UNIVERSIDADE DE LISBOA
FACULDADE DE CIÊNCIAS
DEPARTAMENTO DE ENGENHARIA GEOGRÁFICA, GEOFÍSICA E ENERGIA
Investigation of relationship between newly imposed
requirements for daylight factor in DS/EN 16798 and energy use
in office buildings designed according to Danish building class
2020
Marco António Sousa Miguel
Mestrado Integrado em Engenharia da Energia e do Ambiente
Dissertação orientada por:
Acknowledgement
I am grateful for having the opportunity to work with numerous people while I was conducting this project in Denmark Technical University. They received me with open arms and made me feel at home. A special thank you to Jakub Kolarik, that gave me all the help that I could ask for. I am also grateful to my coordinator from Faculty of Sciences of University of Lisbon, Guilherme Carrilho, for helping and for being always available.
I would like to thank my family and friends for all the support they gave me and for making me feel that Portugal and Denmark are not so far apart.
I am grateful to my girlfriend, Catrina Pinto, who supported me from the start and always pushed my forward during this journey.
This thesis is dedicated to my grandmother and my mother, to whom I have the most profound gratitude and love.
v
Resumo
O crescimento populacional, o aumento do tempo passado dentro de edifícios e a criação de requisitos mínimos para a qualidade do ambiente interior, fazem com que o consumo de energia associado ao sector dos edifícios aumente para níveis elevados. O consumo de energia atribuído a habitações e ao sector não doméstico deverá crescer 67% e 33%, respetivamente, até 2030, o que significa que a eficiência energética neste sector será crucial para atingir os objetivos propostos na estratégia energética 2020. Vários esforços estão a ser feitos na União Europeia de forma a alcançar os objetivos 2020, que, para o sector das alterações climáticas/sector energético, são menos 20% em emissão de gás de estufa (ou mesmo 30%, se as condições estiverem favoráveis) em comparação com 1990, 20% da energia proveniente de fontes renováveis e aumento de 20% na eficiência energética.
Existe também a preocupação de melhorar a qualidade do ambiente interior nos edifícios. Por conseguinte, existe uma nova Norma Europeia - EN 16798 - que está atualmente a ser apresentada ao CEN (Comité Europeu de Normalização). Esta norma vai substituir a EN 15251 e especifica diferentes tipos de critérios relativos ao dimensionamento de edifícios, aquecimento, arrefecimento, ventilação e iluminação, que podem ter uma influência significativa no consumo energético dos edifícios. De modo analisar o impacto das novas normas, relativas à disponibilidade de luz natural, no consumo de energia dos edifícios, são usados os critérios relativos à disponibilidade de luz natural especificados na EN 16798. Todos os restantes parâmetros relativos à qualidade do ambiente interior são considerados.
Neste projeto, pretende-se analisar o impacto da disponibilidade de luz natural no consumo de energia do edifício e no consumo de energia dos escritórios, de acordo com a sua classificação de disponibilidade de luz natural. Para isso, são utilizadas simulações dinâmicas por computador (IDA ICE) e é criado um edifício modelo que respeita os critérios de construção de edifícios 2020 na Dinamarca.
A geometria do edifício é projetada para ser esteticamente interessante, do ponto de vista arquitetónico, de modo a acompanhar a tendência dos novos edifícios de escritórios. É um edifício de dois andares, com doze escritórios (seis virados a sul e seis virados a norte), uma área comum (que pode ser vista como uma sala de estar ou como uma sala de reuniões) e uma casa de banho. O tamanho do escritório é destinado a uma pessoa e é pensado para criar uma boa iluminação natural aos trabalhadores. Os escritórios virados a sul são separados dos escritórios virados a norte por um corredor que atravessa o comprimento do edifício. Os escritórios do segundo andar, além das janelas, possuem uma claraboia que é pensada com o intuito de otimizar a distribuição e a disponibilidade de luz natural. A entrada do edifício está voltada para Este, enquanto que a escada, que dá acesso ao segundo andar, está virada para o Oeste.
A disponibilidade de luz natural é categorizada em quatro níveis (não existente, Baixo, Médio e Forte) de acordo com a EN 16798. De modo a recrear cenários onde a disponibilidade de luz natural corresponda à categorização descrita anteriormente, o tamanho das janelas de cada escritório é alterado. São então definidos cenários principais que representam os níveis de disponibilidade de luz natural nos escritórios. Neste projeto, apenas três níveis de disponibilidade de luz natural são avaliados: Baixo, Médio e Forte, que são representados pelo valor de daylight factor associado e calculado para o centro do escritório, no plano de trabalho de 0,8 m acima do chão (EN 12464). Para tornar a problemática da pesquisa um pouco mais complexa, o impacto que o tipo de ventilação utilizada no edifício e a utilização de dispositivos de sombreamento também são estudados dando origem à criação de dezoito cenários com diferentes características.
Algumas conclusões tiradas da analise ao consumo energético dos edifícios representativos dos dezoito cenários indicam que, mesmo para um edifício bem isolado em Copenhaga, é impossível alcançar a meta um consumo igual ou inferior a 25 kWh / m2.ano de energia primária sem usar energia renovável; a área necessária para instalar um sistema fotovoltaico, que gera a energia restante, representa 15,6-21,3 % do espaço disponível no telhado; expandir o tamanho das janelas provoca um aumento no aquecimento e arrefecimento quando a ventilação híbrida e natural são utilizados. Porém, o aumento no aquecimento é baixo em comparação com o aumento no arrefecimento; a poupança de energia na iluminação proveniente do incremento das janelas é menor que a energia extra necessária para o arrefecimento e aquecimento e, por conseguinte, não é suficiente para compensar o consumo energético extra; para os casos de Baixa e Forte disponibilidade de luz natural, a ventilação natural é preferível à ventilação mecânica e híbrida, mas para o caso de Média disponibilidade de luz natural a ventilação mecânica tem melhor desempenho; escritórios do primeiro andar possuem um melhor desempenho energético que escritórios do segundo andar; para os casos de Baixa e Média disponibilidade de luz natural, escritórios orientados a sul têm um melhor desempenho do que escritórios orientados a norte, mas para o caso de Forte disponibilidade de luz natural, escritórios orientados a norte são preferíveis, pois o consumo energético em arrefecimento é muito alto; a distribuição da luz natural é melhor em escritórios no segundo andar, devido à implementação da claraboia, e em escritórios orientados a sul; o risco de glare effect é inexistente para escritórios com Baixa e Média disponibilidade de luz natural, mas para escritórios com Forte disponibilidade de luz natural existe risco de glare effect entre a área de trabalho e as superfícies não adjacentes; Em futuros trabalhos, seria interessante levar a cabo a mesma pesquisa para países onde as condições climáticas fossem diferentes das que caracterizam a região da Dinamarca para observar o impacto da categorização da disponibilidade de luz natural sobre o desempenho energético do edifício de escritórios nesses países.
Palavras-chave: Edifícios de escritório; disponibilidade da luz natural; desempenho energético;
vii
Abstract
The population growth, the increasing indoor environment criteria and the rise in time spent inside buildings makes the energy consumption associated to this sector raise to high levels. Energy consumption attributed to dwellings and non-domestic sector is expected to grow 67% and 33% respectively, until 2030, which means that energy efficiency in this sector will be crucial to achieve the goals proposed in the European 2020 energy strategy and onwards. In European Union, a lot of efforts are being made to achieve the Europe 2020 targets, which, for energy sector/climate changes, are 20% less greenhouse gas emissions comparing to 1990 records (or even 30%, if the conditions are right); 20% of energy from renewables and 20% increase in energy efficiency.
