Ventilation Rates and Office Work Performance

The influence of ventilation rates on objective (measured) office work performance has been assessed experimentally in call centers and laboratory settings representative of real offices. In call center studies [1-5], the time required to interact with clients via the telephone and perform related information processing via a computer was used as the performance outcome. The laboratory studies [6-10] had participants perform tasks representative of office work, such as proof reading of text, text typing, and simple arithmetic operations. Speed and accuracy in these simulated work tasks were measured. These studies experimentally manipulated ventilation rates while holding other factors constant to investigate the influence of ventilation rate on performance. The subjects were uninformed of the ventilation rates provided.

As an example, Figure 1 shows results from controlled laboratory studies [7, 9, 10] performed using a section of well-used 20-year old carpet (pollutant source) removed from a complaint building. Performance was improved by increasing the ventilation rate per person or by removing the carpet. For this figure, the relative performance was based on the combination of performance in typing, addition, and proof reading tests. Other data from the same research demonstrated an improvement on a test of creative thinking when the ventilation rate was increased from 6 to 20 cfm per person.

Figure 1: Controlled laboratory studies performed in Denmark show that performance, based on typing, addition, and proof reading tests, improved when an indoor pollutant source was removed (left sets of bars) or when the ventilation rate per person was increased with the pollution source present. The pollution source was a carpet taken from a complaint building. [Figure 1 reproduced with permission.]

Seppänen et al.[11] conducted a statistical analysis of data available from studies of how ventilation rates affected office work performance (which included call center work and simulated office work), plus one study of how ventilation rate in schools affected concentration and vigilance, to assess the average relationship between ventilation rate and performance of work. Figure 2 illustrates estimates of how office work performance varies with ventilation rate derived from the results of the statistical analyses of Seppänen et al. [11]. Performance (speed and accuracy) of typical office tasks improves with increased ventilation rate. For initial ventilation rates between 14 and 30 cfm (6.5 and 14 L/s) per person, the average performance increases by approximately 0.8% per 10 cfm (4.7 L/s) per person increase in ventilation rate. At higher ventilation rates, the average performance increase is smaller, approximately 0.3% per 10 cfm (5 L/s) per person increase in ventilation rate. For ventilation rates less than 14 cfm (6.6 L/s) per person, performance increases with ventilation rate seem likely; however, sufficient data are not yet available to confirm this hypothesis.

Figure 2.  Predicted performance of office work at various ventilation rates relative to performance at the indicated reference ventilation rates. The curves in Figure 2 are derived from equations representing the best fit composite weighted curve shown in Figure 2 of Seppänen et al. [11]. For ventilation rates less than 28 cfm (10.4 L/s) per person, the increased performance with ventilation rate have a 10% or smaller probability of being the result of chance (i.e., the 90% confidence interval excluded unity).

Values of relative performance (RP) can be estimated with the following equations.

 

  (1)

where X is the new ventilation rate in cfm per person and y0 equals 5.8127, 11.9260, and 20.1553 for reference (i.e., initial) ventilation rates of 15, 20, and 30 cfm per person, respectively. For other values of reference ventilation rate, y0 can be calculated as follows

 

  (2)

where XR is the reference (i.e., initial) ventilation rate in cfm per person. The equations should not be used for ventilation rates smaller than 13.8 cfm (6.5 L/s) per person or larger than 80 cfm (38 L/s) per person. The “Supporting Information” section of this document includes tabulated values of RP for convenient use in cost-benefit calculations.

Figure 2 and equations 1 and 2 are based on only nine studies and 26 data points. These studies involved only call center work and work tasks for which speed and accuracy could be readily quantified. While the predicted performance increases with ventilation rate increases are statistically significant over much of the range shown, there remains a high uncertainty about the magnitude of performance increases one should expect in actual practice. It is likely that the effects of ventilation rate on work performance varies substantially with type of work, with outdoor air quality, and with indoor pollutant emission rates or other building features that affect indoor environmental quality.

Since completion of the analysis leading to Figure 2 and equations 1 and 2, the results of six new intervention studies that changed ventilation rates and held other factors constant have been published. The designs of these studies minimize potential sources of error common to cross sectional studies, although the intervention studies have small numbers of subjects and short periods of exposure at the different ventilation rates. The key features and findings of these new intervention studies are summarized in Table 1. Each of the six studies finds statistically significant increases in some measures of performance when ventilation rates are higher. The magnitude of performance increases range among studies and among the performance tests within studies. Typically, the performance improvements with increased ventilation rates are less than 10%, but in one case the improvement is 18% and in another case the improvement is 29%. All studies also found that performance did not increase significantly in some tests and for a couple tests performance decreased significantly with increased ventilation rate. These new intervention study findings continue to indicate that higher ventilation rates improve performance but it is not known how well the results coincide with the relationship shown in Figure 2.

