Adapting building design to climate change for an office building in Stockholm through solar control techniques

IN

DEGREE PROJECT CIVIL ENGINEERING AND URBAN

MANAGEMENT,

SECOND CYCLE, 30 CREDITS STOCKHOLM SWEDEN 2020 ,

Adapting building design to climate change for an office building in Stockholm through solar control techniques

MATTEO COSTANZO

KTH ROYAL INSTITUTE OF TECHNOLOGY

SCHOOL OF ARCHITECTURE AND THE BUILT ENVIRONMENT

- 1 -

Abstract

Climate change will affect many human activities and sectors. Among those, the built environment will face several challenges with respect to the varying climate conditions.

The present study investigated the global warming impacts on energy demand and indoor climate comfort for an office building in Stockholm. Considering a service life of 50 years, the future climate conditions were investigated for the only air temperature increase in 2070, in accordance with the medium forecasted greenhouse gas emissions scenario provided by the International Panel on Climate Change (IPCC). Another climate morphing approach was adopted to develop the climate file for the year 2080 considering the variation of all the weather parameters. Three different passive cooling solutions, such as external roller shade, electrochromic glazing, and internally ventilated shading, have been implemented in the case study building to decrease the cooling demand. The characteristics of the strategies were preliminarily assessed and then implemented into the building energy simulation software IDA-ICE to evaluate the energy performances with respect to the different climates. The results indicated that an increment of the cooling demand and a reduction of the heating usage will be experienced in the future.

The different morphing approaches displayed the inherent uncertainties when future

evaluations are performed, although similar weather patterns were found. The

improvement of the solar and optical properties, such as the introduction of the exhaust

air extraction and the electrochromic technology, implied a lower cooling and ventilation

usage. The EC technology reported the lowest cooling demand, while the internally

ventilated shading option outperformed the others in terms of annual energy

consumption.

- 2 -

Abstrakt

Klimatförändringar kommer att påverka många mänskliga aktiviteter och sektorer.

Bland dem kommer den byggda miljön att möta flera utmaningar med avseende på de

olika klimatförhållandena. Denna studie undersökte effekterna av den globala

uppvärmningen på energibehovet och inomhusklimatkomforten för en kontorsbyggnad i

Stockholm. Med hänsyn till en livslängd på 50 år undersöktes de framtida

klimatförhållandena för ökningen av lufttemperaturen utomhus till 2070, i enlighet med

det medelprognoserade växthusgasutsläppsscenariot som tillhandahålls av International

Panel on Climate Change (IPCC). En annan klimatförändringsmetod antogs för att

utveckla klimatfilen för år 2080 med tanke på variationen i alla väderparametrar. Tre

olika passiva kyllösningar, såsom utvändigt solskydd (vertikalmarkis med screenväv),

elektrokromt glas och invändigt ventilerat solskydd, har implementerats i

fallstudiebyggnaden för att minska kylbehovet. Karaktären av strategierna utvärderades

preliminärt och implementerades sedan i programvaran för byggenergisimulering IDA-

ICE för att utvärdera energiprestanda med avseende på de olika klimaten. Resultaten

indikerade att en ökning av kylbehovet och en minskning av värmeanvändningen

kommer att ske i framtiden. De olika klimatförändringsmetoderna visade de

inneboende/medföljande osäkerheterna när framtida utvärderingar utförs, även om

liknande vädermönster hittades. De passiva kyllösningarnas reducering av total

solenergitransmission, såsom införandet av frånluftsutsug och den elektrokroma

tekniken, innebar en lägre kyl- och ventilationsanvändning. EC-tekniken rapporterade

det lägsta kylbehovet, medan det invändiga ventilerade solskyddet överträffade de andra

när det gäller årlig energiförbrukning.

- 3 -

Acknowledgements

First of all, I would like to express my deepest appreciation to my supervisor at Politecnico di Milano, Professor Andrea Giovanni Mainini, for his support, help, and continuous guidance throughout the development and finalization of this master thesis research. Without his constant encouragement, supervision, and an endless number of valuable advices the study research would not be what is it now.

