Scholarly article on topic 'Evaluation of the Effect of the Different Distances between Two Facades Natural Ventilation on Atrium Buildings with DSF and PMV-PPD Comfort'

Evaluation of the Effect of the Different Distances between Two Facades Natural Ventilation on Atrium Buildings with DSF and PMV-PPD Comfort Academic research paper on "Civil engineering"

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{"Double Skin Façade" / "Thermal Performance" / "Airflow Modelling" / "Indoor Thermal Comfort" / PMV-PPD / "Natural Ventilation ;CFD."}

Abstract of research paper on Civil engineering, author of scientific article — Enes Yasa

Abstract The energy efficiency and thermal performance of double facade glazed buildings are often questioned. However, nowadays especially glazed double skin facades buildings are increasingly being built around the world; the building facade plays an important role in achieving thermal comfort and energy conservation. Due to technological advances, transparency and the use of glass has become an attractive envelope option in architectural design. Building glass facades can provide outdoor views and an excellent level of natural light as well as the potential for natural ventilation. However, with the use of glass, heat loss during the winter and solar gain during the summer will increase energy loads. This study of aim is to determine the effect of thermal comfort in building and performance of surfaces, to determine if a DSF configuration will provide a better thermal comfort through mechanically assisted natural ventilation. By using the CFD program, this study were analysed the thermal comfort statuses of different atrium buildings volumes with double skin facades.

Academic research paper on topic "Evaluation of the Effect of the Different Distances between Two Facades Natural Ventilation on Atrium Buildings with DSF and PMV-PPD Comfort"

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Procedía Engineering 121 (2015) 667 - 674

Procedía Engineering

www.elsevier.com/locate/proeedia

9th International Symposium on Heating, Ventilation and Air Conditioning (ISHVAC) and the 3rd International Conference on Building Energy and Environment (COBEE)

Evaluation of the Effect of the Different Distances between Two Facades Natural Ventilation on Atrium Buildings with DSF and

PMV-PPD Comfort

Assist.Prof.Dr.Enes Yasa a,b?*

aN.E.U. Deparment of Architecture, Faculty of Architecture, 42090, Meram, Konya,Turkey; bTexas A&M University, Department of Architecture, Texas Engineering Experiment Station, Energy Systems Laboratory, 402 Harvey Mitchell Parkway South, College Station, TX 77845, United States(Visiting Scholar)

Abstract

The energy efficiency and thermal performance of double facade glazed buildings are often questioned. However, nowadays especially glazed double skin facades buildings are increasingly being built around the world; the building facade plays an important role in achieving thermal comfort and energy conservation. Due to technological advances, transparency and the use of glass has become an attractive envelope option in architectural design. Building glass facades can provide outdoor views and an excellent level of natural light as well as the potential for natural ventilation. However, with the use of glass, heat loss during the winter and solar gain during the summer will increase energy loads. This study of aim is to determine the effect of thermal comfort in building and performance of surfaces, to determine if a DSF configuration will provide a better thermal comfort through mechanically assisted natural ventilation. By using the CFD program, this study were analysed the thermal comfort statuses of different atrium buildings volumes with double skin facades.

© 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 underresponsibilityof theorganizingcommitteeofISHVAC-COBEE2015

Keywords: Double Skin Façade; Thermal Performance; Airflow Modelling; Indoor Thermal Comfort; PMV-PPD; Natural Ventilation;CFD.

* Corresponding author. Tel.: +90 532 505 17 05. E-mail address: enesyasa@yahoo.com; eyasa@tamu.edu

1877-7058 © 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 the organizing committee of ISHVAC-COBEE 2015 doi: 10.1016/j.proeng.2015.08.1064

1. Introduction

The energy efficiency and thermal performance of double facade glazed buildings are often questioned. However, nowadays especially glazed double skin facades buildings are increasingly being built around the world. The most pleasant architectures are known as systems which are able to maintain great correlation with nature. These systems make the best out of natural potentials to maintain thermal comfort for buildings occupants. To that aim, the first step is to manage the effect of outside weather condition on building's envelope. DSF is known as architects' solution to control incoming wind speed, manage the amounts of solar heat gains and reduce noise pollution in noisy city area. DSF is able to decrease cooling loads by ventilating away the solar heat built up in the cavity [1]-[2]-[3]. However previous researchers have suggested that the risk of overheating within (DSF) envelope is high in tropical climate. Modern buildings are known with their fully glazed facades. Apart from facade aesthetic, the desire to have more transparent facade and get the best out of outdoor illuminate, encourage architects to increase the window to wall ratio in modern buildings.