Table 1. Intervention studies published since 2011 investigating the association of ventilation rate with human performance.

Study

Design

Controlled Confounders

Key findings

[8]

Intervention study to change ventilation rates in chamber facility with new finishing materials that are sources of volatile organic compounds. 24 subjects. Employed various tests of typing, addition, proof reading, memory, initiative and changes in performance were assessed within individuals.

All personal factors, environmental conditions not affected by ventilation rate

As ventilation rate increased from 10.6 to 42.4 cfm per person (5 to 20 L/s per person), performance in addition, text typing, and memorization tests increased 4.7%, 5.2%, and 8.0%, respectively, with intermediate magnitude increases in performance at 21.2 cfm per person (10 L/s per person). The increases were statistically significant. In judgment, comparison, searching, and initiative tests, performance increases were smaller and not statistically significant.  

[12]

Intervention study to change ventilation rates in chamber facility. 16 subjects. Employed two-chamber design to: 1) vary ventilation rate per person while maintaining very low and constant levels of pollutants from the chamber and its furnishings; and 2) vary ventilation rate per floor area while maintaining a high and constant ventilation per person. Employed tests of decision making performance and assessed changes in performance within individuals.

All personal factors, environmental conditions not affected by ventilation rate, day of week, time of day

With an increase in ventilation rate per person from 5.5 to 18 cfm per person (2.6 to 8.5 L/s per person), there were statistically significant increases in in 7 of 8 domains of decision making performance and a statistically significant decrease in 1 domain of decision making. Relative to a large reference data set of scores, with an increased ventilation rate per person, decision making performance generally increased by 2 to 5 percentile points.

With an increase in ventilation rate per unit floor area from 0.16 to 1.1 cfm per square foot of floor area (0.8 to 5.5 L/s per square meter of floor area), there were statistically significant increases in 7 of 8 domains of decision making and a statistically significant decrease in 1 domain of decision making. Relative to a large reference data set of scores, with an increase in ventilation rate per floor area decision making generally improved by 2 to 7 percentile points.

[13]

Intervention study to change ventilation rates in chamber facility with low levels of pollutants from sources other than occupants. 24 subjects. Employed tests of decision making performance and assessed changes in performance within individuals.

All personal and environmental factors.

On average, the doubling of ventilation rate from 20 to 40 cfm per occupant (9.4 and18.8 L/s per occupant) was associated with a statistically significant 18% increase in scores in the various domains of decision making performance.

[14]

Intervention study to change ventilation rates in a chamber facility with low levels of pollutants from sources other than occupants. 25 subjects. Employed various tests of typing, addition, proof reading, attention, memory, reaction time. Changes in performance were assessed within individuals.

All personal factors, environmental conditions not affected by ventilation rate

With the high ventilation rate of 70.6 cfm per person (33.3 L/s per person) yielding 500 ppm CO2 compared to the low ventilation rate of 3.8 cfm per person (1.8 L/s per person) yielding 3000 ppm CO2, there were statistically significant improvements in speed of addition and cue utilization, and a statistically significant worsening of response time, but no statistically significant changes in several other performance tests. With 70.6 versus 15.2 cfm per person (33.3 versus 7.2 L/s per person) of ventilation, cue utilization improved but there were no statistically significant changes in other tests of performance.

[15]

Intervention study to change ventilation rate in a tutorial room. 28 subjects. Employed tests of memory, reaction time, perception, mental arithmetic. Changes in performance were assessed within individuals.

Personal factors, environmental conditions not affected by ventilation rate, except there was a slightly higher temperature (about 1 oF or 0.5 oC) when the ventilation rate was higher.

With an air exchange rate of 1.65 h-1 yielding CO2 concentrations less than 1000 ppm compared to an air exchange rate of 0.78 h-1 yielding CO2 concentrations of 1709 to 2690 ppm, there were statistically significant improvements in tests of memory, reaction time, perception, and mental arithmetic. In 7 performance tests, scores improved by 8% to 66%, with an average improvement of 29%.

[16]

Intervention study to change ventilation rates in a chamber facility with low levels of pollutants from sources other than occupants. 36 subjects. Employed various tests of typing, attention, memory, and creative thinking. Changes in performance were assessed within individuals, except the analysis of performance on two tasks compared performance of groups.

All personal factors, environmental conditions not affected by ventilation rate. The analysis of two performance tasks which compared performance of groups did not fully control for personal factors.

The reduced ventilation rate of 4.9 cfm per person (2.3 L/s per person) with a CO2 concentrations of 2260 ppm, relative to the higher outdoor air flow rate of 60.0 cfm per person (28.2 L/s) per person with a CO2 concentration of 540 ppm was associated with a statistically significant decrease in performance in one task assessing memory and with a nearly significant decrease in performance in another tasks of memory.  No other tests of performance were significantly affected by ventilation rate.