Scholarly article on topic 'Thermal Comfort Analysis of PMV Model Prediction in Air Conditioned and Naturally Ventilated Buildings'

Thermal Comfort Analysis of PMV Model Prediction in Air Conditioned and Naturally Ventilated Buildings Academic research paper on "Earth and related environmental sciences"

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Energy Procedia
Keywords
{"PMV (Predicted mean vote)" / "NV (naturally ventilated) buildings" / "ASH (ASHRAE thermal sensation scale) ;"}

Abstract of research paper on Earth and related environmental sciences, author of scientific article — Syed Ihtsham ul Haq Gilani, Muhammad Hammad Khan, William Pao

Abstract Energy saving in commercial and residential buildings have a potential with respect to improvement of thermal comfort standard. Predicted Mean Vote (PMV) model is considered to be most recognized in thermal comfort standards. Analysis of PMV model in naturally ventilated and air conditioned buildings present the percentage of under/over estimation level. PMV equation underestimates thermal sensation by 13% in summer season and overestimates by 35% in winter season, for NV buildings whereas in case of HVAC buildings overestimation is found to be 31% and 33% in the summer and winter seasons respectively. Percentage deviation of overestimation rate in HVAC buildings is higher than NV buildings.

Academic research paper on topic "Thermal Comfort Analysis of PMV Model Prediction in Air Conditioned and Naturally Ventilated Buildings"

Procedía

The 7th International Conference on Applied Energy - ICAE2015

Thermal comfort analysis of PMV model Prediction in Air conditioned and Naturally Ventilated Buildings

Syed Ihtsham ul Haq Gilania*, Muhammad Hammad Khanb, William Paoc

_abcMechanical Engineering Department. Universiti Teknologi PETRONAS, Seri Iskandar 31750, Malaysia_

Abstract

Energy saving in commercial and residential buildings have a potential with respect to improvement of thermal comfort standard. Predicted Mean Vote (PMV) model is considered to be most recognized in thermal comfort standards. Analysis of PMV model in naturally ventilated and air conditioned buildings present the percentage of under/over estimation level. PMV equation underestimates thermal sensation by 13% in summer season and overestimates by 35% in winter season, for NV buildings whereas in case of HVAC buildings overestimation is found to be 31% and 33% in the summer and winter seasons respectively. Percentage deviation of overestimation rate in HVAC buildings is higher than NV buildings.

© 2015TheAuthors.Publishedby ElsevierLtd.Thisis 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 Applied Energy Innovation Institute

"Keywords: PMV (Predicted mean vote); NV (naturally ventilated) buildings; ASH (ASHRAE thermal sensation scale);"

CrossMark

Available online at www.sciencedirect.com

ScienceDirect

Energy Procedia 75 (2015) 1373 - 1379

1. Introduction

Optimization of energy in buildings is considered to be highlighted area in the modern era of scientific research. Energy consumption in buildings have been increased from 24% to 40% in developed countries [1,2]. Designers play a vital role in defining the air conditioning load on the basis of thermal comfort standard [3]. Thermal comfort is defined as a state in which heat balance across the body and environment is in equilibrium state. There are two well-known thermal comfort models that are used internationally to establish the thermal comfort conditions in an air conditioned and naturally ventilated buildings, namely (i) Predicted Mean Vote (PMV) model [4], and (ii) the adaptive model [5]. The objective of this study is to find out the percentage deviation in prediction level of PMV model for NV and AC buildings and to highlight the over prediction behavior of PMV model in air conditioned buildings.