I would like to thank my supervisor at KTH, Professor Ivo Martinac, for his cooperation, support, and suggestions, who helped me to work with this topic and accomplish an important task in my academic carrier. My deepest gratitude and appreciation must be expressed as well to my supervisor at WSP, David Parsman, for his supervision, help, and cooperation from the earliest to the final stages of this research. I am extremely thankful to all of them, as they were always present whenever I needed help to accomplish this project.

I would like to express my gratitude to my friends, who supported me through the years in many ways, who did not let me give up and shared with me everlasting memories.

Last but not the least, I am extremely grateful to my parents, who never stopped believing

in me throughout my whole academic life, supported me in all the choices I made that

brought me here today and made countless sacrifices to allow me to follow my own way.

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Table of Contents

LIST OF ABBREVIATIONS ... - 7 -

LIST OF FIGURES ... - 9 -

LIST OF TABLES ... - 11 -

1 INTRODUCTION ... - 13 -

1.1 B

ACKGROUND

... - 13 -

1.2 P

ROBLEM

S

TATEMENT

... - 14 -

1.3 O

BJECTIVES AND RESEARCH QUESTIONS

... - 15 -

1.4 R

ESEARCH

M

ETHODOLOGY

... - 16 -

2 CLIMATE CHANGE ... - 17 -

2.1 I

NTRODUCTION TO CLIMATE CHANGE

... - 17 -

2.2 M

AIN CONSEQUENCES

... - 18 -

2.3 C

LIMATE CHANGE IN

S

WEDEN

... - 21 -

2.3.1 Different Climate Scenarios ... - 22 -

2.3.2 Main Consequences in Sweden ... - 25 -

3 BUILDING SECTOR AND ENERGY REQUIREMENTS ... - 31 -

3.1 B

ACKGROUND

... - 31 -

3.2 E

NERGY

R

EQUIREMENTS IN

S

WEDEN

... - 33 -

3.3 I

NDOOR COMFORT REQUIREMENTS IN

S

WEDEN

(O

FFICES

) ... - 35 -

4 PASSIVE COOLING STRATEGIES (PCSS) ... - 40 -

4.1 I

NTRODUCTION TO THE

PCS

S

... - 41 -

4.1.1 Heat Protection Strategies ... - 42 -

Microclimate and Site ... - 42 -

Solar Control Techniques (SCTs) ... - 43 -

4.1.2 Heat Modulation Strategies ... - 46 -

Thermal Mass ... - 47 -

Phase change materials ... - 48 -

Green Roofs ... - 50 -

4.1.3 Heat Dissipation Strategies ... - 51 -

Natural night ventilation ... - 52 -

Buoyancy-driven stack ventilation ... - 53 -

4.2 S

TUDY CASE TECHNIQUES

... - 55 -

4.2.1 Internally ventilated shading ... - 55 -

- 5 -

4.2.2 Electrochromic glazing ... - 59 -

4.2.3 External roller shades ... - 63 -

5 CASE STUDY ... - 67 -

5.1 S

OLAR

C

ONTROL

T

ECHNIQUES

E

VALUATION

... - 67 -

5.1.1 Materials ... - 67 -

Glazed units ... - 67 -

Shading elements ... - 68 -

5.1.2 Window Properties Calculation ... - 69 -

LBNL Window 7.7 ... - 69 -

WIS (Advanced Window Information System) ... - 70 -

Preliminary assessment – energy balance ... - 70 -

5.2 IDA ICE S

IMULATION

T

OOL

... - 72 -

5.2.1 Daylight Analyses ... - 74 -

5.3 C

ASE

S

TUDY

B

UILDING

... - 75 -

5.3.1 Miljöbyggnad requirements and Input Data ... - 76 -

General and Zones Parameters ... - 78 -

AHU Integration and other systems ... - 82 -

5.4 C

LIMATE

F

ILE

... - 84 -

5.4.1 Alternative Future Climate File ... - 87 -

5.5 L

IFE

-C

YCLE

C

OST

A

NALYSIS

... - 91 -

6 RESULTS ... - 94 -

6.1 B

ACKGROUND

... - 94 -

6.2 S

