Daylighting utilization in the window energy balance ... · 4/22/2014 · This report was printed...

Daylighting utilization in the window energy

balance metric:

Development of a holistic method for early

design decisions

Authors:

Jiangtao Du

Bengt Hellström

Marie-Claude Dubois

Division of Energy and Building Design, Department of Architecture and the

Built Environment, LTH, Lund University

April 22, 2014

Lund University, Energy and Building design Daylighting utilization in the window energy balance metric

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Daylighting utilization in the window energy

balance metric:

Development of a holistic method for early

design decisions

April 22, 2014

AUTHORS

Primary author:

Jiangtao Du (Lund University)

Contributor:

Bengt Hellström (Lund University)

Project leader and editor:

Marie-Claude Dubois (Lund University)

Distribution Classification: Unrestricted

This report was printed and is available at:

Division of Energy and Building Design

Department of Architecture and Built Environment

LTH, Lund University


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KEYWORDS

Houses, energy use, energy balance, daylighting, daylight utilization, electric lighting,

heating, cooling, natural ventilation, shading, screens, simulation.


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ACKNOWLEDGEMENTS

The authors thank the Swedish Energy Agency (Statens energimyndighet, project 36241-1)

and the VELUX Group, Denmark for funding this research.


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Preface

This report presents a study of the impact of windows on overall energy performance of

single family, detached houses located in two European climates: the middle of Sweden

(cold climate) and Southern France (warm climate). The parameters studied include climate

and house characteristics, window properties (sizes, thermal, solar and visual

transmittances) and positions as well as shading devices (interior and exterior) and natural

ventilation. The heating, cooling and lighting energy demands are analysed in order to

demonstrate how various windows and shading systems settings may affect the overall

energy balance of a typical house in different climatic conditions.

This project pursues the main objective of developing a methodology for obtaining a holistic

energy balance metric of window performance that includes the effect of daylight utilization,

with and without the use of shading devices. This number would be a key figure for

architects and planners to demonstrate the energy saving potential linked to daylight

utilization at an early design stage. A secondary objective of this project is to assess the

daylight utilization potential for the residential sector in the Swedish climate.

The project was achieved in collaboration with the VELUX Group, who provided basic house

models descriptions and detailed advice regarding the settings in the simulations.


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Executive summary


single family, detached houses in two European climates: the middle of Sweden (cold

climate) and Southern France (warm climate). The parameters studied include climate and

house characteristics, window properties (sizes, thermal, solar and visual transmittances,

positions), as well as shading devices (interior and exterior) and natural ventilation. The

heating, cooling and lighting energy use were analysed using advanced dynamic energy

simulations with DesignBuilder (interface of EnergyPlus) in order to demonstrate how

various windows and shading systems may affect the overall energy balance of typical

houses in different climatic conditions. The Swedish house model was defined based on the

Swedish building code BBR 19: BFS 2011:26 (6:251) for ventilation and BBR 20: BFS

2013:14 (9:2) for construction U-values, thermal bridges, etc. The French house model was

defined based on information provided directly by the Velux Group.

The study shows that the house’s basic construction (U-values, airtightness, ventilation with

heat recovery) and architectural aspects have a large impact on the overall energy balance.

In this case for instance, the Southern house had a higher energy demand than the Northern

house, and this was mainly due to the fact that the Southern house had higher U-values and

air change rate for the building envelope, no heat recovery on the ventilation, and a higher

envelope-to-volume ratio (thus more heat losses). The Southern house thus had an energy

balance dominated by the heating demand, which would have been expected for the

Northern house. Interestingly, the good construction (low U-values, airtight construction, heat

recovery on ventilation) used for the Northern house resulted in an energy balance where

the lighting demand played a secondary but significant role in the overall energy balance

although heating was still the dominant energy end-use.

For the Northern house under cold climate, larger window sizes give rise to higher heating

and cooling demand but lower lighting demand while for the Southern house, larger window

sizes yield lower heating and lighting demands but higher cooling demand. In addition, the

results clearly show that the impact of orientation is more or less negligible on the overall

energy balance, mainly due to the fact that windows were distributed rather evenly on all

facades in the studied cases. Furthermore, the results indicate that the use of an outside

screen is clearly the most efficient measure to reduce cooling energy demand compared to

the use of inside screen or natural ventilation. For small window sizes (10%-window-to-floor-

ratio-WGR), the selection of environmental control strategy (shading or natural ventilation)


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has a relatively negligible impact on overall energy demand, as long as one of these

strategies is applied.

For both the Northern and Southern houses, the lighting energy savings from daylight

utilization are clearly demonstrated in this study, even in a smaller window area (WGR 0% --

- 10%). Interestingly, when comparing 0% with 10% WGR, the study shows that the

additional heat losses due to windows are compensated by free daylight and passive solar

heat gains. Generally, increasing the window area beyond 10%-WGR does not bring

significant additional savings in terms of lighting energy use, especially in the Southern

house. This could be due to the fact that 10%-WGR is sufficient to reach the desired

average illumination levels considered in this study (150 lux). However, for the Northern

house, larger WGR permit to offset the effect of shading on the lighting performance.

This study showed that daylight utilization could provide electricity savings corresponding to

at least one third of electric lighting demand in Swedish and French houses, going from

about 12 kWh/m2yr to about 7-8 kWh/m2yr, with most savings achieved with the use of 10%-

WGR and only marginal additional savings obtained with larger windows (30%-WGR). Thus,

it can be concluded that the potential for daylight utilization is real and significant in the

residential sector, even considering reasonable window sizes that would limit the heating

and cooling demands.

Although this study yields a series of valuable results and information, it is solely based on

theoretical energy simulations, using inputs and settings that could be very different from a

real context. The results of this study should be considered bearing in mind the basic

limitations of the simulation settings.


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Table of Contents

Preface ................................................................................................................................................... 5 Executive summary .............................................................................................................................. 6 Table of Contents .................................................................................................................................. 8 List of abbreviations ............................................................................................................................. 9 List of figures ...................................................................................................................................... 10 List of tables ........................................................................................................................................ 11 1 Introduction ................................................................................................................................. 12

1.1 OBJECTIVES OF THIS RESEARCH ............................................................................................... 12

2 Literature review ......................................................................................................................... 13 3 Method .......................................................................................................................................... 13

3.1 LOCATIONS, ORIENTATION AND SURROUNDING CONDITIONS ....................................................... 13 3.2 HOUSE MODELS ....................................................................................................................... 14

3.2.1 Northern house .............................................................................................................. 14 3.2.2 Southern house ............................................................................................................. 15

3.3 WINDOW AND SHADING SYSTEMS ............................................................................................. 17 3.3.1 Northern house .............................................................................................................. 17 3.3.2 Southern house ............................................................................................................. 23

3.4 SIMULATIONS .......................................................................................................................... 28

4. Results ............................................................................................................................................. 30

4.1. NORTHERN HOUSE........................................................................................................................ 30 4.1.1. Window areas and energy performance ............................................................................. 30 4.1.3 Overall energy performance................................................................................................. 43

4.2. SOUTHERN HOUSE ........................................................................................................................ 46 4.2.1. Window areas and energy performance ............................................................................. 46 4.2.2. Natural ventilation, shading devices and energy performance ........................................... 54 4.2.3. Overall energy performance................................................................................................ 57

5. Conclusions and discussion ......................................................................................................... 61 6. References ....................................................................................................................................... 64


