Scholarly article on topic 'A Questioning of the Thermal Sensation Vote Index Based on Questionnaire Survey for Real Working Environments'

A Questioning of the Thermal Sensation Vote Index Based on Questionnaire Survey for Real Working Environments Academic research paper on "Earth and related environmental sciences"

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{"Thermal comfort" / "thermal manikin" / "real environment assesement"}

Abstract of research paper on Earth and related environmental sciences, author of scientific article — Ilinca Nastase, Cristiana Croitoru, Cătălin Lungu

Abstract Throughout this paper, we present the results of the thermal comfort analysis in a real office using subjective data from questionnaires survey and experimental data from a thermal manikin prototype and a standardized measurement system was presented. The comparison between TSV of the questionnaires and the PMV of the Comfort Sense data showed a great dispersion for the TSV while the values of the PMV from the standardized system and from the thermal manikin were found to be close. The agreement between the thermal manikin data and the standardized system data should be related in our opinion to the possibility of having of a large scale distributed measurement system that reproduces both the global predicted thermal sensation of a real space but also gives the possibility of investigating local discomfort trough the local distributions of the equivalent temperature of the segments of the manikin. This kind of representation allows for instance the inspection of the uniformity of an environment.

Academic research paper on topic "A Questioning of the Thermal Sensation Vote Index Based on Questionnaire Survey for Real Working Environments"

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Energy Procedía 85 (2016) 366 - 374

Sustainable Solutions for Energy and Environment, EENVIRO - YRC 2015, 18-20 November

2015, Bucharest, Romania

A questioning of the Thermal Sensation Vote index based on questionnaire survey for real working environments

Ilinca Nastasea*, Cristiana Croitorua, Catalin Lungua

a CAMBI, Technical University of Civil Engineering in Bucharest, Building Services Department, 66 Avenue Pache Protopopesc; 020396,

Bucharest, Romania

Abstract

Throughout this paper, we present the results of the thermal comfort analysis in a real office using subjective data from questionnaires survey and experimental data from a thermal manikin prototype and a standardized measurement system was presented. The comparison between TSV of the questionnaires and the PMV of the Comfort Sense data showed a great dispersion for the TSV while the values of the PMV from the standardized system and from the thermal manikin were found to be close. The agreement between the thermal manikin data and the standardized system data should be related in our opinion to the possibility of having of a large scale distributed measurement system that reproduces both the global predicted thermal sensation of a real space but also gives the possibility of investigating local discomfort trough the local distributions of the equivalent temperature of the segments of the manikin. This kind of representation allows for instance the inspection of the uniformity of an environment.

© 2016Published byElsevierLtd. Thisisanopenaccess article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee EENVIRO 2015 Keywords: Thermal comfort; thermal manikin; real environment assesement

1. Introduction

Indoor environment in a building must meet two requirements: to be comfortable and functional in accordance with the requirements of the occupants. The building must protect them from adverse external conditions and to provide a pleasant ambient and indoor air quality. Thermal comfort is a subjective term defined by a plurality of

* Corresponding author. E-mail address: ilinca.nastase@cambi.ro

1876-6102 © 2016 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee EENVIRO 2015 doi: 10.1016/j.egypro.2015.12.263

sensations and is secured by all factors influencing the thermal condition experienced by the occupant, therefore is difficult to give a universal definition of this concept. Human thermal comfort is sometimes defined as all conditions for which a person would not prefer a different environment [1]. Another definition proposed in the American standard ASHRAE 55 [2] explains thermal comfort as a subjective concept related to physical and psychological well-being in agreement with the environment.