OLAR

C

ONTROL

T

ECHNIQUES

... - 94 -

6.2.1 Glazing and Shading Definition ... - 94 -

6.2.2 Internal Ventilation Evaluation ... - 95 -

6.2.3 SCT characteristics ... - 99 -

6.2.4 Daylight analyses – Visual Comfort Assessment ... - 101 -

6.3 C

URRENT

C

LIMATE

... - 102 -

6.3.1 Annual Energy demand and Ventilation Needs ... - 103 -

6.3.2 Thermal comfort levels (PPD, Temp, etc) ... - 107 -

6.4 F

UTURE

C

LIMATE

... - 109 -

6.4.1 Annual Energy demand and Ventilation Needs ... - 110 -

Fans usage optimization ... - 112 -

- 6 -

Cooling peaks optimization – cooling room units ... - 113 -

Annual energy demand and ventilation needs for the three techniques ... - 119 -

6.4.2 Thermal comfort levels (PPD, Temp, etc) ... - 122 -

6.4.3 Current and Future climate comparison ... - 124 -

6.5 M

ILJÖBYGGNAD RATING SCALE

... - 126 -

6.6 A

LTERNATIVE FUTURE CLIMATE

... - 128 -

6.7 L

IFE

-C

YCLE

C

OST

A

NALYSIS

... - 133 -

7 DISCUSSIONS ... - 138 -

8 CONCLUSIONS ... - 143 -

9 FUTURE WORK ... - 145 -

10 REFERENCES ... - 147 -

- 7 -

List of Abbreviations

ACH: Air Changes per Hour ACT: Active Cavity Transition AHU: Air Handling Unit AR5: Fifth Assessment Report

ASHRAE: American Society of Heating, Refrigerating and Air-Conditioning Engineers A

temp

: Enclosed area by the building envelope for temperature-controlled spaces heated

to more than 10 ºC, including the area occupied by internal walls.

BBR: Boverket’s Building Rules

BFS: Boverkets författningssamling (Boverket’s Constitutional Collection) BPS: Building Performance Simulation

CAV: Constant Air Volume

COP21: 21

^st

Conference of the Parties DA: Daylight Autonomy

DC: Direct Current DF: Daylight Factor DGI: Daylight Glare Index DHW: Domestic Hot Water DTM: Dynamic Thermal Model EC: Electrochromic

EPBD: Energy Performance of Buildings Directive EP

pet

: Building’s Primary Energy

ESM: Earth System Model

FFLP: Fraction of Full Load Power g-value: Solar Heat Gain Coefficient GHG: Greenhouse gas

HVAC: Heating, Ventilation and Air Conditioning HX: Heat Exchanger

IDA-ICE: IDA Indoor Climate and Energy I

dir,norm

: Solar Direct Normal Irradiation

I

diff,hor

: Solar Diffuse Irradiation on the Horizontal plane IEA: International Energy Agency

IGDB: International Glazing Database

IPCC: International Panel on Climate Change LAI: Leaf Area Index

NASA: National Aeronautics and Space Administration NOAA: National Oceanic and Atmospheric Administration PC: Photochromic

PCMs: Phase Change Materials PCS: Passive Cooling Strategy

PDLC: Polymer Dispersed Liquid Crystal

PE: Primary Energy Factor

- 8 - PEC: Photo-Electrochromic

PHAS: Public Health Authority of Sweden PLR: Part Load Flow Ratio

PMV: Predicted Mean Vote

PPD: Predicted Percentage of Dissatisfied PVB: Polyvinyl Butyral

PVC: Polyvinyl Chloride Q

HT

: Sum of Heat Transfers Q

int

: Internal Heat Gains Q

load

: Heat Loads

Q

sol

: Solar Heat Gains

Q

v,cool

: Ventilation Heat Transfer Q

v,extr

: Extraction Heat Transfer Q

v,leak

: Leakages Heat Transfer Q

tr

: Transmission Heat Transfer

RCP: Representative Concentration Pathway RF: Radiative Forcing

RH: Relative Humidity SFP: Specific Fan Power SCT: Solar Control Technique SD: Shading Device