1.1. The Performance of Double Skin Facade Buildings As A System

The building design team should take into account the design constraints at an early stage of the decision making process, in order to achieve an overall approach and more accurate predictions. Unpleasant surprises resulting in an increase in the building's life cycle cost and/or impairment of its performance as to energy use and indoor climate can be avoided. These constraints are; *climate (solar radiation, outdoor temperature, etc), *site and obstructions of the building (latitude, local daylight availability, atmospheric conditions, exterior obstructions, ground reflectance, etc),*use of the building (operating hours, occupant density, schedule and activity, etc), *building and design regulations [4,5,6]. It is obvious that optimum building design (maximization of the output) cannot be achieved, since the overall goodness can be defined in different ways depending both on the design constraints and on the way that the design team prioritizes its goals and needs. In sustainable building design the integration of solar technologies is a delicate matter [7,8,9].

1.2. CFD Approaches in an Indoor Environment Simulation and Airflow Analysis

CFD programs, in particular, can be used to deal with problems associated with the thermal environment, indoor air quality, and building safety as they estimate important parameters such as temperature, airflow, and relative humidity [10,11,12,13]. CFD applications in indoor environments are very diverse and there are many recent examples of its use for natural ventilation design the study of building material emissions for indoor air quality assessment building elements design and for building energy and thermal comfort simulations [14,15,16,17,18,19,20].

2. Research Methodology

Computational Fluid Dynamics (CFD) analysis by using FloEFD and Star CCM + software, Antalya, Turkey in terms of interior comfort for the steady-state has been analysed.

2.1. Limitations and Assumptions and Boundary Conditions

This study is limited to comparative analyses between three different DSF building configurations considered for application in plot centers of "Hot-Humid Climate", characteristic dominant in southern part of Turkey. In order to observe the effect of the variable DSF with the shaft corridor and corridor distance on the building comfort design and energy performance on solar radiation and consequently the necessary energy of the building, different thermal factors except solar heat gain were fixed throughout the research. In DSF atrium buildings options, mechanical HVAC is not considered. Heat gain is expected to result from only solar heat gain. Each floor height of DSF atrium buildings has been considered 3.00 in average.

The indoors comfort limit temperature value for the heating and cooling load within the building has been considered 23 °C in all DSF atrium building options. The user makes entry of the meteorological data and geographic

data pertaining to the climatic region of the building. Meteorological data entered to FloEFD and Star CCM+ software is an index pertaining to Republic of Turkey General Directorate of Meteorology for the outdoors weather temperatures, direction and intensity of wind, intensity of the direct and common solar radiation, and sky cloudiness in the region. The heat flux coefficient, which is defined as the product of the density, thermal conductivity and specific heat capacity quantifies the ability of the material to absorb heat. It has been found to reflect the influence on thermal comfort of different surfaces and is therefore used as the basic thermophysical property defining the materials. The heat flux coefficients for the different layers of each element of the building (walls, roof, floor) are considered as design variables. The thicknesses of the different layers of each building element are also considered as design variables.

2.2. Creation of the Models And The Analysis Phase In CFD

The geometries of DSF atrium models examined were drawn and the digital mesh networks of the models belonging to each defined DSF atrium option were created, the thermal regions of each model were defined and surfaces of the models were created and restricting conditions were decided upon.Then, geographical and climatic data of different climatic regions were entered into the FloEFD and Star CCM+ simulation program. Further, data such as permeability and reflectivity of the structure envelope, constructional components and constructional materials were entered. The thermal regions, building surfaces and elements there of previously decided upon during the pre-analysis meshing phase were defined. Later, the data comprising the inter-building thermal gains were entered and analysis commenced. As criteria of the case study; for the heating period, average temperature distribution on DSF surface and inner building total temperature gain and loss values, outside air velocity movements, direction of air, layering of air, air change ratio pertaining to DSF buildings zones, for DSF both of building surfaces; overall and average heat transition amount, surface temperatures, pressures, and velocity distributions and wind speed values will be analyzed, and taking into consideration such values, internal temperature and average temperature distributions, overall temperature gain, total temperature loss calculations and also sunlight gains on the surface of the DSF building will determined and calculated.