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List of abbreviations

WGR Window-to-floor ratio

ach Air change(s) per hour


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List of figures

Figure 1: 3D model of Northern house. ................................................................................................................ 14 Figure 2: Plan and section of northern house (units: mm). .................................................................................. 15 Figure 3: Space plan in the Northern house. ........................................................................................................ 15 Figure 4: 3D model of Southern house. ................................................................................................................ 16 Figure 5: Plan and section of Southern house (unit: mm). ................................................................................... 16 Figure 6: Space plan in the Southern house. ........................................................................................................ 17 Figure 7: Window distributions of Northern house – WGR 10%. ......................................................................... 18 Figure 8: Window distributions of Northern house – WGR 10%. ......................................................................... 19 Figure 9: Window distributions of Northern house – WGR 30%. ......................................................................... 20 Figure 10: Window distributions of Northern house – WGR 30%. ....................................................................... 21 Figure 11: Window distributions of Southern house – WGR 10%. ....................................................................... 24 Figure 12: Window distributions of Southern house – WGR 10%. ....................................................................... 25 Figure 13: Window distributions of Southern house – WGR 30%. ....................................................................... 26 Figure 14: Window distributions of Southern house – WGR 30%. ....................................................................... 27 Figure 15: Heating, cooling and lighting demand in Northern house (no natural ventilation and no shading device). ................................................................................................................................................................. 34 Figure 16: Heating, cooling and lighting demand in Northern house (natural ventilation and without shading). .............................................................................................................................................................................. 35 Figure 17: Window areas and heating, cooling and lighting demand in northern house (outside screen and no natural ventilation). .............................................................................................................................................. 36 Figure 18: Heating, cooling and lighting demand in Northern house (natural ventilation and outside screen). . 37 Figure 19: Heating, cooling and lighting demand in Northern house (inside screen and no natural ventilation). .............................................................................................................................................................................. 38 Figure 20: Heating, cooling and lighting demand in northern house (inside screen and natural ventilation). .... 39 Figure 21: Annual energy performance between six environmental settings (Northern house, WGR 10%). ...... 41 Figure 22: Annual energy performance between six environmental settings (Northern house, WGR 30%). ...... 42 Figure 23: Annual energy demand according to orientation (Northern house, WGR 10%). ................................ 44 Figure 24: Annual energy demand according to orientation (Northern house, WGR 30%). ................................ 45 Figure 25: Heating, cooling and lighting demand in Southern house (no natural ventilation and no shading device). ................................................................................................................................................................. 48 Figure 26: Heating, cooling and lighting demand in Southern house (natural ventilation and no shading). ....... 49 Figure 27: Heating, cooling and lighting demand in southern house (outside screen and no natural ventilation). .............................................................................................................................................................................. 50 Figure 28: Heating, cooling and lighting demand in Southern house (natural ventilation and outside screen). . 51 Figure 29: Heating, cooling and lighting demand in Southern house (inside screen and no natural ventilation). .............................................................................................................................................................................. 52 Figure 30: Heating, cooling and lighting demand in Southern house (natural ventilation and inside screen). .... 53 Figure 31: Annual energy performance between six environmental settings (Southern house, WGR 10%). ...... 55 Figure 32: Annual energy performance between six environmental settings (Southern house, WGR 30%). ...... 56 Figure 33: Annual energy performance according to orientation (Southern house, WGR 10%). ........................ 59 Figure 34: Annual energy performance according to orientation (Southern house, WGR 30%). ........................ 60


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List of tables

Table 1: Thermal, solar and visual transmittances of windows on South, East and West facades (two panes). . 22 Table 2: Thermal, solar and visual transmittances of windows on North facade (three panes). ......................... 22 Table 3: Thermal, solar and visual transmittances of windows on South roof (two panes). ............................... 22 Table 4: Thermal, solar and visual transmittances of windows on North roof (three panes). ............................. 22 Table 5: Properties of shading screen. ................................................................................................................. 23 Table 6: Thermal, solar and visual transmittances of windows at facade walls (two panes). .............................. 28 Table 7: Thermal, solar and visual transmittances of windows on roof (two panes). .......................................... 28


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1 Introduction

The indoor environment and energy use of a house are substantially affected by the window

characteristics and configurations (Urbikain & Sala, 2009) (EN/ISO, 2000). In general, the

evaluation of windows is carried out in a specific built environment since both building type

and outdoor climate conditions may have a significant effect on the energy and

environmental performance (Schultz & Svendsen, 1998).

Window energy performance relating to the thermal environment could be the first key issue

to consider by the house inhabitants, architects or builders. The thermal transmittance of the

window (even one with a good thermal performance) could be four to five times larger than

that of a well-insulated wall (Schultz & Svendsen, 1998) (and up to ten times in a passive

house). Overall, heat losses from windows could even be responsible for around one third of

the total energy losses in a typical residential building (Karabay & Arici, 2012). On the other

hand, windows can contribute to passive energy gains by allowing solar radiation and natural

light into the house, which may also increase the risk for overheating (Schultz & Svendsen,

1998). An optimal energy balance for windows is therefore a basic requirement for houses

with high energy performance.

Windows also provide daylight, which has been regarded as one indispensable

environmental factor in residential buildings (British Standard, 2008). Daylight can illuminate

the indoor tasks, replace electric lighting and contribute to improve human health and well-

being on the ground of physiological and psychological aspects (British Standard, 2008)

(Veitch & Galasiu, 2012). Windows could be used as an efficient approach to deliver daylight

into buildings (CIBSE, 2012).

1.1 Objectives of this research


single family, detached houses in two European climates: the middle of Sweden (cold

climate) and Southern France (warm climate). The parameters studied include climate and

house characteristics, window properties (sizes, thermal, solar and visual transmittances,

positions), as well as shading devices (interior and exterior) and natural ventilation. The

heating, cooling and lighting energy use were analysed in order to demonstrate how various

windows and shading systems may affect the overall energy balance of a typical house in

different climatic conditions.


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The main goal of this research is to assess the effect of different house, climate, window and

environmental settings (natural ventilation and shading) on energy use, including heating,

cooling and lighting energy demands, considering realistic house conditions and settings for

a Northern and Southern European climate.

2 Literature review

For the window use and lighting energy savings, most previous studies have been carried

out in commercial and public premises (LBNL, 2000). However, this topic has recently

received more attention in the residential building sector (Veitch & Galasiu, 2012)

(Mardaljevic, Andersen, Roy, & Christoffersen, 2011). In Europe, a recent study (Foldbjerg,

Roy, Duer, & Andersen, 2010) investigated the impact of windows on overall energy use

(lighting, cooling, heating) in a single family house (with 20% window-to-floor area ratio)

located in different cities. The results indicated that the window was the most energy-efficient

technology to provide biological light levels (500-2500 lx). Even though the basic conditions

for energy analysis were significantly oversimplified, a clear relationship between windows

and electrical lighting savings was expressed in this study. Another study achieved in

Sweden in passive houses (Persson, Roos, & Wall, 2006) pointed out that enlarging a North

oriented window glazing was actually a potentially good solution to increase daylight

utilization and save energy, provided that energy-efficient windows are used. Furthermore,

the integration of daylighting and electric lighting systems has been suggested in several

important building standards in order to achieve energy-efficiency in buildings (CIBSE, 1999)

(CIBSE, 2012).

3 Method

3.1 Locations, orientation and surrounding conditions

The first location studied for the basic house was Stockholm (Latitude 59.65°, Longitude

17.95°), the Swedish capital, which represents a Northern house located in cold climate

conditions. The second location was Agen (Latitude 44.16°, Longitude 0.60°) in Southern

France, which represents warmer climatic conditions. Three orientations were analysed for

each house: South, North and West. In addition, it was assumed that each house was

surrounded by neighbouring buildings or obstructions, which was simulated in the computer

program by a shading wall with an obstruction angle of 5.


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3.2 House models

3.2.1 Northern house

A two-story, single family detached house (Figure 1) was modelled in the computer program

Design Builder with typical Swedish building characteristics and features (Myresjöhus,

2013). This house had a ground floor and an attic floor (Figure 2) with a simple rectangular

plan and South orientation (basic model). The house’s main dimensions were: length 12m,

width 8m, wall height 3.2m. The house had a 45° double sloped roof. The house was

modelled including interior partitions as represented in Figure 3. The ground and attic floors

each included three main zones. The windows were installed on the external wall and sloped

roof.

Figure 1: 3D model of Northern house.

The thermal properties (U-value) of the house envelope were as follows: U(wall) = 0.15

W/m2K; U(roof) = 0.1 W/m2K; U(ground floor) = 0.2 W/m2K. The building envelope was

generally based on Swedish light-weight construction.


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Figure 2: Plan and section of northern house (units: mm).

Figure 3: Space plan in the Northern house.

3.2.2 Southern house

A one-story single family detached house (Thiers, Beinsteiner, & Peuportier, 2011) (Kragh,

Laustsen, & Svendsen, 2008) (Figure 4) was studied as the Southern house located in


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Agen. This house had a single ground floor (Figure 5) with a simple rectangular plan and a

South orientation (basic model). The house’s dimensions were: length 12m, width 8m, wall

height 2.5m (Thiers, Beinsteiner, & Peuportier, 2011). The roof was, in this case, a 15°

double sloped roof. The ground floor included three rooms separated by internal partitions

(Figure 6). The windows were installed on both the wall and roof.