SMHI: Swedish Meteorological and Hydrological Institute Sveby: Standardize and Verify Energy Performance in Buildings SWEA: Swedish Work Environment Authority

TC: Thermochromic T

air

: Air Temperature T

sol

: Solar Transmittance T

sup

: Supply Air Temperature T

vis

: Visible Transmittance U-value: Thermal Transmittance

U

f

: Window Frame Thermal Transmittance U

g

: Window Glazing Thermal Transmittance UDI: Useful Daylight Illuminance

UHI: Urban Heat Island

UNDP: United Nation Development Programme

UNFCCC: United Nations Framework Convention on Climate Change VAV: Variable Air Volume

WIS: Window Information System

WWR: Window-to-Wall-Ratio

Ψ

g

: Linear Thermal Bridge Value

L

Ψ

: Linear Thermal Bridge Length

- 9 -

List of Figures

Figure 1 – Global average annual surface temperature increase from 1880 to 2019 ... - 19 -

Figure 2 - Total annual anthropogenic greenhouse gas (GHG) emissions for the period 1970 to 2010 by gases ... - 19 -

Figure 3 - Global sea level increase from 1880 ... - 20 -

Figure 4 - Energy accumulation within the Earth’s climate system between 1970 and 2010 ... - 21 -

Figure 5 - GHG emission pathways 2000-2100 for all AR5 scenarios ... - 25 -

Figure 6 - Estimated change in annual average air temperature in Stockholm county compared to mean value from period 1961-1990 [RCP4.5] ... - 26 -

Figure 7 - Estimated change in winter average air temperature in Stockholm county compared to mean value from period 1961-1990 [RCP4.5] ... - 26 -

Figure 8 - Estimated change in summer average air temperature in Stockholm county compared to mean value from period 1961-1990 [RCP4.5] ... - 27 -

Figure 9 - Average annual rainfalls in Sweden between 1860 and 2018 ... - 27 -

Figure 10 - Annual maximum ice content in the Baltic Sea and Kattegat regions between 1957 and 2019 ... - 29 -

Figure 11 - Sea level rise in Sweden between 1886 and 2018 ... - 29 -

Figure 12 - Calculated change in annual maximum wind gust (m/s) for the period 2071-2100... - 30 -

Figure 13 - Swedish energy consumption by sector in 2017 ... - 31 -

Figure 14 - Energy consumption by sector for commercial buildings in Europe ... - 32 -

Figure 15 - PPD as a function of PMV, Source ... - 36 -

Figure 16 - Classification of PCMs ... - 49 -

Figure 17 - Operative modes of solar chimneys ... - 54 -

Figure 18 - (a) Typical ACT façade operational mode; (b) ACT façade implemented in Fest AutomationCenter building ... - 58 -

Figure 19 - ACT façade schematic design ... - 59 -

Figure 20 - Generic electrochromic device design ... - 59 -

Figure 21 - 3D representation of the building model and surrounding ... - 74 -

Figure 22 - Typical floor layout ... - 76 -

Figure 23 - IDA-ICE Deck for the Zone parameters management. ... - 82 -

Figure 24 – IDA-ICE deck for AHU settings and ventilation element definition. ... - 84 -

Figure 25 - Outdoor air temperature for the current climate in Stockholm ... - 85 -

Figure 26 - Estimated change of mean temperatures in Stockholm for the year 2070, Scenarios RCP 4.5 ... - 86 -

Figure 27 – Current outdoor air temperature (red line) and future outdoor air temperature in Stockholm for the year 2070 (blue line) ... - 87 -

Figure 28 - Outdoor air temperature for the current climate given by Sveby-SMHI and IWEC file .... - 88 -

Figure 29 - Outdoor air temperature for the future climate file year 2070 and 2080... - 89 -

Figure 30 - Solar Radiation (Direct Normal) in the future climate files for the year 2070 and 2080 .... - 90 -

