Search for an optimised building envelope
configuration during early design phase with
regard to the heating and cooling energy
consumption
Mitja KOŠIR, Tamara GOSTIŠA, Živa KRISTL
Faculty of Civil and Geodetic Engineering, University of Ljubljana, [email protected]
Introduction
 Implementation of nZEB buildings is one of key instruments
of EUs 20-20-20 till 2020 policy.
 Implementation of nZEBs is an interdisciplinary problem,
nonetheless early stage of building design holds the largest
potential for reducing the energy consumption of buildings.
 During the early design phases characteristics like:
 building SHAPE
 ORIENTATION and
 the AMOUNT OF GLAZING are defined.
Introduction
 When the envelope shape is defined, energy performance
information is usually non-existent, since modelling for
energy simulation is a time-consuming task and not
undertaken by architects until later phases of the design
project.
This is particularly true for small projects and small design teams,
which make up the majority of designed and built buildings.
Therefore, designers mostly rely on presumptions regarding
“dominant” climatic influences at a given location affecting the
energy performance of a building.
 The objective was to study the influence of BUILDING
SHAPE, GLAZING AREA and ORIENTATION on the heating
and cooling energy consumption under „realistic“ climatic
conditions but with simplified and generic building
characteristics.
Methodology
 Simplified building geometry, 5 basic shapes (1000m3)
CASE 1:2
CASE 1:1.5
CASE 1:1
CASE 1.5:1
CASE 2:1
 Glazing was gradually increased (WWR from 0 to 100%)
 Orientation changed in steps of 30°
ENVELOPE
U opaque = 0.14 W/m2K
U window = 1.06 W/m2K
g factor = 0.58
VENTILATION
Natural & constant = 0.7 ACH
SET-POINTS
Winter = 20°C
Summer = 26°C
Methodology
 CLIMATE
Ljubljana has a typical Central European climate with slight
Mediterranean influences.
Köppen-Geiger climatic classification: Dfb.
Humid continental with cold winters and warm summers.
Corresponds to the ASHRAE climate type 5A.
Slovenia
Ljubljana
14°30´E
46°03´N
Results
 140 baseline cases was calculated using EnergyPlus.
 For each case yearly energy balance was determined for
heating (QH), cooling (QC) and total (QT) energy consumption.
EXAMPLE:
14.00
Yearly thermal balance
kWh/m2
transmission loses
12.00
window loses
10.00
solar gains
8.00
ventilation loses
6.00
ventialtion gains
4.00
CASE 1:1.50.0
2.00
0.00
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
-2.00
QH = 70.43 kWh/m2
QC = 6.35 kWh/m2
QT = 76.78 kWh/m2
Results
 WWR and building geometry (orientation 0°)
The rate of increase in QC
depends on the ratio
between glazing area and
total area of the building
envelope.
COOLING & HEATING
With increasing of WWR
the heating energy (QH)
steadily decreases while
the cooling energy (QC)
consumption
increases
almost exponentially.
100
kWh/m2
90
80
70
QH
60
50
40
QC
30
20
10
0
120
kWh/m2
QT CASE 1:1
QT CASE 1.5:1
QT CASE 2:1
QT CASE 1:1.5
QT CASE 1:2
115
110
105
100
TOTAL
Without
shading
at
WWR≥50% cooling energy
becomes a decisive factor
governing the overall
energy performance (QT)
of the building.
QH CASE 1:1
QC CASE 1:1
QH CASE 1.5:
QC CASE 1.5:
QH CASE 2:1
QC CASE 2:1
QH CASE 1:1.
QC CASE 1:1.
QH CASE 1:2
QC CASE 1:2
QT
95
90
85
80
75
70
0%
25 %
WWR
50 %
100 %
Results
 Building geometry and orientation (WWR 50%)
At higher values of WWR
(≥50%) the orientation of
buildings becomes more
important due to the peak
in QC at ±60° orientations.
HEATING
COOLING
Largest cooling energy
consumption is at SE and
SW orientation (azimuth
±60°), smallest at E and W
orientations,
although
comparable
to
S
orientation.
kWh/m2
85
QH
80
75
70
65
60
20
QC
15
10
5
0
95
TOTAL
Lowest heating energy
consumption is at S
orientation and in case of
buildings with largest
glazing area (CASE 2:1).
90
kWh/m2
CASE 2:1
A2.50
CASE 1.5:1
A1.50
90
QT
85
CASE 1:1
A0.50
CASE 1:1.5
B1.50
CASE 1:2
B2.50
80
75
90°
60°
30°
0°
-30°
ORIENTATION
-60°
-90°
Results
Best performing case:
1.5:1, south oriented, 100% WWR,
shaded from 15th of May till 15th of October
 Influence of shading
QC
120
100
80
QH
kWh/m2
110,03
100,12
76,78
78,56
6.35
3.00
70.43
75.56
unshaded
shaded
74,96
2.29
81,18
40.36
8.22
72.67
50.62
84,15
59.76
72.96
77,32
10.96
14.18
10.03
60
40
73,30
63.27
59.68
cooling season
shaded
unshaded
73.19
63.14
20
0
cooling season
shaded
unshaded
shaded
shaded
CASE 1:1.50.0
CASE 1.5:1.100.0
CASE 2:1.100.0
(Aw=50.00m2)
(Aw=122.47m2)
(Aw=141.42m2)
cooling season
shaded
Conclusions
 Cooling energy demand is negligible at lower portions of glazing
(<6 % of total envelope), but it becomes a decisive factor at larger
portions (>12 % of total enevelope), where the cooling energy
demand is almost equal to the heating energy demand.
Appropriate shading reduces the total
energy consumption by ≈30%
Difference in heating energy
consumption between S and E
orientation is ≈25%, peak is at SE and SW
 Elongated building forms with larger glazing portions in the longer
façade and appropriate shading are energy more efficient than
compact buildings with small or medium glazing portions.