Loomans, M.G.L.C., Melhado, M.D.A., Zoon, W.A.C. & Hensen, J.L.M. (2007). Performance based building and its application to the operating theatre. In Meinhold, U. & Petzhold, H. (Eds.), Proceedings of the 12th Symposium for Building Physics, 19-31 March 2007, pp. 681-688, paper-1237. Dresden: Technische Universität Dresden.
Performance Based Building and its application to the operating theatre Loomans, M.1, Melhado, M.1, Zoon, W.1,2, Hensen, J.1 1. Eindhoven University of Technology, Eindhoven, The Netherlands. 2. Deerns, Rijswijk, The Netherlands
[email protected]
Abstract (150 words)
1. Introduction The basic concept of Performance Based Building (PBB) and its methodology already have been described in 1982 in the CIB-Report 64 [1]. It summarizes into: - The performance approach is thinking and working in terms of ends rather than means. - Performance is concerned with what a building or building product is required to do and not with prescribing how it is to be constructed. - A design solution, traditional or novel, will always need a quantitative base for testing and evaluation of its performance. Despite this straightforward definition the actual practical application has shown to be more difficult. In order to apply it to its full extent, objective assessment methods should be available. They should be valid for application in the design phase, but should also allow for performance assessment in the use phase. Furthermore, applicability should not be limited to current solutions, but also allow for the assessment of innovative designs. The complexity of such an assessment increases when multiple parameters should be dealt with in the assessment. Of course, this is generally the case. Building simulation tools can play an important role in the further development of this approach and have done so already in the past [2]. Correct performance of buildings in use has generally been an underestimated topic. Focusing on the indoor environment, e.g., post-occupancy evaluation studies until now have found relatively little feed back to new designs. Nevertheless, major concerns about for example the indoor environment are well known. A more rigorously applied performance based approach might give a contribution to arrive at more healthy living environments. An area where the performance of the indoor environment is very important is the operating theatre. This environment, amongst others, searches for an optimum between air quality, with respect to minimizing the risk of surgical site infections, and, e.g., the thermal comfort for the operating personnel, with respect to their working conditions. The assessment of the indoor air quality in operating theatres has gained specific attention in recent years (e.g. [3]). In this paper the above described performance based approach is defined and clarified further and translated into a practical approach. As an example the performance approach is applied to the operating theatre, more specifically the indoor environment of the operating theatre. A methodology has been developed for performing such an assessment. This will be described, together with an example of the application of the CFD technique for this assessment. Such an application is in line with the above PB approach. A critical analysis is planned to bring the
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current approach more close to practical reality. This is where PBB and the development and application of simulation tools come together.
2. Performance Based Building (PBB) The performance approach in relation to the indoor environment has been developed further within the EU 5th FW Thematic Network PeBBu. A definition of performance is context based. With respect to buildings, examples of contexts are the stakeholder, the building phase or a building object. E.g., with respect to the stakeholder, the user will have very different performance requirements than the contractor. The user wants to live comfortably in the building, whereas the contractor is interested in the performance of individual building objects to obey to the design plan. In the end of course everyone is interested in the total performance, in the building process this is not necessarily the case. This also means that PBB does not end with the completion of the building. Performance during the building life is considered just as important. Performance therefore is also a function of time. With PBB the initiator does not have to deal with the indoor air temperature or the insulation thickness. He just can identify that he would like it to be comfortable under given specific conditions and/or that he wants the building to be energy efficient and healthy. In the design process then however translation rules are required to convert this subjective information into objective design rules and to define evaluation procedures. Translation and evaluation procedures are found in, e.g. legislation, rules of thumb and more sophisticated tools as modeling and case/knowledge based reasoning. The above described definition of performance in the building process has been visualized in Figure 1. The figure was adapted from Huovila and Leinonen [4] and originates from illustrations by the Dutch Government Building Agency. The total figure was developed and agreed on during two workshops that have been organized within the context of PeBBu [5].
Figure. 1: Visualization of the Performance Based Building approach.
Given the number of performance definitions and the different contexts that can be found, it is difficult to keep track on all the building performance information that is available. This also accounts for all the translation rules that can be derived. Therefore a system should be developed that allows a logical structuring of all the information related to performance based building, but also may improve the applicability of the PBB-approach. Obviously we are looking for a
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framework in which we can fit the PBB-approach and the available information in a logical and unambiguous way. Several parameters should be incorporated in the framework. The most important parameter is the performance requirements that are set by the stakeholders. Furthermore, the point of time in the building process will determine the type of requirements that are set. This will be closely related to the building phases that can be identified. Finally, the actual building performance is of interest. This parameter has a close relation with the building objects. Interrelations between the building phase and the type of stakeholder are obvious, as is the case for building objects and building phase. Each specific performance criterion therefore can be related to the individual contexts. By presenting these contexts on axes in a three-dimensional format a matrix is developed that facilitates the performance-based matrix. This approach has been derived from the work of Mallory-Hill [6] and can also be found, though in a different context, in Foliente et al. [7]. The framework is visualized in Figure 2.