Figure 31 - g-value results with respect to the airflow rate analysed, Source: WIS calculations ... - 97 -

Figure 32 - Window Scheme ... - 99 -

- 10 -

Figure 33 – DF Graphical representation over office 5 daylight measuring plane ... - 101 -

Figure 34 - IDA-ICE deck for the EC glazing control macro for tint state switching ... - 103 -

Figure 35 - Graphical representation of the heating and cooling needs in the current climate ... - 106 -

Figure 36 - Indoor air and operative temperature for the worst room ... - 108 -

Figure 37 – Annual cooling consumption in the future climate for the standard solution ... - 111 -

Figure 38 – Annual heating consumption in the future climate for the standard solution ... - 111 -

Figure 39 - Building supply airflow in the future climate for the standard solution ... - 112 -

Figure 40 - Fan usage curve for variable fan speed systems ... - 113 -

Figure 41 - Cooling consumption for the 4th week of July in the future climate ... - 114 -

Figure 42 - Outdoor air temperature for the 4th week of July in the future climate ... - 114 -

Figure 43 - AHU temperatures in the 4th week of July for the future climate ... - 115 -

Figure 44 - Relative Humidity for the 4th week of July in the future climate ... - 116 -

Figure 45 - Psychrometric chart ... - 116 -

Figure 46 - Annual cooling consumption in the future climate, comparison with and without room units ... - 117 -

Figure 47 - Cooling consumption for the 4

^th

week of July in the future climate, comparison with and without room units ... - 118 -

Figure 48 - Building supply airflow in the future climate, comparison with and without room units ... - 118 -

Figure 49 - Annual cooling consumption in the future climate, comparison External shading and EC glazing ... - 120 -

Figure 50 - Annual cooling consumption in the future climate, comparison External shading and Internal Shading ... - 120 -

Figure 51 - Building supply airflow in the future climate, comparison External shading and EC glazing ... - 121 -

Figure 52 - Building supply airflow in the future climate, comparison External shading and Internal Shading ... - 121 -

Figure 53 - Indoor air and operative temperature for the worst room ... - 123 -

Figure 54 - Graphical representation of the heating and cooling needs in the current (C) and future (F) climates ... - 124 -

Figure 55 - Maximum building supply airflow, comparison of the solutions for the current (C) and future (F) climate ... - 125 -

Figure 56 - Annual cooling consumption, comparison year 2070 and 2080 ... - 129 -

Figure 57 - Annual heating consumption, comparison 2070 and 2080 ... - 129 -

Figure 58 - Indoor air and operative temperature for the worst room ... - 132 -

Figure 59 - Graphical representation of all the present values and resulting LCC ... - 137 -

- 11 -

List of Tables

Table 1 – RCP Scenarios descriptions ... - 24 -

Table 2 - Projected change in global mean surface temperature and global mean sea level rise for the mid- and late 21st century, relative to the 1986–2005 ... - 25 -

Table 3 - Maximum permitted primary energy and average heat transfer coefficient for different types of buildings ... - 34 -

Table 4 - Primary energy factors in BBR 28 and BBR 29... - 35 -

Table 5 - Different energy performance and U-value values in BBR 28 and BBR 29 ... - 35 -

Table 6 - Thermal sensation scale corresponding to indoor climate conditions perceptions by users ... - 36 -

Table 7 - Operative temperature requirements by the SWEA and EN 7730 ... - 38 -

Table 8 - Solar control glasses performances ... - 68 -

Table 9 - Screen Fabrics Properties ... - 69 -

Table 10 - Reflectance values for daylight analyses ... - 75 -

Table 11 - Energy and Comfort Indicators ... - 77 -

Table 12 - Construction Parameters ... - 78 -

Table 13 - Internal Gains Input data ... - 79 -

Table 14 - Metabolic Rates for Typical Tasks ... - 79 -

Table 15 - Clothing Insulation Values for Typical Ensembles ... - 80 -

Table 16 - Zone Setpoints ... - 81 -

Table 17 - AHU and other systems settings ... - 83 -

Table 18 - Window and shading elements initial investment costs ... - 91 -

Table 19 - Exhaust air ventilation elements costs... - 91 -

Table 20 – Estimated service life proposal for each window system element based on the literature .. - 92 -

