Click to edit Master title style Cost optimal facade design solutions of office buildings Tallinn Martin Thalfeldt PhD student in TUT

O BJECTIVES 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

M ETHODS 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 €

S TEP 1 M INIMUM WINDOW SIZE Average daylight factor ≥ 2% Minimum sized windows

S TEP 1 M INIMUM WINDOW SIZE Gla- zing U, W/(m 2 K) g, -τ vis, - 2/C /C /C /SC /C /D /D

S TEP 2 H IGHLY TRANSPARENT OR SOLAR PROTECTION GLAZING ? Highly transparent glazing allows reaching better energy efficiency! Delivered energyPrimary energy

S TEP 3 N UMBER 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)

S TEP 4 E NERGY EFFICIENT FACADE SOLUTIONS

M OST ENERGY EFFICIENT FACADE SOLUTION No of panes WWR, % Ext. shading Insulation thickness, mm Primary energy, kWh/m 2 Invest- ment €/m 2 20 year NPV €/m 2 Lõuna560%No Ida560%Yes Lääs560%Yes Põhi560%No F INANCIALLY MOST FEASIBLE SOLUTION No of panes WWR, % Ext. shading Insulation thickness, mm Primary energy, kWh/m 2 Invest- ment €/m 2 20 year NPV €/m 2 Lõuna337.5%No , Ida337.5%No , Lääs337.5%No , Põhi337.5%No , Office floor primary energy=93.6 x 1.2 = kWh/m 2 Office floor primary energy=85.5 x 1.2 = kWh/m 2

C OOLING CAPACITIES Window size affects cooling capacities in addition to energy consumption Triple glazing with WWR ca 25% might be a more sensible solution

F ROM LOW ENERGY TO N ZEB 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)

C ONCLUSION 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