The thermal properties (U-value) of the envelope were as follows: U(wall) = 0.45 W/m2K;

U(roof) = 0.28 W/m2K; U(ground floor) = 0.4 W/m2K. The building envelope was a typical

French heavy construction.

Figure 4: 3D model of Southern house.

Figure 5: Plan and section of Southern house (unit: mm).


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Figure 6: Space plan in the Southern house.

3.3 Window and shading systems

3.3.1 Northern house

The WGR (window-to-floor ratio) was defined as the ratio of window area to the internal

heated floor area. Three different WGR were studied including 0% (no window),

approximately 10% (small size) and approximately 30% (large size). Figure 7 shows the

window distribution and sizes for different facade walls and roofs in the Northern house,

which had two small WGR values of 10.8% at attic floor level and 10% at ground floor level.

The positions of windows across the envelope were naturally set in the centre of external

wall or roof for each room (Figure 8). Similarly, a larger window area (WGR 30%) was

studied (Figure 9, Figure 10).


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Figure 7: Window distributions of Northern house – WGR 10%.


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20



21


According to thermal, solar and visual transmittances, various window systems were studied

for different facades and roofs in the Northern house model. The windows used on South,

East and West walls were double-pane windows with properties presented in Table 1.

However, the North wall had more energy-efficient windows with three panes (Table 2).

Table 3 and Table 4 show the size, U-value, g-value and visual transmittance of windows for

the South (two panes) and North roof (three panes) respectively. The linear loss between

glazing and frame was 0.049 W/mK. The windows used in this study were defined based on

VELUX products and the DesignBuilder window library (DesignBuilder, 2013).


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Table 1: Thermal, solar and visual transmittances of windows on South, East and West facades (two panes).

Size

(mm)

U(window)-

value (W/m2K)

U(glazing)-

value (W/m2K)

U(frame)-

value

(W/m2K)

g-

value

Visual

Transmittance

500x500 1.50 1.19 1.30 0.61 0.70

1000x1000 1.39 1.19 1.30 0.61 0.70

1200x1200 1.36 1.19 1.30 0.61 0.70

1600x1800 1.32 1.19 1.30 0.61 0.70

Table 2: Thermal, solar and visual transmittances of windows on North facade (three panes).

Size

(mm)

U(window)-

value (W/m2K)

U(glazing)-

value (W/m2K)

U(frame)-

value

(W/m2K)

g-

value

Visual

Transmittance

800x800 1.20 0.78 1.30 0.50 0.66

1500x1500 1.03 0.78 1.30 0.50 0.66

Table 3: Thermal, solar and visual transmittances of windows on South roof (two panes).

Size

(mm)

U(window)-

value (W/m2K)

U(glazing)-

value (W/m2K)

U(frame)-

value

(W/m2K)

g-

value

Visual

Transmittance

1140x1178 1.57 1.49 1.30 0.64 0.73

1140x1400 1.57 1.49 1.30 0.64 0.73

Table 4: Thermal, solar and visual transmittances of windows on North roof (three panes).

Size

(mm)

U(window)-

value (W/m2K)

U(glazing)-

value (W/m2K)

U(frame)-

value

(W/m2K)

g-

value

Visual

Transmittance


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1140x1178 1.10 0.79 1.30 0.50 0.66

1140x1400 1.08 0.79 1.30 0.50 0.66

A medium-opaque screen was used as the basic shading device for each window (wall and

roof windows) when required. The basic properties of the shading screen are presented in

Table 5. The screen was installed either inside or outside the window.

Table 5: Properties of shading screen.

Thick-

ness

(m)

Conduc-

tivity

(w/mK)

Solar

transm.

Solar

reflec-

tance

Visible

transm.

Visual

reflec-

tance

Long

wave

emiss.

Long wave

transm.

0.001 0.10 0.15 0.5 0.15 0.50 0.80 0.10

3.3.2 Southern house

The French house had three WGR including 0% (no window), approximately 10% (small

size) and approximately 30% (large size). Figure 11 shows the window distribution and size

for different facade walls and roofs for the Southern house, which had a small WGR of

10.5% at ground floor. The positions of windows across the envelope were evenly set in the

centre of the external wall or roof of each room (Figure 12). A larger window area (WGR

30.8%) was also studied (Figure 13). The positions of the larger windows are shown in

Figure 14.


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Figure 11: Window distributions of Southern house – WGR 10%.


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26



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In this case, all windows studied were double pane assemblies. The properties of wall

windows are shown in Table 6, while Table 7 displays the properties of roof windows. The

linear loss between glazing and frame was 0.049 W/mK. The windows used in the study

were defined based on VELUX products and the DesignBuilder window library

(DesignBuilder, 2013).


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Table 6: Thermal, solar and visual transmittances of windows at facade walls (two panes).

Size

(mm)

U(window)-

value (W/m2K)

U(glazing)-

value (W/m2K)

U(frame)-

value

(W/m2K)

g-

value

Visual

Transmittance

600x600 1.47 1.19 1.30 0.61 0.70

800x800 1.42 1.19 1.30 0.61 0.70

1000x1200 1.37 1.19 1.30 0.61 0.70

1200x1000 1.37 1.19 1.30 0.61 0.70

1200x1200 1.36 1.19 1.30 0.61 0.70

1200x1400 1.35 1.19 1.30 0.61 0.70

Table 7: Thermal, solar and visual transmittances of windows on roof (two panes).

Size

(mm)

U(window)-

value (W/m2K)

U(glazing)-

value (W/m2K)

U(frame)-

value

(W/m2K)

g-

value

Visual

Transmittance

780x980 1.74 1.70 1.30 0.60 0.70

1140x1178 1.70 1.70 1.30 0.60 0.70

1140x1400 1.70 1.70 1.30 0.60 0.70

The same screen shading device (Table 5) was used in this Southern house. The screen

was installed either inside or outside windows.

3.4 Simulations

The energy performance of the house models was simulated using the DesignBuilder

program, which is an advanced interface to the well-known dynamic simulation program

EnergyPlus. This program allows predicting heating, cooling and lighting demands

simultaneously. It is a state-of-the-art and dynamic simulation package, which provides a

comprehensive range of energy consumption and environmental data (thermal and visual

comfort, ventilation, etc) shown in annual, monthly, daily, hourly or sub-hourly intervals

(DesignBuilder, 2013) (EnergyPlus, 2013).

For Northern and Southern houses, the annual heating and cooling demands (kWh/m2) were

the first part to be considered. Under the French climate, it is normal to include cooling


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systems into the Southern house as part of the normal building installations. Although it is

not necessarily common in Sweden, the cooling demand was studied here in order to obtain

a proxy for overheating. For thermal environment, the set points of 21°C and 26°C were

used for heating and cooling systems respectively. The simulations were performed

considering a single thermal zone for the ground and attic floors. Internal heat gains

corresponding to 2 W/m2 (excluding electric lighting) were also considered in the

simulations.

Airtightness and ventilation rates and schedules were set differently in each house. In the

Northern house, a constant infiltration rate of 0.1 ach was programmed. A mechanical

ventilation system was also programmed considering a minimum fresh air supply of 0.35 l/s-

m2 (corresponding in this case to 0.5 ach) and a heat recovery with an efficiency of 80%.

The mechanical ventilation and heat recovery were set as ‘always on’ (even during the

summer). However, note that the windows were considered opened by the program when

indoor temperature rose above 24C and the air change rate was very high at 3 ach (and

constant) in this case. Cooling was initiated when the indoor temperature rose above 26C.

The Southern house, however, had a high infiltration rate of 0.5 ach. No mechanical

ventilation was assumed in this case, which is more typical for French construction standard.

In both Northern and Southern houses, natural ventilation through windows was added with

the aim to reduce overheating during the cooling season. The natural ventilation for cooling

was programmed to be initiated at 24°C (set point); it was turned off when outdoor

temperature was higher than the indoor temperature in order to avoid heating the indoor air

with outside air.

