C.B. Beggs

The Airborne Transmission of Infection in Hospital Buildings: Fact or Fiction?

Airborne transmission is known to be the route of infection for diseases such as tuberculosis and aspergillosis. It has also been implicated in nosocomial outbreaks of MRSA, Acinetobacter spp. and Pseudomonas spp. Despite this there is much scepticism about the role that airborne transmission plays in nosocomial outbreaks. This paper investigates the airborne spread of infection in hospital buildings, and evaluates the extent to which it is a problem. It is concluded that although contact-spread is the principle route of transmission for most infections, the contribution of airborne micro-organisms to the spread of infection is likely to be greater than is currently recognised. This is partly because many airborne micro-organisms remain viable while being non-culturable, with the result that they are not detected, and also because some infections arising from contact transmission involve the airborne transportation of micro-organisms onto inanimate surfaces.

The use of solar desiccant cooling in the UK: a feasibility study

The desiccant cooling cycle is a novel open heat driven cycle which can be used both to cool and dehumidify air. Being a heat driven cycle, desiccant cooling affords an opportunity to utilise heat which might otherwise be wasted. It can therefore be coupled to solar collectors to produce a cooling system which, in theory, should be environmentally friendly. This paper discusses the feasibility of using solar energy to power the desiccant cooling cycle and also presents a study, in which a solar desiccant cooling model is used to evaluate installations located in the southeast and east midlands of England, and in central Scotland. The paper demonstrates that solar powered desiccant cooling is a feasible solution for cooling and heating buildings in the United Kingdom.

The potential for solar powered single-stage desiccant cooling in southern Europe

Desiccant cooling is an environmentally friendly technology which can be used to condition the internal environment of buildings. Unlike conventional air conditioning systems, which rely on electrical energy to drive the cooling cycle, desiccant cooling is a heat driven cycle. Desiccant cooling systems have been used successfully in northern Europe and a number of studies have demonstrated that solar energy can be used to drive the system in this region. However, to date, desiccant cooling has not been used in southern European. This paper presents the results of a study, in which a solar desiccant cooling model was used to evaluate the potential for using solar power to drive a single-stage desiccant cooling system in various locations in southern Europe. The study demonstrates that solar desiccant cooling is feasible in parts of southern Europe, provided that the latent heat gains experienced are not excessive. However, if the relative humidities experienced are too high then desiccant cooling becomes impracticable simply because the regeneration temperatures required are excessive.

A theoretical study of the thermal performance of the TermoDeck hollow core slab system

The TermoDeck hollow core slab system is a versatile energy storage technique for controlling the environment within large and medium sized buildings. It utilises the hollow cores within pre-cast concrete floor slabs as ventilation ducts to produce an environment which is thermally stable. Although many TermoDeck systems have successfully been installed in Scandinavia, the United Kingdom and in other northern European countries, the thermal performance of the system is not fully understood. This paper presents the results of a theoretical study, using a numerical model, into the thermal performance of the TermoDeck system. In particular, the role of the bends in the system is investigated and the conclusion reached that their impact on overall heat transfer is minimal. It is also concluded that greater thermal attenuation is achieved by using a five-core pass system in comparison with a three-core system.

A quantitative method for evaluating the germicidal effect of upper room UV fields.

With the general increase in the worldwide incidence of tuberculosis there is increasing interest in the use of upper room ultraviolet germicidal irradiation (UVGI) systems to disinfect air. A number of researchers have demonstrated experimentally the ability of such systems to inactivate airborne microorganisms. However, relatively little theoretical work has been done to explain the results observed and few models exist to describe the performance of upper room UVGI systems. This paper presents a new model, which can be used both to design such systems and to evaluate their germicidal effectiveness. A theoretical study is undertaken, which indicates that although upper room UVGI systems work well at lower ventilation rates, they are of limited benefit in highly ventilated applications. The paper also demonstrates and quantifies the relationship between inter-zonal air velocity and room ventilation rate. In particular, the paper shows that under steady-state conditions the number of passes made by bioaerosol particles through an upper room UV field is independent of the ventilation rate.

