Journal of Environmental Treatment Techniques (J. Environ. Treat. Tech.)  ISSN: 2309-1185, 2015, Volume 3, Issue 1, Pages: 12-14 |Download PDF|

 

Comparing the Performance of Conventional Windows and Double Glazed Windows in Building Energy Consumption

 

Farzaneh Mahlab *, Mohsen Mirmohammadi

 

Department of Environmental Engineering, University of Tehran, Iran.

 

Received: 05/11/2014                Accepted: 21/01/2015              Published: 30/03/2015

 

Abstract

In this paper, a building is chosen as a case study and its annual energy consumption and carbon dioxide emissions are calculated. Simulation software (Designbuilder) is employed in this study, where DesignBuilder simulations are applied to enable facade design studies considering building materials, window sizes and orientations. Building loads and wasting heat from various parts of the building are calculated as well. To improve the performance of building, windows replaced with double glazed PVC windows. It was observed that the thermal load of the building in the cold months decline by 46 percent. With the reduction of energy consumption in building, the annual carbon dioxide emission decline by 11 percent.

 

Key words: Energy consumption, double glazed, CO2 emission

  

1 Introduction

Based on Figure 1 the building and housing sector with the energy consumption more than 40 percent is considered as a biggest consumer of energy in Iran [1]. How to design buildings as one of the major energy consumers will have an important effect in reducing energy consumption [2]. The wasting of energy causes air pollution in cities as well as destroying natural resources [3]. It is estimated that Buildings in Tehran produce more than 40 percent of the carbon dioxide in Iran [4].

Iran has rich resources of fossil fuels such as crude oil and natural gas but these resources are non-renewable energy and Sooner or later come to an end [1]. On the other hand, fossil fuels are the main source of carbon dioxide in Earth. Increasing in the amount of carbon dioxide in recent decades causes an intensification of the greenhouse effect and the most distinctive change Earth's environmental crisis of the century means global warming [5]. Thus conserving fossil fuels is one of the goals of sustainable development at the global level [6]. Figure 1 shows energy consumption in different sector. As it has been shown, this amount is approximately 41% in the residential and commercial sector.

 

2 Methodology

The educational building in Tehran is simulated in DesignBuilder software [7]. Building information such as its function, The information of the number of people living in each sector, heating and cooling systems, fuel type, materials used in the construction of the building shell and the type and size of opening entered as input data [8]. One of the main indicators in this study which is considered for evaluating the effect of replacing the windows on the building's energy consumption, are heating and cooling loads. So the heating and cooling loads of the building are calculated for detecting the changes associated with replacing the windows. Base temperatures for heating and cooling considered 21 and 25 degree.

Figure 1: Energy Consumption in different sector

 

3 Results and Discussion

Following tables show the heating and cooling loads of the building before replacing the windows as well as heat exchanged from different parts of the building. In the reporting of data  has been tried that a set of output which comprise the total heating and cooling load of the building, considered next to each other. Thus, accurate knowledge of heat transfer components for building and the contribution of each of them will gain and the effects of optimization will be assessed separately. According to Table 1, the most heat loos occur through the windows.

 

 

Table 1: Heating and cooling loads before Optimization

 Heating/ cooling loads

Building shell

Windows

Ventilation

Internal heat gain

Heat Transfer in Building

Heat gain

Heat loss

Heat gain

Heat loss

Heat gain

Heat loss

64508

2389

56915

23652

11287

0

80996

58791

Heating period 6 months

99309

34167

11976

32575

480

9259

9825

45928

Cooling period 6 months

173195

36256

68893

56227

11767

9259

90821

103719

Year

 

 

 

3.1 Evaluation the performance of existing windows

Windows used in building are single glazed with painted frames. In general, these kinds of buildings considered as major weaknesses due to their high heat transfer coefficient. In total, the building has 55 northern, southern and western facing windows. Area of windows varies quite a bit, and the average is equal to 4 m.

Table 2 shows Direct and diffuse solar radiation in summer and winter from northern and southern facing windows. As the Expected, southern facing windows receive direct sunlight in winter in high amount and far less in summer. For northern facing windows the situation is different. Also receiving diffused solar radiation on both southern and northern facing windows is worth noticing issue.

