|Reference: Article on ventilation opening area technology|
"3 EXISTING TERMINOLOGY
Table 1 details terms used to describe the areas of PPOs [purpose provided ventilation openings] in a number of international and national documents relevant to the design of natural ventilation systems. Here, user guidance for well-known software tools is included because they are an integral part of the design process.
The table shows that there are matters of uncertainty regarding term definitions, contradictions, and deviations. Firstly, terms are used without definition in several guideline documents (CIBSE, 2002; 2005; 2007; 2015; AIC, 1981), software guidance (Walton & Dols, 2014; DoE, 2015a,b), text books (Hensen & Lamberts, 2011; Mumovic & Santamouris, 2009; Oughton & Wilson, 2015), and national standards (BSI, 1991). Here the reader must interpret the term using their own domain knowledge or a companion document. The latter approach can be problematic because some documents give different definitions of the same terms; for example, ASHRAE (2013) defines the term effective area using Equation (2) whereas CIBSE (2005) uses Equation (4). It is interesting to note that CIBSE (2005) introduces uncertainty into its definition (see Table 1) thus asserting that other definitions may exist. One national standard (BSI, 1991) defines the term equivalent area but also uses the undefined term effective equivalent area. This is potentially confusing, especially if one is aware of differing definitions of effective and equivalent areas; see Section 2.
Further divergence in terms occurs in documents pertaining to non-standard PPOs such as smoke ventilators. For example, the statutory document B2 (ADB2) (H.M. Government, 2010b) uses the term aerodynamic free area to describe an area based on the length ݀d2 (shown in Figure 3) and is the same as the definition of free area given by Equation (1). ADB2 also states that an aerodynamic free area can be “declared […] in accordance [with] BS EN 12101-2”. However, EN 12101-2 (BSI, 2003a) defines aerodynamic free area as the “product of the geometric area multiplied by the coefficient of discharge”, which is the same as the definition of effective area described by Equation (2). EN 12101-2 also uses the term geometric area whose definition is equivalent to that of the free area described by Equation (1). Similarly, AIVC GU03 (Liddament, 1996) uses the terms cross sectional and openable area in place of the free area described by Equation (1). These are all direct contradictions that only serve to confuse the reader and lead to engineering failures.
These examples demonstrate the importance of clear terminology; for example, it is possible that the term aerodynamic, used by ADB2 and EN 12101-2, is unhelpful because it is not clear why a particular area is more or less aerodynamic than any other. They also highlight the importance of defining a term before it is used. The statutory Approved Document F (H.M. Government, 2010a) gives clear definitions of free and equivalent areas (and other key terms in a glossary) that agree with the European standard EN 12792 (BSI, 2003b). The text book Ventilation of Buildings (Awbi, 2003) includes a glossary of the terms free and equivalent areas at the beginning of its chapter on air diffusion devices that agree with those given in Equations (1) and (2), respectively. Accordingly, any error in their application is solely the responsibility of the reader."
Benjamin Jones et al., "A review of ventilation opening area terminology" (Energy and Buildings · March 2016), pp. 7-8
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| Charles Davis|
Works in field
Native speaker of: English
PRO pts in category: 32