A survey of decorative materials on the energy consumption of mid-rise residential buildings in Mashad, Iran

Abstract

Polyvinylchloride (PVC) panel is one of the most favorite decorative materials that has been popularly applied as finishing of ceiling in residential buildings. It is about five years that the people incline to redecorate the ceiling of old buildings with PVC panel in big cities of Iran, such as Mashad. In this study, the influence of ceiling PVC panel on the cooling and heating loads of studied apartment were determined by software DeST-h. In addition, the summer natural ventilation of the mentioned apartment is investigated by determining the wind speed into the apartment through the computational fluid dynamics (CFD) software. The evaluation of environment indoor wind velocity showed that most of the apartment space is a comfortable zone. The results of studied building analyses demonstrated that using PVC panel on the ceiling can decline the energy consumption of the penthouse (fifth level) of the investigated building, which is about 3.7% and 7% for studied methods of without and with air layer, respectively. In addition, although the existence of air layer can decline the cooling and heating loads, the increase in air layer thickness did not show significant decrease on building energy consumption. However, the PVC panel is expensive and is not suitable to be used for ceiling thermal insulation, but adding a thin layer of air between ceiling and PVC panel can be a good step toward sustainable building, when the people are inclined to utilize it as a decorative ceiling.

Keywords

residential apartments / natural ventilation / energy consumption / decorative materials / Mashad

Introduction

The residential buildings are the major sector of energy consumption in Iran [1]. The building envelopes and the gradient between indoor and outdoor temperatures highly influence the energy consumption in the arid regions. Mashad (capital of Khorasan Province) is one of the biggest cities in Iran, and it is located in an arid region of north-east Iran [2], where, in summer, the outdoor temperature can reach up to 40°C and, in winter, the outdoor temperature comes down to -5°C or less [3]. There is a special type of residential buildings with 4–7 stories in Mashad, located between one or two stories houses, so top floors have vast wall in touch with outside air. These especial types of residential apartment buildings have evolved in Mashad over the last two decades. The ceilings of these building are constructed by Concrete-Joist and hollow clay block, which have low thermal resistance. Meanwhile, the penthouses (top floor) of these buildings have vast wall and ceiling. Therefore, the wall and ceiling are the main factors of energy consumption in these apartments.

As the living standard in the world increases, more energy and resources are used for more comfort. It has been about five years that the people have been inclined to using decorative materials (PVC panel) in new buildings or in redecorating old residential buildings. However, the people prefer to use air conditioning system (for cooling) instead of swamp-cooler (evaporative cooler) in the arid regions of Iran, but researches showed that natural ventilation has been used in Iran for passive cooling of buildings for centuries until now [4–6]. In addition, during the last two decades, applying computational fluid dynamic (CFD) has increased for determining or predicting the indoor building environment. There is a significant number of scientific research referring to applying CFD models for indoor environment of different building such as apartments [7], terminals [8,9], offices [10,11], and museums [12]. In this study, we tried to determine the influence of ceiling PVC panel on cooling and heating loads of the mentioned buildings in intermittent air conditioning with natural ventilation. Hence, the summer-winter seasons energy consumption in a studied apartment (penthouse of a five stories residential building) with five different studied ceiling construction methods is investigated.

Methodologies

The algorithm of study has been presented in Fig. 1. In this study, the apartment was analyzed to determine the amount of energy consumption during summer-winter time for different ceiling construction. According to the algorithm, the thermal properties of conventional building materials were needed first, which are used in Iran. Hence, some of them was measured in the laboratory (Building Environment and Energy Laboratory, BEEL, South China University of Technology), and the others, such as thermal property of hollow clay block, were simulated and calculated by software Therm-6. On one hand, the increase in natural ventilation could decrease the cooling load of residential building [13,14]; on the other hand, with the availability of numerical technology, CFD has been thought to be an affordable, accurate, and informative method among all the prediction methods and popularly used in the prediction to the building environment [15]. Therefore, the simulation of real condition CFD software PHOENICS was applied to simulate wind velocity around and inside the building and determine the amount of air change rare (ACR) of building in natural ventilation condition. Finally, the building was analyzed by DeST-h (annual dynamic energy simulation software) to evaluate the effects of decorative materials on the building cooling-heating loads. Because there are only Chinese cities meteorological data in DeST-h library, we measured Mashad meteorological data on summer (June, July and August) and winter (December, January and February) of 2008–2009 and added them in DeST-h library. In the next sections, the different steps of algorithm are discussed completely.