There is also a concern for improving the indoor environment quality in buildings. Therefore, there is a new European Norma - EN 16798 - that is currently submitted to the CEN (European Committee of Standardization). This standard is going to supersede the EN 15251 and specifies different types of criteria regarding dimensioning of buildings, heating, cooling, ventilation and lighting, which may have a significant influence on buildings energy demand. To analyse the impact of the new standards, concerning the daylight availability, in the energy consumption of the buildings, the categorization of daylight availability specified in EN 16798 is used. All other parameters concerning the quality of the indoor environment are considered.
In this project, an office building is created according building regulation 2015. The characteristics of the desire type of building and its properties are recreated and various simulations are made in IDA ICE. The variable parameters considered were the type of ventilation, daylight availability and the use of shading device. The combination of these variables originates 18 scenarios and their energy performance is analysed.
Some of the finding of this project are: shading devices increase heating demand and decrease cooling demand which contributes to higher energy consumption; while increasing the size of the windows, the increment on cooling demand is higher in mechanical ventilation scenarios than in hybrid and natural ventilation scenarios, however, until a certain windows size, savings on heating overcome extra energy spent on cooling, which results in a better energy performance of mechanical ventilation scenarios; increasing the size of the windows increases heating and cooling demand when hybrid and natural ventilation are used, but the increment on heating demand is low compared to the increment on cooling demand; energy saved on lighting brought from the increment of windows is lower than the extra energy needed for cooling and heating demand and, therefore, it is not sufficient to compensate the extra energy demand;
Table of contents
Acknowledgement ... iv Resumo ... v Abstract ... vii List of figures ... x List of tables ... xiList of appendices ... xii
List of abbreviations and symbols ... xiii
Chapter 1 - Introduction ... 1
1.1 - Contextualization ... 1
1.2 - Scientific Background ... 1
1.3 - Legal Contextualization ... 3
1.4 - Goal and scoop ... 3
1.4.1 - Research main questions... 4
Chapter 2 - Denmark ... 5
2.1 - Danish energy policy – priorities and targets ... 5
2.1.1 - Building Class 2020 – nearly-zero energy buildings in Denmark ... 5
2.1.1.1. Buildings envelope ... 5
2.1.1.2. Insulation requirements... 5
2.1.1.3. Components ... 5
2.1.1.4. Primary energy factors ... 6
2.1.1.5. Thermal indoor climate ... 6
2.1.1.6. Daylight ... 6
2.1.1.7. Air Quality ... 7
2.1.1.8. Recommended criteria for lighting ... 7
2.2 - Weather of Copenhagen ... 8
Chapter 3 - Theoretical concepts ... 9
3.1 - Heat conservation ... 9
3.2 - Illuminance ... 9
3.3 - Luminance ... 10
3.4 - Glare ... 10
3.5 - Solar Radiation ... 11
3.6 - Sunlight and Solar Energy ... 12
3.7 - Daylight factor ... 12
3.8 - The Comfort Indexes ... 12
ix
3.8.2 - Predicted Percentage of Dissatisfied Index ... 13
3.9 - Renewable Energy ... 14
3.9.1 - Photovoltaic System ... 14
Chapter 4 - Simulation tools ... 15
4.1 - IDA ICE ... 15
4.2 - Building specifications ... 15
4.2.1 - Air handing unit ... 15
4.2.2 - Heating and Cooling units ... 16
4.2.3 - Primary energy factors ... 17
4.3 - VELUX Daylight Visualizer ... 17
Chapter 5 - Method... 18
5.1 - Design of the building ... 18
5.2 - Scenarios description ... 19
5.2.1 - General specifications of the scenarios ... 20
5.3 - Main case scenario 1 – Low daylight availability ... 26
5.3.1 - Mechanical ventilation without shading device ... 27
5.3.2 - Mechanical ventilation with shading device ... 28
5.3.3 - Hybrid ventilation without shading device ... 28
5.3.4 - Hybrid ventilation with shading device ... 28
5.3.5 - Natural ventilation without shading device ... 29
5.3.6 - Natural ventilation with shading device ... 29
5.4 - Main case scenario 2 – Medium daylight availability ... 29
5.5 - Main case scenario 3 – Strong daylight availability ... 30
5.6 - Performance Evaluation ... 31
Chapter 6 - Results ... 32
6.1 - Energy performance - all scenarios ... 33
Energy performance – Types of ventilation systems ... 34
6.2 - Energy performance – Daylight availability ... 35
6.3 - Office room performance ... 37
6.4 - Natural lighting on the task area ... 43
6.5 - Photovoltaic system ... 46
Chapter 7 - Discussion ... 47
Chapter 8 - Conclusion ... 53
Chapter 9 - References ... 55
List of figures
Figure 1: Heat balance inside the room (from source [19]) ... 9
Figure 2: Solar radiation process (from source [18]) ... 11
Figure 3: Predicted Percentage of Dissatisfaction (from source [25]) ...13
Figure 4: Building geometry ... 18
Figure 5: Scenarios and sub-scenarios ... 19
Figure 6: Distribution system losses ... 22
Figure 7: Air handing unit scheme ... 22
Figure 8: Fan schedule ... 23
Figure 9: Skylight layout on the roof of the office rooms and meeting room ... 25
Figure 10: Windows layout – Low daylight availability ... 27
Figure 11: Window opening controller scheme ... 28
Figure 12: Windows layout - Medium daylight availability ... 29
Figure 13: Window layout - Strong daylight availability ... 30
Figure 14: Annual primary energy consumption of all the case ... 33
Figure 15: Annual demand energy consumption for different types of ventilation system (Low - DA) ... 34
Figure 16: Annual demand energy consumption for different types of ventilation system (Medium - DA) ... 34
Figure 17: Annual demand energy consumption for different types of ventilation system (Strong - DA) ... 35
Figure 18: Annual demand energy consumption for different types of Daylight availability using the same mechanical ventilation ... 35
Figure 19: Annual demand energy consumption for different types of Daylight availability using the same hybrid ventilation ... 36
Figure 20: Annual demand energy consumption for different types of Daylight availability using the same Natural ventilation ... 36
Figure 21: Annual demand energy consumption according to O.R orientation and floor (Low - DA) ... 37
Figure 22: Illuminance plan view Low North O.R - 2nd Floor ... 38
Figure 23: Illuminance plan view Low North O.R - 1st Floor ... 38
Figure 24: Illuminance plan view Low South O.R - 1st Floor ... 38
Figure 25: Illuminance plan view Low South O.R - 2nd Floor ... 38
Figure 26: Annual demand energy consumption according to O.R orientation and floor (Medium - DA) ... 39
Figure 27: Illuminance plan view Medium South O.R - 2nd Floor ... 40
Figure 28: Illuminance plan view Medium South O.R - 1st Floor ... 40
Figure 29: Illuminance plan view Medium North O.R - 2nd Floor ... 40
Figure 30: Illuminance plan view Medium North O.R - 1st Floor ... 40
Figure 31: Annual demand energy consumption according to O.R orientation and floor (Strong - DA) ... 41
Figure 32: Illuminance plan view Strong South O.R - 2st Floor ... 42
Figure 33: Illuminance plan view Strong South O.R - 1st Floor ... 42
Figure 34: Illuminance plan view Strong North O.R - 2st Floor ... 42
Figure 35: Illuminance plan view Strong North O.R - 1st Floor ... 42
