Click to edit Master title style

Cost optimal facade design solutions of office buildings

Tallinn 10.10.2013

Martin ThalfeldtPhD student in TUTwww.nzeb.ee

OBJECTIVES• Developing energy and cost efficient facade design

principles for nearly zero energy building (non-residential)

• Studies so far: window U>1.0

• Questions: optimal size of windows, highly transparent or solar protection glazing, external shading or not, insulation thickness, facade vs PV

• Influenced: daylight, heating, cooling, electric lighting, investment

• Study procedures: Energy and indoor simulations + financial calculations of

a generic office floor model Number of window panes up to 5, U=0.21 Financial feasability -> min. 20 year NPV Best possible energy efficiency

METHODS• Criteria for most financially feasible case is minimum

net present value, which includes investment cost and 20 year energy use.

• Calculations according to Estonian energy efficiency requirements

Smallest energy consumption ≠ min €

STEP 1 MINIMUM WINDOW SIZE• Average daylight factor ≥ 2% • Minimum sized windows

𝑨𝒘=¿¿

STEP 1 MINIMUM WINDOW SIZEGla-zing

U, W/(m2K)

g, - τvis, -

2/C 1.1 0.61 0.78

3/C 0.54 0.49 0.70

4/C 0.32 0.36 0.63

3/SC 0.54 0.36 0.60

5/C 0.21 0.24 0.56

2/D 1.0 0.27 0.50

3/D 0.54 0.24 0.45

STEP 2 HIGHLY TRANSPARENT OR SOLAR PROTECTION GLAZING?

Highly transparent glazing allows reaching better energy efficiency!

Delivered energy Primary energy

STEP 3 NUMBER OF PANES AND INSULATION THICKNESS IN BALANCE!

• 3 pane glazing – insulation 200 mm (U=0,16)

• 4 pane glazing – insulation 250 mm (U=0,13)

• 5 pane glazing – insulation 390 mm (U=0,09)

STEP 4 ENERGY EFFICIENT FACADE SOLUTIONS

MOST ENERGY EFFICIENT FACADE SOLUTION

No of panes

WWR, %

Ext. shading

Insulation thickness, mm

Primary energy, kWh/m2

Invest-ment€/m2

20 year NPV€/m2

Lõuna 5 60% No 390 86.3 136.1 168.0

Ida 5 60% Yes 390 84.6 175.8 211.9

Lääs 5 60% Yes 390 84.7 175.8 211.9

Põhi 5 60% No 390 87.3 136.1 170.2

FINANCIALLY MOST FEASIBLE SOLUTION

No of panes

WWR, %

Ext. shading

Insulation thickness, mm

Primary energy, kWh/m2

Invest-ment€/m2

20 year NPV€/m2

Lõuna 3 37.5% No 200 96.7 96,3 140.3

Ida 3 37.5% No 200 95.7 89,9 140.6

Lääs 3 37.5% No 200 97.3 89,9 142.1

Põhi 3 37.5% No 200 97.8 96,3 143.4

Office floor primary energy=93.6 x 1.2 = 112.6 kWh/m2

Office floor primary energy=85.5 x 1.2 = 102.6 kWh/m2

COOLING CAPACITIES

• Window size affects cooling capacities in addition to energy consumption

• Triple glazing with WWR ca 25% might be a more sensible solution

FROM LOW ENERGY TO NZEB

3 panes, WWR 37.5% (Cost optimal)4 panes, WWR 37.5% (North 60%)5 panes, WWR 29.5%5 panes, WWR 60% (Energy efficient)

CONCLUSION• Space heating dominates in case of double and triple windows, the

proportion of heating reduces as no of panes increases

• Smaller windows result in better energy efficiency in case of double and triple glazing

• Financially most feasible case is triple glazing with high thermal resistance (U=0.54 g=0.49), window to wall ratio ca 25%, insulation thickness 200 mm (U=0.16)

• Best energy efficiency was achieved with quintuple glazing (U=0.21 g=0.24), window to wall ratio 60%, insulation thickness 390 mm (U=0.09)

• In case of quadruple glazing (U=0.32 g=0.36) the optimal window to wall ratio is ca 40%

• External shading is not necessary if windows are sized according to average daylight factor 2%

• It is more reasonable to use cost optimal facade solution and install more PV panels

• Necessity to study the influence of external shading control strategies and double facade on energy efficiency occurred