The numerical and visual reports of all such values will prepared and relying on such values; evaluations and comments will made on internal temperature and average temperature distributions on the DSF atrium building surface, overall temperature gain, total temperature loss calculations, investigation of architectural solutions for better cooling and ventilation as well as their effects on cooling and ventilation. The building chosen as the reference in the study of analyzed model is considered as having 2 storeys, with a floor height of 4.00 m, with external building dimensions of 7,80m X 7,80m X 7,80m and atrium dimensions of 7.40m X 7.60 X 2.85 m.

2.3. Modelling and Simulation

In this study, three different double skin façade configurations are examined. (Figure 1).

Fig. 1. double skin façade aperture configurations of the study

These are DSF-1, DSF-2, DSF-3 configurations. Each configuration has three different sub-configuration case studies. Also three different sub-models were acquired as 80 cm, 160 cm, 240 cm as distance between two building envelopes for DSF-1. These entail four different sub-configurations as follows: all of the apertures on the internal building envelope are closed configuration, all of the apertures on the internal building envelope are open configuration, the aperture on the upper side of the apertures on the internal building envelope is closed and the aperture on the downside is open configuration, and the aperture on the upper side of the apertures on the internal building envelope is open and the aperture on the downside is closed configuration. (Table 1).

Table 1. Double Skin Façade atrium building configurations of the study

Double Facade Distance Configurations Wind Speed Aperture Configurations

5 m/s All apertures Closed

15 m/s

DSF-1 5 m/s All apertures Open

80 cm 15 m/s

5 m/s Upperside aperture Closed,

15 m/s Downside aperture Open

5 m/s Upperside aperture Open, Downside aperture Closed

15 m/s

DSF-2 160 cm 5 m/s All apertures Closed

15 m/s

5 m/s All apertures Open

15 m/s

5 m/s Upperside aperture Closed, Downside aperture Open

15 m/s

5 m/s Upperside aperture Open, Downside aperture Closed

15 m/s

DSF-3 240 cm 5 m/s All apertures Closed

15 m/s

5 m/s All apertures Open

15 m/s

5 m/s Upperside aperture Closed, Downside aperture Open

15 m/s

5 m/s Upperside aperture Open, Downside aperture Closed

15 m/s

Two different wind speeds have been examined for each configuration as 5 m/s and 15 m/s. For Antalya-Turkey, the chosen climatic region, the long-term meteorological data of the region, have been examined and thus, 5 m/s the frequent wind speed of the region, as well as 15 m/s, the highest average wind speed value of the region, have been taken into consideration.

3. Discussion and Result Analysis

It has been observed that in the three different configurations considered distance between two building envelopes, the flow between two building envelopes increased in proportion with increasing distance. However, as to the speed of the amount of flow increasing in proportion with the same flow, it was seen that speed values were higher as distance was smaller, and the flow ratio to the internal volume of the atrium was less.

Thermal comfort - Temperatures of the internal wall: Since the air inside the double skin façade cavity is warmer than the outdoor air during the heating period, the interior part of the façade can maintain temperatures that are closer to the thermal comfort levels. On the other hand, it is really important that the system and space between double facade should well designed, so efficient heat extraction ensures that the temperatures inside the cavity do not increase dramatically, leading to high operative temperatures.

One of the main advantages of the double skin façade systems is that they can allow natural (or fan supported) ventilation. Different types can be applied in different climates, orientations, locations and building types in order to provide fresh air before and during the working hours. The selection of double skin façade type can be crucial for temperatures, air velocity, and the quality of the introduced air inside the building. If designed well, the natural ventilation can lead to a reduction in energy use during the occupation stage and improve the comfort of the occupants. In this study, atrium internal volume temperature value has been taken as 23 °C. Since the external flow to the internal space is 15°C in the configuration where all of the apertures on the internal building envelope are open, this caused a reduction in the temperature values within the space to 16-17°C in places close to the aperture, and to 18-19°C in places farther to the aperture (Figure 2). Consequently, such departures to be used in the summer cooling period for Antalya region, the region of the study featuring hot climate, will be helpful in reduction of the cooling energy load indoors, and formation of comfortable areas.