Figure 36: Natural illuminance on the task area Low South O.R - 2st floor ... 43
Figure 37: Natural illuminance on the task area Low South O.R - 1st floor ... 43
xi
Figure 39: Natural illuminance on the task area Low North O.R - 2st floor ... 43
Figure 40: Natural illuminance on the task area Medium South O.R - 2st floor ... 44
Figure 41: Natural illuminance on the task area Medium South O.R - 1st floor ... 44
Figure 42: Natural illuminance on the task area Medium North O.R - 2st floor ... 44
Figure 43: Natural illuminance on the task area Medium North O.R - 1st floor ... 44
Figure 44: Natural illuminance on the task area Strong South O.R - 2st floor ... 45
Figure 45: Natural illuminance on the task area Strong South O.R - 1st floor ... 45
Figure 46: Natural illuminance on the task area Strong North O.R - 2st floor ... 45
Figure 47: Natural illuminance on the task area Strong North O.R - 1st floor ... 45
List of tables
Table 1: Classification daylight supply (from EN 16798) ... 6Table 2: Maintained illuminance at working areas ... 7
Table 3: Predicted Mean Vote (from source [25]) ...13
Table 4: Building spaces dimensions ... 19
Table 5: Glazing properties... 20
Table 6: Building envelope properties ... 21
Table 7: Lighting system input data ... 24
Table 8: Primary energy factors ... 24
Table 9: Surface reflectance of the objects ... 25
Table 10: PV system specification to be set on PVsyst software ... 26
Table 11: Supply air flow of building space ... 27
Table 12: Gains through the windows for low DA ... 37
Table 13: Gains through the windows for medium DA ... 39
Table 14: Gains through the windows for strong DA ... 41
List of appendices
Figure A - i: Building spaces geometries ... 57
Figure A - ii: Dimensions of the building ... 57
Figure A - iii: Roof ... 58
Figure A - iv: Skylight layout on the roof of the corridor ... 58
Figure A - v: Skylight layout on the roof of the office rooms of Strong DA scenarios ... 58
Figure B - i: Building thermal bridges ... 59
Table C - i: Low DA - Hybrid ventilation with shading ... 60
Table C - ii: Low DA - Hybrid ventilation ... 60
Table C - iii: Low DA - Mechanical ventilation with shading ... 60
Table C - iv: Low DA - Mechanical ventilation... 60
Table C - v: Medium DA - Mechanical ventilation with shading ... 61
Table C - vi: Medium DA - Mechanical ventilation... 61
Table C - vii: Low DA - Natural ventilation with shading ... 61
Table C - viii: Low DA - Natural ventilation ... 61
Table C - ix: Medium DA - Hybrid ventilation with shading ... 62
Table C - x: Medium DA - Hybrid ventilation ... 62
Table C - xi: Medium DA - Natural ventilation ... 62
Table C - xii: Medium DA - Natural ventilation with shading ... 62
Table C - xiii: Strong DA - Mechanical ventilation with shading ... 63
Table C - xiv: Strong DA - Mechanical ventilation ... 63
Table C - xv: Strong DA - Hybrid ventilation with shading ... 63
Table C - xvi: Strong DA - Hybrid ventilation ... 63
Table C - xvii: Strong DA - Hybrid ventilation with shading ... 64
Table C - xviii: Strong DA - Natural ventilation ... 64
xiii
List of abbreviations and symbols
AC Alternating current
AHS Air handing system
AHU Air handing unit
B.A.R Buildings length-width ration
BC2020 Building class 2020
BR15 Building regulations 15
CAV Constant air volume
CEN European Committee of Standardization
COP Coefficient of performance
DA Daylight availability
DC Direct current
DF Daylight Factor, %
dPmax Maximum pressure differential
Em Maintained illuminance
EU European Union
HRD Heat recovery device
HVAC Heating, ventilation and air conditioning
IDA ICE IDA Indoor Climate and Energy
IEQ Indoor environment quality
MET Metabolic equivalent
NFC Normal fan control
NFC Normal fan control
NZEBD National plan for nearly zero-energy buildings of Denmark
NVO Night vent operation
NVO Night vent operation
O.R Office room/s
PEF Primary energy factors
PMV Predicted mean vote
PMV Predicted mean vote
PPD Predicted percentage of dissatisfaction
PV Photovoltaic
RE Renewable energy
S.W.S South façade area-south windows area ratio
VAV Variable air volume control
LMV Low daylight availability Mechanical ventilation
LMVS Low daylight availability Mechanical ventilation with shading
LHV Low daylight availability Hybrid ventilation
LHVS Low daylight availability Hybrid ventilation with shading
LNV Low daylight availability Natural ventilation
LNVS Low daylight availability Natural ventilation with shading
MMV Medium daylight availability Mechanical ventilation
MMVS Medium daylight availability Mechanical ventilation with shading
MHV Medium daylight availability Hybrid ventilation
MNV Medium daylight availability Natural ventilation
MNVS Medium daylight availability Natural ventilation with shading
SMV Strong daylight availability Mechanical ventilation
SMVS Strong daylight availability Mechanical ventilation with shading
SHV Strong daylight availability Hybrid ventilation
SHVS Strong daylight availability Hybrid ventilation with shading
SNV Strong daylight availability Natural ventilation
SNVS Strong daylight availability Natural ventilation with shading
A Room floor area, m2
Af Floor area of the room, m2
An Area of the walls, m2
Cp Specific heat at constant pressure, J/kg.K
dPmax Maximum pressure differential
G Solar irradiance, W/m2
Gabs Absorbed irradiance, W/m2
Gcl Climatization gains, W
GE Global efficiency of the light system, %
Gi Internal gains of the room, W
Gref Reflected irradiance, W/m2
Gs Solar gains, W
Gtr Transmitted irradiance, W/m2
Gv Ventilation gains, W
n Number of persons in the room
Ƞ Efficiency of the system, %
P Power of the light source, W
qB Minimum ventilation rate for emission from the building, l/s.m2 qper Ventilation rate for occupancy per person, l/s.person
Tint Temperature inside the room, K
Tout Outside temperature of the walls, K
Un Thermal transmittance of the room surface, W/m2.K
Vr Volume of the room, m3
αs Absorptivity
ρ Air mass density, kg/m3
ρs Reflectivity
τs Transmissivity
Chapter 1 - Introduction
1.1 - Contextualization
“Energy is the life blood of our society. The well-being of our people, industry and economy depends on safe, secure, sustainable and affordable energy. At the same time, energy related emissions account for almost 80% of the EU’s total greenhouse gas emissions [1].”
We live in a time where energy efficiency is one of the keys to our future. It is imperial to make the world a place where we can ensure that the energy that we are consuming is coming from the most efficient source and it is being used in the most efficient way possible. With that in mind, the European Union (EU) has pledged to cut its energy consumption by 20% by 2020. Energy efficiency is the most cost-effective way of maintaining an equivalent level of economic activity, energy security and competitiveness while energy consumption is being reduced. Most of all, it is a well-accepted strategy across all sectors due the possibility of reducing expenditures [2].
As a result of the European 2020 energy strategy, in 2014 the EU-28’s gross inland consumption of energy fell to its lowest level since 1994 [3]. This outcome points to an effectiveness of the strategy that has been implemented on this sector. However, we must ensure that our efforts are put on improving this result in the future.