Table 21 – Maintenance operations and costs proposal for each window system element based on the literature ... - 93 -

Table 22 - Energy prices and other economic input data for LCC analysis ... - 93 -

Table 23 - Optical and thermal properties of the three window systems ... - 95 -

Table 24 – Extraction input data of the study cases by (Denz, et al., 2018) and (Gustafsson & Säfblad, 2014)... - 95 -

Table 25 – Thermal and optical properties for the ventilated solution ... - 96 -

Table 26 - Window Properties ... - 97 -

Table 27 - Environmental Conditions and Input Data for energy balance ... - 98 -

Table 28 - Energy Balance Results for the summer period ... - 99 -

Table 29 - Dimensional and thermal properties of the three window systems ... - 100 -

Table 30 - Optical and thermal properties of the three window systems ... - 100 -

Table 31 - Mean and Punctual DF values for the three solutions ... - 101 -

Table 32 - Window systems control signals for the current climate ... - 102 -

Table 33 - Annual energy consumption for the standard case in the current climate ... - 104 -

Table 34 - Annual building energy consumption in the current climate ... - 105 -

Table 35 - Ventilation results for the current climate ... - 106 -

- 12 -

Table 36 - Thermal comfort levels for annual simulations in the current climate during the

summer period ... - 107 -

Table 37 - Thermal comfort levels for annual simulations in the current climate during the winter period ... - 107 -

Table 38 - Window systems control signals for the future climate ... - 109 -

Table 39 - Annual building energy consumption for the standard case, future climate, without fans curve and cooling room units ... - 110 -

Table 40 - Energy usage, the standard case for the future climate with fans optimization ... - 113 -

Table 41 - Building annual energy consumption for the standard technique in the future climate, with fans curve and room units ... - 117 -

Table 42 - Annual building energy consumption in the future climate ... - 119 -

Table 43 - Ventilation results for the future climate ... - 122 -

Table 44 - Thermal comfort levels for annual simulations in the future climate during the summer period ... - 122 -

Table 45 - Thermal comfort levels for annual simulations in the future climate during the winter period ... - 123 -

Table 46 - Miljöbyggnad ranking for the results with the current climate file ... - 126 -

Table 47 - Miljöbyggnad ranking for the results with the future climate file (year 2070) ... - 126 -

Table 48 - Annual energy consumption years 2070 and 2080 for the external shading ... - 128 -

Table 49 - Annual energy consumption years 2070 and 2080 for the EC glazing ... - 130 -

Table 50 - Annual energy consumption years 2070 and 2080 for the internal shading ... - 130 -

Table 51 - Thermal comfort levels for annual simulations in the alternative future climate during the summer period ... - 131 -

Table 52 - Thermal comfort levels for annual simulations in the alternative future climate during the winter period ... - 131 -

Table 53 - Initial Investment - Material and installation costs for extraction system ... - 133 -

Table 54 - Initial investment – Total material and installation costs for each window system ... - 134 -

Table 55 – Annual operational costs and relative present value ... - 134 -

Table 56 - Annual maintenance costs and expected service life for each window system element .... - 135 -

Table 57 - Maintenance and Renovation annual costs and relative present value ... - 136 -

Table 58 - LCC results ... - 136 -

Table 59 - Building’s total primary energy (EP

pet

) for each solution in the different climates ... - 139 -

- 13 -

1 Introduction

1.1 Background

World population is constantly increasing, and with it also its needs, consumptions, and emissions. In 2020 it has reached 7.519 billion, with a parallel growth in industrial, infrastructure, and construction sectors (IEA, 2020). Among all the human activities, the industrial and building sectors represent the main responsible for the rise in electric energy demand and greenhouse gasses (GHG) emissions. The increase of the energy- related CO

2

emissions from buildings was detected all over the globe, achieving 10Gt in 2019 (IEA, 2020). In the European Union (EU), researches and analyses about energy consumption and GHGs emissions reported how the built environment was responsible in 2018 for approximately 40% of the energy consumption and 36% of all the CO

2

emissions in the EU countries (European Commission, 2019). In addition to the latter trend, which is expected to increase, even more, 35% of the whole European building stock resulted to be older than 50 years, and about 75% was found to be energy inefficient.