The annual electric lighting demand (kWh/m2) was included as one important part of the total

energy calculation of each house. The zone settings for lighting calculations follow the

spaces divided by partition walls. The light sensors were installed at the centre of each room

in the two houses. In general, the target illuminance was 150 lx, which is regarded as the

minimum lighting level for visual purposes in residential buildings. This level was considered

representative as an average workplane illuminance value roughly corresponding to what

people would normally use in residential spaces in the early morning or at night. A working

plane (0.8 m above the floor) was assumed for daylighting and lighting calculations. The

electric lighting was controlled through a simple linear model corresponding to the daylight

illuminance level. The lighting power density was set to 2 W/m2 per 100 lx (EnergyPlus,

2013). The 150 lx ambient electric lighting was considered to be turned on from 06:00-08:00

and 16:00-23:00 hours on weekdays and from 07:00-24:00 hours on weekends. Thus, the


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internal heat gains from electric lighting combined with other internal heat gains were

between 2 and 5 W/m2, depending on whether the electric lighting was switched on or off.

The reflectance of internal walls, floor and ceiling was set to 0.5, 0.3 and 0.7 respectively,

which corresponds to the materials in the building construction settings.

For the two houses, the screen shading device was operated by a model called ‘Night

heating and day cooling’ in DesignBuilder. In this model, the shading device is down at night

when heating is on and during daytime when there is a cooling load (based on the previous

hour in the iterative calculation) (DesignBuilder, 2013) (EnergyPlus, 2013). Note that the

program does not allow to evaluate the effect of both shading device (interior and exterior)

active simultaneously.

In addition, the photometric properties of the external ground surface (affecting solar and

daylight calculation) were as follows: ground reflectance of 0.2 without snow and 0.8 with

snow. DesignBuilder evaluates the occurrence of snow based on climate data and adjusts

ground reflectance accordingly.

4. Results

4.1. Northern house

This section presents the results obtained regarding the impact of window area and

environmental settings (shading device and natural ventilation) on energy performance in the

Northern house.

4.1.1. Window areas and energy performance

This section presents results related to window areas and energy use under six different

environmental settings:

1. without natural ventilation and shading device;

2. with natural ventilation and without shading device;

3. with outside screen and without natural ventilation;

4. with natural ventilation and outside screen;

5. with inside screen and without natural ventilation;

6. with natural ventilation and inside screen.

Setting 1 (without natural ventilation and shading device)


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The results for the first setting are presented in Figure 15. In general, annual heating and

cooling demands increase with increasing WGR while the reverse effect is obtained for

electric lighting: increasing WGR results in a reduction in annual lighting demand. The

cooling demand increases from an average of 1.0 kWh/m2yr for the case without windows to

7.1 kWh/m2yr for 10%-WGR and 38.3 kWh/m2yr for 30%-WGR (average for the three

orientations). The increase in cooling with larger windows is thus substantial but the cooling

demand of the no-window model is very small. Figure 15c also shows that the no window

model yields the highest electric lighting energy use, while 10%-WGR and 30%-WGR yield

lighting energy savings of 34% and 42% respectively compared to the no window case.

Therefore, the effect of increasing the WGR beyond 10% is marginal for electric lighting,

which is probably due to the fact that there is sufficient daylight in the space to reach an

average 150 lux on the sensor with 10%-WGR. Note also that most electric lighting is used

early in the morning and at night when there is no or little daylight outdoors. A significant

effect of orientation on heating and cooling energy demand is obtained for large WGR only

(30%). As expected, facing South results in heating energy savings compared to other

orientations while the cooling demand is minimised with the North orientation. The

orientation has no significant effect on electric lighting energy use under the Swedish climate

conditions in this study. This may be explained by the predominance of overcast sky

conditions and position of the measurement point in the simulations (middle of room), where

most daylight is reflected and diffuse.

Setting 2 (with natural ventilation and without shading device)

The results for the simulations with natural ventilation and no shading device are presented

in Figure 16. The variations of heating, cooling and lighting energy use are similar to the

ones presented for the previous environmental setting (setting 1). However, the use of

natural ventilation has a clear beneficial effect on the cooling demand, especially for the

large WGR (30%-WGR). Note, as stated earlier, that the windows were considered opened

by the program when indoor temperature rose above 24C and the air change rate was very

high at 3 ach (and constant) in this case. Cooling was initiated when the indoor temperature

rose above 26C. In the case without natural ventilation and shading, the cooling demand

was 1.0 kWh/m2yr for the no-window case, 7.1 kWh/m2yr for 10%-WGR and 38.3 kWh/m2yr

for 30%-WGR (average for the three orientations). Adding natural ventilation resulted in a

cooling demand which was on average 2.0 kWh/m2yr for 10%-WGR and 22.5 kWh/m2yr for

30%-WGR (average for the three orientations). Natural ventilation thus reduces the cooling

demand by more than 40% for the 30%-WGR, which is a substantial reduction.


32

Setting 3 (with outside screen and without natural ventilation)

The results for the cases with outside screen and without natural ventilation are presented in

Figure 17. In this case, the heating demand varies in a similar way as shown previously.

Note however that the heating demand increases slightly (by 0.6 kWh/m2yr for the 10%-

WGR and by 2.9 kWh/m2yr for the 30%-WGR compared to results of setting 1 – no shading

and no natural ventilation). This could be an effect of a sub-optimisation of the control

system for the shading device. In this case, it is possible that the program sets the screen

down when it would be preferable to have it up. This can happen when shading is still in use

for the hours where the solar gains would exceed the increased insulation gains (early and

late hours of the day). This parameter is sensitive and can be refined or adjusted to

determine the best use of the shading device in a given climate.

The outside shading screen results in the same cooling demand for the small window size

(10%-WGR) as the no-window case. The large window case (30%-WGR) sees a substantial

decrease of cooling demand with the use of outside screen compared to the previous setting

(natural ventilation and no screen). The cooling demand with screen is around 1/10 of the

case with natural ventilation and around 1/20 of the setting without screen and natural

ventilation. However, the screen slightly increases the lighting energy consumption of the

house with windows, but this effect is negligible compared to the effect on cooling loads.

Setting 4 (with natural ventilation and outside screen)

With outside screen and natural ventilation (Figure 18), the general varying trends of heating

and lighting are similar to the previous setting (Figure 17). However, cooling demand in the

house with windows is lower than for the house without windows. The results show that the

combination of shading and natural ventilation is an efficient strategy to control overheating

in summer time, even for houses with large glazing.

Setting 5 (with inside screen and without natural ventilation)

With inside screen and without natural ventilation (Figure 19), heating and lighting demands

vary in a similar trend as in the previous setting (Figure 18). However, the cooling demand is

much higher than the setting with outside screen, which is due to the fact that the inside

screen is not as efficient in cutting down solar radiation as the outside screen.


33

Setting 6 (with inside screen and natural ventilation)

With inside screen and natural ventilation (Figure 20), the variations of heating and lighting

demands are similar as shown previously but the cooling demand is reduced by the addition

of natural ventilation.


34

Figure 15: Heating, cooling and lighting demand in Northern house (no natural ventilation and no shading device).

0

5

10

15

20

25

30

35

40

0% 10% 30%

Hea

tin

g d

eman

d (k

Wh

/m2)

WGR (window area / floor area)

Annual Heating demand in Northern House

Orientation - south

Orientation - north

Orientation - west

0

5

10

15

20

25

30

35

40

0% 10% 30%

Co

olin

g d

eman

d (k

Wh

/m2)


Annual Cooling demand in Northern House

Orientation - south

Orientation - north

Orientation - west

0

5

10

15

20

25

30

35

40

0% 10% 30%

Ligh

tin

g d

eman

d (k

Wh

/m2)


Annual Lighting demand in Northern House

Orientation - south

Orientation - north

Orientation - west


35

Figure 16: Heating, cooling and lighting demand in Northern house (natural ventilation and without shading).

0

5

10

15

20

25

30

35

40

0% 10% 30%

Hea

tin

g d

eman

d (k

Wh

/m2)



(natural ventilation)

Orientation - south

Orientation - north

Orientation - west

0

5

10

15

20

25

30

35

40

0% 10% 30%

Co

olin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west

0

5

10

15

20

25

30

35

40

0% 10% 30%

Ligh

tin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west


36

Figure 17: Window areas and heating, cooling and lighting demand in northern house (outside screen and no natural ventilation).