There is a concern to increase energy efficiency and to reduce CO2 emissions on buildings sector in general due to its profound impact on energy sector demand and high percentage of CO2 emissions associated. This concern has been increased for the last years in EU where we can see that a lot of efforts are being made to achieve the Europe 2020 targets. When it comes to energy sector/climate changes, the targets are: 20% less greenhouse gas emissions (or even 30%, if the conditions are right) comparing to 1990 records; 20% of energy consumption from renewables and 20% increase in energy efficiency [2].
The population growth, the increasing indoor environment criteria and the rise in time spent inside buildings make the energy consumption associated to this sector raise to high levels. Energy consumption attributed to dwellings and non-domestic sector is expected to grow 67% and 33% respectively, until 2030 [4], which means that energy efficiency in this sector will be crucial to achieve the goals proposed in the European 2020 energy strategy and onwards.
1.2 - Scientific Background
There is a tendency of new buildings to have highly fenestrated façades. Part of this tendency is based on the belief that buildings highly fenestrated can benefit of more daylight and,
therefore, decrease the lighting consumption and energy used on heating demand in the building.
On the another hand, occupants work better and tend to be less depressed when working in an environment where the daylight availability (DA) is high [5], [6], [7]. Thus, this tendency goes along with the wellbeing of the occupants. However, there are many studies pointing to a different reality regarding the energy efficiency of this tendency. According to Motuziene & Juodis [8], as a general idea, the concept of using a large area of glazing façade in the building does not bring energy savings to the whole building. The author also mentions that, contrary to previous beliefs, the rooms facing north are the most efficient comparing to rooms facing south. From the analysis, they conclude that cooling energy demand is more dependable of the orientation and fenestration comparing to heating energy demand; south façades need to spend more energy on cooling and the energy saved on lighting is not sufficient to compensate the increased energy demand on cooling and heating. The same conclusions are made by Skarning [9], where he concludes that maximising solar gains in south-oriented rooms have limited potential when it comes to reduce space heating demand on buildings level, even in colder countries, such as Denmark. From his analysis, he concludes that g-value does not have a great impact on decreasing the heating demand in south oriented façade and for high g-values there is a risk of overheating. However, increasing g-value in north oriented façade can decrease the heating demand several times more than observed in south façades. He also concludes that G-value has a bigger impact in warmer climates than in colder climates; U-value should be the lowest possible in any choice so that the space losses can be minimize in the winter; light transmittance should be the highest possible so that DA can be the highest possible; Focus on increasing g-values to decrease the heat demand in south oriented facades should not be made. Instead, improvements on the utilization of coating products that can achieve better light-to-solar-gain ratio are preferable.
These studies have a clear message pointing out some misdirection that have been followed in the past. Moreover, they suggest that a personalized study regarding the windows properties and size should be made to obtain the best energy performance in the building. Following this line of thought Inanici and Demirbilek [10] conducted a study where they analyse the buildings length-width ration (B.A.R) and south façade area-south windows area ratio (S.W.S) in hot and cold climates. The results show that a small B.A.R is preferred in cold climates while a bigger B.A.R is preferred in hot climate; S.W.S should be increased in cold climates, but only to a certain point due the risk of overheating while in hot climates S.W.S should be kept maximum at 25% due the risk of overheating. From another perspective, a recent study was made in Denmark by Vanhoutteghem [11] and his team with focus on the relationship between size orientation and glazing properties of glazed façades for different room geometries. The research shows that, for south oriented rooms, low u-values, high light transmittance (τv) values and low g-values should be preferable. For north oriented rooms, the decision can be taken in a more freely way, however, the energy demand will be as lower as the lowest u-value, higher τv and higher g-value. Independently of the glazing characteristics, the best geometry (regarding daylight and thermal comfort) is found to be the one with a lowest depth and larger width.
These studies provide information regarding building/glazing properties that should be considered, but it is necessary to understand what is the final impact that can be brought from these researches in terms of overall buildings energy performance. Moreover, it is imperial to perceive if the specific energy and environment indoor quality (IEQ) goals for Denmark are possible to achieve when all this knowledge is applied to the buildings construction.
1.3 - Legal Contextualization
Reducing the energy demand in buildings can be especially difficult to achieve, since there is a tendency to improve IEQ. This tendency aims to improve the work environment and, according to several studies [5], [6], [7], these improvements are related to higher productivity of the occupants. The office indoor environment quality consists on the impact of several factors on occupants according to their health and well-being. IEQ is set from the following indicative parameters: Thermal comfort; Indoor air quality indicators; lighting indicators and noise indicators [12].
As mentioned before, there is a concern for improving the indoor environment quality in buildings. Therefore, there is a new European Norma - EN 16798 - that is currently submitted to the CEN (European Committee of Standardization). This Norma is going to supersede the EN 15251 and specifies different types of criteria regarding size of the buildings, heating, cooling, ventilation and lighting, which may have a significant influence on buildings energy demand. Thermal environment criteria for the heating season (winter) and cooling season (summer) are also specified.
1.4 - Goal and scop
The aim of this thesis is to contribute to the development of new office buildings energy design, to create nearly zero energy buildings (NZEB) that are more sustainable for the environment and, at the same time, are provided with good indoor environment quality. As a specific topic, the impact that increasing daylight availability can have on office room (O.R) and on the building itself is put into analysis.
The new EN 16798 aims, as a general goal, to improve the IEQ and energy efficiency of buildings. The EN includes lighting criteria where it is specified the Daylight availability classification as a function of the daylight factor. The building is classified as Strong, Medium, Low and None according to its daylight availability. These criteria go alongside with the tendency of the new office buildings having an elevated amount of glazing façade, making possible the creation of a well illuminated space using natural light.
In this thesis, it is intended to analyse the impact on energy consumption of the building and on energy consumption of the O.R facing north and south according to its daylight availability classification specified in the new EN 16798. To do so, a dynamic computer
simulation software (IDA ICE) is used and a building model that fallows the 2020 building criteria in Denmark is created. It is believed that this analyses can contribute to the clarification of the impact of daylight availability in office building located in cold climates.
1.4.1 - Research main questions
How does the daylight availability of the room influence the energy consumption in office buildings?
o Do highly fenestrated façades reduce energy consumption and increase IEQ on office buildings?
o Is the energy saved on lighting sufficient to compensate for the extra demand energy on heating and cooling?
o What is the impact of a shading device on energy consumption of the building?
o Which ventilation system type (mechanical, hybrid or natural) bring less energy consumptions to the building?
In the following chapters, it is described the base concepts of this project, the approach used, the results obtained, the discussion and the conclusions, where all the research questions are answered.
Chapter 2 - Denmark
2.1 - Danish energy policy – priorities and targets
By the year of 2020 Denmark aims to a reduction of 75 % in energy consumption in relation to the year of 2006. The reduction will take place in 3 smaller steps: reduction in energy consumption of at least 25 % in 2010, a further 25 % in 2015 and a further 25 % in 2020.
2.1.1 - Building Class 2020 – nearly-zero energy buildings in Denmark
The building class 2020 (BC2020) is based on several considerations that ensure that energy requirements of Building Regulation can provide a good solution for the low-energy buildings of the future. These considerations also contemplate people’s expectation for the indoor environment quality.