Nomenclature

CS Comfort Sense

mrt mean radiant temperature

PMV predicted mean vote

PPD predicted percentage of dissatisfied

RH relative humidity

teq equivalent temperature

ti indoor air temperature

tOP operative temperature

TM thermal manikin

TSV thermal sensation vote

Given that humans are different, thermal comfort concept usually refers to a set of optimal parameters, for which the highest percentage possible of a group of people, feel comfortable about the environment [3]. There were many attempts during the three past decades of proposing different assessment methods of this complex concept which is thermal comfort. Several models and indexes are available and standardized nowadays, proposing a quantification of the thermal comfort for buildings and other occupied spaces [4-8]. In the same time, the majority of these models or indexes usually lead to wrong results and incorrect assessment of a thermal ambiance when the depending parameters are not within a relatively narrow range of values [9-11]. The studies conducted by Fanger more than 30 years ago are the basis for the two main standards [12, 13] that are currently used for assessing thermal comfort in all types of enclosures occupied by humans. Fanger's studies, as well as many of the experimental investigations conducted afterwards, are based on real human subjects in standardized clothing and doing standardized activities, exposed to laboratory homogenous thermal environments. These studies proposed specific parameter ranges - named comfort zones - in which a large percentage of occupants of same sex, age, activity and clothing, will characterize the environment as acceptable. However, it is currently recognized that in buildings pure steady-state conditions are rarely encountered in practice, given the interactions between the building structure, the occupants, the climate conditions and the HVAC systems. On the other hand, there are several other parameters that are affecting the human perception of thermal comfort, but which are not taken into account in either of these models. After a thorough survey of the literature [14] our conclusion is that currently proposed models can be either too generalist or either too difficult to implement and judge. For instance, experimental campaigns show high discrepancies between numerical results and in situ evaluation [15] and furthermore even higher discrepancies between human subjects' response and experiments using other methods of evaluation [16, 17]. The main questions that we are addressing in our review paper [14] are: Which is the "best" thermal comfort model? Are these models adapted to nowadays indoor evaluation methods, since they have not been updated for decades? Do we need extra evaluation or just a better implementation of existing models? What are the future perspectives for thermal comfort predicting?

We wanted to check by ourselves what is happening with several standardized methods and models in a real building working environment and in this paper we are proposing several comparisons and discussion of experimental data.

2. Experimental set-up

The experimental data and correlations that we are presenting in this paper were obtained in a real office environment from the Thermal-Hydraulic Systems Laboratory at the Faculty of Building Services of Technical

University of Civil Engineering in Bucharest, Romania. The building is situated in the climatic zone II, according to climate zoning map of Romania. The laboratory building dates since 1968 and it was renovated in 2007. Its resistance structure is made of reinforced concrete and its walls are built from cellular concrete. The windows are partially operable and all are double glazed, with PVC joinery. A gas central heating system provides heating water for the steel radiators which are placed under the windows. The office is situated on first floor of the building, oriented to NNE on main façade, situated on Pache Protopopescu Avenue, as can be seen in Fig. 1 a and b. In Fig. 1 c are given dimensional characteristics of the office and a picture inside it. The net height of the office is 2.75 m. It has four big double glazed windows.

Fig. 1. (a) Position of the office Façade in the Laboratory Building, (b) Position of the office in the Laboratory , (c) Plan of the office with

dimensions

•B !■ HI ■ to mea #H

¡■B TTFff jjl 11

00 AM 9/24/14 12:00 AM 9/25/14 12:00 AM 9/26/14 12:00 AM 9/27/14 12:00 AM 9/28/14 12:00 AM 9/29/14 12:00 AM 9/30/14 12:00 AI

Fig. 2. Evolution of the outdoor and indoor temperatures and relative humidities for the entire experimental campaign

During the experimental surveys the inner heat sources were constantly the same: 20 neon lamps, 4 computers, 2 printers and 1 surveillance system. There was no direct sun light into the office. The office was occupied from 8 to 18 by 4-5 persons. 2 were women and 3 were men, with ages between 24 and 40 years old. The study was conducted during five days, between 24.09.2014 and 29.09.2014. The experimental recordings began at 9:00 AM each day and were performed during the entire period of office activity up to 3:00 PM. Exterior measurements have shown high daily temperature oscillations for both days (from 5°C to 20°C). Fig. 2a shows the hourly thermal evolutions during the considered days. The blue line corresponds to the recordings of the National Institute of Meteorology and Hydrography INMH. The points on the graphs represent measured values in our site for the outdoor temperature to as well as the indoor air temperature ti and radiant mean temperature rmt As it can be seen, in the office it was recorded a slightly constant temperatures over the working hours. In Fig 2b are given the corresponding values of the outdoor and indoor relative humidity. Three methods of evaluating thermal comfort were used: a standardized measurement device the Comfort Sense system from Dantec, a thermal manikin prototype and a questionnaire survey.

2.1. Questionnaire survey

Survey questionnaires were given hourly to the occupants of the office. A total number of 120 questionnaires were completed. The general information requested by a questionnaire was: date and time of filling, information about the person who completed the questionnaire (position in the office, age and sex). For the assessment of the thermal sensation the subjects had to choose an option on the ASHRAE 7-points scale and they also had to choose the thermal preference at the time of completion. They had to answer about the acceptability of the thermal environment and about local thermal discomfort. The questionnaire included a checklist with clothing items for people to choose from. Based on the questionnaires we could estimate the Thermal Sensation Vote (TSV) and the PPD.

