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The most efficient position of shading devices in a double-skin facade

Elisabeth Gratia *, Andre De Herde

Universite Catholique de Louvain, Architecture et Climat, Place du Levant 1, B-1348 Louvain-La-Neuve, Belgium

Received 16 August 2006; received in revised form 26 August 2006; accepted 1 September 2006

Abstract

In recent years, there has been a great deal of interest in double-skin facades due to the advantages claimed for this technology in terms of energy

saving in the cold season, protection from external noise and wind loads and their high-tech image.

The advent of computers and other office equipment has increased the internal heat gains in most offices. Highly glazed facades, together with

the extra heat gains from the electric lighting made necessary by deep floor plans and the wider use of false ceilings, have increased the risk of overheating. To preserve comfort and reduce cooling loads, it is important to apply natural cooling strategies, including solar protections use.

External solar protections are more effective than internal shading devices. In the case of the double-skin facade, the blinds can be integrated in

the cavity. It is thus protected from the bad weather and pollution. Solar protection can remain in place even in the event of important wind, which

represents an undeniable advantage for the buildings with great height.

This article examines the influence of the position and the colour of the blinds on the cooling consumption of an office building with a double-

skin facade.

# 2006 Elsevier B.V. All rights reserved.

Keywords: Double-skin facade; Thermal modelling; Office building; Shading devices; Cooling strategies

1. Introduction

The double-skin facade is an architectural phenomenon

driven by an aesthetic desire for an all-glass facade.

Transparency is often seen as the main architectural reason

for a double-skin facade, because it allows close contact with

the surroundings. From the client’s point of view, physical

transparency may appear to indicate a transparent organisation

with a large degree of openness [1].

This ‘‘emerging technology’’ of heavily glazed facades is

also often associated with buildings whose design goals include

energy efficiency, sustainability, and a ‘‘green’’ image.

So there has been an increase in the numbers of this type of

building. The success of these facades also lies in the fact thatthey admit a large amount of daylight, exhibit a uniform

exterior, and have attractive aesthetics.

The costs of double-skin facades are higher than those of

normal facades, but claims of energy and productivity savings

are used to justify some of these increased costs [2].

The advent of computers and other electric office equipment

hasincreased theinternalheat gain in most offices. Highlyglazedfacades, often with poor shading, have become very common.

This, together with the extra heat gain from the electric lighting

made necessary by deep floor plans, and the widespread use of

false ceilings, has increased the risk of overheating [3,4].

In the 1990s, concern about global warming resulted in a

resurgence of interest in natural cooling strategies, including

solar protections use [5–7].

There is also an increasing demand for high-quality office

buildings. The occupants and developers of office buildings

require healthy and stimulating working environments [8]. This

is usually provided by an air conditioning system. But in many

cases, with some effort to reduce internal heat gain (well chosenequipment), solar protection and natural ventilation may be

sufficient to ensure good comfort levels for the buildings’

occupants.

In that case, air conditioning system will not be necessary,

which will result in considerable energy and cost savings. It will

also indirectly reduce the burden on the environment, since the

use of energy is always associated with the production of waste

materials [9].

Double-skin facades are assuming an ever-greater impor-

tance in modern building practice. They are already a common

www.elsevier.com/locate/enbuildEnergy and Buildings 39 (2007) 364–373

* Corresponding author. Tel.: +32 10 47 22 23; fax: +32 10 47 21 50.

E-mail addresses: [email protected] (E. Gratia),

[email protected] (A. De Herde).

0378-7788/$ – see front matter # 2006 Elsevier B.V. All rights reserved.

doi:10.1016/j.enbuild.2006.09.001

mailto:[email protected]


http://dx.doi.org/10.1016/j.enbuild.2006.09.001

http://dx.doi.org/10.1016/j.enbuild.2006.09.001





feature in architectural competitions in Europe; but there are

still relatively few buildings in which they have actually been

used, and there is too little information on their behaviour in

operation [10,11].

There are many unknowns: optical and thermal modeling of

these systems is not routine and coupling heat transfer and air

flows from an isolated facade system to the whole building is

complex. A variety of thermal coupling strategies must be

simulated.

