Investigating the Performance of Mechanically Ventilated Double-Skin Facades

1
Investigating the Performance of Mechanically Ventilated Double-skin Facades with Solar Control Devices in the Main Cavity Carmelo G. Galante - Newtecnic Ltd, London, England, UK. Internal Blinds 4.2 m 0.245 m Air Inlet Air Outlet Solar Radiation Double Glazing Units (90% Ar + 10% Air) Figure 1. Building Scale (South-oriented Facade) Figure 2. Typical Bay Figure 3. Double-skin Unit Figure 4. System Description (COMSOL Input Geometry) INPUTS INVESTIGATION ON MATERIALS PROPERTIES AND AIR INLET VELOCITY FINAL DESIGN (Absorptivity = 0.5, Emissivity = 0.72) SYSTEM DESCRIPTION AND CONTEXT OF THE ANALYSIS Low-e coating Insulation Aluminium Property Unit Value α_g1 (absorptivity outer glass) [-] 0.2 τ_g1 (transmissivity outer glass) [-] 0.73 ρ_g1 (reflectivity outer glass) [-] 0.07 α_g2 (absorptivity inner glass) [-] 0.33 τ_g2 (transmissivity inner glass) [-] 0.51 ρ_g2 (reflectivity inner glass) [-] 0.16 Property Unit Value α_g3 (absorptivity outer glass) [-] 0.2 τ_g3 (transmissivity outer glass) [-] 0.73 ρ_g3 (reflectivity outer glass) [-] 0.07 α_g4 (absorptivity inner glass) [-] 0.18 τ_g4 (transmissivity inner glass) [-] 0.58 ρ_g4 (reflectivity inner glass) [-] 0.24 GLASSES ENERGY PROPERTIES OUTER DOUBLE GLAZING UNIT INNER DOUBLE GLAZING UNIT Parameter Unit Value Air Inlet Velocity [m/s] Variable (0.1 - 1) Air Inlet Temperature [degC] 26 MECHANICAL VENTILATION INPUTS Material Unit Value Aluminium [-] Variable (0.1 - 1) Glass [-] 0.89 Glass (Low-e Coating) [-] 0.03 EMISSIVITY OF MAIN MATERIALS Parameter Unit Value Outdoor Temperature [degC] 50 Indoor Temperature [degC] 24 Global Radiation [W/m^2] 1020 SUMMER PEAK DAY-TIME CONDITIONS Aluminium [-] Variable (0.1 - 1) ABSORPTIVITY OF MAIN MATERIALS The purpose of this study is to investigate the thermal behaviour and performance of a DSF being designed for a real project in the Middle East. The DSF is comprised of two double glazing units, a mechanically ventilated air cavity and solar control (shading) devices placed within the cavity (Figure 4). 0 20 40 60 80 100 120 0 0.2 0.4 0.6 0.8 1 1.2 Temperature [degC] Air Inlet Velocity [m/s] Temperature vs. Air Inlet Velocity Figure 6. Maximizing Cooling Efficiency 0 10 20 30 40 50 60 70 80 90 100 0 0.2 0.4 0.6 0.8 1 1.2 Temperature [degC] Absorptivity [-] Temperature vs. Internal Blinds Absorptivity 0 10 20 30 40 50 60 70 80 90 100 0 0.2 0.4 0.6 0.8 1 1.2 Temperature [degC] Emissivity [-] Temperature vs. Internal Blinds Emissivity Max T Max T (Inner Pane) Average T (Ventilated Cavity) Figure 7. Material Selection: Absorptivity of Blinds Figure 8. Material Selection: Emissivity of