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Espacios. Vol. 36 (Nº 07) Año 2015. Pág. 6

Subjective productivity in different states of thermal comfort

Produtividade subjetiva em diferentes estados de conforto térmico

Etianne Alves Souza de OLIVEIRA a *; Antonio Augusto de Paula XAVIER b; Ariel Orlei MICHALOSKI b; Flávia TORRES b; Elisandra Montes PIZYBLSKIA b

Recibido: 23/11/14 • Aprobado: 18/12/2014

Contenido

1. Introduction

2. Materials and Methods

3. Results

4. Discussion

5. Conclusion

References

1. Introduction

The aim of this article is to present the results of the analysis of statistical parameters from the scores of workers' subjective productivity in actual work situation, subjected to different states of thermal comfort. Experimental lab research, which simulate office environment, has provided evidence stating that the temperature has its effects over the workers' performance and it's measurable within a range of thermally acceptable settings. More research about ergonomic real work situation is necessary (THAM, 2010; LAN, et al, 2009; LAN, LIAN, PAN, 2010).

In lab studies Lan et al. (2009); Lan, Lian, Pan (2010); Lan, Wargocki, Lian (2011), Araújo (2012) e Batiz, et al (2009) used analytical and subjective evaluations of performance to measure the productivity of workers. These evaluations allow us to gauge how much an individual is being asked to accomplish a task that is called the human cost. It can be physical, psychological, cognitive and emotional. One of the ways to evaluate the subjective productivity is by measuring the mental workload, which involves psychical and cognitive aspects, not only from labor but also from personal environmental and social-cultural factors. According to the authors, there is no standard procedure among the Ergonomists to measure the workers' productivity, therefore NASA-TLX tool is widely used to measure the subjective productivity (CARDOSO & GONTIJO, 2012; ARAÚJO, 2012; LAN, LIAN, PAN, 2010; LAN et al, 2009).

On the other hand, researcher Gaoua (2010) questions the effects of thermal conditions over cognitive performance. It states that these effects are still vague due to the methodological variances to evaluate whether the exposure to heat itself has an adverse effect over the cognitive function and in which environmental conditions these effects occur, highlighting the need for more researches in this field. Brazilian researchers, state that there is little research that investigate characteristics of mental workload in real situation of work from ergonomic studies (CARDOSO & GONTIJO, 2010)

For the sensitivity in human responses and variability of intervening variables, the researcher Chen and Chang (2012) defends the need to care for the search criteria. Specially the ones related to the workplace and the selection of the sample group, since according to their cultural traits results can skew the results of the survey, especially in certain subjective aspects in relation to the satisfactory level of comfort.

This research used NASA-TLX tool to measure the productivity through measurement of subjective workload. It's applied worldwide for over 25 years (HART, 2006). The monitoring of environmental thermal conditions of spaces where workers perform their tasks  been made with the appliance Confortímetro Sensu. The isolation of the clothes of workers was obtained with the application of the questionnaire of subjective evaluation of thermal comfort and the metabolic rate was a search criteria previously established. Analytical comfort was calculated and grouped into; neutral, slight warm and slight cool. The groups were statistically analyzed using parametric and non-parametric analysis.

2. Materials and Methods

Site

The research was set in five different companies, 49 works was research. These company's  office make use of naturally ventilated buildings, located in a region with thermal regime that allows the human thermal comfort. The selected region has annual average temperature between 17º and 18º C, with average minimum of 13º and 14º C and maximum 24º and 25º C (FIGURE 01-05). These thermal characteristics foment the usage of buildings with natural ventilation systems, favorable to human comfort during sedentary activity (LAN, LIAN, PAN, 2010).

Search criteria

All the companies have sedentary activity as the main task performed by its workers. The metabolic rate of 70 W/m², typical for office works. The mental workload is greater than the physical load. All the companies develop their activities in naturally ventilated environment. The employees work under the same thermal environmental conditions. The companies are located in the same geographic region, which ensures a similar thermal acclimation to workers. Workers perform their duties for at least six months ensuring familiarity with the task performed. All protocols of Ethics Committee on Researchhave been met according to Resolução 466/12 of NationalHealth Council –BR.

Tools

The subjective productivity assessment tool used was NASA TLX - Workload that consists of six questions that identify: mental, physical demand, forecast, performance, effort, frustration. It measures productivity and worker's perspective and it's a tool used internationally for this purpose (NASA AMES RESEARCH, 1986; LAN, LIAN, PAN, 2010; CARDOSO & GONTIJO, 2012).

