CFD modelling of transient pathogen release in indoor environments due to human activity

Certain routine hospital activities have been identified as a potential source for the airborne dispersal of micro-organisms. With increasing use of CFD to model hospital situations a method of modelling this type of spread within a simple steady state model is required. Since this type of dispersal will vary with space and time a single point source would not provide adequate information to represent these sources. Instead a zonal bioaerosol source is introduced to represent the time average of the varying release from the activity. In this paper, data from experiments conducted in a bioaerosol test chamber are compared to CFD results. Numerical validation is also carried out comparing the zonal source to an equivalent transient source. The results indicate that the zonal source provides excellent comparison to the time averaged behaviour of a moving source, but greatly underestimates the maximum value at any one location

Model-predictive control for non-domestic buildings: a critical review and prospects

Model-predictive control (MPC) has recently excited a great deal of interest as a new control paradigm for non-domestic buildings. Since it is based on the notion of optimisation, MPC is, in principle, well-placed to deliver significant energy savings and reduction in carbon emissions compared to existing rule-based control systems. In this paper, we critically review the prospects for buildings MPC and, in particular, the central role of the predictive mathematical model that lies at its heart; our clear emphasis is on practical implementation rather than control-theoretic aspects, and covers the role of occupants as well as the form of the predictive model. The most appropriate structure for such a model is still an open question, which we discuss alongside the development of the initial model, and the process of updating the model during the building’s operational life. The importance of sensor placement is highlighted alongside the possibility of updating the model with occupants’ comfort perception. We conclude that there is an urgent need for research on the automated creation and updating of predictive models if MPC is to become an economically-viable control methodology for non-domestic buildings. Finally, more evidence through operating full scale buildings with MPC is required to demonstrate the viability of this method

Monitoring Performance of a combined water recycling system

Global water demand is expected to outstrip supply dramatically by 2030, making water recycling an important tool for future water security. A large combined grey water and rainwater recycling system has been monitored in response to an identified knowledge gap of the in-use performance of such systems. The water saving efficiency of the system was calculated at −8ṡ5% in 2011 and –10% in 2012 compared to the predicted 36%. This was due to a lower quantity of grey water and rainwater being collected than the system filter required to backwash alone. Top-up potable water was therefore required to complete the backwash process and flush WCs and urinals. The efficiency of the filter itself was calculated at 0ṡ68, much lower than current figures used in grey water saving predictions. Using direct mains water with no recycling system would be more efficient in this case, highlighting the importance of realistic system analysis before future installations

An experimental study of the flow induced by the motion of a hinged door separating two rooms

The indoor air flow and mass exchange induced by the rotating motion of a hinged door separating two rooms is investigated. Experiments were conducted in a scale model based on Reynolds number matching. Flow visualisations show the transport mechanism associated with the open and close phases of the door motion. In the room into which the door is opened a large-scale vortex is formed during opening, which is advected along the walls. In the adjacent room, a volume of fluid spreads both longitudinally and transversely. Concentration measurements were carried out to quantify the mass exchange generated by these flow patterns. Results are presented in dimensionless form for the volume of fluid exchanged and are compared to earlier data. The effects of hold open time and door speed on the exchanged fluid volume are investigated. The exchange volume increases with hold open time, but it does not vary considerably with door speed for a constant hold open time. Further, three-dimensional velocity measurements were carried out near the doorway and the characteristics of the velocity field developed are also presented

Battery storage systems in smart grid optimised buildings

The building sector is responsible for a significant proportion of the consumed energy and the consequent carbon emissions. Currently, electricity and natural gas are the most popular fuels used in the UK Services sector and the industry. Furthermore, buildings constitute a key component of the power network, in both its current conventional form and its evolution, the smart grid. The smart grid is expected to integrate energy storage, distributed generation and buildings into the network. This paper introduces the concept of Smart Grid Optimised Buildings (SGOBs), recognising the importance of energy storage to establish a dynamic interaction between the building and the smart grid. SGOBs are expected to be fully electric, make the best use of the available resources and utilise their embedded battery storage systems to respond to notifications issued by the smart grid and to dynamic electricity prices. Assuming that buildings have access to the day-ahead electricity market, initial results show that battery storage can be successfully used to change a building’s electricity profile and perform load-shifting (arbitrage) and peak-shaving while the excess electricity is exported back to grid to take advantage of the price difference and relieve pressure on the infrastructure

Experimental and Modelling Investigations of Air Exchange and Infection Transfer due to Hinged-Door Motion in Office and Hospital Settings

Occupants spend a significant amount of time indoors where temperature and air quality has an important impact on their comfort, health and work performance. Understanding the role of airflow exchange between spaces is crucial to describe the processes of mixing and transport of substances driven by air motion and therefore essential for evaluating indoor air quality. This work presents the results of field measurements and laboratory experiments designed to characterise door operation and to quantify its influence on air volumes exchanged between rooms due to door motion. The field study was conducted to identify typical total door cycle times in single person offices. The laboratory experiments were conducted in a scale model to investigate the exchange flow between two generic rooms. The model consisted of a water filled tank divided into two equal rooms, which were connected by a computer-controlled hinged door. Flow visualisations were used to describe flow patterns and concentration measurements of Rhodamine WT were performed to quantify exchange volumes. With hold open times of between 0s and 26.67s the total fluid volume exchanged was found to be between 67% and 98% of the total volume swept. Based on the exchange volume found in these experiments combined with the Wells-Riley equation the effect of ventilation rate on the probability of occupants in an adjacent room becoming infected was investigated. With ventilation rates for a medium air quality the risk of infection is low (<0.05). However, the probability of infection quickly rises with lower ventilation rates

