We investigated the relationship between ventilation rates and work performance in a call center. We randomized the ventilation controls and measured ventilation rate, differential carbon dioxide (∆CO 2 ) concentration, temperature, humidity, occupant density, degree of under-staffing, shift length, time of day, and time required to complete two different work performance tasks (talk and wrap-up). ∆CO 2 concentrations ranged from 13 to 611 ppm. We used multi-variable regression to model the association between the predictors and the responses. We found that agents performed talk tasks fastest when the ventilation rate was highest, but that the relationship between talk performance and ventilation was not monotone. We did not find a statistically significant association between wrap-up performance and ventilation. At high temperatures agents were slower at both the talk and wrap-up tasks. Agents were slower at wrap-up during long shifts and when the call center was under-staffed. INDEX TERMSVentilation rates, Productivity, Offices, Worker performance, Carbon dioxide INTRODUCTION This paper describes part two of a two-part analysis from a productivity study performed in a call center operated by a health maintenance organization. The companion paper (Fisk et al., 2002) describes the analysis of group performance data that has good time resolution. The objective of this paper is to report the on the analysis of individual performance data acquired from the same experiment. The analysis described in this paper confirms the findings in the companion paper and reveals additional insight into the relationship between environmental factors and work performance.

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is an equal opportunity employer. DISCLAIMERPortions of this document may be illegible in electronic image products. Images are produced from the best available original document. AbstractTo test proposed methods for reducing SBS symptoms and to learn about the causes of these symptoms, a double-blind controlled intervention study was designed and implemented. This study utilized two different interventions designed to reduce occupants' exposures to airborne particles: (1) high efficiency filters in the building's HVAC systems; and (2) thorough cleaning of carpeted floors and fabric-covered chairs with an unusually powerful vacuum cleaner. The study population was the workers on the second and fourth floors of a large office building with mechanical ventilation, air conditioning, and sealed windows. Interventions were implemented on one floor while the occupants on the other floor served as a control group. For the enhancedfiltration intervention, a multiple crossover design was used (a crossover is a repeat of the experiment with the former experimental group as the control group and vice versa). Demographic and health symptom data were collected via an initial questionnaire on the first study week and health symptom data were obtained each week, for eight additional weeks, via weekly questionnaires. A large number of indoor environmental parameters were measured during the study including air temperatures and humidities, carbon dioxide concentrations, particle concentrations, concentrations of several airborne bioaerosols, and concentrations of several microbiologic compounds within the dust sampled from floors and chairs.This report describes the study methods and summarizes the results of selected environmental measurements. The environmental conditions measured during this study were typical of the conditions commonly encountered inside office buildings. Air temperatures were sometimes outside of the boundaries of the ASHRAE thermal comfort zone. The spatial and temporal variations in air temperature ranged up to a few degrees Celsius--large enough to suggest that it 1 may be important to account for variations in temperature in the evaluations of the interventions. Relative humidities were maintained within a narrow and widely accepted range (42% to 58%). Carbon dioxide concentrations were always below the 1000 parts per million guideline concentration recommended by. ASHRAE but occasionally above the lowest suggested guideline value of 800 parts per million. Carbon dioxide concentrations tended to be higher on the second floor. The effective time-average steady ventilation rates (ESVRs) were approximately equal to or above the recommended minimum rates in the ASHRAE ventilation standard. For the nineweek study period, the average ESVRs were relatively constant (e.g., f 15%), thus, temporal variation in ventilation rates were not likely to be a major confounding factor distorting the apparent effects of the interventions on SBS symptoms. The use of high efficiency air filters greatly decreased the indoor...

Mechanical ventilation of residences, with heat recovery in air-to-air heat exchangers, is an increasingly common practice. When this technique of ventilation is used in cold climates, however, freezing can occur in the air-to-air heat exchanger and substantially reduce its performance.A laboratory investigation was conducted to determine the indoor and outdoor environmental conditions that lead to freezing, the impact of freezing on performance, and the effect on performance of a common freeze protection strategy based on periodic defrosts. In experiments with three different models of air-to-air heat exchangers, the temperature of the inlet cold airstream at which freezing was initiated ranged from _3 0 C to _12 0 C and varied with the humidity of the inlet warm airstream. Freezing caused the temperature efficiency of a cross-flow heat exchanger to decrease at a rate that ranged from 1.5 to 13.2 percentage points per hour. Small rates of decrease in efficiency (0.6 to 2.0 percentage points per hour) resulted from freezing in a counterflow exchanger. The rate of decrease in efficiency depended on the airstream temperatures and humidities, and the duration of the period of freezing. The amount of time required to defrost the heat exchanger's core was 6 to 26% of the total operating time. The average temperature efficiency for freeze-defrost cycles ranged from 48 to 64 percent in tests of the cross-flow exchanger and 70 to 82 percent in tests of the counterflow exchanger. When the frequency and duration of defrosts were nearly optimal, approximately a ten to fifteen percentage point decrease in average temperature efficiency was attributed to the freezing and required defrosts. The results' suggested that the rate of performance deteriorations due to freezing can be reduced by avoiding small airflow passages that can easily be plugged with ice and by designing the exchanger so that condensed water does not drain toward the cold regions of the core. Based on this investigation, suggestions are made for future experimental studies of freezing and for improved control of freeze-protection systems.iii 9