* Corresponding author. Tel.: +60-5-3687029; fax: +60-5-3656461. E-mail address: syedihtsham@gmail.com

1876-6102 © 2015 The Authors. 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 Applied Energy Innovation Institute

doi: 10.1016/j.egypro.2015.07.218

Nomenclature

PMV Predicted mean vote

NV Naturally ventilated

MCI McIntyre index

TSV Thermal sensation vote

ASH ASHRAE thermal sensation scale

Pa Partial water vapour pressure

Icl Thermal resistance of clothing

tcl Surface temperature of clothing

hc Convective heat transfer coefficient

tr Radiant temperature

ta Air temperature

PPD Predicted percentage of dissatisfied

HVAC Heating ventilation and air conditioned

AC Air conditioned M Metabolism rate W External work

1.1. Literature survey

PMV model is considered as widely used and standard model but its universal behavior has been questioned when applied in different climate zones and type of buildings [6]. On the basis of field studies, the misinterpretation in expected value such as metabolism rate in PMV equation is one of the cause due to which deviation occur from neutral sensation [7]. Expectancy factor 'e' in PMV model was introduced in the naturally ventilated buildings due to different field studies verifying under prediction of PMV model [8,9]. A number of over predictions have been found among the end user with respect to PMV model for air conditioned buildings, In Singapore onsite survey in office building reveals that PMV model and TSV (thermal sensation vote) has a difference of 1.5 degree Celsius [10]. ASHRAE standard incorporate the adaptive model as another method to calculate the thermal comfort for naturally ventilated buildings which determines the validity of PMV Model [11]. Current field base analysis (ASHRAE RP-884 database) reveals about the over prediction of PMV model in comparison to actual mean vote in AC buildings, whereas De Dear's adaptive model [5] conclude that PMV model prediction in AC buildings found to be acceptable.

2. Methodology

2.1. ASHRAE standard

American Society of heating refrigeration and air conditioning engineers (ASHRAE) standard 55-2004 elaborates the use of Fanger's heat balance equation for the calculation of PMV to determine the scale of thermal comfort as shown in equation (1). A prime goal of air conditioning is to provide neutral sensation (comfort) of personnel by adding and removing heat of the space. To improve the performance of buildings and thermal comfort standard, ASHRAE provide the guidelines for the designers [12].

PMV = (0.303exp-0.0336M + 0.028) x { (M - W ) - 3.5 x 10-3 [5733 - 6.99 ( M - W )- pa ] - 0.42 (M - 58.5) - 1.7 x10-5 x M (5867 - pa ) - 0.0014M (34 - ta ) - 3.96 x 10-8 fcl [ ( tcl + 273 )4 - ( tr +

PMV is calculated on the basis of 4 measurable quantities (air velocity, air temperature, mean radiant temperature and relative humidity) and 2 expected parameters (clothing and metabolism rate), Vote generated from PMV is also considered as index value to determine the thermal sensation of the subject as shown in fig. 1(b).

273 )4] -fcl x hc ( tcl - ta ) }

McIntyre index (MCI) is a 3-point sensation scale with the responses 'Cooler', 'No change' and 'warmer' as shown in Fig.1(a), whereas ASHRAE thermal sensation (ASH) is 7-point scale on the basis of Fanger's heat balance equation as shown in Fig. 1(b).

Fig. 1. Thermal sensation scale (a) MCI (McIntyre Index); (b) ASH (ASHRAE thermal sensation scale) and PMV scale

ASH and MCI scale were used to find out the subject's feeling about the environment by casting a vote, whereas PMV model value is calculated through inputs of six parameters as discussed in equation (1). In order to find out the accuracy of PMV model, Comparison have been made of ASH, MCI thermal sensation scale with PMV scale.

2.2. Thermal acceptability criterion

Thermal environment that satisfies 100% of the occupant is impossible due to individual thermal conception, therefore a criterion is setup by ISO 7730 (international standard organization) to satisfy a maximum number of subjects [13]. Class A, B and C given in Table 1 describe the range of thermal sensation of PMV equation. Class A represent the highest satisfaction of environment whereas class B is the moderate requirement of satisfaction level and class C is minimum requirement of examination criterion within the thermal comfort criterion.

