The causes of air movement in hidden indoor micro-environments: measurements in historic bookshelves

1. At the abstract, it has been stated that "the use of ventilation holes in small micro-environments has been proposed as a mechanism to improve the environmental conditions of moisture and temperature within bookshelves". However, this has not been discussed on the results nor on the conclusions.

2. The stack effect is a natural thermodynamic phenomena, but how this related to the improvement of the "moisture excess" that you would like to partially eliminate? This would be a valuable research statement for your research.

3. Please refer as indoor/ outdoor environmental conditions. Indoor air relative humidity or indoor air pressure, etc.

4. Are you interested on the air motion to then determine an effective way to estimate a mass air flow rate (to dilute the presence of excessive moisture) depending on the air psychrometric conditions? In this case, is your contribution aimed to complement the current understanding on temperature and humidity modelling simulations?

5. Please explain why have you selected those heights for the anemometers locations. What is the rationale behind? It should be clear at the introduction of section 2.1.

6. Improve the quality of Figure 3. The data lines are difficult to see.

7. Please refers as air pressure in your hypothesis stated in Section 3.2.

8. Is it possible that air leakage on the window's frame could affect air speed together with some of the indoor/ outdoor openings in the buildings? If yes, can this be introduced in your methodology or for further research?

The paper analyses data from continuous monitoring of air temperature, relative humidity, and velocity behind books in bookshelves and in the space in front of the shelves at three locations.

The driving forces behind air movements behind the books are seen as the result of differences in air temperatures influencing air density and the activities in the buildings housing the historic bookshelves including movements by visitors, renovation works and opening of doors.

The paper presents a simple model assumed to predict air velocities that is demonstrated to have some prediction capability but lacks precision and inclusion of important parameters such as surface temperatures of walls behind bookshelves and more precise information about openings between space and hidden environments.

The analysis would benefit from more precise modelling of boundary layers and buoyancy taken from more comprehensive fluid dynamic and heat transfer theory. The analysis would also benefit from more precise modeling of wall surface temperatures and information about outdoor temperatures during measurements.

Mold will normally start growing in the range 70-75 %RH. Absolute humidity measured as water weight per weight of dry air will without sinks and sources be constant in air flows being heated and cooled. Analyses of water content based on temperature and relative humidity would also be relevant in the available data. Moisture content of the cold exterior walls could be at equilibrium with somewhat higher relative humidity than measured in the air and be at higher risk of mold growth.

My thinking is that increased air flows behind the books in bookshelves may not be sufficient to prevent mold growth on cold outer walls but may increase the temperature of the books and their margin to mold formation.

Paper would benefit from more precise modeling of air flows, assessment of wall temperatures and inclusion of absolute humidity in the analysis.

Wall temperatures could be approximated by knowledge of outdoor temperatures and properties of the walls. This information needs to be included. The intended more comprehensive analysis could be included in the present paper to increase relevance and credibility.