Moreover, although subjective claims abound in the

architectural literature, it is extremely difficult to find any

objective data on the actual performance of buildings with

double-skin facades.

Results of simulations show that heating loads are

decreased in an office building with a double-skin facade.

Indeed, the temperature of the air layer in the double-skin is

more important than the outside temperature and so the cavity

protects the building from the cold. Moreover, double-skin hot

air can be recovered to heat the coldest zones of the building

[12].The addition of a double-skin decreases the heating loads of

11.3–13%. The greatest reduction is observed for the northern

double-skin, indeed, in this case, the southern zones benefit

fully from the solar profits which are not filtered by the double-

skin and the zones north are protected by a buffer space [13].

On the other hand, results of simulations show that cooling

loads are increased in an office building with a double-skin

facade. Indeed, the hot air layer becomes an obstacle with the

cooling of the building. Application of natural cooling

strategies becomes still more important in the building with

double-skin than in building without double-skin.

If no natural strategy is implemented to try to decrease

cooling consumption, the addition of a southern double-skin

increases the cooling loads of 19.7%. Indeed, since no

strategy is applied, the temperature in the double-skin is

quickly very important. There is an important transfer o

direct solar radiation and heat by transmission towards the

offices through the windows. The addition of a double-skin in

an east-west oriented building increases the cooling loads of

16.8–18.4%.

If no natural strategy is implemented to try to decrease

cooling consumption (the double-skin remains closed, solar

protections are not used, the strategies of day and night natural

ventilation are not used, etc.), cooling loads in an insulated

building are more important than heating loads.

Cooling loads are 2.5 to three times more significant in the

case of a building well insulated, two times more significant inthe case of a mean insulated building.

On the other hand, if everything is implemented to reduce

cooling loads by natural cooling strategies use, cooling loads

are divided by six comparatively to the case without natural

cooling strategies use.

If double-skin is south oriented, for buildings with various

insulation levels, the repartition of the loads is as follow:

E. Gratia, A. De Herde / Energy and Buildings 39 (2007) 364–373 365

Fig. 1. Temperature evolution in a closed double-skin according to orientation and use of mean coloured solar shading devices.



Well insulated building

Heating loads = 67% of the energy demand

Cooling loads = 33% of the energy demand

Mean insulated building



Not insulated building



So, application of natural cooling strategies becomes

extremely important in a building with double-skin [14].

One of the most efficient natural cooling strategies is the use

of solar blinds.

The temperature of the air layer in the double-skin is

influenced by many factors (solar radiation, outside tempera-

ture, wind speed, windows openings, type of glazing, etc.) but

also by the presence of shading systems [15].

Fig. 1 gives, by clear sky conditions, temperature evolution

in a double-skin facade according to the orientation of this oneand according to the use or not of mean coloured solar shading

devices in the double-skin facade. Shadings devices are then

placed just along the windows of the internal skin in the cavity.

All the openings of the double-skin are closed. When the solar

protection devices are shut down, an important temperature

increase is observed in the double-skin. The greenhouse effect

increases since an additional part of the sun rays is absorbed by

the solar protection devices rather than transmitted in the

offices.

The position of the blind within the air cavity affects the rate

of the heat transfer to the interior and amount of thermal stress

on the glazing layers. Placed too close to the interior facade,inadequate air flow around the blind may occur and conductive

and radiative heat transfer to the interior are increased. The

blind should be placed toward the exterior pane with adequate

room for air circulation on both sides. With wind-induced

ventilation or high velocity thermal-driven ventilation, the

bottom edge of the blind should be secured to prevent fluttering

and noise.

To undertake the study, we chose an office building with a

high level of thermal insulation. With the thermal program TAS

we simulated various features of the double-skin. The research

will help us to understand how the double-skin operates.

Many studies have already simulated the behaviour of

double-skin facades [16–19].

This research is only one step in the search for a better

understanding, in a qualitative way, of the thermal behaviour of

one particular type of double-skin.

Architectural design guidelines would help architects and

owners achieve a better understanding of the applicability of

various concepts to their specific building projects.