Office buildings can be classified as Building Class 2020 when the overall primary energy for heating, ventilation, cooling, hot water and lighting per m² heated floor area does not exceed 25 kWh over the year. However, it is stated on the National plan for nearly zero-energy buildings of Denmark (NZEBD) that this requirement is difficult to meet without using Renewable Energy (RE) plants [13].
2.1.1.1. Buildings envelope
Buildings envelope requirements are included to ensure the quality of the basic building, which is designed to last for many years and it is expensive to change once it is built. Requirements for the building envelope states the maximum amount of heat that may be lost per m² of building envelope (walls, foundation, floors and roof), which does not include windows or doors. In BC2020, the requirement is that the dimensioning heat loss must not exceed 4,7 W/m² building envelope in a two-storey building.
2.1.1.2. Insulation requirements
Leakages have an impact on the comfort of the office workers and its reduction can result in significant energy savings, so the implementation of an insulation figure of 0,5 l/s.m2 (at 50 Pa over/under pressure) is required.
2.1.1.3. Components
The requirements for the energy balance of windows (heating season) state that the balance between heat loss and solar gains must be positive (higher than 0 kWh/m2 of windows area),
meaning that, over the heating season, the amount of solar gains must be higher than the amount of heat losses from the building to the outside. The requirements are even stricter when it comes to skylights, where the balance between the heat loss and the solar gains during the same season must be over 10 kWh/m2 of skylight area. The U value of outer doors and openings must not be higher than 0,8 W/m2.K. If the door contains glass the U value can be as higher as 1 W/m2.K or the solar gain through the door, in the heating season, has to less than 0 kWh/m2. Entrance doors must have a U value lower that 1,4 W/m2K.
2.1.1.4. Primary energy factors
The primary energy factors (PEF) to be used in BC2020 are 0,6 for district heating; 1,8 for electricity; 1,0 for fossil fuels and 0,0 for renewable energy.
2.1.1.5. Thermal indoor climate
For office buildings, it is the contractor who stipulates the maximum number of hours that the inside temperature can exceed 26oC and 27 oC. However, for this thesis purpose, it is considered the requirements that are applied to homes under the BC2020, which means that the inside temperature must not exceed 26oC by more than 100 working hours and 27oC for more than 25 working hours over the year. The temperature set up must be between 20oC and 26oC.
2.1.1.6. Daylight
Using daylight in office buildings can lead to energy saving by reducing the need of having lamps during part of the day. A good access to daylight can also improve the productivity of office workers by improving their concentration and their mood. For office buildings, working areas must have, at minimum, a windows area corresponding to 15% of the floor area and the glass must have a light transmittance (τv) of at least 0,75. The new EN 16798 will also include a standard regarding the daylight classification, where the daylight supply will be classified as shown in the table 1:
Daylight factor (DF)
Vertical Façades Roof lights Classification daylight supply
DF ≥ 6 % DF ≥ 7 % Strong
6 % > DF ≥ 4 % 7 % > DF ≥ 4 % Medium
4 % > DF ≥ 2 % 4 % ≥ DF Low
2 % > DF ≥ 0 % 2 % > DF ≥ 0 % None
2.1.1.7. Air Quality
According to section B.1.2 in EN 15251 [14], for buildings with mechanical ventilation, the recommended minimum ventilation rate during working hours is 0,7 l/s.m2 and it should be added a 7 l/s.person ventilation rate when the room is being used (this values correspond to a low polluting building category II). For multi-story buildings, there is a further requirement installation of ventilation systems with heat recovery units (with a dry temperature efficiency of no less than 85%).
The total ventilation rate for a room is calculated from the following equation: 𝐪tot= 𝒏 · 𝐪per + 𝐀 · 𝐪B [
l
s] (2.1) Where:
qtot = total ventilation rate of the room, l/s;
n = number of persons in the room;
qper = ventilation rate for occupancy per person,
l/s.person;
A = room floor area, m2;
qB = minimum ventilation rate for emissions from the
building, l/s.m2
There are strict requirements for the permissible amount of CO2 for buildings under BC2020. The ventilation rates must be adequate to the need of the building so that the CO2 concentration does not exceed 900 ppm, apart from in shorter periods.
2.1.1.8. Recommended criteria for lighting
In order to provide a well-lit environment there are some recommended criteria for light provided in office buildings spaces, described in DS-EN 12464-1 [15], that must be fallowed. The criteria used in this project are shown in the table 2:
Table 2: Maintained illuminance at working areas Type of area Maintained illuminance (Em) at working areas, (lx) Single Office 500 Corridor 100 Stairs 100 Toilet 200
2.2 - Weather of Copenhagen
The city of Copenhagen is located in Denmark, in the north of Europe. The city is surrounded by see and has a cold and temperate climate. There is a significant rainfall throughout the year, even in the driest month, which makes the air very humid (usually over 70%). Copenhagen has an annual average low temperature of 8,0oC and 613 mm is the average annual rainfall. In February, which is the driest month, the precipitation is around 30 mm. July, August and November are the months with more precipitation and where the records show a rainfall over 60 mm. July and August are the hottest months of the year where the average temperature is 20,0°C during the day (13,0oC at night). With an average temperature of 2,0° C (-2,0oC at night), January and February are the months with the lowest temperature throughout the year [16]. The number of hours of sunlight varies widely during the year in Copenhagen. June is the month with more hours of sunlight with around 17 hours and therefore the month with more irradiation (5780 Wh/m2/day on horizontal surface). On the other hand, December has less than 7 hours and it is the month with less hours of sunlight and with the lowest irradiation value (346 Wh/m2/day on horizontal surface) [17].
9
Chapter 3 - Theoretical concepts
In this chapter, all the theoretical concepts used in this project are explained.
3.1 - Heat conservation
The first law of thermodynamics can be applied to the heat transference that occurs between the building and its surroundings and the conservative process can be described by the following expression [18]: 𝐺𝑖+ 𝐺𝑠+ 𝐺𝑣+ 𝐺𝑐𝑙 = 𝜌 ∙ 𝐶𝑝∙ 𝑉𝑟 𝜕𝑇𝑖𝑛𝑡 𝜕𝑡 + ∑ 𝐴𝑛∙ 𝑈𝑛∙ (𝑇𝑖𝑛𝑡 𝑘 𝑛=1 − 𝑇𝑜𝑢𝑡)
[𝑊] (3.1)
Where:Gi are the internal gains of the room, 𝑊;
Gs are solar gains, 𝑊;
Gv are ventilation gains, 𝑊;
Gcl are climatization gains, 𝑊;
ρ is the air mass density, kg/m3;
Cp is the specific heat at constant pressure, J/kg ·K;
Vr is the volume of the room, m3;
Tint is the temperature inside the room, K;
Tout is the outside temperature of the walls, K;
An is the area of the walls, m2;
Un is the thermal transmittance of the room surface,
W/m2K;
The heat balance that occurs in the room can be pictured as below:
Figure 1: Heat balance inside the room (from source [19])
3.2 - Illuminance
Illuminance, expressed in lux [lx], is the amount of visible light falling onto a given surface area. It is calculated as the density of lumens per unit area [lm/m2]. There are strict requirements regarding the illuminance that must be applied to a specific work area
depending on the type of work that is developed in that area. To measure the energy used with illuminance it is necessary to know how efficient is the light source, thus luminous efficacy. This parameter is a measure of how well a source produces visible light and it is the ratio of luminous flux [lm] to power [W], measured in lumens per watt [lm/W] [20].
