Josephine Lau

(1) The association of the indoor environmental conditions in classrooms with illness-related absenteeism (IRA) was not well investigated. In addition, studying the association between heating and non-heating seasons were very limited; (2) To fill this knowledge gap, a research team collected various indoor air quality (IAQ) and thermal comfort conditions (TC) of 85 elementary classrooms in two school districts from the Midwestern United States throughout an academic year; in total, 255 classroom visits were performed. A negative binomial regression model was implied to associate the classroom’s IAQ and TC with IRA, separating for heating and non-heating seasons; (3) During non-heating season, a 3% increase of IRA was estimated with 1,000,000-counts/L increase of particles that had a diameter less than 2.5 μm (PN2.5); during the heating season, a 3% increase of IRA were expected with 100 ppm increase of room averaged CO₂ concentration; and (4) These results suggested that the IAQ and TC factors could associated with IRA differently between heating and non-heating seasons.

Recently, the requirement to continuously collect bioaerosol samples using shorter response times has called for the use of real-time detection. The decreased cost of this technology makes it available for a wider application than military use, and makes it accessible to pharmaceutical and academic research. In this case study, real-time bioaerosol monitors (RBMs) were applied in elementary school classrooms—a densely occupied environment—along with upper-room ultraviolet germicidal irradiation (UVGI) devices. The classrooms were separated into a UVGI group and a non-UVGI control group. Fluorescent bioaerosol counts (FBCs) were monitored on 20 visiting days over a four-month period. The classroom with upper-room UVGI showed significantly lower concentrations of fine size (<3 μm) and total FBCs than the control classroom during 13 of the 20 visiting days. The results of the study indicate that the upper-room UVGI could be effective in reducing FBCs in the school environment, and RBMs may be applicable in reflecting the transient conditions of the classrooms due to the dynamic activity levels of the students and teachers.

In Part 1 of this article, a CO₂-based dynamic reset was proposed and evaluated as an energy-saving demand-controlled ventilation strategy by reducing the outdoor airflow rate when the occupancy is under design occupancy. Further energy-saving potential still exists when the zone primary airflow rate is modulated or reset instead of only resetting the outdoor airflow. Two new control strategies are presented: a CO₂-based dynamic reset, now combined with a zone primary airflow set-point reset in Part 2. The system level of these control strategies is the same as CO₂-based dynamic reset in Part 1. The additional control features are added at the zone level. The zone primary airflow rate minimum set-point will first be reset to increase system ventilation efficiency, which will lead to a reduced system outdoor airflow rate. With this proposed dynamic reset with zone primary airflow set-point reset, the design minimum zone primary airflow rate can be designed lower than the regular set-point used in variable air volume terminal box minimum set-points. This new setting reduces the energy consumption for the system supply fan as well as energy consumption for terminal reheating. Both energy simulation and airflow simulation were conducted in different locations of a building. In this article, the results show that the proposed strategies of CO₂-based dynamic reset with zone primary airflow set-point reset consume less energy when compared to CO₂-based dynamic reset presented in Part 1 and the baseline case “without demand-controlled ventilation.” The average annual system outdoor airflow rates for the two options of the proposed demand-controlled ventilation are 44.1% and 45%, respectively, less than the outdoor airflow rate for the case without demand-controlled ventilation. Therefore, the proposed demand-controlled ventilation control strategies are suggested to consider for CO₂-based demand-controlled ventilation for multiple-zone single duct VAV systems with terminal reheat.

This article describes a casestudythe authors conducted in an elementary school in the Midwest. The objective was to evaluate the performance of ultraviolet germicidal irradiation (UGVI) to reduce the bioaerosol concentration in a classroom. Two fourth grade classrooms with the same dimensions were studied. One classroom was designated as the UVGI group and the other as the control group. Two-stage Tisch culturable impactors were utilized for collecting airborne bacteria with monthly samples collected from October 2012 to January 2013. Nonparametric methods were applied and p-values smaller than .05 were deemed significant. The concentrations of airborne cultural bacteria with a smaller size (1-8 pm) and the total bacterial concentrations from the UVGI classroom were significantly lower than those of the control room in three of four sampling months. These results could provide the preliminary results necessary to determine the effectiveness of upper-room UVGI in reducing the concentration of airborne cultural bacteria in classrooms and other buildings.

Upper room ultraviolet germicidal irradiance (UVGI) has been shown to reduce the concentration of bioaerosols in controlled chambers. However, there is a lack of experimental results on the reduction of bioaerosol concentrations by UVGI devices in actual uncontrolled buildings. This study was carried out in an American elementary school in the Midwest. Two sampling procedures were carried out in six selected classrooms with similar dimensions that were separated into two groups: (1) UVGI exposure group and (2) non-UVGI control group. Two-stage Tisch culturable impactors were utilized to collect airborne culturable bacteria and fungi. Monthly samples were collected during unoccupied period in sampling Procedure A and during close-to-occupied periods in sampling Procedure B. Student absenteeism data were collected. Nonparametric statistical methods were applied. Neither analysis of microorganisms nor student absenteeism showed a significant difference between the UVGI exposure and non-UVGI control groups in Procedure A. Analysis of the airborne culturable fine and total bacteria levels (1–8 µm) was significantly lower in the exposure classroom than those of the control classroom using Procedure B (P values < 0.05). The result indicates that collecting airborne bacteria close to occupied time could be more effective in evaluating the performance of upper room UVGI. In this case study, upper room UVGI can reduce culturable bioaerosols in a crowed environment like classrooms.

Demand controlled ventilation (DCV) is used to reduce the system outdoor airflow (OA) when the occupancy of the system is under design occupancy. However, the new versions of ASHRAE Standard 62.1-2010 make DCV more difficult to implement for multiple zone HVAC systems. This article proposes a CO₂-based and occupancy-sensor-based dynamic reset of OA rate for multiple zone HVAC systems (“CO₂-based DR”). This control strategy uses bioeffluent load estimation with a steady-state assumption to calculate and dynamically reset the system OA rate minimum set-point by solving the multiple-zone system equations for current conditions. Building energy and airflow simulations were implemented to assess the energy performance and indoor air quality of this control strategy. The simulation results showed that the average annual system OA rate for CO₂-based DR is 14.6% less than the OA rate for without DCV, in which case the system OA is always maintained as constant. The annual monetary saving as a percentage of the baseline case (without DCV) is between 0.3% and 11.0% for 16 climate zones in the United States.