In order to understand the implications of natural ventilation design strategies on how the building typologies function, three case studies have been investigated.
The selected buildings are all within the temperate maritime climatic zone, in the UK and Ireland and purposefully not within the known heat island of London (which is arguably an exception to the temperate maritime climate zone). Thus ventilation strategies are climatically appropriate and comparable, responding too, to similar local building regulations and regulatory bodies. Each building was completed in the last twenty years and has also been operational for at least a decade. The case
studies, therefore, have had the time to go through periods of calibration and recalibration of their ventilation strategies and operational systems. They have had some level of post occupancy study (see individual case studies) undertaken which may have led to the recalibration of systems or the confirmation of design intent predictions.
The selected case study buildings each are used by the public and demonstrate a variety of ventilation demands and a range of different strategy responses.
Through studying these three buildings in the context of other naturally ventilated examples, we can assess appropriate strategy responses for generic building
ventilation loads and through this understand the appropriate architectural response.
The building typologies were selected to represent differing occupancy loads; the occupation density of the buildings determines the ventilation load that is required both for thermal comfort and for good IAQ. These typologies present differing
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ventilation requirements: firstly offices, a typology with a relatively low ventilation load from occupation levels of an average of one workspace per 10.9sqm (British Council for Offices 2013); secondly, auditoria with conversely a high ventilation load from occupation levels of circa 1sqm per person; and thirdly a library with a medium ventilation load and occupation levels of circa 3sqm per person and a deep plan spatial layout (both figures from the Metric Handbook 2002).
In addition to the different typologies each building type exhibits a different architectural response to its ventilation strategy: the Auditorium is vented through thermal buoyancy and extract stacks; the Office building utilises a combination of cross ventilation and thermal buoyancy; the Library uses stack ventilation in a deep plan building - an Advanced Natural Ventilation (ANV) strategy.
3.3 Methodology
The Case study typically is used to research a topic using set procedures, often with different combinations of data collection. This form uses triangulation
techniques gathering three sources of varied evidence. The advantage of this form of research is that it allows the researcher to evaluate three different sources of
information to test a particular concept on the basis that a consensus on findings will yield more robust results (Proverbs D., Gameson R. 2008). This form of research uses mixed mode (quantitative and qualitative data) comprising of a combination of research techniques including interviews, reviews of documents and observations where the intention is to achieve a convergence of findings.
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The methodology for the case study research involves the gathering of basic building data as part of desk top research study based on a framework developed by CIBSE and Hegger M. et al (2008) and modified to suit the relevance of the three case study buildings:
• Site data – location, urban/rural/ suburban
• Human Data – client, use, design team.
• Climate data – cooling days, diurnal range, prevalent wind directions
• Building data – plan, section, shape, surface to volume, size, structure, thermal mass
• Envelope data –glazing levels, solar shading.
• Ventilation data – strategy, type, inlet outlet design
• Operational Control system utilised
Firstly, the ventilation issue is defined for each building type and case studies are initially referenced against energy bench marks of standard air-conditioned building and natural ventilation equivalents, against thermal comfort benchmarks and against internal air quality (IAQ) bench marked data. Utilising available data an assessment is made under the headings of Energy use, IAQ and Thermal Comfort. A schematic is drawn of how the ventilation system functions in the differing modes.
Secondly, field research was conducted with visits to the Case Study buildings.
These were used to investigate issues of detail in the above data against the four qualifiers of Energy use, Thermal Comfort provision, Internal Air Quality and Ease of Operation. The latter in particular relied on interviews with the building facilities
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managers to discuss the building’s performance. A follow up questionnaire, designed for the building managers, was used to pick up or clarify any outstanding issues. These qualitative interviews (Haigh R. 2008) were used as an open ended exchange focused on a particular topic using both structured and unstructured techniques. The interview was guided by a specific set of themes and questions which were utilised as the basis for each case study. These themes and questions centred on the direct experience of the building facilities manager with the operation of the ventilation system in providing comfort and good internal air quality. Their usefulness was partly for validation of the case study literature review but more significantly in providing an insider’s guide to the daily and seasonal issues surrounding the management of the internal environment of the building.
Thirdly, in order to define the architectural vocabulary of ventilation for each of the three building types, research was undertaken into the design strategies of the architects involved. This research was through a review of publications of the architect’s work; including a recently published series of essays authored by one of the architects. In addition an interview was conducted with the other of the two architects; this also used structured and unstructured techniques.
The literature review assisted in establishing an inventory of the architecture of natural ventilation and corroboration for findings from the case studies has been sought through the examination of published buildings that relate closely to the chosen case study themes. Conclusions are then drawn in regard to how architectural design in both form and details were combined to achieve the required performance
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levels - defined by the categories of Energy, IAQ and Thermal comfort and ease of Operation.
Building type: Auditorium Library Offices
Occupant density: 1 sqm per person 3 sqm per person 10.9 sqm per person
Ventilation load: high medium low
Spatial challenge: Single enclosed volume Deep plan layout Shallow plan with atrium
Table 5: Case study selection criteria
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