0

5

10

15

20

25

30

35

40

0% 10% 30%

Hea

tin

g d

eman

d (k

Wh

/m2)



(outside screen shade)

Orientation - south

Orientation - north

Orientation - west

0

5

10

15

20

25

30

35

40

0% 10% 30%

Co

olin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west

0

5

10

15

20

25

30

35

40

0% 10% 30%

Ligh

tin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west


37

Figure 18: Heating, cooling and lighting demand in Northern house (natural ventilation and outside screen).

0

5

10

15

20

25

30

35

40

0% 10% 30%

Hea

tin

g d

eman

d (k

Wh

/m2)



(natural ventilation & outside screen shade)

Orientation - south

Orientation - north

Orientation - west

0

5

10

15

20

25

30

35

40

0% 10% 30%

Co

oli

ng

de

man

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west

0

5

10

15

20

25

30

35

40

0% 10% 30%

Ligh

tin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west


38

Figure 19: Heating, cooling and lighting demand in Northern house (inside screen and no natural ventilation).

0

5

10

15

20

25

30

35

40

0% 10% 30%

Hea

tin

g d

eman

d (k

Wh

/m2)



(inside screen shade)

Orientation - south

Orientation - north

Orientation - west

0

5

10

15

20

25

30

35

40

0% 10% 30%

Co

olin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west

0

5

10

15

20

25

30

35

40

0% 10% 30%

Ligh

tin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west


39

Figure 20: Heating, cooling and lighting demand in northern house (inside screen and natural ventilation).

0

5

10

15

20

25

30

35

40

0% 10% 30%

Hea

tin

g d

eman

d (k

Wh

/m2)



(natural ventilation & inside screen shade)

Orientation - south

Orientation - north

Orientation - west

0

5

10

15

20

25

30

35

40

0% 10% 30%

Co

olin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west

0

5

10

15

20

25

30

35

40

0% 10% 30%

Ligh

tin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west


40

4.1.2 Natural ventilation, shading devices and energy performance

This section presents a comparison of energy performance between the six environmental

settings described previously (Figure 21, Figure 22). For small windows (10%-WGR), the

South is the best orientation in terms of heating energy demand but generally, there are only

small variations between the results of the different orientations, which could be an effect of

the fact that the windows are distributed rather evenly on all facades. Thus the South and

North orientated houses are in fact almost equivalent in terms of sun exposure. Furthermore,

only small differences of heating demand were found for the six environmental settings. The

outside screen yields the smallest cooling demand. A slightly higher cooling demand is

obtained with the two settings (‘with natural ventilation and with inside screen’ and ‘natural

ventilation’). The highest cooling demand occurs with the setting of ‘inside screen’ and the

setting ‘without screen and natural ventilation’. In addition, note that the lighting energy does

not vary significantly with different settings. It is generally increased by about 3 kWh/m2yr by

the addition of the shading screen.

For large windows (30%-WGR), the South orientation yields the lowest heating demand, as

expected, compared to the North and West orientations. Figure 22(a) also shows that

heating energy is slightly higher with the use of outside screen than with other environmental

settings. In reality, this should not be the case since the shading device should be removed

whenever passive solar gains exceed heat losses through windows. It could be due to the

fact that the shading screens are down at moments when it would be more beneficial to have

them removed and thus, small adjustments in the simulation settings may be required to

avoid this effect. Note also that the four environmental settings (without outside screen) yield

a similar heating energy demand. On the contrary, the two cases with outside screen bring

the minimum cooling demand while the setting of ‘no shading device and no natural

ventilation’ give rise to the maximum cooling demand. Interestingly, the setting of ‘natural

ventilation’ and the setting of ‘inside screen’ have a similar cooling demand. For electric

lighting, as expected, the use of outside and inside screen yields a slight increase in energy

use but this effect is not significant in absolute terms compared to the effect of the screens

on the cooling demand.


41

Figure 21: Annual energy performance between six environmental settings (Northern house, WGR 10%).

0

5

10

15

20

25

30

35

40

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation

inside screen inside screen

& natural ventilation

He

atin

g d

em

and

(kW

h/m

2)

Annual Heating demand in Northern House (WGR: 10%)

Orientation - south

Orientation - north

Orientation - west

0

5

10

15

20

25

30

35

40

no shade and

no natural ventilation

natural

ventilation

outside

screen

outside screen




Co

oli

ng

de

man

d (

kWh

/m2

)

Annual Cooling demand in Northern House (WGR: 10%)

Orientation - south

Orientation - north

Orientation - west

0

5

10

15

20

25

30

35

40

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation



Ligh

tin

g d

em

and

(kW

h/m

2)

Annual Lighting demand in Northern House (WGR: 10%)

Orientation - south

Orientation - north

Orientation - west


42

Figure 22: Annual energy performance between six environmental settings (Northern house, WGR 30%).

0

5

10

15

20

25

30

35

40

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation



He

atin

g d

em

and

(kW

h/m

2)

Annual Heating demand in Northern House (WGR: 30%)

Orientation - south

Orientation - north

Orientation - west

0

5

10

15

20

25

30

35

40

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation



Co

oli

ng

de

man

d (

kWh

/m2

)

Annual Cooling demand in Northern House (WGR: 30%)

Orientation - south

Orientation - north

Orientation - west

0

5

10

15

20

25

30

35

40

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation



Ligh

tin

g d

em

and

(kW

h/m

2)

Annual Lighting demand in Northern House (WGR: 30%)

Orientation - south

Orientation - north

Orientation - west


43

4.1.3 Overall energy performance

This section presents the comparison of overall energy performance (sum of heating, cooling

and lighting energy use) for the six environmental settings described previously in addition to

the case without window.

For small window size (WGR10%) (Figure 23), the maximum overall energy demand is

obtained with the setting ‘without shading device and natural ventilation’ and the setting

‘inside screen’, on all three orientations. The energy demand in these two cases is higher

compared to the case with no window. Other environmental settings (‘with natural ventilation

and without shading device’, ‘with outside screen and without natural ventilation’, ‘with

natural ventilation and outside screen’, ‘with natural ventilation and inside screen’), yield

similar overall energy demand, which is also similar to the case with no windows. Note also

that Figure 23 generally shows the dominance of the heating demand in the overall energy

balance, especially for small WGR (10%). The lighting demand is the second most important

energy end-use affecting the overall energy balance.

In the case of large windows (30%-WGR) (Figure 24), the energy balance is dominated by

cooling in two cases; heating is relatively less important (except for the outside screen and

no window cases). Heating remains an important end-use - and the main energy consumer

for four of the environmental settings (no window, outside screens with and without natural

ventilation and inside screen with natural ventilation). For two of the environmental settings

(natural ventilation or inside screen), the heating demand is approximately equivalent to the

cooling demand.

Figure 24 shows that the case without windows generally yields the minimum overall energy

demand while the case of large windows without shading device and natural ventilation

yields the highest energy use, as expected. With the occurrence of large windows, the two

settings of outside screen could be the best choice in terms of overall energy savings. The

three settings (natural ventilation or inside screen), nevertheless, have a higher overall

energy use compared with the setting of outside screen. These results generally show the

importance of selecting an appropriate shading strategy, especially when the house has

large windows.


44

Figure 23: Annual energy demand according to orientation (Northern house, WGR 10%).

0

10

20

30

40

50

60

70

80

no

windows

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation

inside

screen

inside

screen & natural

ventilation

Pri

mar

y e

ne

rgy

con

sum

pat

ion

(kW

h/m

2)

Northern House (WGR: 10%; Orientation: south)

Lighting demand

Cooling demand

heating demand

0

10

20

30

40

50

60

70

80

no

windows

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation

inside

screen

inside

screen & natural

ventilation

Pri

mar

y e

ne

rgy

con

sum

pat

ion

(kW

h/m

2)

Northern House (WGR: 10%; Orientation: north)

Lighting demand

Cooling demand

heating demand

0

10

20

30

40

50

60

70

80

no

windows

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation

inside

screen

inside

screen & natural

ventilation

Pri

mar

y e

ne

rgy

con

sum

pat

ion

(kW

h/m

2)

Northern House (WGR: 10%; Orientation: west)

Lighting demand

Cooling demand

heating demand


45

Figure 24: Annual energy demand according to orientation (Northern house, WGR 30%).

