The effect of indoor daylight spectrum and intensity on viability of indoor pathogens on different surface materials

Built environments play a key role in the transmission of infectious diseases. Ventilation rates, air temperature and humidity affect airborne transmission while cleaning protocols, material properties and light exposure can influence viability of pathogens on surfaces. We investigated how indoor daylight intensity and spectrum through electrochromic (EC) windows can impact the growth rate and viability of indoor pathogens on different surface materials (polyvinyl chloride (PVC) fabric, polystyrene (PS), and glass) compared to traditional blinds. Our results showed that tinted EC windows let in higher energy, shorter wavelength daylight than those with clear window and blind. The growth rates of pathogenic bacteria and fungi were significantly lower in spaces with EC windows compared to blinds: nearly 100% growth rate reduction was observed when EC windows were in their clear state followed by 41-100% reduction in bacterial growth rate and 26-42% reduction in fungal growth rate when EC windows were in their darkest tint. Moreover, bacterial viabilities were significantly lower on PVC fabric when they were exposed to indoor light at EC-tinted window. These findings are deemed fundamental to the design of healthy modern buildings, especially those that encompass sick and vulnerable individuals.

Evaluating the Environmental Performance of 3D Printed Shelters in Jordan

Three-dimensional (3D) printed shelters are an innovative housing solution for those in need of a shelter after a disaster. The Middle East generated a huge number of refugees due to internal conflicts. The technology has been investigated earlier from a cost and time perspectives and has performed better than steel shelters in Jordan. This research article investigates environmental performance of 3D printed shelters in Jordan in terms of energy, fuel, cooling and ventilation. Syrian refugees of Jordanian camps were selected as a case study. The energy simulation of the steel shelter to that of a printed shelter showed that the latter can achieve higher ventilation rates, lower energy consumption, less electricity cost and better thermal insulation than steel shelters.

The Efficiency of Obtaining Electricity and Heat from the Photovoltaic Module under Different Irradiance Conditions

This paper proposes a modification to the design of a standard PV module by enclosing the skeleton space and using forced ventilation. The purpose of this research was to develop a method for calculating the amount of heat gained during PV module cooling. A simplifying assumption was to omit the electrical energy consumed by the fans forcing the airflow. For testing at low irradiance, a prototype halogen radiation simulator of our own design was used, which is not a standardized radiation source used for testing PV modules. Two measurements were also made under natural, stable solar radiation. The modified PV module was tested for three ventilation rates and compared with the results obtained for the standard PV module. In all tested cases, an increase in electrical efficiency of about 2% was observed with increasing radiation intensity. The thermal efficiency decreased by about 5% in the analyzed cases and the highest value of 10.47% was obtained for the highest value of cooling airflow rate. In conclusion, the study results represent a certain compromise: an increase in electrical efficiency with a simultaneous decrease in thermal efficiency.

Beyond well-mixed: a simple probabilistic model of airborne disease transmission in indoor spaces

We develop a simple model for assessing risk of airborne disease transmission that accounts for non-uniform mixing in indoor spaces and is compatible with existing epidemiological models. A database containing 174 high-resolution simulations of airflow in classrooms, lecture halls, and buses is generated and used to quantify the spatial distribution of expiratory droplet nuclei for a wide range of ventilation rates, exposure times, and room configurations. Imperfect mixing due to obstructions, buoyancy, and turbulent dispersion results in concentration fields with significant variance. The spatial non-uniformity is found to be accurately described by a shifted lognormal distribution. A well-mixed mass balance model is used to predict the mean, and the standard deviation is parameterized based on ventilation rate and room geometry. When employed in a dose-response function risk model, infection probability can be estimated considering spatial heterogeneity that contributes to both short- and long-range transmission.

Do increased flow rates in displacement ventilation always lead to better results?

Indoor ventilation is essential for a healthy and comfortable living environment. A key issue is to discharge anthropogenic air contamination such as CO $_2$ gas or, of potentially more direct consequence, airborne respiratory droplets. Here, by employing direct numerical simulations, we study mechanical displacement ventilation with a wide range of ventilation rates $Q$ from 0.01 to 0.1 m $^3$ s $^{-1}$ person $^{-1}$ . For this ventilation scheme, a cool lower zone is established beneath a warm upper zone with interface height $h$ , which depends on $Q$ . For weak ventilation, we find the scaling relation $h\sim Q^{3/5}$ , as suggested by Hunt & Linden (Build. Environ., vol. 34, 1999, pp. 707–720). Also, the CO $_{2}$ concentration decreases with $Q$ within this regime. However, for too strong ventilation, the interface height $h$ becomes insensitive to $Q$ , and the ambient averaged CO $_2$ concentration decreases towards the ambient value. At these values of $Q$ , the concentrations of pollutants are very low and so further dilution has little effect. We suggest that such scenarios arise when the vertical kinetic energy associated with the ventilation flow is significant compared with the potential energy of the thermal stratification.

Indoor air quality in a high school classroom in Rijeka, Croatia (sick classrooms caused by rising CO2 levels)

School’s indoor air quality (IAQ) is very important as it can affect student’s learning abilities and lead to health issues. Therefore, indoor air quality, and in particular the CO2 concentration, was monitored on a daily basis from mid-November till the end of December 2017, by using several low-cost instruments. The measuring was performed in the physics classroom of a grammar school in Rijeka, Croatia. Detailed CO2 generation rates, air exchange rates, and ventilation rates are calculated and reported in this work, from the experimentally obtained data. Very high concentrations of over 4.000 ppm were recorded, indicating that ventilation rates are far below 5 Ls-1 per person, which is the lowest recommended value of ventilation rate according to the European standard EN 13779. The experimentally obtained data are compared with the theoretical models and a strong correlation are achieved. This is one of the first comprehensive studies of this kind in Croatia; therefore, we hope that it will stimulate interest between health workers, scientists, and school management to implement indoor air quality monitoring practices and perhaps introduce automated ventilation systems in classrooms for the benefit of students’ health and their learning abilities.

