numerical simulations [2, 4-7] or/and in situ or laboratory experiments [2,3,7-11].

3. Materials and Methods. Line 76-78 Each wall consists of the very same 12 cm thick layer of historic normal format bricks(from now on called the original wall) on a cold side - The authors must clarify what kind of bricks were used, dimensions?

 

We added the dimensions of the bricks. We also changed the term “normal format bricks” to a “regular solid bricks”.  This term is common English expression for the type of the bricks that we used and denotes the solid brick made of fired clay. The dimensions of the brick are 25 cm x 12 cm x 6.5 cm. In order to clarify this, we added a reference ([13] = Klun, M.; Antolinc, D.; Bosiljkov, V. Out-of-Plane Experimental Study of Strengthening Slender Non-Structural Masonry Walls. Applied Sciences 2021, 11, 9098), where the whole article was dedicated to the partition masonry walls made of regular solid brickwork and we used the same type of bricks in the present study.

Each wall consists of the very same 12 cm thick layer of historic regular solid bricks [13] of the size 25 cm ´ 12 cm ´ 6.5 cm (from now on called the original wall) on a cold side.

 

 

4. Line 87-88 Figure 1. The test walls consist of different internal thermal insulation on the hot side and brick wall (original wall) on the cold side. Units are in cm- The units of measurement of the dimensions should be indicated in the figure.

Units are now indicated in Figure 1.

 

5. Line 106-107 Thus, they provide us with the information of the surface contact temperatures, namely Tinon the warm side of the insulation, and Tout on the cold side of the original wall, i. e. in the refrigerator. Line 99-100 The air temperature and relative humidity (RH) in the laboratory RHin and the refrigerator RHout. - Write correctly like in Line 122 The contact temperatures T_in, T_out, relative humidity R_Hin, RH_out. Line 90 

We have to apology for the typographical errors and thank to the reviewer for noticing them. We changed the fonts into subscripts.

6. For the simulation of the cold conditions- It is necessary to indicate the temperature.

 

This temperature (-1.5 deg C) has already been indicated in the Experimental Results section. The temperature is added in Materials and Methods section:

 

For the simulation of the cold conditions (“cold box”), a refrigerator is used where temperature stabilizes at approximately -1.5 ^oC.

 

7. Line 99 The air temperatureand relative humidity - Specify temperature and humidity.

 

The air temperature and relative humidity are added in the sentence.

 

The air temperature (between 18 ^oC and 22 ^oC) and relative humidity (RH, ~ 60 %) in the laboratory RH_in and the refrigerator RH_out are measured with VOLTCRAFT DL-121TH Multi-channel data logger (Figure 3).

 

8. Experimental section. The authors mentioned that: Line 131 the period of 8 daysfor three different interior insulations - The authors must clarify why the investigation was 8 days.

 

The period of 8 days was chosen as a compromise between

• reaching the steady-state conditions (approximately 24 hours) and collecting enough amount of the condensed water in the brick wall to be accurately measured after re-assembling the wall on the one hand, and
• not waiting too long for the results and starting the measurements with new configuration.

 

We have to mention that in addition to the described experiments we also test the set-up with a often used mineral wall as an insulation with and without the water barrier.

 

We added the explanation of the 8 days investigation at the first occurrence (Materials and Methods, line 129) as follows:

 

The period of 8 days was long enough for accurate determination of mass difference.

 

9. Line 185 Table 1. The expected thermal conductivities (Literature ?) and the measured ones (Experimental) - How to understand (Literature ?) ? 

 

We have to apology for this typographical error and thank to the reviewer for noticing it. It should be “lambda”. We corrected the error.

 

 

10. Formulas (1), (2), (3) and (4) must be attached to the methodological part.

 

Formulas (1), (2), (3) and (4) are moved to the Materials and Methods part.

Reviewer 2 Report

The paper presents the applicability of capillary active system on the historic masonries. Several sentences are not referenced. Thus, they seem not correctly supported by the literature review. For example you wrote: “In many cases, e.g. in cultural heritage buildings where façade needs to be kept unaffected, interior insulation is the only possible solution for reducing heating and/or cooling costs and increasing indoor temperature comfort”. It is not the only possibile, but it is the one suggested by public authorities and with low constrains. Similar, you wrote “Usually, vapour-tight interior insulation (e.g. mineral wool and vapour barrier) is used to prevent the original wall from an unacceptable increase of moisture content”. This is true for middle European climate. There are some applications without vapor barrier. For example the European research Project Hello! Consider the use of Rockwool without vapor barrier (see https://hellomscaproject.eu/category/publications/). The construction of the masonry mus be documented more. It is not a historic wall. Why you select this configuration? What are the specificities to be similar to a historic wall? And the differences? In the experimental research describe the standard you used. Is a standard test or not? The application of the header method is too much easy. What are the specificities of its application in historic walls? The innovative aspects of your research are not documented. Similar, the gap in literature is not considered.

Author Response

The paper presents the applicability of capillary active system on the historic masonries.

We would like to thank the Reviewer for positive and constructive comments.

1) Several sentences are not referenced. Thus, they seem not correctly supported by the literature review. For example you wrote: “In many cases, e.g. in cultural heritage buildings where façade needs to be kept unaffected, interior insulation is the only possible solution for reducing heating and/or cooling costs and increasing indoor temperature comfort”. It is not the only possibile, but it is the one suggested by public authorities and with low constrains. Similar, you wrote “Usually, vapour-tight interior insulation (e.g. mineral wool and vapour barrier) is used to prevent the original wall from an unacceptable increase of moisture content”. This is true for middle European climate. There are some applications without vapor barrier. For example the European research Project Hello! Consider the use of Rockwool without vapor barrier (see https://hellomscaproject.eu/category/publications/).