2. Methods

2.1. TAS program

TAS is a software package for the thermal analysis of

buildings. It includes a 3D modeller, a thermal/energy analysis

module, a systems/controls simulator and a 2D CFD package.

There are also CAD links into the 3D modeller as well as report

generation facilities. It is a complete solution for the thermal

simulation of a building, and a powerful design tool in the

optimisation of a building’s environmental, energy and comfortperformance [20].

2.2. The building

The simulations where undertaken using the building

proposed in Subtask A of Task 27 (performance of solar

facade components) of the International Energy Agency, Solar

Heating and Cooling Program. Some modifications were made

to adapt this to Belgian practices. This is a medium-sized office

building with office modules on two facades separated by a

central corridor and staircase/service spaces at both ends of the

building. It comprises 150 offices, distributed over five floorsand two orientations: 15 offices on either side of the building

per floor. Fig. 2 presents the geometrical data for the office

building.

A vertical cross section of an office with its main

measurements, is shown in Fig. 3.

The internal wall between the office module and corridor has

an openable window above the door to facilitate the air flow

between northern and southern spaces (the false floor is not

included in the drawing).

Each office has four windows (two top and two bottom) to

allow natural day or night ventilation.

E. Gratia, A. De Herde / Energy and Buildings 39 (2007) 364–373366

Fig. 2. View of the office building studied.



Each floor is divided into 5 zones; the building thus

comprises 25 zones plus the double-skin space.

Thermal characteristics

Building envelope

Roof: U = 0.3 W mÀ

2 K À1

Ground floor: U = 0.379 W mÀ2 K À1

Opaque part of facade: U = 0.373 W mÀ2 K À1

Low-e double glazing: U = 1.8 W mÀ2 K À1, direct solar transmission:

0.62, total solar transmission: 0.708

Double skin

Clear single glass: U -value = 5.33 W mÀ2 K À1, shading factor = 0.76

Width of the air cavity: 1.2 m

H (double-skin facade) = H (building) + 1 m

Use of the building (internal heat gains in the offices: 29.37 W mÀ2)

HVAC system

For heating

Monday–Friday 0 a.m. ! 7 a.m. (15 8C)

7 a.m. ! 6 p.m. (21 8C)6 p.m. ! 12 p.m. (15 8C)

Weekend 0 a.m. ! 12 p.m. (15 8C)

For cooling

Monday–Friday 0 a.m. ! 7 a.m. (nothing)

7 a.m. ! 6 p.m. (24 8C)

6 p.m.! 12 p.m. (nothing)

Week end 0 a.m. ! 12 p.m. (nothing)

Each stage was divided into 5 zones; the building thus counts

25 zones + the double-skin space.

2.3. Climatic data assumptions

The simulations were performed with climatic data from

UCCLE (Belgium). For this study, we chose a sunny summer’s

day (24 July). Fig. 4 shows the climatic data for this day. Ten

days preceding the chosen day were also modelled to take

account of the effect of inertia.

2.4. Subdivision of the double-skin

In Tas, only one temperature per zone is calculated. To try to

understand more precisely the various phenomena which occur

in the double-skin, we subdivided this one in several zones.

Separations are factitious walls which can be completely open.

The factitious walls have a very small thermal resistance and a

solar transmission of 1. Vertically and horizontally subdivisions

are possible.

The horizontal subdivisions are tracked floors. The Track

label has a special function which allows the floor to bemodelled as an air flow aperture. The solar radiation which

strikes the tracked floor is not stopped by the floor and enters in

the adjacent zone.

The vertical subdivisions are modelled by permanently open

window.

2.5. Shading devices

Shading devices (roller blind, venetian blind with orientable

slats, etc.) are modelled only as transparent layers; so optical

properties areonlyangular dependent. There is thusno difference

between roller blind and venetian blind if the solar transmittanceand the external and internal reflectance are the same. The

convection coefficient for gas layer adjacent to blind is

automatically increased by a factor 4/3 to allow for the effects

of convection currents in the largergas space enclosing the blind

In a double facade, the shading device can be placed in

various positions.

