A study of the relationship between outside air ventilation rate and concentrations of volatile organic compounds (VOCs) generated indoors was conducted in a call center office building. The ...building, with two floors and a total floor area of 4600
m
2, is located in the San Francisco Bay Area, CA. Ventilation rates were manipulated with the building's four air handling units (AHUs). VOC and CO
2 concentrations in the AHU returns were measured on 7 days during a 13-week period. VOC emission factors were determined for individual zones on days when they were operating at near steady-state conditions. The emission factor data were subjected to principal component (PC) analysis to identify groups of co-varying compounds. Potential sources of the PC vectors were ascribed based on information from the literature. The per occupant CO
2 generation rates were 0.0068–0.0092
l
s
−1. The per occupant isoprene generation rates of 0.2–0.3
mg
h
−1 were consistent with the value predicted by mass balance from breath concentration and exhalation rate. The relationships between indoor minus outdoor VOC concentrations and ventilation rate were qualitatively examined for eight VOCs. Of these, acetaldehyde and hexanal, which likely were associated with material sources, and decamethylcyclopentasiloxane, associated with personal care products, exhibited general trends of higher concentrations at lower ventilation rates. For other compounds, a clear inverse relationship between VOC concentrations and ventilation was not observed. The net concentration of 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate isomers, examples of low-volatility compounds, changed very little with ventilation likely due to sorption and re-emission effects. These results illustrate that the efficacy of ventilation for controlling VOC concentrations can vary considerably depending upon the operation of the building, the pollutant sources and the physical and chemical processes affecting the pollutants. Thus, source control measures, in addition to adequate ventilation, are required to limit concentrations of VOCs in office buildings.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Abstract Background The promising utility of multi-modality evoked potential batteries to objectively measure multi-tract dysfunction has been evaluated by several groups using different methods. ...Objective To independently evaluate the use of multi-modality evoked potential batteries as surrogate biomarkers for both physical and cognitive status in a cohort of Primary Progressive Multiple Sclerosis patients and identify the most potentially useful scoring method of those described. Methods 28 Patients with Primary Progressive Multiple Sclerosis underwent clinical evaluation with Kurtzke’s Modified EDSS and the Multiple Sclerosis Functional Composite (MSFC). 19 Participants also underwent the Minimal Assessment of Cognitive Function in Multiple Sclerosis. Visual, Brainstem Auditory, Somatosensory and Motor Evoked Potentials were recorded on all. Results were graded by variants of the Global Evoked Potential Score, Multiple Evoked Potential Score and Summation of Z transformed Evoked Potential Latencies for correlation against the clinical scores. Conclusions Multi-modal evoked potential batteries generally show moderate and useful correlation with clinical status as measured by the regulatory standard of EDSS (r= .65 vs. mEPS p <.005) and MSFC (r= .39 vs. mEPS p <.05). The graded qualitative mEPS scoring system displayed the strongest relationship although the influence of scoring system applied appeared reassuringly minimal. Non-association with cognitive impairment is an important limitation however.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
In chamber experiments, we investigated the ventilation effectiveness and thermal comfort of a task ventilation system with an air supply nozzle located underneath the front edge of a desk and ...directing air towards a heated mannequin or a human volunteer seated at the desk. The task ventilation system provided outside air, while another ventilation system provided additional space cooling but no outside air. Test variables included the vertical angle of air supply (-15 degrees to 45 degrees from horizontal), and the supply flow rate of (3.5-6.5 l/s). Using the tracer gas step-up and step-down procedures, the measured air change effectiveness (i.e., exhaust air age divided by age of air in the breathing zone) in experiments with the mannequin ranged from 1.4 to 2.7 (median, 1.8), whereas with human subjects the air change effectiveness ranged from 1.3 to 2.3 (median, 1.6). The majority of the air change effectiveness values with the human subjects were less than values with the mannequin using comparable tests. Similarly, the tests run with supply air temperature equal to the room air temperature had lower air change effectiveness values than comparable tests with the supply air temperature lower ( approximately 5 degrees C) than the room air temperature. The air change effectiveness values are higher than typically reported for commercially-available task ventilation or displacement ventilation systems. Based on surveys completed by the subjects, operation of the task ventilation system did not cause thermal discomfort.
With a desk-edge-mounted task ventilation system it is possible to obtain an increase in the effective ventilation rate of 50%. This could lead to reduced energy use. Also, this improvement can be gained while maintaining thermal comfort for occupants. Thus occupants can be thermally comfortable and save energy at the same time.
Full text
Available for:
BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
We investigated the relationship between ventilation rates and individual work performance in a call center, and controlled for other factors of the indoor environment. We randomized the position of ...the outdoor air control dampers, and measured ventilation rate, differential (indoor minus outdoor) carbon dioxide (DeltaCO(2)) concentration, supply air velocity, temperature, humidity, occupant density, degree of under-staffing, shift length, time of day, and time required to complete two different work performance tasks (talking with clients and post-talk wrap-up to process information). DeltaCO(2) concentrations ranged from 13 to 611 p.p.m. We used multivariable 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 strong or monotonic. We did not find a statistically significant association between wrap-up performance and ventilation rate. Agents were slower at the wrap-up task when the temperature was high (> 25.4 degrees C). Agents were slower at wrap-up during long shifts and when the call center was under-staffed.
The productivity benefits of ventilation rates that exceed common standards such as ASHRAE Standard 62 may be small (0-2%), and other factors may have a larger impact on productivity. Understaffing and long shifts should be avoided because both showed a negative impact on performance. In this study, high temperature had the largest statistically significant impact on productivity and was caused by occupants fighting over the thermostat setpoint. Care should be taken to avoid high temperatures in call centers. If occupants are allowed to adjust temperature setpoints, then the size and/or duration of the setpoint change should be restricted.
Full text
Available for:
BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
PDF
