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

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    The causes of air movement in hidden indoor micro-environments: measurements in historic bookshelvesCrossref
    Paper would benefit from more comprehensive analysis and inclusion of wall temperatures
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    The causes of air movement in hidden indoor micro-environments: measurements in historic bookshelves

    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. The National Trust, for example, has used these mechanisms to encourage air movement behind books as a possible strategy to reduce the risk of mould growth. It is believed that including ventilation holes as a passive design solution to promote airflow within micro-environments could prevent decay from occurring in archives of historic buildings. This paper investigates the mechanisms that cause airflow behind bookshelves using field measurements in three National Trust historical libraries. The measurements indicate that small but measurable velocities, up to 4 cm/s, can be generated passively behind bookshelves. Air movement in such confined micro-environments is caused by a combination of natural convection, caused by temperature differences between the interior and the exterior of the bookshelf(stack effect), and forced convection due to drafts in the surrounding environment. While in some cases one mechanism prevailed, both mechanisms may be present simultaneously in most cases. Finally, this paper proposes that air movement as a result of the stack effect in these micro-environments can be predicted with a simple mathematical model, which offers a good fit with the experimental data in the cases where temperature differences promote air motion.
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      Review information

      10.14293/S2199-1006.1.SOR-ENG.ALCSN1.v1.RUELYY
      This work has been published open access under Creative Commons Attribution License CC BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Conditions, terms of use and publishing policy can be found at www.scienceopen.com.

      Engineering,Architecture
      Preventive conservation,Historic buildings,Built environment,Micro-environment,Air movement,Mould
      ScienceOpen disciplines:
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      Review text

      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.

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