2.5.1. Shading device against a facade

If the shading device is against a facade it is modelled as a

device associated to an external window. TAs allows having

substitute building element. The construction and feature


Fig. 3. Geometrical data of the office building.

Fig. 4. Climatic data of the sunny summer day.



shading properties of the building element are replaced by those

of a Substitute Building Element at certain times. These times

are specified by the Substitution Schedule. In the most common

application of this feature, the main building element represents

a window and the substitute building element the same window

with a blind. The substitution process then represents the

drawing of the blind.

2.5.2. Shading device far from the facade

If the shading device is far from the facade, the double

facade can be divided into several zones and air movement

can be studied. The impact of the size, the colour and the

localization of those can be studied.

3. Study of the most efficient position of shading devices

in a double-skin facade

3.1. Efficiency of the solar protections placed in a

double-skin facade

The most effective solar protections are external shading

devices. In the case of the double-skin facade, the blinds can

be integrated in the cavity. They are thus protected from the

bad weather and pollution. Solar protection can remain in

place even in the event of important wind, which represents

an undeniable advantage for the buildings with great height.

However, the heat retained by the blinds involves a rise in

the temperature in the air layer. If it is possible to crate an

opening in the bottom and in the top of the double-skin

facade, by the stack effect, hot air goes up and escapes

outside.

If no strategy is used to reduce cooling consumption in awell insulated building with southern double-skin, cooling

consumption is 1123 kWh/day during a sunny summer day.

The addition of blinds directly in front of the glazings of the

interior skin makes it possible to reduce this consumption of

17.5% if the double-skin remains closed and of 25.7% if this

one is open.

3.2. Mean coloured blinds—double-skin closed

The characteristics of the mean coloured blinds are

coefficient of solar absorptance—0.42,

coefficient of solar reflexion—0.40.

3.2.1. Mean coloured blinds placed against the windows of

the inside skin

The blinds strongly warm up and reach a temperature of

69.8 8C at 1 p.m. They communicate part of their heat to the

glazing although this one is quite insulating. The glazing

temperature on the side of the offices is of 37.6 8C. The

phenomenon would be marked more if the glazing were

normal double glazing. The window sill warms up strongly

too; but as it is good insulated, it communicates less heat in

the offices.

Fig. 5 compares cooling loads and windows temperature of

the inside skin (side offices) at 1 p.m. for the three positions

When the double-skin is sunny and closed, a movement of thermocirculation is established. Indeed, the inside skin of the

double-skin and the blinds warm up: the air in contact with

these walls warms up and acquires an upswing. Quite to the

contrary, along the external skin in single glass, the air cools

and acquires a downward movement.

The thermocirculation of the air is present day and night.

It is accompanied by exchanges of air between the zones close

to the external skin and the zones close to the interior skin.

Air movements are illustrated in Fig. 6. Air flows are

expressed in kg/s.

3.2.2. Mean coloured blinds placed against the windowsof the outside skin

The cooling consumption is lower than in the preceding

case, whereas the air temperature inside the double-skin is

higher. The air temperature in the double-skin is more

important because cooling along the external skin in single

glass is removed. On the contrary the single glazing becomes a


Fig. 5. Cooling loads and windows temperature of the inside skin (side offices) at 1 p.m. for the three positions (mean coloured blinds—double-skin closed).



very hot surface since it is covered by the sunscreens. The

temperature of the interior blind reaches 65.6 8C at 1 p.m.

It is also for this reason that the movement of thermo-

circulation is reversed. It is to be noticed that during the night,

the movement of air takes again its normal direction ( Fig. 6).On the other hand, we note that the cooling need in the

offices is weaker. If we observe the temperatures of the inside

skin, we note, that being safe from any solar radiation and not

being overheated by the blinds, the glazing and the window sills

have a temperature lower than in the preceding cases.

Temperature of the windows on the side of the offices is of

33.5 8C (Fig. 5).