Table 1. Thermal Acceptability criterion [13]

Class A B C

PMV -0.2 < PMV < +0.2 -0.5 < PMV < +0.5 -0.7 < PMV < +0.7

PPD (%) <6 <10 <15

2.3. RP-884 Database

ASHRAE RP-884 online database is used for determining under/over prediction in NV and AC buildings [14,15]. Data set have been divided into 3 climate zones (hot and dry, mediterranean and tropical) and 2 seasons (winter and summer) for NV and AC buildings to examine the PMV model with different kind of climate zones and seasons. Data set containing 39,163 votes which consist of 17,969 thermal sensation vote in NV buildings and 21,194 votes for AC buildings. The votes contained the information that how the subjects feels about the surrounding environment, In according to that feeling the subjects cast his/her thermal sensation vote in the range of -3 to 3 as shown in figure 1. The data set also contained the values of six parameters as stated in equation (1) to calculate the value of predicted mean vote (PMV).

Table 2. Climate Zone

Climate Zone Number of votes w.r.t Seasons Winter / Summer City(Country)

Hot and Dry 3,422 / 4,779 Multan, Saidu shareef, Peshawar (Pakistan),

Kalgoorlie (Australia)

Mediterranean 5,063 / 8,307 San Francisco, San Ramon CA, Auburn CA (United

Sates), Athens (Greece)

Tropical 7,499 /10,093 Brisbane, Darwin, Townsville (Australia), Karachi

(Pakistan), Honululu(United States)

3. Result and Discussion

Current study elaborate the comparison of prediction level on the basis of actual mean vote given by the subjects and predicted mean vote (PMV) calculated as per Fanger's equation (1). Percentage of over/under prediction was calculated on the votes of neutral sensation. Mean value of MCI and ASH against the neutral sensation was considered to find out the percentage deviation of PMV from neutral thermal sensation.

3.1 Naturally ventilated buildings

PMV comparison with ASH and MCI is shown in Fig. 2(a) illustrating the under prediction by 21% for summer season and 7 % for winter season in hot and dry climatic region. Fig. 2(b) for mediterranean climatic region under prediction by 9% in summer season and over prediction by 37% in winter season. Tropical climatic region was under estimated by 8 % in summer season and 33% over estimation in winter season as shown in Fig. 2(c).

Results shown in hot and dry climatic region explain the trend towards 1,2 and 3 sensation of vote due to high temperature conditions in summer season and vice versa in winter season. Tropical climatic region have a high humidity level due to which trend is on positive side of thermal sensation scale in summer season whereas in winter season condition of the subject are more stable towards the neutral preference. Whereas temperature and humidity level ranges are not towards extreme condition therefore the feeling is more towards neutral sensation both in winter and summer season

PMV model under prediction was explained by Fanger in warm climates [8] but the over prediction for winter season is noticeable in thermal comfort model. Percentage difference of over prediction of PMV equation in winter season is more evident as compared to summer season.

□ PMV calculated as per equation I ASH actual vote as per questional McIntyre Index actual vote as per questional

Fig.2. Comparison of PMV with ASH and MCI for different regions in NV buildings. (a) Hot and dry climatic region (b) Mediterranean climatic region (c) Tropical climatic region

3.2. Air conditioned Buildings

Over prediction has been found by 25% in summer season whereas 34 % in winter season as shown 100%

j. § 3 a,

c '5b ? 2

ti 60% H

I 40% -| o

Z 20°/o H

Summer season

0% 100%

S 60% H

Winter Season

-3-2-10 12

3-3-2-10 1

0% .00%

20% 0%

Summer season

Winter season

-3-2-10123

-2-10123

Summer Season

Winter Season

-3-2-10123 -3-2-10123 Thermal sensation scale

□ PMV calculated as per equation ■ ASH actual vote as per questional Mclntyre Indes actual vote as per questional

Fig.3. Comparison of PMV with ASH and MCI for different regions in AC buildings. (a) Hot and dry climatic region (b) Mediterranean climatic region (c) Tropical climatic region

in Fig 3 (a). Mediterranean region has an overprediction of 30% in summer season and 29% in winter season illustrated in Fig.3 (b). Tropical region has the highest overprediction of 39% in summer season and 37.5 % in winter season in Fig. 3(c). Comparison of percentage deviation shown in Fig. 2 and Fig. 3 are on the relative basis of PMV model with the actual vote (ASH and MCI) casted through questionnaire.