Modelling the Performance of Upper Room Ultraviolet Germicidal Irradiation Devices in Ventilated Rooms: Comparison of Analytical and CFD Methods

Models to evaluate upper room ultraviolet germicidal irradiation (UVGI) devices can be used to improve the understanding of the behaviour of UV devices in ventilated rooms and so enable more confident predictions to be made of their performance. This paper presents two- and three-zone mixing models for investigating the effect of upper room UVGI devices in a typical ventilated room. The results from these analytical models are compared to a CFD simulation of the same room that incorporates the biological inactivation of micro-organisms in the presence of an ultraviolet field. The study demonstrates that analytical mixing models give reasonably good average zone concentrations and are therefore useful in estimating overall performance. However, the CFD simulations are necessary to fully examine the interaction of the room airflow with the inactivation of micro-organisms due to the UV field.

A quantitative method for evaluating the photoreactivation of ultraviolet damaged microorganisms

The lethal effect of ultraviolet (UV) light on microorganisms is well known and many studies have been undertaken into the effects of UV induced damage. Most of this work has been experimental; by comparison relatively little theoretical work has been undertaken to analyse the kinetics of the UV inactivation process, or to develop quantitative methodologies to support the experimental work. This paper presents a new and simple model for quantifying the photolysis rate. A theoretical study is also presented in this paper which quantifies photolysis rates for E. coli O26 and E. coli O157:H7. This study uses experimental data collected by Tosa and Hirata, and reveals the photolysis rate for E. coil O26 during the UV irradiation process to be 4.69 x 10(-3) m2 J(-1). By comparison, E. coli O157:H7 is much more susceptible to UV induced damage than E. coli O26, having a photolysis constant of only 2.09 x 10(-3) m2 J(-1).

The Threat Posed by Airborne Micro-Organisms:

Over the past 20 years there has been increasing interest in the quality of air in buildings. Initially this interest was focused mainly on the perceived problem of ’sick building syndrome’. However, as time has passed, many building designers and scientists have come to realise that indoor air quality has a profound effect on both the performance and health of building occupants, since people spend most of their lives indoors. Most of the work undertaken in this field has concentrated on non-viable chemi-

Susceptibility of Burkholderia cepacia and other pathogens of importance in cystic fibrosis to u.v. light

G. CAIRNS, K.G. KERR, C.B. BEGGS, P.A. SLEIGH, L. MOONEY, P. KEIG AND J.K. DONNELLY. 2001 To investigate the potential usefulness of u.v. germicidal irradiation (UVGI) in preventing the spread of Burkholderia cepacia, an important pathogen in cystic fibrosis (CF), the in‐vitro susceptibility of B. cepacia to UVGI was determined. Five strains were exposed to UVGI from a 7·2‐W source. Burkholderia cepacia was less susceptible to UVGI than other important CF‐related pathogens, namely Staphylococcus aureus and Pseudomonas aeruginosa, but was more susceptible than Stenotrophomonas maltophilia. No strain of B. cepacia survived longer than an 8 s exposure to UVGI, with doses required to achieve 1 log reduction in bacterial numbers ranging from 28·3 to 57·5 J m–2.

Desiccant Cooling at the University of Lincoln: A Case Study

The desiccant cooling cycle is a novel open heat-driven cycle which can be used both to cool and to dehumidify air. Although desiccant cooling systems have been used in Scandinavian buildings for over 20 years, they have only relatively recently been used in the United Kingdom (UK). This paper describes the operation of a desiccant cooling system at the University of Lincoln, which was among the first facilities in the UK to install such a system. The desiccant system at the University of Lincoln was monitored for the period September 1998 to August 1999. The results of this monitoring programme reveal the system to be an effective low-energy solution.