Blinds The solar studies (Figure 5) provide a means of assess- ing the level of exposure and the amount of direct solar radiation at any point on the facade. The double-skin fa- cade is south-oriented, and therefore more exposed to the sun. However, the effect of the external shading has to be taken into account in order to evaluate the cor- rect amount of radiation hit- ting the facade. The other main input pa- rameters used for the anal- ysis are shown in the tables above. Figure 5. Solar Radiation Study The “Conjugate Heat Transfer” and the “Surface-to-Surface Radiation” interfaces have been used to model the heat transfer mechanisms in the double-skin facade. Figure 13. Thermal Loading on Glass Air Inlet Velocity = 0.5 [m/s] Air Inlet Velocity = 0.5 [m/s] INITIAL DESIGN FINAL DESIGN Outlet Outlet Inlet Inlet The current study demonstrates how COMSOL Multiphysics ® can be used as an important design tool within the process of optimiz- ing complex facade systems. The results show that the thermal be- haviour and performance of the DSF depends on many parameters such as material properties and the mechanical ventilation rate. Thanks to COMSOL Multiphysics ® , the system can be explored in de- tail and relevant parameters can be computed to check that all the technical requirements are met. The energy efficiency of the facade depends on the U-value, defined in the following way: U-value = Q tot /(A*(T out - T in )) For the double-skin facade considered it is: Excerpt from the Proceedings of the 2014 COMSOL Conference in Cambridge Initial Design Max. T Average T (Ventilated Cavity) Max. T (Inner Pane) Final Design Max. T (Inner Pane) Average T (Ventilated Cavity) Max. T Max. T (Inner Pane) Average T (Ventilated Cavity) Max. T Inlet Area Inlet Area Outlet Area Outlet Area Figure 10. Temperature Profile [degC] Figure 9. Air Flow in the Main Cavity [m/s] U-Value < 0.3 W/m^2*K In order to meet blast resistance requirements, the inner glazing pane must not exceed 40 degC (Figure 11). Figure 11. Inner Pane Temperature Profile Figure 12. Heat Flux Top of inner layer 3.58 m Bottom of inner layer 0 m Temperature [degC] y coordinate [m] Air Inlet Velocity = 1 [m/s] Q tot T in T out 0.978 -0.0415 0. 943 0.9 18 0.8 92 0. 892 0.86 7 0. 841 0. 81 6 0.7 90 0 .79 0 0. 7 65 0 .7 3 9 0.714 0.688 0. 688 0.6 63 0.637 0 . 6 1 2 0.586 0 .561 0.535 0 .510 0.48 4 0.459 0.433 0.4 08 0 .3 8 2 0. 382 0.357 0.331 0.306 0.280 0.255 0.229 0.204 0.204 0.178 0.153 0.153 0.127 0.102 0.0765 0.0765 0.0765 -0.0414 0.0255 0.0255 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 oad Enlarged by 150.0 0.00 1.00 2.00 0.978 -0.042 [mm] www.newtecnic.com y - coord. Temperature [degC]