0

10

20

30

40

50

60

70

80

no

windows

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation

inside

screen

inside

screen & natural

ventilation

Pri

mar

y e

ne

rgy

con

sum

pat

ion

(kW

h/m

2)

Northern House (WGR: 30%; Orientation: south)

Lighting demand

Cooling demand

heating demand

0

10

20

30

40

50

60

70

80

no

windows

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation

inside

screen

inside

screen & natural

ventilation

Pri

mar

y e

ne

rgy

con

sum

pat

ion

(kW

h/m

2)

Northern House (WGR: 30%; Orientation: north)

Lighting demand

Cooling demand

heating demand

0

10

20

30

40

50

60

70

80

no

windows

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation

inside

screen

inside

screen & natural

ventilation

Pri

mar

y e

ne

rgy

con

sum

pat

ion

(kW

h/m

2)

Northern House (WGR: 30%; Orientation: west)

Lighting demand

Cooling demand

heating demand


46

4.2. Southern house

This section presents the results related to the impact of window area and environmental

factors (shading and natural ventilation) on energy performance in the Southern house.

4.2.1. Window areas and energy performance

This section presents the results related to window area and energy use under the six

environmental settings described previously.

Setting 1 (without natural ventilation and shading device)

For the case without shading device and natural ventilation (Figure 25), the larger the WGR,

the smaller the heating demand. The cooling demand increases with an increasing WGR, as

could be expected, and the lighting energy demand decreases with increasing WGR.

However, note that the reduction in lighting energy savings is not significant beyond 10%-

WGR. On average, 3.3% and 11% less heating is required with 10%-WGR and 30%-WGR

respectively compared to the case with no window. For cooling, the 0%-WGR, 10%-WGR

and 30%-WGR yield a cooling demand of 0.5, 2.0 and 13.9 kWh/m2yr respectively (average

for the three orientations). Therefore, the effect of increasing the WGR beyond 10% is

significant on the cooling demand. However, the results obtained with other environmental

settings show that it is possible to control the cooling demand using an appropriate shading

solution (exterior) and a natural ventilation strategy. The no window case results in the

highest energy use for electric lighting while the 10%-WGR and 30%-WGR yield reductions

of 40% and 46% respectively in lighting energy use. The benefits in terms of lighting energy

reduction of increasing the WGR beyond 10% are thus marginal, which is probably due to

the fact that at 10%-WGR, the daylight level already reaches 150 lux at the sensor.

Increasing the WGR will only increase the light level beyond 150 lux.

The impact of orientation is only significant for the cooling and heating demands and the

large WGR (30%). In general, the results indicate that the lighting demand is not significantly

affected by the orientation under the French climate conditions in this study. This could be

an effect of the simulation methodology (one sensor in the middle of the room) and the

house design with rather uniform window distribution (thus equivalent solar exposure for the

different house orientations).

Setting 2 (with natural ventilation and without shading device)

With natural ventilation and no shading device (Figure 26), the general varying trends in

heating, cooling and lighting demands are similar to those of the previous settings. However,


47

the natural ventilation clearly contributes to reduce the absolute cooling demand, which is

especially significant for the large WGR (30%). This obviously shows that houses with larger

windows should be well ventilated to avoid overheating.

Setting 3 (with outside screen and without natural ventilation)

With outside screen and no natural ventilation (Figure 27), similar variations in heating,

cooling and lighting demands are obtained. However, the absolute cooling demand is greatly

reduced with the outside screen compared to the previous settings (natural ventilation and

no shading device). The use of outside screen does not significantly affect the energy

demand of heating and lighting systems. For lighting, it could be explained by the fact that

most lighting use occurs at night when there is no or little daylighting outdoors.

Setting 4 (with natural ventilation and outside screen)

With outside screen and natural ventilation (Figure 28), the cooling demand’s absolute value

is further reduced, especially in the case of large WGR (30%), which shows that it is possible

to control overheating and high cooling loads using an efficient shading and ventilation

strategy.

Setting 5 (with inside screen and without natural ventilation)

With inside screen and no natural ventilation (Figure 29), heating and lighting demands vary

in a similar trend as the setting of outside screen. However, the cooling demand is higher

than the setting with outside screen, especially for the large WGR (30%). This is obviously

due to the fact that the inside screen is not as effective in cutting down solar gains as the

outside screen.

Setting 6 (with inside screen and natural ventilation)

With inside screen and natural ventilation (Figure 30), the variations of heating and lighting

demands are similar as in the previous settings except that the cooling demand is reduced

by adding natural ventilation.


48

Figure 25: Heating, cooling and lighting demand in Southern house (no natural ventilation and no shading device).

0

10

20

30

40

50

60

70

0% 10% 30%

Hea

tin

g d

eman

d (k

Wh

/m2)


Annual Heating demand in Southern House

Orientation - south

Orientation - north

Orientation - west

0

10

20

30

40

50

60

70

0% 10% 30%

Co

olin

g d

eman

d (k

Wh

/m2)


Annual Cooling demand in Southern House

Orientation - south

Orientation - north

Orientation - west

0

10

20

30

40

50

60

70

0% 10% 30%

Ligh

tin

g d

eman

d (k

Wh

/m2)


Annual Lighting demand in Southern House

Orientation - south

Orientation - north

Orientation - west


49

Figure 26: Heating, cooling and lighting demand in Southern house (natural ventilation and no shading).

0

10

20

30

40

50

60

70

0% 10% 30%

Hea

tin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west

0

10

20

30

40

50

60

70

0% 10% 30%

Co

olin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west

0

10

20

30

40

50

60

70

0% 10% 30%

Ligh

tin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west


50

Figure 27: Heating, cooling and lighting demand in southern house (outside screen and no natural ventilation).

0

10

20

30

40

50

60

70

0% 10% 30%

Hea

tin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west

0

10

20

30

40

50

60

70

0% 10% 30%

Co

olin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west

0

10

20

30

40

50

60

70

0% 10% 30%

Ligh

tin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west


51

Figure 28: Heating, cooling and lighting demand in Southern house (natural ventilation and outside screen).

0

10

20

30

40

50

60

70

0% 10% 30%

Hea

tin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west

0

10

20

30

40

50

60

70

0% 10% 30%

Co

oli

ng

de

ma

nd

(kW

h/m

2)




Orientation - south

Orientation - north

Orientation - west

0

10

20

30

40

50

60

70

0% 10% 30%

Ligh

tin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west


52

Figure 29: Heating, cooling and lighting demand in Southern house (inside screen and no natural ventilation).

0

10

20

30

40

50

60

70

0% 10% 30%

Hea

tin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west

0

10

20

30

40

50

60

70

0% 10% 30%

Co

olin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west

0

10

20

30

40

50

60

70

0% 10% 30%

Ligh

tin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west


53

Figure 30: Heating, cooling and lighting demand in Southern house (natural ventilation and inside screen).

0

10

20

30

40

50

60

70

0% 10% 30%

Hea

tin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west

0

10

20

30

40

50

60

70

0% 10% 30%

Co

olin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west

0

10

20

30

40

50

60

70

0% 10% 30%

Ligh

tin

g d

eman

d (k

Wh

/m2)




Orientation - south

Orientation - north

Orientation - west


54

4.2.2. Natural ventilation, shading devices and energy performance

This section compiles results to allow a comparison of total energy balance between the six

environmental settings described previously.

For small WGR (10%) (Figure 31), the South orientation is the best one in terms of heating

demand and West also has a slightly lower heating demand than the North orientation but

the absolute difference between these two orientations is small. No significant differences of

heating demand are obtained between the six environmental settings for the small WGR.

The two settings using outside screen result in the minimum cooling demand. A slightly

higher cooling demand is obtained with the two settings ‘with natural ventilation and with

inside screen’ and ‘natural ventilation’. The second highest cooling demand occurs with the

setting ‘with inside screen’ and the highest demand is for the setting ‘without screen and

natural ventilation’. Lighting energy use does not vary with the different environmental

settings.