2.2. Comfort Sense system

The thermal comfort parameters were evaluated with the Comfort Sense device, a system for measurement according to International Standard ISO 7730 [7] and to the standard EN ISO 14505/2[18]. The Comfort Sense sensors positioning in the office can be seen in Fig. 1c. Several measurements were performed in the same time as completion of questionnaires surveys. These measurements were continuous acquisitions of 10 minutes periods. Instantaneous values of the comfort parameters were sampled at each 2.5 seconds. In total there were obtained 120 instantaneous values for all parameters: operative temperature, relative humidity, air temperature, air speed, and draught rate for each measurement. These instantaneous values are reduced by the Comfort Sense software to average values and main index of thermal comfort, the Predicted Mean Vote (PMV) and the percentage Predicted Percentage of Dissatisfied (PPD) are calculated. The estimated values for the clothing level and for the metabolic rate were respectively 0.7 clo and 1.2 met. The positioning height of the probes on the measurement tripod of Comfort Sense was 1.2 m for the operative temperature and for the air speed probe and 1m for the humidity probe. The inclination angle for the operative temperature probe was 30° from vertical, when it stimulated a sitting person, given that the majority of occupants were sitting at desk.

2.3. Thermal manikin prototype

The thermal manikin that we used in this study is among the five prototypes of thermal manikins conceived at the CAMBI Research Center at the Technical University of Civil Engineering. The prototype used in this study as a heating source and a measurement device is presented in Fig. 3a. Its working principle is to control the surface temperature of each individual zone and to record the electrical power consumption as an indication of the thermal state of each zone. For each heating circuit (i.e. zone or "segment" of the manikin) surface temperature is maintained as a function of the indication of a process controller which in its turn depends on the temperature recording of the sensors placed on each zone. In our case there are 36 individually controlled heating zones, each of them provided with two temperature sensors. A dedicated software interface is allowing the user to specify set-point values for each surface temperature of the zones, to monitor the evolution of each temperature of the 72 available sensors and to record the electric power consumption of the segments. In this study the 36 zones were grouped in 18 zones in order to comply to the standardized procedure of the equivalent temperature (teq) evaluation as in EN ISO 14505 [19].

Fig. 3. (a) Working principle of the thermal manikin and zones, (b) Map of the zones of the manikin; (c) Manikin in the office

3. Results and analysis

Thermal comfort is a subjective response or condition of mind that people have to express satisfaction with the surrounding environment [20]. This definition highlights the high degree of subjectivity of the concept mainly due to the fact that it depends on many cultural and energy factors difficult to quantify. The office that we studied is situated in a building that is mechanically ventilated and air conditioned all the year. The windows are always closed mainly for security reasons, so the people reactions to reduce the discomfort sensations are drastically reduced.

Fig. 4 shows Evolutions of the TSV and of the global PMV from the Comfort Sense and Thermal Manikin measurements during 25.09.2014 and 26.09.2014. The acquisition times for the Comfort Sense and for the Thermal manikin were the same. In Fig.5 a and b are presented the comparison of the PMV and PPD values and of the global TSV during the same days.

Some important discrepancies can be noticed between the results derived from the Comfort Sense and the Thermal Manikin measurements and the subjective ones from questionnaires. Generally, sensations of both warmness and coldness are amplified in questionnaire answers, in comparison with the experimental results. This result is in agreement with previous analysis carried out in other studies [21, 22]. Fig. 5c shows a good correlation between tOP recorded with the standardized Comfort Sense system and the teq recorded with the thermal manikin. The results are comforting us regarding the experimental validation of the thermal manikin prototype in real field conditions against the standardized Comfort Sense system. In the same time in Fig 5d we are representing values of the TSV from the questionnaire survey and the PMV estimated from measured data from the Manikin and the Comfort Sense system versus the operative temperature for the entire experimental campaign (23-29.09.2014). This figure shows once again a great dispersion of the data collected from the questionnaire survey compared to the measured and predicted comfort indexes.

