Cornell University Ergonomics Web

Effects of Indoor Environmental Conditions on Computer Work Performance


By Alan Hedge & Daniel Gaygen


Indoor environmental conditions can affect measures of productivity. The performance of simulated office tasks improves with an increase in the ventilation rate from 3 to 30 l/s/p [1].  Call center operator performance has been shown to improve with a high outdoor air supply and a new filter [2,3]  although not all studies have found this effect  [4.  When the temperature is outside of a range from 21- 25C there is an average 2% decrement in work performance per degree C temperature rise [5].  It has been suggested that providing workers with individual control over a +3C range should produce ~3% increase in cognitive and skilled manual performance and ~ 7% increase in typing performance [6].  In experimental laboratory studies, computer task performance has been shown to be impaired by polluted air from an old carpet [7,8] and by emissions from old personal computers [9] . In field studies negative associations have been found between self-reports of productivity and sick building syndrome complaints [10] and positive associations with the use of personal ventilation control [11].


The present study investigated the effects of environmental changes in the office workstation microclimate on objectively measured changes in work output at that workstation over an extended period in the offices of a participating law firm housed in a 2 story air conditioned office building in Garden City, New York, USA.  Sixteen employees participated in the study.  A web-based software system (Prodyx-PDX) was being used to gather computer work performance data minute by minute.  Air temperature, relative humidity, carbon dioxide (CO2), respirable particulates at 10 microns (PM10) and total volatile organics (TVOC) were used as measures of indoor environmental quality (IEQ). These measures also were logged minute by minute by a custom-built unit. Air temperature and relative humidity also were measured at some of the workstations for some of the study period using portable data logger. All data were aggregated as means over 1 hour periods and these data were analyzed iteratively using the Mixed models procedure to find the best solution. All data distributions were examined for normality. Mean correct keystroke and error rates were log transformed (ln). Data also were lagged in one-hour intervals.


Results show significant contemporaneous effects of mean CO2 had a significant effect on mean mouseclicks/minute (p= 0.001) and air temperature affected the ln mean correct keystrokes/minute (p= 0.031). At 19C the average keying rate was 12 keystrokes/minute, at 20C this rose to 25/minute, at 22C is was 35/minute, at 26C is was 38/minute and at 28C it was 40/minute. There was a 40% increase in keying output when the  temperature was 22C rather than 20C.


Results also showed significant lagged effects for the 1 hour lagged data for mean CO2 (p = 0.05) and mean PM10 (p = 0.017) on ln mean error keystrokes/minute (i.e. conditions experienced at one time affected work performance 1 hour later). There were no effects for the 2 hours lagged data.


Findings from this study show that certain indoor environmental quality variables (air temperature and carbon dioxide) have immediate effects on objective measures of the quantity of computer work activity performed and that indoor environmental quality variables (CO2 and respirable particulates) also can have short-term lagged effects on the accuracy of computer work.

 

Acknowledgements

This research was funded by the U.S. E.P.A. We also thank Jim Smith, Syracuse University, for help with this work.
 


References
 

  1. Wargocki, P., Wyon, D.  & Fanger, P. O.(2000) Productivity is affected by the air quality in offices Proceedings of Healthy Buildings 2000, Vol. 1, pages: 635-640, 2000, Helsinki, Finland.

  2. Wargocki, P., Wyon, D.P., & Fanger, P.O. (2003) Call center operator performance with new and used supply air filters at two outdoor air supply rates, Proc. Healthy Buildings 2003, 3, 213-218, Singapore.

  3. Tham, K.W., Willem,H.C., Sekhar,S.C., Wyon, D.P. & Wargocki, P. (2003) Temperature and ventilation effects on the work performance of office workers: study of a call-center in the Tropics, Proc. Healthy Buildings 2003, 3, 280-286, Singapore.
     

  4. Fisk, W.J. (2002) Health and productivity gains from better indoor environments and their relationship with building energy efficiency, Annual Rev. Energy Environ., 25, 53766.
     

  5. Seppnen, O., Fisk, W.J., & Faulkner, D. (2003) Cost benefit analysis of the night-time ventilative cooling in office building, Proc. Int. Conf. on Healthy Buildings, Singapore 7-12 Dec.
     

  6. Wyon, D.P. (1996) Individual microclimate control: required range, probable benefits, and current feasibility. Proc. Indoor Air 96, 7th Int. Conf. Indoor Air Qual. Clim. 1, 106772. Nagoya, Jpn: SEEC Ishibashi.
     

  7. Wargocki, P., Wyon, D.P., Baik, Y.K., Clausen, G. and Fanger, P.O. (1999) Perceived air quality, sick building syndrome (SBS) symptoms and productivity in an office with two different pollution loads, Indoor Air, 9, 165-179.
     

  8. Lagercrantz, L., Wistrand, M., Willen, U.,Wargocki, P., Witterseh, T., & Sundell, J. (2000) Negative impact of air pollution on productivity: Previous Danish findings repeated in new Swedish test room. Proc. Healthy Buildings 2000, 1, 653-658, Helsinki.
     

  9. Bako-Biro, Z., Wargocki, P., Weschler, C.J., & Fanger, P.O. (2002) Personal computers pollute indoor air: effects on perceived air quality, SBS symptoms and productivity in offices, Proc. Indoor Air 2002, 2, 249-254, Monterey.
     

  10. Hedge, A., Burge, P.S., Wilson, A.S. & Harris Bass,  J. (1989) Work related illness in office workers: a proposed model of the sick building syndrome, Environment International, 15, 143 158.
     

  11. Kroner, W.M., & Stark-Martin, J.A. (1992) Environmentally responsive workstations and office worker productivity. In Proc. Indoor Environ. Product., June 2326, Baltimore, MD, H. Levin (Ed.), Atlanta, GA, ASHRAE.

 

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