3.2.3. Mean coloured blinds placed in the middle of the

cavity

The blinds protect completely the inside skin from the sun

ray. They are placed over all the width and the height of the

facade, only a space of 5 cmis left free in the higher part of eachstage to simulate the mechanism of operation. Moreover one

space of 50 cm is left free in bottom to allow the movement of

thermocirculation. The part of the double-skin exceeding the

building is also not occulted. The movement of thermocircula-

tion is well established, with small passages of air by the slits of

5 cm. The air of the zones close to the interior skin rises due to

the heating of the blinds (and not either due to the heating of the

inside skin and the blinds); and it goes down in the zones close

to the external skin due to the low temperature of the single

glazing of the external skin (Fig. 6).

The temperature of the interior facade is definitely lower

than in the preceding cases. For that reason, cooling loads are

still reduced. Indeed, the interior facade is completely protected

from the solar radiation, and the blinds cannot transmit their

heat directly to the inside skin (except by radiation). Moreover,

the air of the double-skin can cool partially by licking the single

external glazing (Fig. 5).

3.3. Light coloured blinds—double-skin closed

The characteristics of the light coloured blinds are

coefficient of solar absorptance—0.17,

coefficient of solar reflexion—0.65.

3.3.1. Light coloured blinds placed against the windows

of the inside skin

Compared to the case of mean coloured blinds, the effect of

greenhouse is less important since the colour of the blinds is

lighter. The temperature in the double-skin is decreases abou2.5 8C. The movements of air have the same directions but are

slightly weaker. The solar gains in the double-skin decrease

since the solar radiation reflected by the blinds arises mainly by

the external glazing. On the other hand, the solar gains very

slightly increase in the offices, that is due to the increase in the

coefficient of reflexion to the back of the blinds (Fig. 7).

Compared to the case of mean coloured blinds, blind

temperature is decreased of 12 8C. This one passes from 69.8 to

57.8 8C. That has as a consequence that the temperature of the

glazing side offices decreases from 37.6 to 34.9 8C. The

temperature of the window sill’s side double-skin decreased

from 75.2 to 73.38

C; that is due only to the fact that the


Fig. 6. Air movement for the three positions (mean coloured blinds—double-skin closed).



temperature in the double-skin is lower. The window sills being

well insulated, that makes it possible to gain only 0.2 8C sideoffices. Thanks to the reduction in surface temperature of the

glazings and in spite of the light increase in solar profits in the

offices, the cooling consumption passes from 926 to 894 kWh/

day (either 3.5% less).

3.3.2. Light coloured blinds placed against the windows of

the outside skin

In this case, most of the solar gains is directly reflected

towards outside. Compared to the case of mean coloured blinds,

the temperature in the double-skin is definitely lower (14 8C of

less). The movements of air have the same directions but are

slightly weaker. The air of the double-skin cannot cool anymore by licking the single glazing, but the solar gains are

definitely weaker. The temperature reached in the blind is also

lower, this one passes from 65.6 to 47.4 8C; so a difference of

18 8C is observed (Fig. 7).

The inside skin being safe from any solar radiation and not

being overheated by the blinds, the glazings and the window

sills have a temperature lower than in the preceding cases.

Thanks to the reduction in surface temperature of the inside

facade and in spite of the fact that the air cannot cool by the

single glazing, the cooling consumption passes from 870 to

830 kWh/day (either 4.5% less).

3.3.3. Light coloured blinds placed in the middle of the

cavity

The blinds protect completely the inside skin from the solar

radiations. They are placed over all the width and the height of

the facade. The movement of thermocirculation is well

established, with small passages of air by the slits of 5 cm.

The air of the zones close to the interior skin rises due to the

heating of the blinds (and not either due to the heating of the

inside skin and the blinds); and it goes down in the zones close

to the external skin due to the low temperature of the single

glazing of the external skin.

Compared to the case of mean coloured blinds, blinds

temperature is decreased of 8.58

C. This one passes from 62.5

to 48.3 8C. That has as a consequence that the temperature of

the glazings side offices decreases from 33.1 to 31.1 8C (Fig. 7).The cooling consumption is decreased because the

temperature of the interior facade and the temperature of the

air of the double-skin which can cool partially by licking the

single external glazing are lower. The cooling consumption

passes from 801 to 768 kWh/day (either 4.2% less).

