The feasibility of natural ventilation in healthcare buildings

Wards occupy significant proportions of hospital floor areas and due to their constant use, represent a worthwhile focus of study. Single-bed wards are specifically of interest owing to the isolation aspect they bring to infection control, including airborne pathogens, but threats posed by airborne pandemics and family-involvement in hospital care means cross-infection is still a potential problem. In its natural mode, ventilation driven by combined wind and buoyancy forces can lead to energy savings and achieve thermal comfort and high air change rates through secure openings. These are advantageous for controlling indoor airborne pathogens and external air and noise pollution. However, there is lack of detailed evidence and guidance is needed to gain optimum performance from available natural ventilation systems. This research is a proof of concept investigation into the feasibility and impact of natural ventilation systems targeting airflow rates, thermal comfort, heating energy and control of pathogenic bio-aerosols in hospital wards. In particular, it provides insights into the optimal areas of vent openings which could satisfy the complex three-pronged criteria of contaminant dilution, low heating energy and acceptable thermal comfort for occupants in a naturally ventilated single bed ward. The main aim of this thesis is the structured study of four systems categorised into three groups: Simple Natural Ventilation (SNV) in which single and dual-openings are used on the same external wall; Advanced Natural Ventilation (ANV) which is an emerging concept; and finally Natural Personalised Ventilation (NPV) which is an entirely new concept borne out of the limitations of previous systems and gaps in literature. The focus of this research is in the exploratory study of the weaknesses and potentials of the four systems, based on multi-criteria performances metrics within three architecturally distinct single-bed ward designs. In contributing to the body of existing knowledge, this thesis provides a better understanding of the performances of three existing systems while presenting the new NPV system. The analysis is based on dynamic thermal modelling and computational fluid dynamics and in the case of the NPV system, salt-bath experiments for validation and visualisation of transient flows. In all cases, wards were assumed to be free of mechanical ventilation systems that might influence the natural flow of air. The thesis meets three major objectives which have resulted in the following contributions to current knowledge: An understanding of the limitations and potentials of same-side openings, especially why and how dual-openings can be useful when retrofitted into existing wards. Detailed analysis of bulk airflow, thermal comfort, heating energy and room air distribution achievable from existing SNV and ANV systems, including insights to acceptable trickle ventilation rates, which will be particular useful in meeting minimum dilution and energy requirements in winter. This also includes qualitative predictions of the airflow pattern and direction obtainable from both systems. The innovation and study of a new natural ventilation system called Natural Personalised Ventilation (NPV) which provides fresh air directly over a patient s bed, creating a mixing regime in the space and evaluation of its comfort and energy performances. A low-energy solution for airborne infection control in clinical spaces is demonstrated by achieving buoyancy-driven mixing ventilation via the NPV system, and a derivative called ceiling-based natural ventilation (CBNV) is shown. A comparative analysis of four unique natural ventilation strategies including their performance rankings for airflow rates, thermal comfort, energy consumption and contaminant dilution or removal using an existing single-bed ward design as case study. Development of design and operational recommendations for future guidelines on utilising natural ventilation in single-bed wards either for refurbishment or for proposed designs. These contributions can be extended to other clinical and non-clinical spaces which are suitable to be naturally ventilated including treatment rooms, office spaces and waiting areas. The findings signify that natural ventilation is not only feasible for ward spaces but that there is opportunity for innovation in its application through further research. Future work could focus on related aspects like: impacts of fan-assisted ventilation for a hybrid flow regime; pre-heating of supply air; integration with passive heat recovery systems as well the use of full-scale experiments to fine-tune and validate findings

The design and simulation of natural personalised ventilation (NPV) system for multi-bed hospital wards

