The Design and Simulation of Natural Personalised Ventilation (NPV) System for Multi-Bed Hospital Wards

Zulfikar Adamu,Andrew Price

doi:10.3390/buildings5020381

Abstract

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.

Highlights

In the United Kingdom (UK), mechanical ventilation contributes over 40% of energy allocated by typical hospitals for space conditioning [1]
The predictions from computational fluid dynamics (CFD) are in agreement with findings from literature that with displacement strategy (i.e., Base Case windows), fresh air from the side-hung openings flood the space at floor level (Figure 4)
Results obtained for all natural personalised ventilation (NPV) concepts investigated in this study, suggest that draught is a risk to be taken into account due to the direct discharge of air over the beds

Summary

Introduction

In the United Kingdom (UK), mechanical ventilation contributes over 40% of energy allocated by typical hospitals for space conditioning [1]. The recent Health Building Notes [6] emphasises the role of window restrictors in maintaining this maximum width. This 100 mm restriction is largely for security and safety reasons [5,6]. It is not evident from historical or contemporary literature that this area of opening has been fully studied in terms of its impact on adequate ventilation rates, for dilution or airborne pollutants of pathogens. There is research evidence pointing towards substantial increase in risk of cross-infection when such windows in multi-bed wards are closed in winter to save heating energy [7]. There is the issue of room air distribution, through displacement or mixing strategies and how this can affect clinical outcomes in multi-bed wards

Objectives

Methods

Results

Discussion

Conclusion