Wishing to reach the most realistic value of energy need for the light sources, it is added a parameter, global efficiency (GE), that represents the dust that is accumulated over the period of utilization on the light source and, also, the efficiency of the light support. The expression below represents the formula used to calculate the light power needed:
𝑃 = 𝐿𝑢𝑚𝑖𝑛𝑎𝑛𝑐𝑒 𝑒𝑓𝑓𝑖𝑐𝑎𝑐𝑦 × 𝐺𝐸𝐼𝑙𝑙𝑢𝑚𝑖𝑛𝑎𝑛𝑐𝑒 × 𝐴𝑓 [W] (3.2)
Where:
P is the power of the light source, W;
Illuminance is the amount of visible light that strikes the surface, lx;
Luminance efficacy is the quality of the light source, lm/W;
Af is the floor area of the room, m2;
GE is the global efficiency of the light system, %.
In this project the light source can be either a lamp or the sun. During the working hours, daylight is preferred over lamps to create a healthier environment and, also, to decrease energy demand on lighting. With that in mind, each O.R has a light sensor that regulates the lighting utilization according to the natural light of the O.R at that point.
3.3 - Luminance
Luminance, expressed in candela [cd/m2], is the reference to the measurement of the amount of light emitted or reflected from a surface. This means that illuminance indicates the brightness of a light source and it can be used to identify sources that produce glare [20].
3.4 - Glare
Glare is the negative sensation produced by luminance in the visual field that is so much greater than the luminance, to each the eyes are adapted, that they cause visual discomfort, reduce visibility or both. It can take two forms: Discomfort glare or disability glare. Disability glare results in reduced visual performance, with excess of luminance leading to a loss of visibility. Discomfort glare is the sensation of discomfort or even pain caused by excessive luminance in the field of view.
11 There are two types of glare: Direct glare and indirect glare. Direct glare is caused as a result of high luminance from a light source present in the field of view. Reflected glare results from the reflection of a high brightness in a polished surface in the field of view [21].
In this project, to evaluate the glare effect, it is used the "1:3:10" rule. This rule consists on the idea that the luminance in the visual field of view must remain in reasonable ration in order to prevent glare effect. The recommended rations are the following: 1:3 between paper and screen; 1:3 between the visual task and the adjacent surfaces; and 1:10 between the visual task and the non-adjacent surfaces [22].
3.5 - Solar Radiation
When the solar radiation hits a surface, portions of the irradiation are reflected, absorbed and transmitted. Reflection is the process of incident radiation being redirected away from the surface, with no effect on the medium; the transmission refers to radiation that passes through the medium and absorption occurs when radiation interacts with the medium, causing an increase in its thermal energy [18].
Figure 2: Solar radiation process (from source [18])
It is defined as reflectivity, the fraction of the irradiation that is reflected (ρs), as absorptivity (αs) the fraction of the irradiation that is absorbed, and as transmissivity (τs) as the fraction of the irradiation that is transmitted. Since all the radiation is reflected, absorbed or transmitted, the fallow expression can be applied:
ρ𝑠+ α𝑠+ τ𝑠= 1 (3.3)
And it can be interpreted:
G ∙ ρ𝑠+ G ∙ α𝑠+ G ∙ τ𝑠 = G <=> 𝐺𝑟𝑒𝑓+ 𝐺𝑎𝑏𝑠+ 𝐺𝑡𝑟= 𝐺 [W/m2] (3.4)
Where:
G is the solar irradiance, W/m2;
Gref is the part of irradiance reflected, W/m2;
Gabs is the part of irradiance absorbed, W/m2;
3.6 - Sunlight and Solar Energy
Solar radiation penetrates inside of a building through the window in two different ways: visibly, in the form of light waves and invisibly, as heat energy. The radiation transmission is measured as the light transmittance and the total energy transmission g-value. This value influences the energy assessment of the window. In other words, it measures the percentage of heat that passes through the glass. The lower the solar factor the higher the solar protection of the glazing.
The daylight availability of the room is controlled by the properties of the glazing of the windows. The light transmittance specifies the proportion of visible irradiation that passes through a transparent component. The higher the value, the higher the amount of light that passes through the glazing. It is recommended to have a high light transmittance to improve the level of daylight in the room, to have a brighter outlook to the outside and a lower distortion of colours [23].
3.7 - Daylight factor
Daylight Factor (DF) is the ratio of the amount of illuminance available indoors to the illuminance present outdoors under overcast sky at the same time. It is calculated by dividing the horizontal work plane illuminance inside the room by the horizontal illuminance outside the room, as it is shown in the following expression:
𝐷𝐹 = 𝐼𝑛𝑑𝑜𝑜𝑟𝑠 𝑖𝑙𝑙𝑢𝑚𝑖𝑛𝑎𝑛𝑐𝑒
𝑜𝑢𝑡𝑑𝑜𝑜𝑟𝑠 𝑖𝑙𝑙𝑢𝑚𝑖𝑛𝑎𝑛𝑐𝑒×100 [%] (3.5)
The DF expresses the illuminance difference between the indoors and outdoors under overcast sky and it can be used as criteria to evaluate the daylight availability of the O.R. The calculation of DF in this project are made by using a simulation tool – IDA ICE.
3.8 - The Comfort Indexes
When the energy design of the building is created, it is essential to have criteria to measure the impact of the choices made regarding the comfort of the people working/living in the building. The indices of comfort are essential to evaluate the complexity of the reactions that occur between the human body, activity, clothing, habits and physical quantities (which are given by the metabolic equivalent – MET) relating to the environment such as: air temperature, mean radiant temperature, air velocity, relative humidity, etc. The comfort index is described as a value that expresses the relationship between the occupant and the
13 environment. It is necessary to define the characteristics of the predicted occupant (age, type of clothing, activities, etc.) and the environment (moderate, hot, cold, indoor, etc.). In this project the comfort indexes used are the predicted mean vote (PMV) and predicted percentage of dissatisfaction (PPD). The minimum recommended condition for indoor environment is defined by PPD < 10 % or a thermal sensation index of |PMV| < 0,5 [24].
3.8.1 - Predicted Mean Vote
The predicted mean vote is expressed according to a 7 points scale from cold (-3) to hot (+3). The levels are the result of an equation that takes into account the indoor climate variables, metabolism and the clothing of the occupant. The PMV interprets as an optimal case situation that leads to the result equal to 0 (zero), where the occupant is in absolutely no discomfort. Value Sensation -3 Cold -2 Cool -1 Slightly cool 0 Neutral 1 Slightly warm 2 Warm 3 Hot
Table 3: Predicted Mean Vote (from source [25])
3.8.2 - Predicted Percentage of Dissatisfied Index
The predicted percentage of dissatisfied is a statistical index correlated to the PMV. This index can also be expressed with respect to other indicators such CO2, the level of illumination, etc. It expresses the expected percentage of people that are not feeling comfortable. The better the condition of comfort, the lower the number of people who have a negative opinion, so the lower the PPD.
3.9 - Renewable Energy
Renewable energy technology is an important way to reduce carbon emissions and fossil fuel demand. Intelligent use of renewable energy applied to buildings should be part of a fully integrated strategy to reduce the buildings energy demand. By carefully applying design principles that capture the energy from the sun the energy used in buildings can be reduce drastically.