The vaccination threshold for SARS-CoV-2 depends on the indoor setting and room ventilation

Background Effective vaccines are now available for SARS-CoV-2 in the 2nd year of the COVID-19 pandemic, but there remains significant uncertainty surrounding the necessary vaccination rate to safely lift occupancy controls in public buildings and return to pre-pandemic norms. The aim of this paper is to estimate setting-specific vaccination thresholds for SARS-CoV-2 to prevent sustained community transmission using classical principles of airborne contagion modeling. We calculated the airborne infection risk in three settings, a classroom, prison cell block, and restaurant, at typical ventilation rates, and then the expected number of infections resulting from this risk at varying percentages of occupant immunity. Results We estimate the setting-specific immunity threshold for control of wild-type SARS-CoV-2 to range from a low of 40% for a mechanically ventilation classroom to a high of 85% for a naturally ventilated restaurant. Conclusions If vaccination rates are limited to a theoretical minimum of approximately two-thirds of the population, enhanced ventilation above minimum standards for acceptable air quality is needed to reduce the frequency and severity of SARS-CoV-2 superspreading events in high-risk indoor environments.

Design and Construction Features that Cause New Houses in New Zealand to Overheat

<p>Analysis of indoor temperature measurements taken in 397 randomly selected houses has revealed that New Zealand houses are becoming warmer in summer. Houses built at the end of the 20th century are during the daytime (9 am to 5 pm), on average, 2.5 degrees C warmer during summer months (December to February) than houses built at the start. For example, in houses built during the 1990s, temperatures above 25 degrees C are found 40% of the time during the summer early evening (4 pm to 6 pm) - temperatures that could be considered as uncomfortably warm in a temperate climate. Since 2006 there has been a rapid uptake of heat pumps in New Zealand, and a survey provides evidence of a growing number of households actively cooling, when traditionally very little cooling has been done. The ability for occupants to cool during the warm summer early evening has the potential to create an additional peak load on the electricity network. The trend towards increasing indoor summer temperatures could be due to a range of features, including house design, construction and operation. These have been explored through analysis of the temperature data and thermal modelling using SUNREL with validated models of five houses. Although the monitored sample was sizable, the variation in occupant behaviour means it was not possible to explore all potential drivers or eliminate other influences. The use of thermal modelling permitted parametric investigation of the role of different features to be explored. The analysis of monitoring data and the thermal modelling showed that the main causes of increasing temperatures are: increasing glazing area; lower ventilation rates; reduction of external shading through reduced eave size; and to a lesser extent increased levels of thermal insulation. These findings have been used to provide guidance for new house designers as well as suggestions for modifications of existing houses.</p>

Design and Construction Features that Cause New Houses in New Zealand to Overheat

<p>Analysis of indoor temperature measurements taken in 397 randomly selected houses has revealed that New Zealand houses are becoming warmer in summer. Houses built at the end of the 20th century are during the daytime (9 am to 5 pm), on average, 2.5 degrees C warmer during summer months (December to February) than houses built at the start. For example, in houses built during the 1990s, temperatures above 25 degrees C are found 40% of the time during the summer early evening (4 pm to 6 pm) - temperatures that could be considered as uncomfortably warm in a temperate climate. Since 2006 there has been a rapid uptake of heat pumps in New Zealand, and a survey provides evidence of a growing number of households actively cooling, when traditionally very little cooling has been done. The ability for occupants to cool during the warm summer early evening has the potential to create an additional peak load on the electricity network. The trend towards increasing indoor summer temperatures could be due to a range of features, including house design, construction and operation. These have been explored through analysis of the temperature data and thermal modelling using SUNREL with validated models of five houses. Although the monitored sample was sizable, the variation in occupant behaviour means it was not possible to explore all potential drivers or eliminate other influences. The use of thermal modelling permitted parametric investigation of the role of different features to be explored. The analysis of monitoring data and the thermal modelling showed that the main causes of increasing temperatures are: increasing glazing area; lower ventilation rates; reduction of external shading through reduced eave size; and to a lesser extent increased levels of thermal insulation. These findings have been used to provide guidance for new house designers as well as suggestions for modifications of existing houses.</p>

Monitoring and Assessment of Indoor Environmental Conditions after the Implementation of COVID-19-Based Ventilation Strategies in an Educational Building in Southern Spain

Since students and teachers spend much of their time in educational buildings, it is critical to provide good levels of indoor environmental quality (IEQ). The current COVID-19 pandemic has shown that maintaining a good indoor air quality level is an effective measure to control the transmission of the SARS-CoV-2 virus. This study used sensors to monitor key IEQ factors and assess several natural ventilation scenarios in a classroom of the University of Granada. Subsequently, the IEQ factors (temperature, relative humidity, CO2 concentration, acoustic environment, and air velocity) were evaluated for the selected ventilation scenarios in the occupied classroom, and the field monitoring was carried out in two different assessment periods, winter and summer. The obtained results show that the CO2 concentration levels were well below the recommended limits. However, the maintenance of the recommended thermal and acoustic IEQ factors was significantly affected by the natural ventilation strategies (temperature and relative humidity values were very close to the outside values, and the background sound pressure level was over 35 dBA during the entire assessment). The proper measurements and careful selection of the appropriate ventilation scenarios become of utmost importance to ensure that the ventilation rates required by the health authorities are achieved.