Construction elements

Typical of the high-rise building type, the framework was built with steel and concrete from which curtain walls are suspended, rather than load-bearing walls of conventional construction. The core and the floors therefore employ a steel skeleton

construction made of reinforced concrete. The curtain wall envelope is highly glazed by Low-E double glazing with a ratio of approximately 89%.

4.2.2.1 Opaque construction elements

From the architectural drawings, the following major composite construction elements, as shown in Table 4.1, were first gathered and then specified in the building energy simulation model.

Table 4.1: Thermal properties of the building construction elements also incorporated to the model.

construction name material name thickness in m layer

curtain wall aluminium 0,0020 outside layer

u-value = 0,29 W/m²-K xps extruded polystyrene 0,0200 layer 2

wall air space 0,1000 layer 3

mw stonewool rolls 0,1000 layer 4

stainless steel 0,0010 inside layer

internal floor gypsum plasterboard 0,0125 outside layer

u-value = 0,98 W/m²-K ceiling air space 0,9900 layer 2

concrete reinforced 0,1250 layer 3

ceiling air space 0,1700 layer 4

plywood 0,0300 layer 5

carpet 0,0060 inside layer

heavyweight internal wall oak wood 0,0130 outside layer

u-value = 1,40 W/m²-K wall air space 0,0250 layer 2

concrete reinforced 0,4000 layer 3

wall air space 0,0250 layer 4

oak wood 0,0130 inside layer

lightweight internal partition gypsum plasterboard 0,0125 outside layer

u-value = 4,00 W/m²-K wall air space 0,0500 layer 2

gypsum plasterboard 0,0125 inside layer

The thermal properties of the building construction materials are collected from different sources and are summarised in Table 4.2.

Table 4.2: Thermal properties of the building construction materials also incorporated to the model.

name source conductivity

name source thermal resistance in m²-K/W

wall air space ASHRAE 05 0,15

ceiling air space ASHRAE 05 0,18

4.2.2.2 Window glazing

According to the manufacturer, the highly glazed façade of the office tower was designed to provide maximum daylight transmittance for the occupants. To reduce heat gains, the tempered outer glazing was coated by invisible silver low-emittance (low-E) coating. This is a glazing type with microscopically thin and virtually invisible metal or metallic oxide layers deposited on the glazing surface, primarily to reduce radiative heat flow. An optimum low-E coating is transparent to the visible solar spectrum to provide maximum light, and reflective of long-wave infrared radiation to block solar heat gains. The design also provides the necessary resistance against high wind loads and sets a security system by preventing any injuries that would occur if a window bursts. The partly tempered inner glazing is composed of two layers of polyvinyl butyral (PVB) laminated glazing.

Table 4.3: Thermal and visual properties of the window glazing¹⁰. LoE doulble glazing initial values as

specifications

daylight transmittance 70% 70% 68%

daylight reflectance 10% 13% 12%

shading coefficient 0,54 0,56 0,51

solar transmission (SHGC) 0,47 0,487 0,444

U-Value (EN 673 is used) 1,4 W/m²-K 1,7 W/m²-K 1,4 W/m²-K

emissivity < 0,20 0,07 0,07

4.2.2.3 Shading devices

Both internal and external devices shade the office zones. The uniform external shading device in summer only partly shades the windows due to their size and also due to the fact that the devices were not selected according to the orientation of the windows.

External

The uniform, external shading devices are designed to allow a free view for the office occupants and to support the architectural appearance of the building composition. Less importance was given to shade the windows and to reduce the incoming heat and the risk of overheating.

10 Technical specifications from the glazing production company Trakya Cam Sanayii A.Ş.

The seven differently sized horizontal shading devices (Figure 4.10 and Figure 4.11) on each floor are mounted from south-west till south-east façade (see Figure 4.7). They are made of beige-silver coloured stainless steel and mounted by a rigid façade suspension. Because of the solar path of the sun, the highly glazed façade is only party shaded, depending on the season, time and orientation.

Horizontal shading devices generally work best for south mountings. For east and west aspects, the sun will be low in the sky for long periods. This means that the sun will come in underneath the horizontal shading devices, making them more ineffective compared to the south orientation. Therefore, with the actual shading devices a partial overheating due to intense solar beam gains occurs with clear sky from external windows.

Figure 4.10: Shading devices from inside. Figure 4.11: External shading device drawing detail.

Simulations done in the context of this study indicate that the actual shading devices reduce the building’s overall transmitted solar gains only by 11% in the cooling season (for the definition of cooling season, see § 5.1.4) compared to a case without any external shading devices.

Figure 4.12: Simulated effectiveness of the actual shading devices in a typical summer and winter 0

5 10 15 20 25 30 35 40 45 50

0 24 48 72 96 120 144 168

transmitted solar per net floor area in W/m²

hour

no shading typical summer week actual shading typical summer week no shading typical winter week actual shading typical winter week

Internal

Internal vertical blinds successfully control light, block glare, and provide privacy but do not achieve effective heat control unlike external blinds. The semi-transparent rolled up interior sunblinds used in the Kanyon building are made of textile (Figure 4.9). According to the Kanyon management, the sunblinds are automatically controlled by the solar intensity, but setpoints and position of the irradiance meter are not known. For the simulation model, it was assumed that the internal shades do not significantly influence the heat balance of the building, and as such are not investigated further.