Building information

The studied apartment has been located on the top floor of a five-story residential building. There are three bedrooms in the north side and also a kitchen, dining room, and living room, which are located in the southern part of apartment. The total height of the building is about 150 m (3 m per story). The area of apartment is about 228 m² in which about 179.4 m² is air conditioning space. The window to wall ratios for south, north, west, and east sides are 0.38, 0.21, 0.03, and 0.06, respectively. Figure 2 shows the site plan of this building among one story houses. Building direction is 40 degrees from the south toward the west. This studied apartment was evaluated with the following assumed five different ceiling constructions: (1) conventional ceiling, which has gypsum plaster for finishing (G1), (2) conventional ceiling with 8 mm PVC-Panel for finishing (GP), (3) conventional ceiling with 5 mm air layer and 8 mm PVC panel (GP1), (4) conventional ceiling with 10 mm air layer and 8 mm PVC panel (GP2), and (5) conventional ceiling with 100 mm air and 8 mm PVC panel (GP3).

Materials and their properties

The considered materials for the studied apartment are as follows. The walls of this apartment were made with hollow blocks (104 mm width) and thin layer of cement mortar (25 mm) in the outside and thin layer of gypsum mortar (20 mm) and gypsum plaster (5 mm) for the inside. The floors were made with gypsum plaster (5 mm), concrete-Joist and clay block (200 mm), cement mortar (25 mm), and parquet floor (8 mm). A normal single glass with thickness of 3 mm and shading coefficient of 0.93 were assumed for the windows. The conventional ceiling has been made by 200 mm of Concrete-Joist and clay block, light-concrete (50 mm), cement mortar (25 mm), bituminous layer (5 mm), and 5 mm of gypsum plaster for inside finishing. To determine the thermal properties of conventional building materials that are used in Iran, some of them were measured in the BEEL laboratory by the quick thermal conductivity meter (KEM, QTM-500) or the guarded hot plate thermal conductivity meter (TPMBE-300) and then used in other steps. In addition, Therm 6 software was utilized for the simulation of equivalent thermal resistance (Reqa) of hollow clay block of wall and ceiling. Therm 6 is a software for analyzing two-dimensional static heat transfer through building products [16]. The simulated Reqa values by Therm 6 software were added to the building materials library of DeST-h software. Thermal conductivity (\lambda) of materials has been shown in Table 1. There are no mentioned materials in Table 1 that are considered as Therm 6 or DeST-h materials library.

Domain of model

In this work, CFD software PHOENICS was used to simulate the wind velocity. PHOENICS is used and validated in other researches [15,17–20] in the case of natural ventilation simulation. The method of finite volume is used on a rectangular Cartesian grid. The airflows that in and around of the residential building group are considered as three-dimensional steady-state incompressible turbulence flow. According to the limit power of the software and the requirements of high-resolution analysis for indoor building environment, we separate the simulation in two steps. First, assuming the building will be simulated among those of other buildings for outdoor wind velocity, and then, according to the results of the first step, the building will be simulated in a smaller boundary to determine indoor wind velocity. Some researches indicated that the k-є model of turbulence was the most appropriate model for practical building airflow applications [21,22]. In this case, the turbulence model adopts the well-known standard k-є model. The analysis of wind environment under natural ventilation is only for summer because it is just used hot seasons in Mashad. According to the report of Mashad meteorological station (www.irimo.ir), the amount of prevailing wind average during June, July, and August (1951–2003) is about 4.7 m/s and from east to west.