3.4. Double-skin opened

When the double-skin is sunny, the opening of the lower

and higher windows in the double-skin causes an upswing of

the air in the majority of the cases. Indeed, the stack effect is

often more important than the effect due to the wind when thedouble-skin is sunny.

The ventilation of the double-skin by the outside air causes

a considerable reduction in the temperature of this one. The

temperature is about 24 8C in the bottom of the double-skin and

about

29 8C in the top for mean coloured blinds,

28 8C in the top for light coloured blinds.

Note. When the double-skin is closed, the temperature is

about

between 51 and 578

C according to the location of the meancoloured blinds,

between 43 and 48 8C according to the location of the light

coloured blinds.

The temperature in the opened double-skin is much lower

than in the closed double-skin. However, the temperature of the

blinds and the opaque walls of the inside skin remains relatively

important due to the direct solar radiation.

In the case of mean coloured blinds placed against the

windows of the inside skin, the temperature of the blinds is

69.8 8C when the double-skin is closed,

51.48

C when the double-skin is open.


Fig. 7. Cooling loads and windows temperature of the inside skin (side offices) at 1 p.m. for the three positions (light coloured blinds—double-skin closed).



A temperature decreasing of 18.4 8C is reached thanks to the

cooling caused by the air circulation in the double-skin. That

has as a consequence that the temperature of the glazings side

offices decreases from 37.6 to 33.1 8C (Fig. 8).

The cooling consumption of the building is 834 kWh/day.When the blind is placed in the middle of the cavity, the

blinds are cooled on the two sides and reach a temperature of

36.1 8C (light coloured blind, open double-skin). When the

double-skin was closed, the blinds temperature was 48.3 8C.

That has as a consequence that the temperature of the glazing

side offices decreases from 31.1 to 28.1 8C (Fig. 8).

The cooling consumption of the building is then 711 kWh/

day.

Fig. 8 presents the two situations.

When the double-skin is opened, the colour impact is

definitely less important. When the blind is located interior side

of the external skin, the cooling consumption of the building is

even slightly lower for mean coloured blinds than for lightcoloured blinds. Indeed, the double-skin being ventilated, the

difference in temperature between the mean coloured and the

light coloured blind decreases. More, the light coloured

blind tends to reflect more light towards the inside of the offices.

That explains the small difference on the level of cooling

consumption.

4. Discussion

Simulations were performed for a double-skin office

building whose inside facade is well insulated and whose

windows are performing. The influence of the choice of the

blinds or the opening of the double-skin would have been much

more important if the inside facade had been less insulated.

4.1. If double-skin is closed

The influence of the position and the size of the blinds is

important. Indeed, the judicious choice of the location and the

size of the blinds makes it possible to save up to 14.1% of the

cooling consumption of the buildingduring a sunny summer day

Table 1 shows the influence of the blinds position on the

cooling consumption.

The colour of the blinds makes it possible to save up to 4.6%

of the cooling consumption of the building during a sunny

summer day (Table 2).

4.2. If double-skin is opened

The influence of the position and the size of the blinds is

important. Indeed, the judicious choice of the location and the

size of the blinds makes it possible to save up to 13.9% of thecooling consumption of the buildingduring a sunny summer day

Table 3 shows the influence of the blinds position on the

cooling consumption.

The colour of the blinds makes it possible to save up to 3.5%

of the cooling consumption of the building during a sunny

summer day (Table 4).

When the blind is located interior side of the externa

skin, the cooling consumption of the building is even slightly

lower for mean coloured blinds than for light coloured blinds

(see Section 3.4).


Fig. 8. Cooling loads and windows temperature of the inside skin (side offices)

at 1 p.m. forthe twoblind positions andtwo blind colours (double-skinopened).