We would like to thank to the the Reviewer for pointing us to the project Hello. We added some already used references from the previous version of the manuscript and one new reference ([2] =  Andreotti, M.; Bottino-Leone, D.; Calzolari, M.; Davoli, P. Applied Research of the Hygrothermal Behaviour of an Internally Insulated Historic Wall without Vapour Barrier: In Situ Measurements and Dynamic Simulations. Energies 2020, 13, 3362) to the suggested sentences. Corrections can be seen as »track changes« in the new version of the manuscript and are copied here:

In many cases, e.g. in cultural heritage buildings where façade needs to be kept unaffected due to the legislation, interior insulation is the only possible solution for reducing heating and/or cooling costs and increasing indoor temperature comfort [1]. The drawback of this solution is a substantial change of temperature and moisture conditions inside the original wall. There are some applications without vapour barrier in mild climate regions [2]. However, in middle European climate, usually a vapour-tight interior insulation (e.g. mineral wool and vapour barrier) is used to prevent the original wall from an unacceptable increase of moisture content [3].

2) The construction of the masonry mus be documented more. It is not a historic wall. Why you select this configuration? What are the specificities to be similar to a historic wall? And the differences?

The historic regular solid bricks were widely used in Slovenia and Central Europe in the 19^th and 20^th centuries (ex Austro-Hugarian), varying only slightly in the size with time. This is the reason we choose to study such a wall. We removed the term historic wall from the paper and described the bricks in more details and reference added:

Each wall consists of the very same 12 cm thick layer of historic regular solid bricks [13] (Klun, M.; Antolinc, D.; Bosiljkov, V. Out-of-Plane Experimental Study of Strengthening Slender Non-Structural Masonry Walls. Applied Sciences 2021, 11, 9098) of the size 25 cm ´ 12 cm ´ 6.5 cm (from now on called the original wall) on a cold side.

Additionally, the thickness of the gable wall in the second floor of cultural heritage buildings in Slovenia and Central Europe is usually 12 cm obtained with a regular solid bricks.  The chosen configuration for testing (5 cm of insulation and 12 cm of brick wall) reflects a very common situation that can be found in many old buildings in Central Europe with a single layer of solid bricks and a moderate thickness of inner insulation. We want to emphasize that the same temperature and moisture profile in the steady-state conditions (with all the described problems with condensation and freezing) is reached when the widths of insulation and solid brick wall are both increased for the same factor.  

3) In the experimental research describe the standard you used. Is a standard test or not? The application of the header method is too much easy.

The experimental set up is not a standard test. As we have no environmental chamber with two sections we used in-house-made set-up.  For the simulation of the cold conditions, a refrigerator is used where temperature stabilizes at approximately -1.5 ^oC, while on the other side of the experimental wall a laboratory conditions (room temperature and RH of approximately 60 %, both precisely monitored) are used. The results (temperature and RH time dependences, Figure 4) show that with such experimental configuration a steady-state conditions can be reached. A quite good correspondence between the experimental and calculated mass of condensed water is additional confirmation of adequately prepared experimental set-up.

4) What are the specificities of its application in historic walls? The innovative aspects of your research are not documented. Similar, the gap in literature is not considered.

The walls made of historic regular solid bricks were chosen because many old buildings in Central Europe with such walls are still in use and their energy consumption needs to be improved. Recently, capillary active interior insulation, is quite often promoted in literature and by practitioners. Only few studies evaluating capillary active interior insulation in cold climate with no obvious conclusions, can be found in literature. As a large part of Central-eastern Europe belongs to a continental climate with cold winters and long periods of temperatures below the freezing temperature we decided to study the applicability of the capillary active interior insulation in cold climate. Our experimental set-up enables us to dismount the insulation from the original wall after the experiment. Due to this original set-up we are able to determine the mass of condensed water in insulation and original wall separately.  Our main conclusions that the water condensates mainly in the original wall and that the capillary active interior insulation is not suitable in cold continental climate are important for scientific community as well for practitioners.

In order to emphasize our original experimental set-up and the main conclusion, we slightly modified the abstract:

Retrofitting for energy efficiency of cultural heritage buildings often require internal thermal insulation of external walls. Most of the in-situ studies of capillary active interior insulation were performed in mild oceanic climate regions and they showed an excellent performance. However, as a large part of Central-eastern Europe belongs to a continental climate with cold winters and long periods of temperatures below the freezing temperature, the applicability of the capillary active interior insulation in cold climate was studied. The hydrothermal behaviour of the three walls were determined, each consists of one of three different interior insulations and the original wall made of historic regular solid bricks. Two interior thermal insulations were capillary active (aerated cellular concrete, calcium silicate) and one vapour-tight (glass foam). A hot box – cold box experiment and a steady-state model were used to demonstrate an increase of the original wall mass due to the water condensation only when the capillary active interior insulation is used. The combination of the water condensation and the low sub zero temperature may lead to a risk of freeze-thaw damage to the original wall. The numerical simulation of the water vapour condensation for the considered walls for the Slovenian town Bled with sub-zero average winter temperatures was performed to obtain the whole temperature and moisture profile. It is shown good agreement between experimentally and numerically obtained amount of water condensation. The capillary active interior insulation proved to be unsuitable for improving the thermal insulation of buildings in cold continental climate and only a vapour-tight system can be recommended.

Round 2

Reviewer 2 Report

Thanks for considering my suggestions