For large WGR (30%) (Figure 32), the South orientation has a lower heating demand

compared to the North and West orientations. The outside screen brings the lowest heating

demand due to the additional insulation layer in the window at night. The outside screen cuts

down long wave radiative heat losses towards the ‘cold’ sky and this effect is important

especially since the French house has a nearly horizontal roof with roof windows facing the

sky. Note, however, that the absolute difference between the six environmental settings is

relatively small. Regarding cooling, the setting ‘with outside screen’ also yields the lowest

cooling demand while the setting ‘no shading device and no natural ventilation’ gives rise to

the highest cooling demand. Interestingly, the setting of ‘natural ventilation’ and the setting of

‘inside screen and natural ventilation’ result in a similar cooling demand, which is higher than

the setting ‘with outside screen’ and lower than the setting ‘without shading device and

natural ventilation’. These results generally indicate that the outside screen is very effective

in cutting down cooling, even without natural ventilation (in a house with high infiltration rate).

The results also indicate that the different settings have no significant effect on the lighting

load. The lighting demand is roughly the same for all six environmental settings.


55

Figure 31: Annual energy performance between six environmental settings (Southern house, WGR 10%).

0

10

20

30

40

50

60

70

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation



He

atin

g d

em

and

(kW

h/m

2)

Annual Heating demand in Southern House (WGR: 10%)

Orientation - south

Orientation - north

Orientation - west

0

10

20

30

40

50

60

70

no shade and

no natural ventilation

natural

ventilation

outside

screen

outside screen




Co

oli

ng

de

man

d (

kWh

/m2

)

Annual Cooling demand in Southern House (WGR: 10%)

Orientation - south

Orientation - north

Orientation - west

0

10

20

30

40

50

60

70

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation



Ligh

tin

g d

em

and

(kW

h/m

2)

Annual Lighting demand in Southern House (WGR: 10%)

Orientation - south

Orientation - north

Orientation - west


56

Figure 32: Annual energy performance between six environmental settings (Southern house, WGR 30%).

0

10

20

30

40

50

60

70

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation

inside screeninside screen


He

atin

g d

em

and

(kW

h/m

2)

Annual Heating demand in Southern House (WGR: 30%)

Orientation - south

Orientation - north

Orientation - west

0

10

20

30

40

50

60

70

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation



Co

oli

ng

de

man

d (

kWh

/m2

)

Annual Cooling demand in Southern House (WGR: 30%)

Orientation - south

Orientation - north

Orientation - west

0

10

20

30

40

50

60

70

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation



Ligh

tin

g d

em

and

(kW

h/m

2)

Annual Lighting demand in Southern House (WGR: 30%)

Orientation - south

Orientation - north

Orientation - west


57

4.2.3. Overall energy performance

This section presents a comparison of overall energy performance (sum of heating, cooling

and lighting) between the six environmental settings described previously in addition to the

case with no window.

For small WGR (10%) (Figure 33), a general trend is found: the maximum overall energy

demand occurs for the setting without windows; the other six settings with small windows

yield a similar overall energy demand. The overall energy demand is clearly dominated by

heating; lighting demand comes second and cooling is almost negligible. Thus with smaller

window sizes, it does not matter so much how shading device and natural ventilation are

assigned and this is probably a result of the fact that the window does affect the overall

energy balance due to its small size. The house also has relatively high U-value and low

airtightness (and no heat recovery system on mechanical ventilation) and thus it has a

higher energy demand dominated by heating. The inside air is constantly replaced due to

high infiltration rate, which results in high energy use for heating.

For large WGR (30%) (Figure 34), a general trend is found: the setting of no windows brings

the highest overall energy demand while the two settings using outside screen result in the

lowest overall energy use. The cooling demand weighs relatively more in the overall energy

balance compared to the case with small WGR (10%). It is interesting and pertinent to

mention that the best energy performance among all cases studied for the Southern house

was obtained for the 30%- WGR cases with outside screens. With the occurrence of large

windows, the setting ‘no shading device and natural ventilation’ and the setting ‘inside

screen’ yield the second highest energy demand after the case with no windows. The two

settings ‘with natural ventilation and with inside screen’ and ‘natural ventilation’ also have a

higher overall energy use compared to the setting ‘outside screen’. These general results

show that an outside screen is a good strategy to reduce energy use on any orientation

including all end-uses (heating, cooling, lighting), especially if the outside screen is also used

at night in the winter to reduce heat losses through the window, as was the case in this

study. However, note that the program limitations and time frame for the study have made it

difficult to operate both screens at the same time or simply optimize the shading schedule to

minimize cooling, heating and electric lighting. This could be a future development of the

present study. Finally, it should be mentioned that the significant effect of the outside screen

is also the great reduction of cooling demand.


58

Regarding electric lighting, the results for the Southern house show that having windows,

even small ones (10% WGR) is beneficial in terms of energy savings for lighting. The electric

lighting demand goes from around 12.4 kWh/m2yr (average for three orientations) for the

case without windows to around 7.5 kWh/m2 and 6.7 kWh/m2yr yr for the small window (10%

WGR) and large window (30% WGR) cases respectively. The energy savings due to daylight

utilization are thus in the order 40-45% depending on the window size. Slightly larger

electricity savings are achieved with larger windows.


59

Figure 33: Annual energy performance according to orientation (Southern house, WGR 10%).

0

10

20

30

40

50

60

70

80

no

windows

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation

inside

screen

inside

screen & natural

ventilation

Pri

mar

y e

ne

rgy

con

sum

pat

ion

(kW

h/m

2)

Southern House (WGR: 10%; Orientation: south)

Lighting demand

Cooling demand

heating demand

0

10

20

30

40

50

60

70

80

no

windows

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation

inside

screen

inside

screen & natural

ventilation

Pri

mar

y e

ne

rgy

con

sum

pat

ion

(kW

h/m

2)

Southern House (WGR: 10%; Orientation: north)

Lighting demand

Cooling demand

heating demand

0

10

20

30

40

50

60

70

80

no

windows

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation

inside

screen

inside

screen & natural

ventilation

Pri

mar

y e

ne

rgy

con

sum

pat

ion

(kW

h/m

2)

Southern House (WGR: 10%; Orientation: west)

Lighting demand

Cooling demand

heating demand


60

Figure 34: Annual energy performance according to orientation (Southern house, WGR 30%).

0

10

20

30

40

50

60

70

80

no

windows

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation

inside

screen

inside

screen & natural

ventilation

Pri

mar

y e

ne

rgy

con

sum

pat

ion

(kW

h/m

2)

Southern House (WGR: 30%; Orientation: south)

Lighting demand

Cooling demand

heating demand

0

10

20

30

40

50

60

70

80

no

windows

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation

inside

screen

inside

screen & natural

ventilation

Pri

mar

y e

ne

rgy

con

sum

pat

ion

(kW

h/m

2)

Southern House (WGR: 30%; Orientation: north)

Lighting demand

Cooling demand

heating demand

0

10

20

30

40

50

60

70

80

no

windows

no shade

and no natural

ventilation

natural

ventilation

outside

screen

outside

screen & natural

ventilation

inside

screen

inside

screen & natural

ventilation

Pri

mar

y e

ne

rgy

con

sum

pat

ion

(kW

h/m

2)

Southern House (WGR: 30%; Orientation: west)

Lighting demand

Cooling demand

heating demand


61

5. Conclusions and discussion

In this project, the effect of window properties (size, position, U-value and visual

transmittance), shading device (inside and outside) and natural ventilation on the total

energy balance was investigated for two typical single detached houses located in a

Northern and Southern European climate. Several general conclusions may be drawn from

this study:

1. Comparing results obtained for the Northern and Southern houses, it is obvious that

the house’s basic construction (U-values, airtightness, ventilation with heat recovery)

and architectural aspects have a large impact on the overall energy balance. In this

case for instance, the Southern house had a higher energy demand than the

Northern house, and this was mainly due to the fact that this house had higher U-

values and air change rate for the building envelope, no heat recovery on the

ventilation, and a higher envelope-to-volume ratio (thus more heat losses). The

Southern house thus had an energy balance dominated by the heating demand,

which would have been expected for the Northern house. Interestingly, the good

construction (low U-values, airtight construction, heat recovery on ventilation) used

for the Northern house resulted in an energy balance where the lighting demand

played a secondary but significant role in the overall energy balance although heating

was still the dominant end-use.