Table 1Influence of the blinds position on the cooling consumption when the double-

skin is closed

Double-skin closed

Mean coloured

blinds

Light coloured

blinds

Blinds placed against the

windows of the inside skin

926 kWh/day 894 kWh/day


windows of the outside skin

À6.0% À7.2%

Blinds placed in the middle

of the cavity

À13.5% À14.1%

Table 2

Influence of the blinds colour on the coolingconsumption when the double-skin

is closed

Double-skin closed

Mean coloured blinds

(kWh/day)

Light coloured

blinds (%)



926 À3.5



870 À4.6


of the cavity

801 À4.1



4.3. Comfort impact

The defenders of the double-skin advance the following

argument: the usable space is increased due to the fact that the

effect of cold surface close to the windows is decreased, and that

the radiators should not any more be obligatorily along sills. Let

us note that the current insulating glazing already mainly make it

possible to limit the problems of cold surface of the glazing.

This argument can be turned over against the defenders of

the double-skin. Indeed, in summer period, the glazing of the

interior facade can reach high temperatures due to the important

temperature in the cavity of the double-skin and due to the hot

radiation coming from the blinds.

So, the study of the optimal position of the blinds makes it

possible to reduce cooling consumption of the building but also

implies an increasing of the occupants comfort.

5. Conclusions

Table 5 compares all the studied cases. We see that a cooling

consumption decreasing until 23.2% can be reached by paying

attention to

the location of the blinds, the blinds colour,

the opening of the double-skin.

The impact of the opening of the double-skin is obviously

important; the reduction of consumption varies from 7.4 to

12.6% (Table 6).

The influence of the position of the blinds is even larger than

that due to the opening of the double-skin.

The judicious choice of the location and the size of the blinds

makes it possible to save up to 14.1% of the cooling

consumption of all the building during this sunny summer

day (Table 7).


Table 3

Influence of the blinds position on the cooling consumption when the double-

skin is opened

Double-skin opened

Mean coloured

blinds

Light coloured

blinds

Blinds placed against thewindows of the inside skin

834 kWh/day 812 kWh/day



À8.9% À6.2%


of the cavity

À13.9% À12.4%

Table 4

Influence of the blinds colour on the cooling consumption when the double-skin

is opened

Double-skin opened

Mean coloured blinds

(kWh/day)

Light coloured

blinds (%)



834 À3.5



760 +0.1


of the cavity

718 À0.8

Table 5

Cooling loads comparison between all the configurations compared with the case where the mean coloured blinds are placed against the windows of the inside skin in

a closed double-facade

Double-skin closed Double-skin opened

Mean coloured

blinds

Light coloured

blinds (%)

Mean coloured

blinds (%)

Light coloured

blinds (%)

Blinds placed against the windows

of the inside skin

926 kWh/day À3.5 À9.9 À12.3


of the outside skin

À6.0% À10.4 À17.9 À17.7

Blinds placed in the middle of the cavity À13.5% À17.1 À22.5 À23.2

Table 6

Impact of the opening of the double-skin on the cooling consumption


Mean coloured

blinds (kWh/day)

Light coloured

blinds (kWh/day)

Mean coloured

blinds (%)

Light coloured

blinds (%)


of the inside skin

926 894 À9.9 À9.2


of the outside skin

870 830 À12.6 À8.2

Blinds placed in the middle of the cavity 801 768 À10.4 À7.4



This study has showed the great influence that the position

and the colour of the blinds have on the cooling consumption in

an office building with a double-skin. It also highlights the

importance of the opening of the double-skin.

Other interesting factor is the impact of the blinds

characteristics on the human comfort. The position and the

colour of the blinds have an influence on the temperature of thewindows of the inside skin and so on the hot radiation coming

from the windows to the occupants.

Acknowledgements

The authors wish to thank the Walloon Regional Govern-

ment of Belgium for its support in funding this research.

We would also thank Jose Flemal (draftsman) who helped us

to illustrate the article.

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Table 7

Impact of the blinds location on the cooling consumption


Mean coloured

blinds

Light coloured

blinds

Mean coloured

blinds

Light coloured

blinds



926 kWh/day 894 kWh/day 834 kWh/day 812 kWh/day



À6.0% À7.2% À8.9% À6.2%


of the cavity

À13.5% À14.1% À13.9% À12.4%

http://www.i6doc.com/

http://www.i6doc.com/

the most efficient position of shading devices in a double-skin facade

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