description

The use of ventilated facades may reduce the cooling and heating energy demands of the building. Double-skin facades (DSFs) belong to the wider group of ventilated facades and currently represent one of the most interesting and studied facade systems. The purpose of this study is to investigate the thermal behaviour and performance of a DSF being designed for a real project. The DSF is comprised of two double glazing units, a mechanically ventilated air cavity and solar control (shading) devices placed within the cavity. The objective of the analysis is to realise the full design of the facade system, particularly looking at the following aspects: - Select appropriate construction materials; - Estimate thermal performance in terms of U-value; - Establish thermal loads on each structural element; - Determine position and design of inlet and outlet; - Determine the effect of the shading devices on fluid flow and temperature distribution.

Transcript of Investigating the Performance of Mechanically Ventilated Double-Skin Facades

Page 1: Investigating the Performance of Mechanically Ventilated Double-Skin Facades

Investigating the Performance of Mechanically Ventilated Double-skinFacades with Solar Control Devices in the Main Cavity

Carmelo G. Galante - Newtecnic Ltd, London, England, UK.

Internal Blinds

4.2 m

0.245 m

AirInlet

AirOutlet

SolarRadiation

Double Glazing Units(90% Ar + 10% Air)

Figure 1. Building Scale (South-oriented Facade) Figure 2. Typical Bay Figure 3. Double-skin Unit

Figure 4. System Description (COMSOL Input Geometry)

INPUTS

INVESTIGATION ON MATERIALS PROPERTIES AND AIR INLET VELOCITY

FINAL DESIGN (Absorptivity = 0.5, Emissivity = 0.72)

SYSTEM DESCRIPTION AND CONTEXT OF THE ANALYSIS

Low-e coating

InsulationAluminium

Property Unit Valueα_g1 (absorptivity outer glass) [-] 0.2τ_g1 (transmissivity outer glass) [-] 0.73ρ_g1 (reflectivity outer glass) [-] 0.07α_g2 (absorptivity inner glass) [-] 0.33τ_g2 (transmissivity inner glass) [-] 0.51ρ_g2 (reflectivity inner glass) [-] 0.16

Property Unit Valueα_g3 (absorptivity outer glass) [-] 0.2τ_g3 (transmissivity outer glass) [-] 0.73ρ_g3 (reflectivity outer glass) [-] 0.07α_g4 (absorptivity inner glass) [-] 0.18τ_g4 (transmissivity inner glass) [-] 0.58ρ_g4 (reflectivity inner glass) [-] 0.24

GLASSES ENERGY PROPERTIESOUTER DOUBLE GLAZING UNIT

INNER DOUBLE GLAZING UNIT

Parameter Unit ValueAir Inlet Velocity [m/s] Variable (0.1 - 1)

Air Inlet Temperature [degC] 26

MECHANICAL VENTILATION INPUTS

Material Unit ValueAluminium [-] Variable (0.1 - 1)

Glass [-] 0.89Glass (Low-e Coating) [-] 0.03

EMISSIVITY OF MAIN MATERIALS

Parameter Unit ValueOutdoor Temperature [degC] 50Indoor Temperature [degC] 24

Global Radiation [W/m^2] 1020

SUMMER PEAK DAY-TIME CONDITIONSAluminium [-] Variable (0.1 - 1)

ABSORPTIVITY OF MAIN MATERIALS

The purpose of this study is to investigate the thermal behaviour and performance of a DSF being designed for a real project in the Middle East. The DSF is comprised of two double glazing units, a mechanically ventilated air cavity and solar control (shading) devices placed within the cavity (Figure 4).

0

20

40

60

80

100

120

0 0.2 0.4 0.6 0.8 1 1.2

Tem

pera

ture

[de

gC]

Air Inlet Velocity [m/s]

Temperature vs. Air Inlet Velocity

Initial Design - Max T New design - Max T

Initial Design - Average T (Ventilated Cavity) New Design - Average T (Ventilated Cavity)

Initial Design - Max T (Inner Pane) New design - Max T (Inner Pane)

Figure 6. Maximizing Cooling Efficiency

0

10

20

30

40

50

60

70

80

90

100

0 0.2 0.4 0.6 0.8 1 1.2

Tem

pera

ture

[de

gC]

Absorptivity [-]

Temperature vs. Internal Blinds Absorptivity

Max T Max T (Inner Pane) Average T (Ventilated Cavity)

0

10

20

30

40

50

60

70

80

90

100

0 0.2 0.4 0.6 0.8 1 1.2

Tem

pera

ture

[deg

C]

Emissivity [-]

Temperature vs. Internal Blinds Emissivity

Max T Max T (Inner Pane) Average T (Ventilated Cavity)

Figure 7. Material Selection: Absorptivity of Blinds Figure 8. Material Selection: Emissivity of Blinds

The solar studies (Figure 5) provide a means of assess-ing the level of exposure and the amount of direct solar radiation at any point on the facade. The double-skin fa-cade is south-oriented, and therefore more exposed to the sun. However, the effect of the external shading has to be taken into account in order to evaluate the cor-rect amount of radiation hit-ting the facade.The other main input pa-rameters used for the anal-ysis are shown in the tables above.

Figure 5. Solar Radiation StudyThe “Conjugate Heat Transfer” and the “Surface-to-Surface Radiation” interfaces have been used to model the heat transfer mechanisms in the double-skin facade.