Boundary conditions for wind velocity around building (step1)

Tominaga noted, for the size of the computational domain, that the blockage ratio should be below 3% [23]. The lateral and the top boundary should be set at 5H or more away from the building, where the H is the height of the target building [24]. The outflow boundary should be set at least at 10H behind the building [23]. Therefore, the computational domain size of 360 m(x) × 360 m(y) × 100€m(z) for the outdoor wind environment of the studied building between other residential houses group was adopted (region A). The numerical grid includes 100(x) × 72(y) × 36(z) (259200 cells). All building blocks were assumed as blockage. The studied building target is 40 degrees from south to west (Figs. 2 and 3). The inlet boundary for different heights was adapted using the Hellman exponent formula [25,26]:

(1)V_h=V_{\mathrm{p}}{\left({\displaystyle \frac{h}{\mathrm{10}}}\right)}^a,

where V_h was wind velocity in height h, V_{\mathrm{p}} was prevailing wind in height of 10 m, h was height, and a Hellman exponent was assumed to be 0.3 over the settlements area.

Using this simulation, the velocity and pressure distributions near the studied building are obtained. Then, these velocity and pressure distributions are taken as boundary conditions to simulate the indoor wind environment in step 2.

Boundary conditions for indoor building environment (step 2)

For the second step, the computational domain size of 45 m(x) × 50 m(y) × 90 m(z) was adopted for the indoor wind velocity (Region B) of the studied building (Figs. 2 and 5). The numerical grid includes 93(x) × 105(y) × 61(z) (595665 cells), and the studied building size is 15 m(x) × 20 m(y) × 15 m(z).

We assumed that the 0.6 m² of every room’s window is opened, so approximately, 20% and 10% of windows are opened in north and south side of studied apartment, respectively.

Air change rate (ACR) is calculated using the following equation [27]:

(2)\mathrm{A}\mathrm{C}\mathrm{R}={\displaystyle \frac{F}{V}},

where F is the wind flux through windows into the apartment, and V is the volume of the apartment.

Conditions of simulation

In this study, the energy consumption of studied buildings has been simulated for summer season. According to the geometry size of the studied residential buildings, its simulation model is established in DeST-h, as shown in Fig. 4. From the analysis of wind environment, the ACR of the apartment building is about 23.2 times per hour. Other simulation conditions have been explained in Table 2. The parameters not mentioned in Table 2 are considered as DeST-h default.

Results and discussion

According to the explained conditions, various simulations were performed on the studied building for the evaluation of natural ventilation and energy consumption in an apartment with five different ceiling constructions. The results of simulations are presented and discussed in the following sections.

Environment indoor wind velocity

The following work is investigating the potential of natural ventilation for this residential apartment. On one hand people cannot feel air flow less than 0.05 m/s (is looked as stagnation), and on the other hand, air speed greater than 1€m/s is too strong and will cause disorder the work of people [28]. Also, if the amount of wind velocity is bigger than 4€m/s, people cannot endure such condition. Therefore, in this study, the regions in which air speeds are above or equal 0.05 m/s but less than or equal 1m/s are thought to be the comfortable zones, and other regions are uncomfortable zones. The velocity distribution at the height of 1.5 m above the floor (level of 13.5 m) of the studied apartment is depicted in Fig. 5. In this figure, wind speed between 0.05 and 1 m/s is captured. Hence, the blank zone in this figure stands for the velocity discomfort area for human body. Moreover, evaluation shows the amount of indoor wind velocity for all rooms that are smaller than 3m/s, so there is no other area in this apartment wherein people cannot endure the wind velocity.

The ratio of the uncomfortable area to the whole occupied region area (UZ) is taken as an important index for the evaluation of results. The calculation results of the UZ evaluation index for all rooms are shown in Table 3. The smaller UZ means more comfortable area for most of the occupants. Table 3 shows that when 0.6 m² of window area are opened in each room, the percentage of UZ in all rooms are less than 20%; moreover, the UZ of total area is about 5.1%. In addition, just the UZ of NE bedroom is more than 10%, which can decrease by shrinkage of windows’ inlet area.

ACR value is another important parameter in natural ventilation condition, which has been analyzed in this study. The evaluation of environment wind velocity showed that the ACR value calculated by PHOENICS for windows inlet is 23.2 t/h, which will be used in the DeST-h software.

Cooling load in different rooms

The results of the simulation of summer energy consumption in the studied apartment for five different ceiling constructions have been presented in the Table 4.