9:36 AM 10:48 AM 12:00 PM 1:12 PM 2:24 PM 3:36 PM

time [h]

♦ Ocup. 1 ■ Ocup. 2 ▲ Ocup. 3 X Ocup. 4 X Ocup. 5 ♦ PMV TM — PMV CS

8:24 AM 9:36 AM 10:48 AM 12:00 PM 1:12 PM 2:24 PM 3:36 PM

time [h]

♦ Ocup. 1 ■ Ocup. 2 k Ocup. 3 X Ocup. 4 X Ocup. 5 ♦PMV TM — PMV CS

Fig. 4. Evolutions of the TSV and of the global PMV from the Comfort Sense and Thermal Manikin measurements : (a) 25.09.2014, (b)

26.09.2014

Fig. 5. a, b) Evolutions of the global PMV and PPD from the Comfort Sense and Thermal Manikin measurements and of the TSV and PPD from questionnaires for the two days 25.09.2014 and 26.09.2014, c) Correlation between the gobal teq from the manikin and t OP from the Comfort Sense, d) TSV, PMV from the Manikin and the Comfort Sense versus the operative temperature for the entire experimental campaign

Compared to classical measurement systems which give the possibility of estimating the PMV, the thermal manikin gives the advantage of assessing locally a predicted local sensation, either through the equivalent temperature or through a derived local PMV. In Fig. 6 we represented for each measurement time the distributions of the local teq and the associated comfort zones diagrams such as defined by Nilsson [23, 24] for the two days 25.09.2014 and 26.09.2014 and in Fig. 7 are given the mean distributions of local PMV and PPD estimated from teq for the same days. The thermal manikin represents a worthy tool for the thermal comfort analysis in laboratory configurations and in real field case studies being a method of investigating local discomfort trough the local distributions of the equivalent temperature of the segments of the manikin. This kind of representation allows for instance the inspection of the uniformity of an environment.

Top Head

Front Torso

R. Upper A

R. Forearm

warm but comfortable I

cold but comfortable I

10:00 AM

too hot

2:03 PM

2:59 PM

R. Upper Arm R. Forearm

9:15 AM 10:08 AM —11:16 AM 12:06 PM

17 PM 13 PM

:01 PM

iii/f f/i/mij

! 11 JI i * 5 " v .f *

warm but comfortable I

cold but comfortable I

Fig. 6. Distributions of local teq corresponding to each measurement time and associated clothing independent comfort diagrams [23, 24] (a)

25.09.2014, (b) 26.09.2014

Top Head

Front Torso

Right Tigh L. Upper Arm

R. Upper Arm R. Forearm

R. Upper A R. Forearm

Fig. 7. Mean distributions of local PMV and PPD estimated from teq : (a) 25.09.2014, (b) 26.09.2014

Returning to the great dispersion that we found from our questionnaire survey, it is suggested by some authors that TSV would not be appropriate to be compared to predictions based on experimental data like the classical PMV index or like the teq index [25]. Indeed, thermal sensation refers to sensory unconscious detection of environmental stimulation by thermal receptors in the skin or the TSV is rather a thermal perception vote that refers to conscious interpretation and elaboration by the human brain of the sensorial data recorded by the human body. On the other hand, in other similar studies [26-29] it was observed that the votes given in the questionnaires vary always in a wider range of values with respect to the measured data, due to the personal sensation and to the possibility of giving only whole numbers. For this reason the TSV questionnaire scale would need, perhaps, to be refined to a 0.5 increment (resulting in 13 values for instance).

4. Conclusions

too hot

R. Low Leg

R. Low Leg

The results of the thermal comfort analysis in a real office using subjective data from questionnaires survey and experimental data from a thermal manikin prototype and a standardized measurement system was presented. Experimentally acquired data with the standardized system displayed the most comfortable conditions while the questionnaires evinced more critical conditions. Only a small percentage of workers often agree with the thermal

environment, and the expressed judgments by occupants amplify the sensation of lightly cold, which is averagely present in all the examined cases.

The comparison between TSV of the questionnaires and the PMV of the Comfort Sense data showed a a great dispersion for the TSV while the values of the PMV from the standardized system and from the Thermal Manikin were found to be close. Such kind of dispersion from the questionnaire survey was observed in other similar studies. A possible explanation could be related to the fact that TSV is rather a thermal perception vote that refers to conscious interpretation and elaboration by the human brain of the sensorial data recorded by the human body. In the future we will propose a redefined TSV questionnaire scale refined with a 0.5 increment.

The agreement between the thermal manikin data and the standardized system data should be related in our opinion to the possibility of having of a large scale distributed measurement system that reproduces both the global predicted thermal sensation of a real space but also gives the possibility of investigating local discomfort trough the local distributions of the equivalent temperature of the segments of the manikin. This kind of representation allows for instance the inspection of the uniformity of an environment.

Acknowledgements

This work was supported by Grant of the Romanian National Authority for Scientific Research, CNCS, UEFISCDI, PN-II-ID-PCE-2011-3-0835. Students George Madalin Chitaru and Ciprian Calianu are gratefully acknowledged.

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