WREF
Itai Danielski
Anna Joelsson Morgan Fröling
Denver, 15 May 2012
THE IMPACT OF THE SHAPE FACTOR
ON FINAL ENERGY DEMAND
IN RESIDENTIAL BUILDINGS
IN NORDIC CLIMATES
1
Department of Engineering and Sustainable Development Mid Sweden University
Definitions
2
The shape factor of buildings:
• The ratio between the building’s thermal
envelope and volume
1. The shape of the building
3
2. The size of the building
4
5
Case studies
6
Shape factor definition:
Thermal-envelope-area-to-floor-area
Floor area Thermal envelope
area
Shape
factor
Building A 2197 m2 2228 m2 1.01
Building B 1711 m2 2018 m2 1.18
Building C 975 m2 1287 m2 1.32
Building D 1069 m2 1561 m2 1.46
Building E 567 m2 913 m2 1.61
Thermal envelope scenarios
Thermal envelope scenarios: Low Medium High
External wall 120 180 420
Roof 120 190 400
Ground floor 100 160 350
Thermal envelope scenarios: Low Medium High
External wall 0.331 0.229 0.103
Roof 0.304 0.202 0.100
Ground floor 0.318 0.208 0.099
Windows 1.7 1.2 0.7
7
Insulation thickness (mm)
Heat transfer coefficient W/(m2K)
Climate scenarios
8
Average outdoor
City temperature
Kiruna: -1 ˚c
Östersund: 3 ˚c
Karlstad: 5 ˚c
Malmö: 8 ˚c
Different thermal envelope scenarios
9
0
20
40
60
80
100
120
140
160
0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
Sp
ec
ific
he
at
de
ma
nd
k
Wh
/(m
2 y
ea
r)
The shape factor
Low thermal envelope scenario
Medium thermal envelope scenario
Large thermal envelope scenario
Different climate scenarios
10
0
20
40
60
80
100
120
140
160
0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
Sp
ec
ific
he
at
de
ma
nd
k
Wh
/(m
2 y
ea
r)
The shape factor
7.7°C 4.8°C 1.8°C -1.7°C
The impact of the shape factor
11
0
10
20
30
40
50
60
70
-3 -1 1 3 5 7 9 11 13 15
Sp
ec
ific
he
at
de
ma
nd
P
er
un
it o
f s
ha
pe
fa
cto
r
kW
h/[
(m2 y
ea
r· S
F)
Annual average outdoor temperature
Low thermal envelope Medium thermal envelope High thermal envelope
y = -3.4702x + 49.126 R² = 0.9942 y = -2.5995x + 32.875
R² = 0.9943
y = -1.6922x + 18.203 R² = 0.9952
0
10
20
30
40
50
60
70
-3 -1 1 3 5 7 9 11 13 15
Sp
ec
ific
he
at
de
ma
nd
P
er
un
it o
f s
ha
pe
fa
cto
r
kW
h/[
(m2 y
ea
r· S
F)
Annual average outdoor temperature
Low thermal envelope Medium thermal envelope High thermal envelope
The impact of the shape factor
12
y = -3.4702x + 49.126 R² = 0.9942 y = -2.5995x + 32.875
R² = 0.9943
y = -1.6922x + 18.203 R² = 0.9952
0
10
20
30
40
50
60
70
-3 -1 1 3 5 7 9 11 13 15
Sp
ec
ific
he
at
de
ma
nd
P
er
un
it o
f s
ha
pe
fa
cto
r
kW
h/[
(m2 y
ea
r· S
F)
Annual average outdoor temperature
Low thermal envelope Medium thermal envelope High thermal envelope
The impact of the shape factor
13
y = -3.4702x + 49.126 R² = 0.9942 y = -2.5995x + 32.875
R² = 0.9943
y = -1.6922x + 18.203 R² = 0.9952
0
10
20
30
40
50
60
70
-3 -1 1 3 5 7 9 11 13 15
Sp
ec
ific
he
at
de
ma
nd
P
er
un
it o
f s
ha
pe
fa
cto
r
kW
h/[
(m2 y
ea
r· S
F)
Annual average outdoor temperature
Low thermal envelope Medium thermal envelope High thermal envelope
The impact of the shape factor
14
Differences in specific heat demand
among case studies with different shape factor
15
0%
4%
8%
12%
16%
20%
24%
-3 -2 -1 0 1 2 3 4 5 6 7 8 9% d
iffe
ren
ce
in
he
at
su
pp
ly
Annual average outdoor temperature
Low thermal envelope Medium thermal envelope High thermal envelope
Summery and conclusions
• The design of the building (shape factor) has
larger impact on its final energy use for
– buildings with lower grade of thermal envelope
– buildings in colder climates
– buildings exposed to strong winds
16
Conclusions and summery
• 10% - 20% differences in specific heat demand
were found in this study due to differences in
building’s design
• The differences could be higher for buildings
designed with larger shape factor
17
Recommendation
• Limitation on the shape factor for future buildings
in cold climates could help to reduce space
heating demand
• Such limitation were introduce for new design
building in China.
18
For future study
• Differences in primary energy by using LCA
including material for construction and demolition
of buildings with different shape factors.
19
Thank you for your attention
20