The simulation results for average of cooling load in different rooms show that the highest amount of cooling load happened in the NW bedroom. Also, the application of PVC panel on the ceiling can decrease about 3.3% of cooling load in this room. Evaluation of cooling load reduction (CLR) by PVC panel shows that NE bedroom with the least effect (about 0.9%) has the highest amount of average cooling load. Also, the living and dining rooms have the most reduction of cooling load by applying PVC panel on the ceiling.

NE bedroom has most cooling load and the lowest influence by PVC panel due to the fact that, in the morning, solar radiation increases the temperature of the vast eastern wall, and according to building target (40 degrees from south to west), this effect continues for a long time during a day. For the living room, the wall to ceiling ratio of this room has a lot influence to the results, which means that due to vast area of the living and dining room, cooling load in these rooms depend more on its ceiling.

Apartment cooling load

The simulation results showed that the summer cooling load decreased about 2.9% by adding PVC panel in the ceiling (GP) of the apartment. Figure 6 shows the average cooling load for the studied apartment with different ceiling construction. Evaluation of cooling load shows that utilizing PVC panel with air layer can improve the amount of decline cooling load to about 5.8%, 6.4%, and 7.5% for GP1, GP2, and GP3 methods, respectively. However, the amount of reduction of cooling load by GP3 method is slightly more than the other methods, but its construction cost is more than the other methods (GP, GP1, and GP2).

Apartment heating load

Figure 7 shows the average heating load for studied apartment with different ceiling construction. The evaluation showed that the winter energy consumption decreased to about 3.9% by adding PVC panel in the ceiling (GP) of the apartment. Utilizing PVC panel with air layer can improve the declining of the heating load to about 6.9%, 7.2%, and 8.5% for GP1, GP2, and GP3 methods, respectively. These results show similar behavior of heating and cooling loads of buildings with different construction method of the ceiling.

Conclusions

From the simulation of environment indoor wind velocity and energy consumption of the residential building under natural ventilation, the following conclusions were obtained:

In the studied residential apartment with natural ventilation, 94.9% of area is comfortable for most occupants; in other words, the ventilation condition inside the apartment with 23.2 t/h ACR is good.

The existence of PVC panel (GP method) reduces the energy consumption of a studied apartment to about 3.7%. Also, the energy consumption decreased to about 6.7% and 7.1% for GP1 and GP2 methods, respectively. Therefore, the existence of the thin layer of air between PVC panel and gypsum (GP1 and GP2) can be a good step toward sustainable building, when the people are inclined to redecorate ceiling with PVC panel. Although the GP3 method showed slightly less energy consumption than GP1 and GP2 methods (about 1.2%), this method is more expensive than the other methods and decreases the inside space. Therefore, GP3 is not a suitable method.

References

[1] Shahraein M T, Zhao L, Meng Q, Zhai Y, Yang X. The influences of the walls and double glazing on the energy consumption in residential building of Mashad-Iran. In: Proceedings of EERB-BEPH Conference. Guilin, 2009, 1369–1376

[2] Ahmadi M T. Iran building national manual, topic 19th: Optimize of energy consumption in building. Ministry of dwelling, Tehran, Iran, 2001(In Persian)

[3] Shahraein M T, Zhao L, Meng Q. Investigation of the neighborhoods on the energy consumption of residential buildings. In: Proceedings of 10th National Building Physics Conference. Guangzhou, 2008, 339–346

[4] Bahadori M M. Passive cooling systems in Iranian architecture. Scientific American, 1978, 238(2): 144–154

[5] Bahadori M M. Viability of wind towers in achieving summer comfort in the hot arid regions of the Middle East. Renewable Energy, 1994, 5(5–8): 879–892

[6] A’zami A. Badgir in traditional Iranian architecture. In: Proceedings of International Conference of Passive and Low Energy Cooling for the Built Environment. Santorini: 2005, 1021–1026

[7] Bojic M, Yik F, Lo T Y. Locating air-conditioners and furniture inside residential flats to obtain good thermal comfort. Energy and Buildings, 2002, 34(7): 745–751

