Good design is only part of the story

Good design is only part of the stor

Modelling buoyant thermal plumes in naturally ventilated buildings

The aim of the work reported in this paper was to evaluate the performance of Large Eddy Simulation (LES) for modelling natural ventilation driven by twin plumes. The flow is characterised by an interface height which separates the warm buoyant air above from the cooler air below, and a merging height for coalescence of the two plumes. Comparison between the LES predictions and theory for the interface height and volume flow rate in the merged plumes is good, giving confidence that LES has potential for modelling this important class of flows

Natural ventilation assessment of an existing apartment building in the Mediterranean using time-dependent CFD

The benefits and limitations of time-dependent and steady state computational fluid dynamics simulations when evaluating natural ventilation were explored in a naturally ventilated case study apartment in the Mediterranean. For wind driven flows, indoor air properties responded quickly (i.e. within 1-min) to changing outdoor conditions, except indoor air temperatures (up to 30-min). The outdoor air temperature variations could reverse the flow direction during buoyancy-driven ventilation. Strong correlations between the steady state and transient simulation results were predicted (<1% error). Comparable indoor temperatures were found from simulations with both coarse and fine time steps, and up to 2% difference was found for indoor velocities

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

Assessing natural cooling strategies in apartment buildings using de-coupled internal-external airflow simulations

Computational fluid dynamics simulations were conducted to investigate the performance of enhanced natural ventilation strategies in an existing multi-storey apartment building in Athens, a typical urban Greek domestic building type. De-coupled airflow modelling was employed to predict the airflow patterns around the case study building at the neighbourhood scale, along with the prediction of the internal airflow patterns and indoor air temperatures at the scale of a single apartment. Implementation of a wind-catcher and a second façade layer have been investigated to enhance the natural ventilation of the building and improve the original single-sided ventilation strategy

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 monitoring of a naturally ventilated city centre library

In order to reduce carbon emissions to tackle climate change, it is becoming increasingly important to improve energy efficiency through more intelligent and sustainable building design. This paper describes the design and environmental performance of the Lanchester Library at Coventry University, which opened in September 2000 and incorporates natural ventilation, daylighting and passive cooling strategies. Computer simulations used in the design phase demonstrated that comfortable indoor conditions could be maintained with a natural ventilation strategy which uses lightwells and perimeter stacks to supply and exhaust air, and careful control of solar gains and night time cooling, avoiding the use of air conditioning or mechanical ventilation. This paper uses data from the Building Energy Management System (BEMS) to assess how well the building is performing 5 years on. Temperature, CO2 and energy consumption data are used to give indications of building performance, and for comparison with the original design criteria and good practice guidelines. The data indicate that comfortable thermal conditions and a sufficient supply of fresh air are maintained in the library throughout the year and that it consumes 50% less energy than a standard air conditioned building

Evaluation of LES and RANS CFD modelling of multiple steady states in natural ventilation

This paper reports research carried out with the aim of evaluating and comparing the performance of Large Eddy Simulation (LES) and Unsteady Reynolds-Averaged Navier-Stokes (URANS) modelling for predicting the multiple steady states observed in experiments on a buoyancy-driven naturally ventilated enclosure. The sub-grid scales of the flow have been modelled using a Van Driest damped Smagorinsky sub-grid scale model in the case of LES and an RNG k-ε turbulence model has been used for URANS. A novel mesh design strategy was introduced to design the LES mesh to identify an optimum 'well-resolved' mesh, assuming that the flow investigated is free-shear dominated. It was found that the URANS solution eventually settled down into a permanent steady state, displaying no evidence of continuing instabilities or periodic unsteadiness. Both URANS and LES solutions captured the existence of three steady states as observed in experimental studies. However, LES was more accurate in predicting the temperatures inside the enclosure compared to URANS. In the URANS solutions, it was observed that for smaller lower opening areas the average indoor temperature had noticeable discrepancies when compared with experimental results. Unlike URANS, LES correctly predicted different steady state temperatures for different opening areas and the time to reach steady state agreed closely with theoretical predictions

Enhancing indoor comfort in existing apartment buildings in Athens using natural ventilation

Computer simulation and field studies were conducted to investigate the implementation of natural cooling strategies in existing apartment buildings in Athens; the most typical urban domestic building type of Greece. Thermal performance analysis and airflow modelling in a specific apartment were conducted for the summer period using dynamic building energy simulation tools. The indoor thermal comfort was evaluated with reference to the adaptive thermal comfort theory. Changes to the fenestration and the utilisation of a light shaft, assist the natural cooling of the building and improve the previous single-sided ventilation strategy. Results indicate indoor air quality in the spaces being significantly enhanced, whilst the percentage comfort hours were increased, suggesting a significant reduction of the buildings' cooling demand

Commissioning hybrid advanced naturally ventilated buildings: a US case-study

A new building for a university near Chicago, Illinois, US, utilizes a hybrid advanced natural ventilation strategy to condition a deep-plan library. The design and construction are described, but the paper focuses on the post-construction, pre-occupancy commissioning trials undertaken to test both the active and passive environmental control systems. These simple qualitative trials confirmed that the advanced natural ventilation strategy functioned broadly as intended, but reveal unexpected features of the mechanical systems, faulty components, errors in the control logic of the building management system, and design omissions. Many of these could be readily corrected before occupancy, thereby improving the likely energy and environmental performance. The trials highlighted the need for forms of contract and methods of working that enable the integrated working of design teams, especially when designing innovative buildings. The benefits of adopting simple qualitative commissioning trials, and some of the current barriers to achieving this, are discussed