Cost optimal facade design
solutions
of
office
buildings
Click to edit Master title style
Tallinn 10.10.2013
Martin Thalfeldt
PhD student in TUT
www.nzeb.ee
OBJECTIVES
•
Developing energy and cost efficient facade design
principles for nearly zero energy building (nonresidential)
•
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
𝑫 × 𝑨 × (1 − 𝑹2
𝑨𝒘 =
𝑻×𝜽×𝒎
STEP 1 MINIMUM WINDOW SIZE
Glazing
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?
Delivered energy
Primary energy
Highly transparent glazing allows
reaching better energy efficiency!
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
Investment
€/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
Office floor primary energy=85.5 x 1.2 = 102.6 kWh/m2
FINANCIALLY
MOST FEASIBLE SOLUTION
No of
panes
WWR,
%
Ext.
shading
Insulation
thickness,
mm
Primary
energy,
kWh/m2
Investment
€/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
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
4
5
5
panes,
panes,
panes,
panes,
WWR
WWR
WWR
WWR
37.5% (Cost optimal)
37.5% (North 60%)
29.5%
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