[8] Meng Q, Li Q, Zhao L, Li L, Chen Z, Chen Y, Wang S. Numerical study on airflow and temperature distribution in an airport terminal building under natural ventilation. In: Proceedings of the sixth international conference on indoor air quality, Ventilation & Energy Conservation in Buildings. Sendai: 2007

[9] Li Q, Yoshino H, Mochida A, Lei B, Meng Q, Zhao L, Lun Y. CFD study of the thermal environment in an air-conditioned train station building. Building and Environment, 2009, 44(7): 1452–1465

[10] Hien W N, Liping W, Chandra A N, Pandey A R, Xiaolin W. Effects of double glazed facade on energy consumption, thermal comfort and condensation for a typical office building in Singapore. Energy and Buildings, 2005, 37(6): 563–572

[11] Stamou A, Katsiris I. Verification of a CFD model for indoor airflow and heat transfer. Building and Environment, 2006, 41(9): 1171–1181

[12] Papakonstantinou K A, Kiranoudis C T, Markatos N C. Computational analysis of thermal comfort: the case of the archaeological museum of Athens. Applied Mathematical Modelling, 2000, 24(7): 477–494

[13] Zhao L H. Analysis of the application of insulated wall in Guangzhou. In: Proceedings of Second Conference for Architecture Design and Technology for Pan Sub-tropical Climates, Guangzhou, 2005 (in Chinese)

[14] Shahraein M T, Zhao L, Meng Q. Influences of the natural ventilation in residential buildings of Mashad. In: Proceedings of 10th National Building Physics Conference. Guangzhou: 2008, 347–352

[15] Chen Q. Using computational tools to factor wind into architectural environment design. Energy and Buildings, 2004, 36(12): 1197–1209

[16] Robin M. Therm 6 user manual. Lawrence Berkeley National Laboratory (LBNL), 2006

[17] Allocca C, Chen Q, Glicksman L R. Design analysis of single-sided natural ventilation. Energy and Buildings, 2003, 35(8): 785–795

[18] Wong N H, Heryanto S. The study of active stack effect to enhance natural ventilation using wind tunnel and computational fluid dynamics (CFD) simulations. Energy and Buildings, 2004, 36(7): 668–678

[19] Tan G, Glicksman L R. Application of integrating multi-zone model with CFD simulation to natural ventilation prediction. Energy and Buildings, 2005, 37(10): 1049–1057

[20] Pappas A, Zhai Z. Numerical investigation on thermal performance and correlation of double skin façade with buoyancy-driven airflow. Energy and Buildings, 2008, 40(4): 466–475

[21] Mathews E H. Numerical solutions of fluid problems related to buildings, structures and the environment. Building and Environment, 1989, 24(1): 1

[22] Launder B E, Spalding D B. The numerical computation of turbulent flows. Computer Methods in Applied Mechanics and Engineering, 1974, 3(2): 269–289

[23] Tominaga Y, Mochida A, Yoshie R, Kataoka H, Nozu T, Yoshikawa M, Shirasawa T. AIJ guidelines for practical applications of CFD to pedestrian wind environment around buildings. Journal of Wind Engineering and Industrial Aerodynamics, 2008, 96(10–11): 1749–1761

[24] Mochida A, Tominaga Y, Murakami S, Yoshie R, Ishihara T, Ooka R. Comparison of various k-e models and DSM applied to flow around a high-rise building Report on AIJ cooperative project for CFD prediction of wind environment. Wind & Structures, 2002, 5(2–4): 227–244

[25] Heier S. Grid Integration of Wind Energy Conversion Systems, John Wiley & Sons, 2005

[26] Kircsi A, Tar K. Profile tests to optimize the utilization of wind energy. Acta Silv Lign Hung, 2008, 4: 107–123

[27] Meng Q, Li Q, Zhao L, Li L, Chen Z, Chen Y, Wang S. A case study of the thermal environment in the airport terminal building under natural ventilation. Journal of Asian Architecture and Building Engineering, 2009, 8(1): 221–227

[28] Kasmayi M. Climate and Architecture. Khak, Tehran, Iran, 2005 (In Persian)

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