Figure 13. Thermal Loading on Glass

Air Inlet Velocity = 0.5 [m/s] Air Inlet Velocity = 0.5 [m/s]

INITIAL DESIGN FINAL DESIGN

Outlet Outlet

Inlet Inlet

The current study demonstrates how COMSOL Multiphysics® can be used as an important design tool within the process of optimiz-ing complex facade systems. The results show that the thermal be-haviour and performance of the DSF depends on many parameters such as material properties and the mechanical ventilation rate. Thanks to COMSOL Multiphysics®, the system can be explored in de-tail and relevant parameters can be computed to check that all the technical requirements are met.

The energy efficiency of the facade depends on the U-value, defined in the following way:

U-value = Qtot

/(A*(Tout

- Tin))

For the double-skin facade considered it is:

Excerpt from the Proceedings of the 2014 COMSOL Conference in Cambridge

Initial Design

Max. T

Average T(Ventilated Cavity)

Max. T(Inner Pane)

Final Design

Max. T(Inner Pane)

Average T(Ventilated Cavity)

Max. T

Max. T(Inner Pane)

Average T(Ventilated Cavity)

Max. T

Inlet Area

Inlet Area

Outlet Area

Outlet Area

Figure 10. Temperature Profile [degC]Figure 9. Air Flow in the Main Cavity [m/s]

U-Value < 0.3 W/m^2*K

In order to meet blast resistance requirements, the inner glazing pane must not exceed 40 degC (Figure 11).

Figure 11. Inner Pane Temperature Profile Figure 12. Heat FluxTop of inner layer

3.58 m

Bottom of inner layer 0 m

Tem

pera

ture

[deg

C]

y coordinate [m]

Air Inlet Velocity = 1 [m/s]

Qtot

Tin

Tout

M 1 : 20

XY

Z

0.978

-0.0415

0.943

0.918

0.892

0.8920.867

0.841

0.816

0.790

0.790

0.765

0.739

0.714

0.688

0.688

0.663

0.637

0.612

0.586

0.561

0.535

0.510

0.484

0.459

0.433

0.408

0.382

0.382

0.357

0.331

0.306

0.280

0.255

0.229

0.204

0.204

0.178

0.153

0.153

0.127

0.102

0.0765

0.0765

0.0765

-0.0414

0.0255

0.0255

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

Deformed Structure from LC 4 thermal load Enlarged by 150.0

Quadrilateral Elements , Displacement in local x in Node , Loadcase 4 thermal load , from -0.0415 to 0.978 step 0.0255 mm

-0.042

-0.025

0.000

0.025

0.051

0.076

0.102

0.127

0.153

0.178

0.204

0.229

0.255

0.280

0.306

0.331

0.357

0.382

0.408

0.433

0.459

0.484

0.510

0.535

0.561

0.586

0.612

0.637

0.663

0.688

0.714

0.739

0.765

0.790

0.816

0.841

0.867

0.892

0.918

0.9430.978

m-1.00 0.00 1.00 2.00 3.00

0.00

1.00

2.00

M 1 : 20

XY Z

0.978

-0.0415

0.943

0.918

0.892 0.8920.867

0.841

0.8160.790

0.7900.765

0.7390.714

0.688

0.688

0.6630.637

0.612

0.586

0.5610.535

0.5100.484

0.4590.433

0.408

0.382

0.382

0.3570.331

0.306

0.280

0.2550.229

0.204

0.2040.178

0.153

0.1530.127

0.102

0.0765

0.0765

0.0765

-0.0414

0.0255

0.0255

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

Deformed Structure from LC 4 thermal load Enlarged by 150.0

Quadrilateral Elements , Displacement in local x in Node

, Loadcase 4 thermal load , from -0.0415 to 0.978 step 0.0255 mm

-0.042

-0.025

0.000

0.025

0.051

0.076

0.102

0.127

0.153

0.178

0.204

0.229

0.255

0.280

0.306

0.331

0.357

0.382

0.408

0.433

0.459

0.484

0.510

0.535

0.561

0.586

0.612

0.637

0.663

0.688

0.714

0.739

0.765

0.790

0.816

0.841

0.867

0.892

0.918

0.943

0.978

m-1.00

0.00

1.00

2.00

3.00

0.00 1.00 2.00

0.978-0.042 [mm]

www.newtecnic.com

y - coord.

Temperature [degC

]