2. For the Northern house under cold climate, larger window sizes give rise to higher

heating and cooling demand but lower lighting demand. The electric lighting demand

goes from 12.4 kWh/m2yr for the no-window case, to 9.6-8 kWh/m2yr for the 10%-

WGR, and to 7.7-7.1 kWh/m2yr for the 30%-WGR (with and without shading screen

respectively). The windows thus allow saving 23-35% and 37-42% electricity use for

lights for the 10%-WGR and 30%-WGR respectively depending on the shading

strategy, which clearly demonstrates the daylight utilization potential. Note that the

absolute reduction in lighting demand (obtained with the larger WGR) is smaller than

the absolute increase in heating and cooling demand. In addition, most of the

benefits of having windows in terms of lighting demand reduction are seen with a

case with 10%-WGR. All cases with shading show an increase in performance in

terms of lighting energy use for the 30% WGR in the Northern house, e.g. from 23%

to 37%, showing that larger windows can offset the effect of using shading on the


62

lighting performance. Increasing the window size from 10 to 30% WGR yields an

additional electric lighting saving of 0.9 kWh/m2yr for cases without shading screen

and by 1.9 kWh/m2yr for cases with shading screens. Overall, the results indicate

that the size of the windows has a larger effect on the heating and cooling demand

than on the electrical lighting demand.

3. For the Northern house, the South orientation has slightly lower heating energy

demand while the North orientation yields a lower cooling demand but the results

generally show that the orientation has a small effect on the overall energy balance.

The lighting demand is not clearly affected by the orientation, which could be due to

the simulation methodology used (measurement point in the middle of the room) and

also the fact that overcast skies are dominant in the Northern climate selected in this

study. It can also be attributed to a rather uniform window distribution between the

different facades resulting in equivalent solar exposure for all house orientations.

4. For the Northern house, natural ventilation and screen shading device could be

regarded as efficient ways to reduce the cooling demand, especially if the house has

a relatively large window size (30%-WGR). The outside screen is clearly the most

efficient measure to reduce cooling energy demand compared to the use of inside

screen or natural ventilation. However, note in this case that the air change rate for

natural ventilation was high at 3 ach. For small window sizes (10%-WGR), the

selection of environmental control strategy (shading or natural ventilation) has a

relatively negligible impact, as long as one of these strategies is applied.

5. For the Northern house, the use of screen shade yields an increase in lighting energy

use. However, the impact of shading device on lighting is relatively small. In addition,

the use of larger (30%) WGR reduced the impact of shading on the lighting

performance of the Northern house.

6. For the Southern house under warm climate, the larger the window sizes, the smaller

the heating and lighting demands. Similarly, the cooling demand increases with the

increasing WGR for a case without shading and natural ventilation. For this specific

case, the absolute increase in cooling demand is about the same in magnitude as the

aggregated reductions in heating and lighting demands.


63

7. The results also show that the shading and ventilation strategies have a substantial

effect on the relative changes in heating, cooling and lighting and they should

obviously be taken into consideration in the overall energy balance.

8. For the Southern house, the North orientation yields the lowest cooling demand but

the orientation generally has a minor effect on heating and lighting demands.

9. For the Southern house, natural ventilation and outside screen shading device are an

efficient way to reduce the cooling demand. The reduction of cooling demand is

relatively small when adopting the inside screen.

10. For the Southern house, the use of screen has a negligible effect on the lighting

demand, especially for large WGR, which could be attributed to the control strategy

used for the screen and electric lighting in this study (lighting mostly at night and

screen mostly under winter nights and when cooling is on). Note that the required

illuminance value was 150 lux - which may be possible to achieve with shading and

large WGR. In the case of large WGR, the effect of screen on the lighting demand is

negligible probably due to the fact that daylight levels higher than 150 lux are easily

reached even when the screen is down.

11. For the Southern house, the outside screen solution yields the lowest overall energy

use especially when large WGR are used. However, the overall energy demand

including heating, cooling, lighting is not significantly affected by the environmental

control strategy (natural ventilation and shading) when small windows are in place

(10%-WGR).

12. For the Southern house, the overall energy use benefits from the window use; the

case with no window yields higher overall energy demand.

13. For both the Northern and Southern houses, the lighting energy savings from daylight

utilization were clearly demonstrated, even with a smaller window area (WGR-10%).

In the Southern house, the electric lighting demand went from 12.4 kWh/m2yr for the

case without windows to 7.5-7.6 kWh/m2 and 6.6-6.7 kWh/m2yr for the small (10%

WGR) and large window (30% WGR) cases respectively (average for three facades).

The energy savings due to daylight utilization are thus in the order 38-47%

depending on the window size; and most of the savings are already achieved with

10%-WGR.


64

14. The thermal transmittance of the window (even one with a good thermal

performance) could be four to five times larger than that of a well-insulated wall (and

up to ten times in a passive house). This study showed that windows can contribute

to passive energy gains by allowing solar radiation and natural light into the house,

which compensates for daytime and night-time window thermal losses.

A secondary objective of this project was to assess the daylight utilization potential for the

residential sector. The study showed that the electric lighting demand could be reduced by

23-42% in the Nordic climate and by 38-47% in Southern French climate, depending on the

window size and shading strategy used. Thus, it can be concluded that the potential for

daylight utilization is real and relatively important in the residential sector.

Although this study yields a series of valuable results and information, it is solely based on

theoretical energy simulations, using inputs and settings that could be very different from a

real context. These are great limitations. The results of this study should be considered

bearing these limitations in mind.

6. References

British Standard. (2008). Lighting for buildings-Part 2: Code of practice for daylight. London, UK: BS. CIBSE. (1999). Daylighting and Window Design. London, UK: Chartered Institute of British Service Engineers. CIBSE. (2012). Guide F: Energy efficiency in buildings. Norwich, UK: Chartered Institute of British Service Engineers. CIBSE. (2012). The SLL Code for Lighting. London, UK: Chartered Institute of British Service Engineers. DesignBuilder. (2013). Manual of DesignBuilder Version 3.0. Retrieved 11 19, 2013, from www.designbuilder.co.uk EN/ISO. (2000). Thermal performance of windows, doors and shutters- calculation of thermal transmittance, part 1: Simplified method. Geneva, Switzerland: European Normalization/International Standardization Organization. EnergyPlus. (2013). Engineering Reference of EnergyPlus. Retrieved 11 19, 2013, from http://apps1.eere.energy.gov/buildings/energyplus/ Foldbjerg, P., Roy, N., Duer, K., & Andersen, P. A. (2010). Windows as a low energy light source in residential buildings: analysis of impact on electricity, cooling and heating demand. Clima. Turkey.


65

Karabay, H., & Arici, M. (2012). Multiple pane window applications in various climatic regions of Turkey. Energy and Buildings , 45, 67-71. Kragh, J., Laustsen, J. B., & Svendsen, S. (2008). Proposal for energy rating system of windows in EU. Lyngby, Denmark: Department of Civil Engineering, Danish Technical University. LBNL. (2000). IEA/SHC/Task21 - Daylight in Buildings - a source book on daylighting systems and components. . Berkeley, CA, USA: International Energy Agency. Mardaljevic, J., Andersen, M., Roy, N., & Christoffersen, J. (2011). Daylighting Artificial Lighting and Non-Visual Effects Study for a Residential Building. Leicestershire: Loughborough University. Myresjöhus. (2013). House models. Retrieved 03 19, 2013, from Myresjöhus: www.myresjohus.se Persson, M. L., Roos, A., & Wall, M. (2006). Influence of window size on the energy balance of low energy houses. Energy and Buildings , 38, 181-188. Schultz, J. M., & Svendsen, S. (1998). WINSIM: a simple simulation program for evaluating the influence of windows on heating demand and risk of overheating. Solar Energy , 4, 251-258. Thiers, S., Beinsteiner, P., & Peuportier, B. (2011). Study of an energy rating system of windows in EU. ARMINES. Thomsen, K. E., Wittchen, K. B., Jensen, O. M., & Aggerholm, S. (2007). ENPER-EXIST Applying the EPBD to improve the Energy Performance Requirements to Existing Buildings, WP3: Building stock knowledge. Intelligent Energy Europe. Urbikain, M. K., & Sala, J. M. (2009). Analysis of different models to estimate energy savings related to windows in residential buildings. Energy and Buildings , 41, 687–695. Veitch, J. A., & Galasiu, A. D. (2012). The physiological and psychological effects of windows, daylight, and view at home: review and research agenda. National Research Council of Canada, Institute for Research in Construction, Ottawa, Canada.

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