Adequate ventilation is necessary for thermal comfort and reducing risks from infectious bio-aerosols in hospital wards, but achieving this with mechanical ventilation has carbon and energy implications. Natural ventilation is often limited to window-based designs whose dilution/mixing effectiveness are subject to constraints of wind speed, cross ventilation, and in the case of hospital wards, proximity of patients to external walls. A buoyancy-driven natural ventilation system capable of achieving dilution/mixing was shown to be feasible in a preceding study of novel system called natural personalised ventilation (NPV). This system combined both architecture and airflow engineering principles of space design and buoyancy and was tested and validated (salt-bath experiment) for a single bed ward. This research extends the previous work and is proof-of-concept on the feasibility of NPV system for multi-bed wards. Two different four-bed ward types were investigated of using computational fluid dynamics (CFD) simulations under wind-neutral conditions. Results predict that NPV system could deliver fresh air to multiple patients, including those located 10 m away from external wall, with absolute flow rates of between 32 L·s−1 and 54 L·s−1 for each patient/bed. Compared to same wards simulated using window design, ingress of airborne contaminants into patients’ breathing zone and summer overheating potential were minimised, while overall ward dilution was maximised. Findings suggest the NPV has potentials for enabling architects and building service engineers to decouple airflow delivery from the visualisation and illumination responsibilities placed upon windows

Natural ventilation with heat recovery: a biomimetic concept

In temperate countries, heat recovery is often desirable through mechanical ventilation with heat recovery (MVHR). Drawbacks of MVHR include use of electric power and complex ducting, while alternative passive heat recovery systems in the form of roof or chimney-based solutions are limited to low rise buildings. This paper describes a biomimetic concept for natural ventilation with heat recovery (NVHR). The NVHR system mimics the process of water/mineral extraction from urine in the Loop of Henle (part of human kidney). Simulations on a facade-integrated Chamber successfully imitated the geometry and behaviour of the Loop of Henle (LoH). Using a space measuring 12 m2 in area and assuming two heat densities of 18.75 W/m2 (single occupancy) or 30 W/m2 (double occupancy), the maximum indoor temperatures achievable are up to 19.3 °C and 22.3 °C respectively. These come with mean relative ventilation rates of 0.92 air changes per hour (ACH) or 10.7 L·s−1 and 0.92 ACH (11.55 L·s−1), respectively, for the month of January. With active heating and single occupant, the LoH Chamber consumes between 65.7% and 72.1% of the annual heating energy required by a similar naturally ventilated space without heat recovery. The LoH Chamber could operate as stand-alone indoor cabinet, benefitting refurbishment of buildings and evading constraints of complicated ducting, external aesthetic or building age

The design and simulation of natural personalised ventilation (NPV) system for multi-bed hospital wards

Adequate ventilation is necessary for thermal comfort and reducing risks from infectious bio-aerosols in hospital wards, but achieving this with mechanical ventilation has carbon and energy implications. Natural ventilation is often limited to window-based designs whose dilution/mixing effectiveness are subject to constraints of wind speed, cross ventilation, and in the case of hospital wards, proximity of patients to external walls. A buoyancy-driven natural ventilation system capable of achieving dilution/mixing was shown to be feasible in a preceding study of novel system called natural personalised ventilation (NPV). This system combined both architecture and airflow engineering principles of space design and buoyancy and was tested and validated (salt-bath experiment) for a single bed ward. This research extends the previous work and is proof-of-concept on the feasibility of NPV system for multi-bed wards. Two different four-bed ward types were investigated of using computational fluid dynamics (CFD) simulations under wind-neutral conditions. Results predict that NPV system could deliver fresh air to multiple patients, including those located 10 m away from external wall, with absolute flow rates of between 32 L·s−1 and 54 L·s−1 for each patient/bed. Compared to same wards simulated using window design, ingress of airborne contaminants into patients’ breathing zone and summer overheating potential were minimised, while overall ward dilution was maximised. Findings suggest the NPV has potentials for enabling architects and building service engineers to decouple airflow delivery from the visualisation and illumination responsibilities placed upon windows