Figure 2: Performance based matrix.
The matrix approach encompasses all the performance requirements that relate to a specific building phase or stakeholder. It may also relate to a specific environmental attribute X or Y that is addressed differently (i.e. different target values and evaluation methods) at different points in the building process. This definition and the develop matrix, both with a focus on the indoor environment, was derived from literature study and review of (inter-)national research. Important input was provided for by experts from over 20 countries worldwide. Within the context of the PeBBu Network, they participated in four specially organized international workshops on the topic. The definition and matrix have been taken as the point-of-departure to develop a performance based approach for the optimal design of the indoor environment of operating theatres. It starts from the stakeholders to derive the various performance requirements. From there it arrives at performance criteria and target values with respect to e.g. the air quality, temperature, etc. An important contribution of this ongoing project will be the development of objective evaluation procedures of the performance and the applicability of simulation tools in these procedures. In the next paragraph this approach is described.
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3. Operating theatre 3.1 Ventilation of operating theatres Many countries encounter high surgical site infection (SSI) rates in their hospitals. Besides economical effects, such infections can have major impact on the health and recovery of the patient. The incidence of SSI depends on many variables, including the type of surgery performed and the type of ventilation system. The air is one of the transfer routes for microbiological contamination, therefore high performance requirements are set with respect to the ventilation system applied. Besides, the ventilation system in an operating theatre affects, e.g., the thermal comfort of the personnel, hypothermia of the patient, drying out of the wound, etc. Nevertheless, there is no general objective procedure to assess whether a chosen ventilation system performs optimal to all these parameters. In general investment costs and minimum prescribed system specifications will determine the eventually chosen design solution. In the Netherlands (so-called) laminar downflow systems are regarded as the minimum required type of ventilation system installed in a (newly built) operating theatre. Specifications for such systems are generally limited to some experience and experimental based information on the minimum required downflow velocity and temperature difference between supply and exhaust. The here developed approach for a performance based assessment should give the design of the ventilation approach and its related HVAC systems for operating theatres a more objective basis and therewith also better tools to assess the functioning of the system in practice. An important function is to minimize the possibility of SSI.
3.2. Building evaluation domain model Performance evaluation of the ventilation system of operating theatres has a basis in the general performance based definition as described above. As we furthermore are interested in the use of simulation tools for such an assessment focus is put on the design phase, taking into account that a design assessment only makes sense when verification by measurement can take place in the use phase (i.e. definition PBB). Referring to the matrix in Figure 2 attention therefore is on one slice of the matrix. A further subdivision is required to focus the problem. Here the Building Evaluation Domain Model (BEDM) as developed by Mallory-Hill and Rutten [6] is applied (see Figure 3). This model also can be visualized as a three dimensional matrix. The three axes in this case refer to ‘Human Systems’, ‘Building Systems’ and ‘Architectural Scale’. A subdivision is provided for each axis. The Human System level focuses on the stakeholders ranging from the individual occupants to the global community and the performance specifications that are set by them. Naturally, the individual occupant is most interested in the basic performance value. For the global community, e.g., the ecological value is more important. The Building System is subdivided in several levels that relate to the number of changes that may occur during the building life time. Finally, the Architectural System has levels that subdivide the level of detail for decision making.
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Figure 3: Building Evaluation Domain Model [6].
The BEDM encompasses the whole building. For the assessment of the ventilation system in an operating theatre, only parts of the model are of interest. Figure 3 indicates the parts of the model that at first instance will be taken into account. Again one can see that the attention is focused to one slice of the matrix. For example, for the Architectural Scale, the operating theatre is divided in workstations, workplace and floor area. The workstations now are defined as the zones of the patient, surgeon and auxiliary nurse, and supporting staff including the anesthesiologist. The workplace encompasses the total environment of the operating theatre, while the floor area includes also the hallways, antechamber, storage and other adjacent areas that are directly connected to the operating theatre. For the Human System in principle all levels may be included with respect to the operating theatre. Focus, naturally, is on the individual, group and owner level. The individual refers to the individual persons in the operating theatre and the group to the surgical team as a whole. The next step is to identify for each point in the model the performance requirements that can be set. Figure 4 presents a part of the result that has been developed. One can notice the axes of the BEDM. Now for each point performance requirements have been identified and performance indicators have been related to these requirements. For this development literature study, in combination with expert interviews and information from attending surgical operations, has been used. The list of requirements and indicators is quite large, nevertheless, several indicators overlap. Furthermore, only those indicators that have an evaluation possibility in the design (simulation) and use (measurement) phase are regarded, in order to adhere to the performance based approach.