3.9.1 - Photovoltaic System
Photovoltaic (PV) technology uses semi-conductors that convert sunlight into electrical energy through direct current (DC). DC is usually converted to alternating current (AC) via inverters, so it can be used in buildings electric system or, in case of all the energy needs of the building are fulfilled, exported to the utility greed. The energy generated from PV systems depends upon the amount of sun received and many other factors, such as tilt, orientation, technology efficiency (panel and inverter efficiencies), shading produced by its surroundings, etc. [26].
15
Chapter 4 - Simulation tools
4.1 - IDA ICE
IDA Indoor Climate and Energy (IDA ICE) is a software to study the indoor climate of individual zones that may or may not be part of a building and the energy performance of the entire building. The geometry can be created directly in the program or it can be imported from other design software tools. In this project case, the geometry of the building is drawn directly into the program. IDA ICE considers several detail properties to create the thermal equation, so that the best output results according to those parameters specification can be generated.
4.2 - Building specifications
In this subchapter, it is described the climatization system that needs to be specified in IDA ICE. The program has a general concept of the buildings energy system that can be changed according to the user.
4.2.1 - Air handing unit
An air handing unit (AHU) is a central air conditioner station that handles air from the outside into the building, usually, by a ductwork ventilation system that distributes the conditioned air through the building and returns it to the AHU. The air is delivered into the building space with thermo-hygrometric and indoor air quality treatment. The AHU treats the air by filtering, cooling and/or heating, humidifying and/or dehumidifying and, depending on the type of building, the accuracy of the treatment can be different. The major components of the air handing system (AHS) are the primary system; coils; filters; humidifiers; mixing chamber; fan and heat recovery device.
• Coil
Coil is a component used to transfer heat between the air that circulates through the AHS and the fluid heated or cooled by the primary system.
• Filter
• Humidifiers
A humidifier is a device that increases humidity in the building. The humidification is necessary in case the continuous heat makes the air dry which could result in uncomfortable air quality for the users.
• Mixing chamber
The mixing chamber is where the air from the outside is mixed with the air that circulates through in the AHS. This provides a better air quality into the building and avoid unappropriated levels of CO2.
• Primary system
The primary system consists in a heating (boiler) and a cooling device (chiller). The efficiency of the chiller and boiler [27] can be described by the following expression:
𝐶𝑂𝑃 = 𝐻𝑒𝑎𝑡 𝑜𝑢𝑡𝑝𝑢𝑡
𝑊𝑜𝑟𝑘 𝑖𝑛𝑝𝑢𝑡 (4.1)
ƞ = 𝐸𝑛𝑒𝑟𝑔𝑦 𝑜𝑢𝑡𝑝𝑢𝑡
𝐸𝑛𝑒𝑟𝑔𝑦 𝑖𝑛𝑝𝑢𝑡 ×100 [%] (4.2) Where:
COP is the coefficient of performance; Ƞ is the efficiency of the system, %.
• Fan
The fan is the device used to blow and draw air through the mixing chamber, filters and coils into the building.
• Heat recovery device
Heat recovery device uses the heat of the outgoing air flow of the circuit to warm up the fresh air coming from the outside.
4.2.2 - Heating and Cooling units
The heating and cooling units are placed in a specific area of the building. It can be in the office room, toilet, corridor, etc. They are connected to the primary system and their function is to create the proper thermal environment at the zone space according to the specified temperature settings.
17
4.2.3 - Primary energy factors
The primary energy factor expresses a comparison between the input primary energy to the system and the energy delivered to the consumer. The calculation of the PEF takes into account the energy required for the extracting, processing, storing and transporting to a power plant, energy conservation, transmission, distribution and the losses associated to the processes [28].
4.3 - VELUX Daylight Visualizer
VELUX Daylight Visualizer simulation tool is used in this project so that an analysis over the office rooms natural illuminance performance can be executed.
VELUX Daylight Visualizer is a lighting simulation tool used for the analysis of daylight conditions in buildings. It is designed to help professionals by predicting daylight levels prior to realization of the building design. The software permits generation of 3D models and importing models from other design tools, such SketchUp. Settings, as location, orientation, date, time of simulation and sky type are considered. Velux Daylight Visualizer is chosen over other simulation tools as its simulation approach method is similar to IDA ICEs.
Chapter 5 - Method
In this chapter, it is explained the approach used to solve the research problem. All the NZEBD requirements regarding IEQ, building envelope, insulation and components are fulfilled in all the scenarios.
5.1 - Design of the building
To evaluate the impact of the daylight in office buildings the characteristics of the desire type of building and its properties are recreated. The geometry of the building is presented in figure 4 and it is designed to be aesthetically interesting from an architectural point of view, to follow the tendency of new office buildings. It is a two-story building, with twelve office rooms (six facing south and six facing north), one common area (that can be seen as a living room or as a meeting room) and one toilet. The O.R facing south are separated from the ones facing north by a corridor that goes across the length of the building. The second-floor O.R, in addition to the windows, have a skylight which optimizes the light distribution and the daylight availability. The entrance of the building faces East, while the stair that gives access to the second floor faces West. In figure A – i, ii and iii goes the full building geometry in appendix, pages 57 and 58.
Figure 4: Building geometry
The size of the office room is destined to one person and is thought to create a good natural illumination for the worker. According to Lies Vanhoutteghem and his team [11], the width of the room should be short enough so that the opposite side of the room relatively to the windows area can get as much natural light as possible, contributing to a better distribution of the light inside the O.R. Table 4 shows the dimensions of the different spaces of the building. The windows should be placed as high as possible in the room façade to increase the DA of the room. However, some considerations regarding the functionality of the windows must be taken in consideration, for instance, they should be place so that the user
19 can have access in order to open them, etc. In this project, the size of the windows is changed to create different DA in different scenarios and they are shown in the beginning of each main scenario, as explained in the next chapter.
Building space
Dimensions
Length (m) Width (m) Height (m)
Toilet 3,00 2,70 2,64
Corridors 16,32 2,00 2,64
Stairs 3,00 4,98 2,64
Office room 4,00 2,70 2,64
Meeting room 3,00 2,70 2,64 Table 4: Building spaces dimensions
5.2 - Scenarios description
Daylight availability is categorized in four levels (none, low, medium and strong) according to the EN 16798. For the recreation of these scenarios, the size of the windows in each office room is changed. In this project, only three levels of DA are evaluated: Low, medium and strong, which are represented by the associated daylight factor value in the middle of the room, at a 0,8m work plan above floor (EN 12464). As so, to create a way to compare the different results obtained, there are defined three main scenarios that represent the three levels of DA in the room. To make the research problem slightly more complex, other parameters related to the energy design of the building, are changed. In total, 18 scenarios are presented and they represent a variation on the size of the windows, type of ventilations system and the utilization of shading devices. Figure 5 shows the general plan of variation for one main scenario.
Figure 5: Scenarios and sub-scenarios
Where:
MVent is mechanical ventilation; HVent is Hybrid ventilation;
NVent is Natural ventilation;
Shading designates the utilization of a shading device on the windows. Daylight availability MVent No Shading Shading HVent NVent No Shading Shading
5.2.1 - General specifications of the scenarios
• Primary system
Primary system works with district heating and district cooling processes and it is composed by a chiller and a boiler. The COP of the chiller is 3,1 and the AHS supply temperature is set to 50C. The boiler efficiency is 90% and the water supply temperature is set to 55oC. The chiller and boiler are fictitious and their purpose is to generate energy consumption data. Therefore, their characteristics represent the minimum requirements stated in NZEBD and BR15 [29].