The tool for measuring thermal comfort was Confortímetro Sensu installed in the workplace, which measures four thermal environmental variables from space where the workers were performing their tasks. The data were collected every five minutes and were installed during the work shift; collecting procedures obey standards from ISO 7730 (2005).

Along with NASA TLX – Workload was also applied subjective thermal comfort evaluation using the seven-point scale. With this evaluation, it was possible to identify the clothing used by the worker. The isolation level of the garment is one of the variables of the equation of thermal comfort analysis (ISO 7730, 2005).

3. Results

Sample characteristics

Four room works of the first company evaluated, each in your room with a variable number of people, in total 10 workers were subjects of the research in the first company. The second, third and fourth companies work in a unique space; seven, eight and four people work in them respectively, in fifth company, four workers evaluated in four different rooms. It reaches 33 workers generated 49 evaluations.

The sample is random, simple and independent; composed by workers of both genders, young and with an average age of 31 years (+/-11.79), most have higher education, and works in the same function for an average of five years.

Sample groups

Analytical evaluation of comfort of workers ranged from 1.43 to-1.39; values according to ISO 7730 (2005) represent, analytically, slightly warm and slightly cool respectively, the average score was 0.05 (+/-0.66) indicating state of neutral thermal.

The sample groups were divided into three groups: Group 01 – scores of productivity of workers in a state analytical neutral thermal; Group 02 – scores of workers' productivity in slightly warm; Group 03 – scores of workers slightly cool, the limit of analytical neutral thermal considered was -0.5 to + 0.5

Normality

The three groups of data, in this survey, presented normality's statistics. They showed no outliers, i.e. discrepant values. The normality of both groups was detected graphically using histogram, boxplot (FIGURES 01 – 09), as well as, by means of statistical tests of normality: K-S, Shapiro-Wilk and Liliefors, all showed values below the critical values and reference P-value > 0.05 except for second group which presented low normality rate.

The results of tests of normality the first group was: K-S= 0.10668 p-valor > 0.05, Lilliefors p-value >0.05 and Shapiro-Wilk- 0.96769 p-value > 0.05, confirming the normality of this group. The second group the results with α = 0.05 was: K-S= 0.32453 p-value < 0.02; Lilliefors p-value <0.01, and Shapiro-Wilk- 0.78438 p-value < 0.007, rejecting the normality. It is noted that the data do not show normality with α=0.05, but present normality with α=0.01. The conclusion is that the data is not strict, so normalcy can make use of testing parameters with low requirement of normality or non-parametric tests that do not require normality for data analysis. the result of the tests of normality in third group were: K-S= 0.19607 p-value > 0.05, Lilliefors p-value >0.05 and Shapiro-Wilk- 0.92073 p-value > 0.05, confirming the normality.

Statistical Parameters

The statistical parameters of the study groups show that, in a state of neutral, the first group the workers had a higher workload request. A similar average was obtained in a state of slight warm. The requirement of the workload in slight cool was about 12.86% lower. It was observed that in a state of slight warm or cool the scores show variability much higher than in state of comfort.

Hypothesis 01: The workload scores of an office worker performing his task in three different states of analytical thermal comfort are derived from samples with the same averages.

Initially a test made with ANOVA, establishing the thermal comfort as one factor.

Hypothesis 02: Was conducted the non-parametric test Kruskal-Wallis, considering:

H 0: equal medians (original statement)                              H 1: different medians

Interpretation:

ANOVA single factor statistics presented P-value = 0.083> 0.05 reference value and Fa < Fc, which leads to support the affirmative that the original data comes from sample with equal average. The non-parametric test Kruskal-Wallis supported the results presented by ANOVA, once it presented p-value 0.214 >0.05. It's not possible to state, statistically in this sample, that workers in these states have greater workload, since the difference between the averages of the three groups is not significant.

4. Discussion

The results of this research show different workload averages, but not statistically different enough to support the state of comfort changes productivity; an explanation for the difference of the results can be in the type of research. Similar experiments of  Lan et al. (2009); Lan, Lian, Pan (2010); Lan, Wargocki, Lian (2011) (2009, 2010) done in laboratory where all variables are controlled or accompanied, and the respondents were under previously defined and idealized working conditions. This research data collection occurred in actual work environments where external factors and several variables can interfere with workers. The same researcher notes that motivated people can maintain high performance for a short period of time under adverse environmental conditions (heat or cold). Chen and Chang (2012) foresees this human sensitivity that can lead to different results.

