Cost optimal facade design solutions of office buildings Tallinn 10.10.2013
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Click to edit Master title styleCost optimal facade design solutions of office buildings
Tallinn 10.10.2013
Martin ThalfeldtPhD student in TUTwww.nzeb.ee
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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
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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 €
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STEP 1 MINIMUM WINDOW SIZE• Average daylight factor ≥ 2% • Minimum sized windows
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STEP 1 MINIMUM WINDOW SIZEGla-zing
U, W/(m2K)
g, - τvis, -
2/C 1.1 0.61 0.783/C 0.54 0.49 0.704/C 0.32 0.36 0.633/SC 0.54 0.36 0.605/C 0.21 0.24 0.562/D 1.0 0.27 0.503/D 0.54 0.24 0.45
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STEP 2 HIGHLY TRANSPARENT OR SOLAR PROTECTION GLAZING?
Highly transparent glazing allows reaching better energy efficiency!
Delivered energy Primary energy
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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)
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STEP 4 ENERGY EFFICIENT FACADE SOLUTIONS
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MOST ENERGY EFFICIENT FACADE SOLUTIONNo of
panesWWR, %
Ext. shading
Insulation thickness, mm
Primary energy, kWh/m2
Invest-ment€/m2
20 year NPV€/m2
Lõuna 5 60% No 390 86.3 136.1 168.0Ida 5 60% Yes 390 84.6 175.8 211.9Lääs 5 60% Yes 390 84.7 175.8 211.9Põhi 5 60% No 390 87.3 136.1 170.2
FINANCIALLY MOST FEASIBLE SOLUTIONNo of
panesWWR, %
Ext. shading
Insulation thickness, mm
Primary energy, kWh/m2
Invest-ment€/m2
20 year NPV€/m2
Lõuna 3 37.5% No 200 96.7 96,3 140.3Ida 3 37.5% No 200 95.7 89,9 140.6Lääs 3 37.5% No 200 97.3 89,9 142.1Põhi 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
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COOLING CAPACITIES
• Window size affects cooling capacities in addition to energy consumption
• Triple glazing with WWR ca 25% might be a more sensible solution
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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)
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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