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Figure 4. Part of the filled in BEDM focusing on the ventilation system in operating theatres.
Following the identification of the performance indicators, as shown in Figure 4, next assessment procedures have to be developed. Again, focusing on the design phase, the application of simulation tools is assumed a prerequisite. These tools can range from conceptual to explicit and focusing on the energy use, air flow, moisture or integral simulation tools. The central point is to use the right tool at the right moment, e.g. [8]. The assessment procedure may support this decision process.
4. Example assessment procedure An example assessment procedure that was derived for the assessment of the air quality in operating theatres has recently become available [9]. In this study a performance based assessment procedure was developed to allow testing of innovative ventilation design solutions for operating theatres. In the design stage the Computational Fluid Dynamics (CFD) technique was applied to evaluate the ventilation design. Evaluation was based on a performance requirement for the air quality, i.e. the contamination level above the operating and instrument tables should be lower than 10 CFU/m3 (ultraclean). Boundary conditions for the contamination sources have been proposed. Given the fact that the air flow in an operating theatre is highly influenced by the persons and equipment in the room, also agreement was required on these, normally less well addressed, parameters. Figure 5 shows CFD results for two cases of a design, i.e. the original and improved one. The assessment procedure allowed for the verification that the original design was not sufficient to adhere to the performance requirement. After design changes the improvement was confirmed.
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Figure 5. Example result of the developed assessment protocol for the air quality in the operating area and instrument tables.
5. Discussion The paper describes a very wide topic. It presents the steps that need to be taken to arrive at a fully performance based design approach. The question of course remains whether that is possible or should be strived for under all situations. The operating theatre was chosen as the
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research case as it can be characterized as a special room with well defined boundary conditions and (to some extent) conflicting performance requirements, e.g., the air quality versus thermal comfort and costs. In this approach it is not the intention to prioritize the individual requirements. This is clearly a design decision made by the design team. The described approach wants to support this decision process by providing objective performance information. The described example assessment protocol showed to be useful and open for assessment of innovative solutions. However, the applied static reference situation may be less representative. This also accounts for the VDI approach [3]. Also, the application of the CFD-technique brings in specific assumptions that may affect the result. Besides a further development of the building evaluation model and the performance assessment protocols, future work will also focus on the evaluation tools and the conditions under which they can be applied, striving for an as realistic assessment as required.
References [1] CIB. 1982. Working with the performance approach in building, CIB Report Publication 64, International Council for Research and Innovation in Building and Construction (CIB), Rotterdam, The Netherlands. [2] Hensen, J.L.M. 2002. Simulation for performance based building and systems design: some issues and solution directions, Proc. 6th Int. Conf. on Design and Decision Support Systems in Architecture and Urban Planning, Eindhoven University of Technology, 7-10 July, Ellecom, The Netherlands [3] VDI. 2004. VDI 2167: Technische Gebäudeausrüstung von Krankenhäusern – Building services in hospitals. Verein Deutscher Ingenieure. Germany. [4] Huovila, P. and Leinonen J. 2001. Managing performance in the built environment, Paper CLI 18, CIB World Building Congress, Wellington, New Zealand. [5] Loomans, M. and Bluyssen, P. PeBBu (PBB) - 2nd Domain: Indoor Environment; Final report, TNO, Delft, The Netherlands (2005). [6] Mallory-Hill, S. 2004. Supporting Strategic Design of Workplace Environments with CaseBased Reasoning, PhD thesis, Eindhoven University of Technology, Eindhoven, The Netherlands. [7] Foliente, G.C., Leicester, R.H. and Pham, L. 1998. Development of the CIB Proactive Program on Performance-based Building Codes and Standards, BCE Doc 98/232, CSORI Building, Construction and Engineering, Highett, Australia. [8] Djunaedy, E. 2005. External coupling between building energy simulation and computational fluid dynamics, PhD thesis, Eindhoven University of Technology, Eindhoven, The Netherlands. [9] Loomans, M., Houdt, W.van, Lemaire, A., Hensen, J.2006. Ventilation of Operating Theatres Requires a Performance . Journal of Hospital Infection Volume 64, Supplement 1, Page S80.
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