 

Table 2: Comparing radiation gain

Northern windows/summer

Northern windows/ winter

Southern windows/summer

Southern windows/winter

Radiation gain per kWh/ m2

388

0

2380

3409

Direct radiation

2860

1905

3520

2008

Diffused radiation

 

3.2 Replacement of windows with double glazed windows

Although the installation of window awnings can partially control the incoming radiation, another key issue is their high heat transfer coefficient. U value of conventional windows is 5 W/m2.k. Characteristics of replaced glass are shown in Table 3 and compared with existing glass.

 

Table 3:  Characteristics of windows

Double

 glazed

Existing

Characteristics of windows

0.4

0.62

Coefficient of total solar radiation passing

0.373

0.48

Coefficient of direct solar radiation passing

0.505

0.57

Light Transmittance

2.665

5.77

U [W/m2.k]

 

According to the table 4, the total heat gain would be reduced by 17 percent in the summer by taking advantage of double glazed windows. And table 5 shows, using double glazed windows reduce the total heat loss through the windows in the winter by 57 percent which lead a decline on a cooling load. Carbon emission from the building based on the fuel type will be calculated by the software (Table 7). As Table 8 shows, CO2 emission will be reduced by such a change in building's windows.

 

Table 4: Comparison of the heat gain in the summer and winter with two types of windows

Summer

Winter

Heat gain Wh/m2

11426

7553

Conventional windows

9404

6850

Double glazed

 

Table 5: Comparison of the heat loss in the winter

Winter

Heat loss Wh/m2

4483

Conventional windows

1889

Double glazed

 

According to table 6, the installation of double glazed window reduce the undesired heat transfer and it leads to a reduction in heating load and cooling load. Energy consumption in the building will decrease as a result.

 

Table 6: Impacts of the installing double glazed building in heat gain and heat loss of the whole building

Heating/cooling loads

Heat loss

Heat gain

 

34490

4207

21409

Before optimizing

Heating

Period

64508

11287

23652

After optimizing

-46%

-62%

-9%

Change

85397

168

19244

Before optimizing

Cooling

Period

99309

480

32575

After optimizing

-14%

-65%

-40%

Change

 

Table 7: The amount of carbon dioxide produced per kilogram of energy CO2 emission

0.658

Electricity(KgCO2/kWh)

0.195

Gas(KgCO2/kWh)

0.273

Oil(KgCO2/kWh)

0.34

Solid(KgCO2/kWh)

 

Table 8: Emissions of carbon dioxide from the results of modeling CO2 Emission

Building with conventional building

Double glazed

Changing percentage

94162

83901

11

 

4 Conclusions

According to all results above, installing double glazed windows will reduce the energy consumption in the building. In the heating period which refers to cold seasons, changing the windows of the building leads to a decline in heating loads by 46 percent. Moreover, less use of energy will cause less carbon dioxide emission. As we can see, co2 emission will decrease by 11 percent after changing the conventional windows of the building.

 

References

1- Nasrollahi, F., Architectural standards for reducing energy consumption in buildings, Committee of the National Energy, Tehran, 2010.

2- Sustainable Development Commission, What Is Sustainable Development, http://www.sd-commission.org.uk/pages/what-is-sustainable-development.html

3- Fisk, WJ., Health and Productivity Gains from Better Indoor Environments and their Relationship with Building Energy Efficiency, Ann Rev Energy Environ, 2000.

4- Sadeghipour, M., The use of computers simulation software in architectural design, M.S Thesis, 2008.

5- Lewis, M., Integrated Design for Sustainable Buildings, Building for the Future: A Supplement to ASHRAE Journal 46, 2004.

6- Bahrami, S., Energy Efficient Building in Warm Climate in The Middle East, Experience in Iran and Israel, Lund University, Sweden, 2008.

7- DesignBuilder Software Library,Versin 3.0.0.101, Construction Material, Material Data, Embodied Carbon.

8- Yilmaz, Z,.Evaluation of Energy Efficient Design Strategies for Different Climate Zones: Comparison of thermal performance of buildings in temperate humid and hot dry climate,Enery and Building, 2007.



Corresponding author: Farzaneh Mahlab, University of Tehran, Iran. E-mail: far.mahlab@gmail.com