3.1. Comparison of the DSF Configuration Comfort Performance Alternatives

In regards to the quality of indoor thermal comfort, it is evident that upper side aperture openings are open configuration provide a more stable environment with fewer dissatisfied occupants. The percentage of dissatisfied occupants increases mainly due to low inner surface temperatures, which is the result of all openings are closed.

Fig. 2. atrium building wind flow and wind speed values

An examination of the wind flow and wind speed values reveals the effect of the distance between two building envelopes on flow rate and flow values. In DSF-1, DSF-2, DSF-3 configurations, it has been observed that the amount of flow between two building envelopes increases as the distance between the two building envelopes increase. However, it has been seen that the speed of the amount of flow, also increasing in proportion with the increase rate, is higher in shorter distances, and also that the flow rate to the internal volume of atrium is less. It has been seen that when the distance between two DSF-1 building envelopes was 80 cm, the external flow speed was 5 m/s and the wind speed values between two building envelopes reached 7-8 m/s speed values. It has been seen that when the distance between two DSF-2 building envelopes was 160 cm, the external flow speed reached 6-7 m/s, that in the case of DSF-3 240, the speed values were between 5-6 m/s. As to the flow rate and values entering indoors, it has been observed that the speed values were higher as the distance is less, and also that the ratio of flow into the internal volume of atrium was less. (Figure 2).

Fig. 3. atrium building PMV and PPD values

3.2. Perception of Thermal Comfort

The PMV-PPD model employed in ISO 7730 Standard is the most accepted and widely applied thermal comfort model.[47]. To discovering its applicability in predicting the quality of indoor climate in the present building, a comparative analysis was carried out between the calculated values of PMV index and the recommendations of the standard. According to ISO 7730 [2005] an indoor environment is considered very comfortable when the values of PMV index varied between [-0.5, +0.5] and it is comfortable between [-1, +1]. These values lead to a PPD of 20% and 10% respectively. In order words, the values of PMV index between the limits of [-1, +1] and [-0.5, +0.5] correspond to the point where 80% and 90% of the respondents feel satisfied. When PMV is zero that is to say for the perfect case, the PMV is 5%. The comparison of the PMV values across the different months showed that PMV values deviated more from the acceptable range [-0.5, +0.5] and [-1, +1]. The thermal comfort indices, PMV and PPD values, were calculated both in FloEFD and DesignBuilder to study the thermal comfort inside the office building.

Fig. 4. Atrium building PMV and PPD values

Figure 3- 4 shows PMV-PPD values in the configuration with all apertures open. A corresponding examination of the PMV values inside at the aperture level on ground floor plane revealed that they were between -1.20 and 2.25, and at the aperture level upstairs they were between -0.40 and -0.80. An examination of the PPD values showed values between 65% and 75% at the aperture level indoors at ground floor plane, while values between 20% and 30% were observed at the aperture level of the plane upstairs.

4. Conclusion

In this study, detailed CFD calculations on three main different DSF, the influence of geometrical characteristics on airflows also was studied as a different aperture effects case compared with each DSF. The obtained results presented as a thermal comfort of occupants. Indoor and outdoor climate simulations have to be carried out already at an early design stage and then be refined during the actual design. This will ensure improved indoor and outdoor atrium climate performance of the building. In order to achieve and improved thermal environment it is essential to (a) validate the calculation methods, (b) carry out simulations on a component level in order, to gain the necessary background to the possibilities and limitations of the system, (c) prioritize the performance and quality requirements to be fulfilled and (d) carry out simulations on a zone and on a building level. Technology and architecture should be integrated to face the challenge of the future.

Acknowledgement

This work was supported by TUBITAK Scientific and Technological Research Projects Funding Program (Grant No. 1059B191400407).

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