PMV model over prediction in air conditioned buildings are the major feature of not satisfying the building environment standards. For improvement of building environment w.r.t PMV model the expected parameters such as metabolism rate and clothing factors need to be reexamined for better interpretation of thermal comfort. Tropical climatic region in summer season have a trend of 0,-1 and -2 actual thermal sensation vote which shows that subjects are overcooled as shown in fig. 3(c). Thus this finding leads to over consumption of energy in tropical climatic region. .

The margin of over prediction in air conditioned building is larger as compared to naturally ventilated building For future work, new coefficient or value shall be interpreted that convert the expected value of metabolism rate to measurable quantity for better prediction level of PMV model.

4. Conclusion

The behavior of PMV model in AC buildings shows a specific trend of over prediction regardless the type of weather zone and season, whereas in NV buildings over prediction of PMV equation in winter season is more evident as compared in summer season. Percentage deviation from neutral sensation were found high in AC buildings as compared to NV building. The over/under prediction of PMV model in AC and NV building as compared to actual votes raises a question mark on prediction level of indoor air quality of building environment and energy consumption therefore restructuring of PMV model would enhance the prediction level of the subjects as compared to actual vote cast by the subjects.

References

[1] Luis Perez Lombard, Jose Ortiz, Christine Pout. A review on buildings energy consumption information. Energy and Buildings Volume 40, Issue 3, 2008, p. 394-398

[2] Liu Yang, Haiyan Yan, Joseph C. Lam. Thermal comfort and building energy consumption implications -A review. Applied Energy 115, 2014, p. 164-173

[3] YH Yau, BT Chew. A review on predicted mean vote and adaptive thermal comfort models. SAGE journal. 2012.

[4] Fanger P. O. Thermal comfort, Analysis and application in environmental engineering, McGraw Hill. 1970

[5] De Dear RJ. The adaptive model of thermal comfort and energy conversation in the built Environment Intl J Biomaterial, 45, 2001; p. 100-108

[6] Humphreys,M.A.,Nicol,J.F.,2004.Do people like to feel "neutral"? Responsetothe ASHRAE scale of subjective warmth in relation to thermal preference,indoorandoutdoortemperature.ASHRAE Transactions110(2), p.569-577

[7] Mohammad Taleghani, MartinTenpierik, StanleyKurvers, Andyvanden Dobbelsteen. A review into thermal comfort in buildings. Renewable and Sustainable Energy Reviews 26, 2013, p.201-215

[8] Fanger P. O. and Toftum J, Extension of PMV model to non-air-conditioned buildings in warm climates, Elsevier science: Energy and Building, 34, 2002, p. 533-536

[9] Humphreys. Thermal comfort requirements, climate and energy., In: Sayigh AAM, editor. The Second World Renewable Energy Congress. 1992, Pergamon.

[10] Ailu Chen, Victor W.-C. Chang. Human health and thermal comfort of office workers in Singapore. Division of School of Civil and Environmental Engineering, Nanyang Technological University, Singapore

[11] Humphreys MA, NicolJF. Understanding theadaptive approach to thermal comfort, field studies of thermal comfortand adaptation.ASHRAE Technical Data Bulletin, 14(1), 1998, p.1-14.

[12] ASHRAE. Standard 55. Thermal Environmental Conditions for Human Occupancy. Atlanta: ASHRAE; 2004

[13] ISO 7730, Thermal comfort using calculation of the PMV and PPD indices and local thermal consideration, International Organization Standardization (2005)

[14] http://aws.mq.edu.au/rp-884/ashrae_rp884.html [Accessed on dated 21-04-2014 ]

[15] de Dear R Brager G, Cooper D. Developing an adaptive model of thermal comfort and preference: Final Report ASHRAE RP-884. Sydney, Australia: Macquarie University; 1997.