Natural personalised ventilation: a novel approach

The need to protect susceptible patients from cross-infection resulting from airborne pathogens is essential in hospitals, especially when patient immunity is either suppressed due to medical procedures or compromised by ailment. Personalised ventilation (PV) is a method of creating a local zone of high air quality around such patients. However, contemporary PV techniques are based on mechanical ventilation, which adds to the energy burden of healthcare buildings. In single-bed wards, a potential source of infection could be other occupants such as visitors and healthcare workers. Threats may also come from airborne pathogens migrating from adjacent zones, especially if the single-bed wards in question are not positively pressurised. While the World Health Organisation (WHO) has issued guidelines on using natural ventilation to control infectious bio-aerosols in hospital wards (with flow rates of up to 60 l/s/patient), how to achieve this rate without high energy and carbon costs, remains unanswered. The objective of the research reported here is to demonstrate a novel approach of using low-energy, buoyancy-driven natural airflow for personalised ventilation of single-bed hospital wards. The investigation has been carried out by undertaking dynamic thermal simulations (DTS) and computational fluid dynamics (CFD) simulations. Findings demonstrate that given appropriate design, it is possible to achieve personal protection for vulnerable patients using a natural mode of ventilation alone. Co-occupants could also benefit from the mixing characteristics offered by the proposed system, which does not occur in typical buoyancy-driven displacement ventilation

Performance evaluation of natural ventilation strategies for hospital wards: case study of Great Ormond Street Hospital

Natural ventilation is attractive due its potential to lower energy consumed by healthcare environments but maintaining steady/adequate airflow rates and thermal comfort is challenging in temperate countries. Although many contemporary hospitals use traditional windows for natural ventilation, there are alternative strategies that are largely under-utilised probably due to lack knowledge of their ventilation performances. Each alternative has design implications and airflow characteristics – both of which affect thermal comfort and heating energy. This study evaluates the performance of buoyancy-driven airflows through four selected natural ventilation strategies suitable for single-bed hospital wards. These strategies are: single window opening, same side dual-opening, inlet and stack as well as ceiling-based natural ventilation (CBNV), a new concept. These strategies have been explored via dynamic thermal simulation and computational fluid dynamics, using a new ward of the Great Ormond Street Hospital (GOSH) London as a case study. Results reveal that 25% trickle ventilation opening fraction is required to achieve required airflow rates and acceptable thermal comfort in winter, and with exception of window-based design, other strategies minimise summer overheating to different extents. The CBNV concept uniquely shields fresh air and delivers it to isolated parts of wards or directly over patients (i.e. personalisation). This provides higher air quality at such locations and creates mixing which aids comfort and dilution. The findings demonstrate how quantitative data from simulations can be used by designers to meet qualitative or sensory design objectives like airflow direction and thermal comfort with respect to the energy consumed in space and time

Social BIM:Co-creation with shared situational awareness

A common data environment (CDE) is a specific requirement for Level 2 BIM in the UK in accordance with BS1192-2007 and PAS1192-2 standards. It is a central repository of BIM data and examples include 4BIM and Autodesk 360. These repositories have some disadvantages:(i) it is after synchronisation or file upload that changes between local and cloud versions of BIM models can be appreciated by remote teams; (ii) there is a cost associated with subscribing to these servers, which could marginalise SMEs wanting to adopt BIM; and (iii) during the design phase, these systems do not permit real-time co-creation capabilities or audio- visual consensus amongst designers. So although these repositories are helpful technologies, it is people who collaborate (not systems) and in the design phase, audio-visual feedback and consensus can augment the collaboration experience and outcomes. With socio-technical input, the quality of BIM data/models generated by team members can be enhanced (and clashes minimised) if visual isolation is eliminated. This research presents a framework and proof-of-concept which redefines Social BIM (SBIM) as a socio- technical mode of BIM that enriches the co-creation process for Levels 2 and 3 BIM. It enables ‘shared situational awareness’ by empowering remote participants with visual and remote control of BIM models using GoToMeeting as a ‘groupware’. The BIM data was hosted by surrogate servers linked to cloud-based storage. A quasi-experiment through a desktop sharing and communication system enabled 14 globally dispersed participants to control the graphical user interface (GUI) of a host PC in the UK running Autodesk Revit. Four audio-visual collaboration protocols were developed and three were tested. Participants interacted via the host PC remotely using computers (which acted as nomadic servers) and with mobile devices. Remote desktop/laptop users had unlimited control of the data in host PC, while real-time audio-visual communication improved the collaboration and co-creation of 3D BIM models. The experience of participants in editing BIM models was a function of internet bandwidth, hardware and operating systems. Unitary optimisation of modelling efforts/outcomes was possible on shared/coordination models. Divisible optimisation of industry-specific tasks (i.e. architectural, engineering and management) by participants was enhanced by feedback which was either on-demand (requested) or just-in-time (spontaneous)