• Heating and cooling units
The heating and cooling units (space units) used in IDA ICE models are a water radiator and a cooling device. The water radiator is placed below the windows (with exception to the scenarios with strong daylight availability, as the window takes all the façade) to compensate the heat loss through the windows. The cooling device is placed on the ceiling to ease the spreading of cold air inside the zone space.
To size the space units, it is calculated the peak demand for cooling and heating. The process consisted in simulate the peak demand for cooling and heating as “ideal cooling and heating”, which is an option of the software. This way the software generates the peak demand to be used in the space units. To ensure that all the needs are fulfilled, the peak demand is multiplicated by a factor of 1,2.
• Windows and frames
There are two different types of glazing in this project. One for the windows and another one for the skylights. The incorporation of a skylight aims to a better light distribution and to increase daylight availability. At the same time, the glare effect must be prevented, so this differentiation is made to avoid or decrease the glare impact that could come from a glazing with high light transmittance properties. The specifications of both glazing types are shown in the table 5:
Glazing type Properties
G U (W/m2K) τ
v
Windows 0,42 0,70 0,75
Skylight 0,32 0,60 0,59
Table 5: Glazing properties
21 • Building envelope
The walls, windows, doors, floors, ground floor, ceilings and roof make part of the building envelope and they are responsible for the most significant loads that affect heating and cooling energy utilization [30]. There are strict requirements for building envelope and they are described in NZEBD as mentioned in Building Class 2020 – nearly-zero energy buildings in Denmark. Table 6 shows the properties of the building envelope that it is chosen in order to meet the desired requirements.
Building envelope Properties
U value (W/m2K) Thickness (m) Internal wall 0,39 0,28 External wall 0,12 0,49 Interior door 1,02 0,12 Entrance door 0,30 0,20 Floor 0,40 0,28 Ceiling 0,40 0,28 Roof 0,12 0,49
Table 6: Building envelope properties
• Thermal bridges
Thermal bridges are parts within the building structure where heat is transferred at a higher rate than through the surrounding envelope area. Figure B – i, shows the value of all thermal bridges in appendix, page 59.
• Ground properties
The ground properties are automatically generated by the software for the specified area of Copenhagen and followed the ISO – 13370.
• Infiltration
The infiltration rates at what the building must be submitted is specified in NZEBD and is set to be 0,5 litters per surface meter square per second [l/m2s] (at 50 Pa over/under pressure).
• Extra energy and energy losses
It is set an average 10 litter of hot water per occupant per day following the specification of the Danish building regulation and it assumed that occupants would only use it during the working hours. The distribution system losses are given in figure 6.
Figure 6: Distribution system losses
• Air handling system
The AHS in the model is composed by the primary system, two coils, filters, humidifiers, one mixing chamber, two fans and a heat recovery device. The primary system is already described in this chapter. One of the coils is used to cool down and the other one to heat the air coming from the outside. The supply fan works at a maximum pressure differential (dPmax) of 600 Pa and the return fan works at a dPmax of 400 Pa and they both have an efficiency of 90%. The heat recovery has an efficiency of 85 %, which is the minimum according to NZEBD.
Figure 7: Air handing unit scheme
Figure 7 represents the AHU scheme. The air is sucked from the outside, passes through the heat recovery, where it suffers a preheating, continues through the coil and ends in a space zone of the building, which can be one of the office rooms, corridors, toilet, living room or stairs. The air space zone supplied temperature is set to always be at 18oC. The value of the supplied temperature was tested in a range of temperatures from 15 to 20oC in order to
23 understands which value is more appropriate for the building characteristics in regard of its energy consumption.
The system aims to use as less energy as possible, so the fans work according to the scheme represented in figure 8.
Figure 8: Fan schedule
There are two different schedules controlling the fans – Normal fan control (NFC) and Night vent operation (NVO). NFC is set for the whole year and says that the fans are operating only on working days (Monday-Friday) and during working hours, which is set to be from 08:00 to 17:00. On weekends, holydays and periods between 17:00 to 08:00, fans do not operate. NVO is set to work from the 1st of May to the 30th of September from Monday to Friday (between 22:00 and 07:00) and it replaces the NFC standard operation only if all the following condition are fulfilled:
- Outdoor temperature is above 16oC;
- Outdoor air temperature is at least 2oC below return air temperature; - Return air is above 26oC.
The implementation of a two schedules control aims to take the maximum advantage possible from the outside environment conditions.
• Set points
Set points used in this project are according BR15
and refer to temperature (20 – 26
oC),
supply air flow (described in each scenario), relative humidity (20 – 80%) and level of
CO
2(0 – 900 ppm).
• Lighting
The lighting system is an auto controlled system that works to fulfilled the needs of the occupants working in the office building. The software measures the illuminance at a 0,80 m work plan above floor (EN 12464). The lighting controllers are set to regulate the artificial light in the building space according to desired illuminance. For instance, when natural light
represents 300 lx of illuminance at the room space, the lighting system provides the remaining 200 lx as artificial light. This system is run by a schedule that works between 08:00 – 17:00 with lunch break from the 12:00 – 13:00 (when the artificial lights are always off). The luminous efficiency of the luminaires is 136 [lm/W], and GE is 70 %. Applying equation (3.2), the total power rated input for lighting is given in table 7.
Building space
Input data
Area (m2) Illuminance (lx) Power (W)
Toilet 8,10 200,00 17,02
Corridors 32,65 100,00 34,30
Stairs 14,93 100,00 15,68
Office rooms 10,80 500,00 56,72
Meeting room 8,10 500,00 42,54 Table 7: Lighting system input data
• Location/climate/wind profile
The building is placed in Copenhagen area, Denmark (55° 40′ 34″ N, 12° 34′ 6″ E). The climate and wind profile are given by the software data base to this specific location.
• Occupants
Each O.R is designed for one person only. Which means that the number of occupants of the building is twelve in total. The occupancy of the building is set to be from the 08:00 to 17:00 with a lunch break between the 12:00 and 13:00. The schedule is only applied for working days (Monday – Friday). The activity level is set to 1,2 MET.
• Primary energy factors
As described in Building Class 2020 – nearly-zero energy buildings in Denmark, the primary energy factors are imposed by the NZEBD
for
building class 2020. Therefore, table 8 displays the values that are used. Thus, it is assumed that all heating and cooling needs are fulfilled using district heating and district cooling, respectively [31].Type of energy supply Primary energy factor
Electricity 1,80
District heating/ cooling 0,60 Table 8: Primary energy factors
25 • Equipment
The power input of the equipment represents one computer and one printer and is set to be 35 W. The equipment is set to work at the same time as the occupant [32], [33].
• Skylight
Skylights are used in O.R, corridor and meeting room of the second floor and it is placed on the roof as shown in figure 9. In Strong DA scenarios, the skylight of the O.R is set to be larger to meet desired DF. The skylight layout used in O.R of Strong DA scenarios, as well as the skylight layout corridor, are shown, respectively, in figure A – iv and figure A - v in appendix, page 58.
Figure 9: Skylight layout on the roof of the office rooms and meeting room
• Reflectance
Table 9 shows the surface reflectance of the objects inside the room.
Surface reflectance Element Reflectance Floor 30% Ceiling 70% Walls 50% Frames 50% Windowsills 50% Table 40% Desktop screen 50% Table 9: Surface reflectance of the objects
0,55 m
1,70 m 3,00 m