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

Natural ventilation is attractive due to its potential 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 of 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.

► Four buoyancy-driven natural ventilation strategies are modelled and ranked.
► Window-based strategy is poorest in comfort/airflow ranking but uses less energy.
► WHO, HTM 03-01 and ENISO 7730 flow rates are met via new strategy (CBNV).
► Minimum trickle ventilation recommended at 25% opening fraction for comfort.
► CBNV creates mixing unlike typical buoyancy-driven displacement strategies.