The data this input research contributes with more Brazilian research about subjective productivity in real working environment. It presents different result than the experimental researches have been observing, which shows that more research in real environment in order to confront the results from lab experiments is needed. (CARDOSO & GONTIJO, 2012).

It confirms Gaoua (2010) position, who argues that the effects of thermal conditions on cognitive performance is still vague; due to methodological discrepancies in evaluating whether the exposure to heat, by itself, has adverse effect on cognitive function and environmental conditions under which these effects appear. Added to this the fact that in real environments have difficult intervening variables to be controlled or even identifiers.

The activation of the nervous system raises the state of mental alert, this is a preferred state of mind in carrying out tasks that require attention, time and demand performance. How long this ideal state of alert lasts, and as thermal comfort may interfere are issues that laboratory and applied research seek to know more accurately (THAM, 2010).

Better understanding of thermal comfort will help improve working conditions influencing health, satisfaction and productivity of employees, important gains can be achieved at individual, organizational and societal level.

Boscolo (2011) it was found that a strategic model that is permeated with notions that combine innovation and value creation can effectively contribute to business performance in several aspects. Productivity and comfort of workers should be associated with company's management.

5. Conclusion

Based on the results of this survey the state of thermal comfort has not Been Able to generate Differences in average scores of Subjective workers' productivity performing the same tasks under different thermal comfort condition, Which Compared with similar research Internationally and nationally Conducted shows the need for more research in real environments.

 The results support what other outside researchers have Identified about NASA TLX tool. It is a well accepted tool, fast and contemplates major workloads Which workers are exposed to.

 Based on the results, this research, shows the need to Identify their situations where workers are in thermal discomfort by warm and cool. In order to ASSESS Whether These thermal sensations are able to change the scores of productivity, since this survey in the States of discomfort Were Obtained analytically slightly warm and slightly cool. Once These states of analytical comfort are too close to the state of comfort preferred by many workers. Stand out more research is Necessary in real work environments.

Acknowledgement

To the "Conselho Nacional de DesenvolvimentoCientífico e Tecnológico" (CNPq), National Counsel for the Scientific and Technological Development, for the financial support.

References

Araújo. M. E. M. (2012); Desempenho Cognitivo em Ambiente. Portugal: UMinho,. Tese (mestrado em Engenharia Humana) Universidade do Minho. Escola de Engenharia.

Batiz, E. C., et al.(2009); Avaliação do conforto térmico no aprendizado: estudo de caso sobre influência na atenção e memória. Produção, v. 19, n. 3, set./dez., p. 477-488.

Roberto Sbragia y Rodrigo Boscolo, (2011); Estratégia, inovação e desempenho: uma análise da relevância da inovação de valor no desempenho das empresas. Espacios. Vol. 32 (1), pg. 37.

Cardoso, M. S, Gontijo, L. A, (2012); Avaliação da carga mental de trabalho e do desempenho de medidas de mensuração: NASA TLX e SWAT. Gestão. Produção., São Carlos, v. 19, n. 4 ,  873-884.

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N. Gaoua. (2010); Cognitive function in hot environments: a question of methodology. Scand J Med Sci Sports.: v.20 (Suppl. 3):60–70.

Sandra G. Hart. (2006); Nasa-Task Load Index (NASA-TLX); 20 Years Later. Proceedings of the Human Factors and Ergonomics Society Annual Meeting 2006 50: 904.

International Organization for Standard, 2005. ISO 7730 - Ergonomics of the thermal environment — Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria, Geneva.

LI Lan, Zhiwei Lian. (2009); Neurobehavioral approach for evaluation of office workers' productivity: The effects of room temperature. Building and Environment 44, 1578–1588.

Li Lan, Zhiwei Lian, Li Pan. (2010); The effects of air temperature on office workers' well-being, workload and productivity-evaluated with subjective ratings. Applied Ergonomics, 42, 29 – 36.

Li Lan, Pawel Wargocki, Zhiwei Lian. (2011); Quantitative measurement of productivity loss due to thermal discomfort. Energy and Buildings, 43, 1057–1062.

Kwok Wai Tham, Henry Cahyadi Willem. (2010); Room air temperature affects occupants' physiology, perceptions and mental alertness. Building and Environment, 45, 40–44

a Department of Higher Education, Federal Institute – Maranhão

*Correspondingauthor. E-mail: etianne­_oliveira@hotmail.com

b Post-graduation Program in Production Engineering - Federal University of Technology Paraná -Campus Ponta Grossa, PR - Brazil