Estimating evapotranspiration from commonly occurring urban plant species using porometry and canopy stomatal conductance

Evapotranspiration (ET) is a key moisture flux in both the urban stormwater management and the urban energy budgets. While there are established methods for estimating ET for agricultural crops, relatively little is known about ET rates associated with plants in urban Green Infrastructure settings. The aim of this study was to evaluate the feasibility of using porometry to estimate ET rates. Porometry provides an instantaneous measurement of leaf stomatal conductance. There are two challenges when estimating ET from porometry: converting from leaf stomatal conductance to leaf ET and scaling from leaf ET to canopy ET. Novel approaches to both challenges are proposed here. ET was measured from three commonly occurring urban plant species (Sedum spectabile, Bergenia cordifolia and Primula vulgaris) using a direct mass loss method. This data was used to evaluate the estimates made from porometry in a preliminary study (Sheffield, UK). The Porometry data captured expected trends in ET, with clear differences between the plant species and the reproducible decreasing rates of ET in response to reductions in soil moisture content

Measurement and rapid assessment of indoor air quality at mass gathering events to assess ventilation performance and reduce aerosol transmission of SARS-CoV-2

To assess risk factors for COVID-19 transmission and address the closure of mass gathering events since March 2020, the UK Government ran the Events Research Programme (ERP), following which it reopened live events in sports, music, and culture in July 2021. We report the rapid post-occupancy evaluation of Indoor Air Quality (IAQ) and associated long-range airborne transmission risk conducted in the Environmental Study of the ERP. Ten large venues around the UK were monitored with CO2 sensors at a high spatial and temporal resolution during 90 events. An IAQ Index based on CO2 concentration was developed, and all monitored spaces were classified in bands from A to G based on their average and maximum CO2 concentrations from all events. High resolution monitoring and the IAQ Index depicted the overall state of ventilation at live events, and allowed identification of issues with ventilation effectiveness and distribution, and of spaces with poor ventilation and the settings in which long-range airborne transmission risk may be increased. In numerous settings, CO2 concentrations were found to follow patterns relating to event management and specific occupancy of spaces around the venues. Good ventilation was observed in 90% of spaces monitored for given occupancies. Practical applications: High-resolution monitoring of indoor CO2 concentrations is necessary to detect the spatial variation of indoor air quality (IAQ) in large mass gathering event venues. The paper summarises COVID-19 ventilation guidance for buildings and defines a methodology for measurement and rapid assessment of IAQ during occupancy at live events that can be implemented by venue managers. Comparisons of the CO2 concentrations measured during the events identified the spaces at high risk of long-range transmission of airborne pathogens. Building operators should be mindful of the ventilation strategies used relative to the total occupancy in different spaces and the occupant’s activities

Big Data and Model Predictive Control for Improved Building Performance

There has been growing interest in the application of ‘big data’ in recent years to understand and reduce energy usage in a range of areas. However, what are the opportunities to use these data to automatically improve a building’s performance? By using a predictive model of the building to test control strategies in advance of their application, Model Predictive Control has the potential to optimise a buildings energy use and internal conditions. This paper will tackle the question of whether it is possible to develop a suitable predictive model from data taken from a building in operation using the case study of a naturally ventilated school. We show that a building-in-use is rarely perturbed enough to provide adequate data to develop a control capable model

The ventilation of multiple-bed hospital wards: Review and analysis

Background: Although the merits of ventilating operating theatres and isolation rooms are well known, the clinical benefits derivedfrom ventilating hospital wards and patient rooms are unclear. This is because relatively little research work has been done in the ventilation of these areas compared with that done in operating theatres and isolation rooms. Consequently, there is a paucity of good quality data from which to make important decisions regarding hospital infrastructure. This review evaluates the role of general ward ventilation to assess whether or not it affects the transmission of infection. Methods: A critical review was undertaken of guidelines in the United Kingdom and United States governing the design of ventilation systems for hospital wards and other multibed rooms. In addition, an analytical computational fluid dynamics (CFD) study was performed to evaluate the effectiveness of various ventilation strategies in removing airborne pathogens from ward spaces. Results: The CFD simulation showed the bioaerosol concentration in the study room to be substantially lower (2467 cfu/m3) when air was supplied and extracted through the ceiling compared with other simulated ventilations strategies, which achieved bioaerosol concentrations of 12487 and 10601 cfu/m3, respectively. Conclusions: There is a growing body of evidence that the aerial dispersion of some nosocomial pathogens can seed widespread environmental contamination, and that this may be contributing to the spread infection in hospital wards. Acinetobacter spp in particular appear to conform to this model, with numerous outbreaks attributed to aerial dissemination. This suggests that the clinical role of general ward ventilation may have been underestimated and that through improved ward ventilation, it may be possible to reduce environmental contamination and thus reduce nosocomial infection rates. (Am J Infect Control 2008;36:250-9.