In the actual building stock, both residential and non-residential buildings are contributing to increase the energy demand and the consequent environmental footprint.

Space heating, cooling, ventilation, and lighting, among all the energy carriers in buildings, resulted to be the major cause of the continuous increase of energy usage by the built environment (GlobalABC, et al., 2019). In 2018 a record increase of 8% in the space cooling energy consumption brought the latter to become the fastest-growing energy carrier in buildings in the 21

^st

century. Therefore, it results clear the severity of the situation and the necessity of taking appropriate actions to reduce the increase in energy consumption and decrease the related environmental impact. Government, engineers, and environmental associations are already working for years on policies and actions to reverse such a trend. Renovation of the existing building stock, initiatives for sustainable buildings, and innovations to improve the building performances and reduce the GHGs emissions are part of the change to prevent a worsening of the actual condition.

Buildings are usually designed and constructed to provide a service life of 50 years.

Consequently, it is of vital importance to analyse and study the building behaviour and response to possible different climatic conditions. The increase of GHGs emissions and the related global warming address in these terms new challenges to the building sector.

The ongoing climate change, with all its consequences on the built environment and

human life, does not allow anymore to design and think about the building in relation to

what the weather has been so far. Therefore, it emerges how important is nowadays an

appropriate evaluation of the building response to the climate change together with the

possible variation of the energy consumption and the consequent adaptation of the

building system to the new conditions. Climate change will affect building design in

different ways (Gethig, 2010). First of all, effects on the indoor thermal comfort and

energy performance of the building, due to the increase of the outdoor air temperature

will occur. In addition, the intensification of extreme conditions will affect the building

materials choice, while effects on water management could cause an increase in flooding

or shortages events.

- 14 -

About the increase of the air temperature, the built environment will face the major challenge adapting to a changing climate. The ongoing increase of space cooling demand to provide sufficient indoor climate conditions it is not expected to decrease unless the emissions and energy consumptions will undergo an effective reduction. Several studies reported how the increase of temperatures and its extent is bonded with many environmental and non-environmental factors, indicating the urban texture as the more prompt to be affected. (Satamouris, 2014) analysed the global warming effect in association with the urban heat island (UHI) effect. Evaluation of the energy impact of the UHI to buildings showed an average cooling load increment of 13% respect to the similar buildings in the adjacent rural area. Thermal comfort and energy usage have been also studied by (Baba & Ge, 2018) for a high-rise commercial building in the Canadian cold climate concerning the climate change issue. The analyses showed an increment of the cooling consumption by 50% respect to the historical weather data. The outdoor air temperature increments also brought an increase in the overheating risks, with twice the number of overheated hours in 2080. On the other hand, the heating demand was reduced, for a total annual demand reduced by 5% respect to the historical analysis.

Therefore, vital importance must be regarded to techniques and design solutions enable to decrease the cooling demand of the buildings and contribute to the indoor thermal comfort. The European Parliament, with the publication of the new Directives on Energy Performance of Buildings (EPBD) in 2010, initiated an important change for energy efficiency and adaptation concept in the building design (EU Commission and Parliament, 2010). The adaptation of the building to a changing climate became a crucial aspect of the design process, with the support and integration of new passive strategies.

The latter solutions are indeed capable of taking advantage of natural and renewable resources to reduce the building energy usage, without impacting on the environment. In this research, some of these technologies will be investigated, with respect to a future climate affected by climate change variations. The assessment of the potential benefits in terms of energy consumption and their extent will be evaluated together with the effect on the indoor thermal comfort of the building.

1.2 Problem Statement

As mentioned before, the building energy needs will undergo a variation in the following years and decades. Global warming and UHI effect will modify the climatic conditions all around the globe, with a series of possible consequences in terms of energy demand and indoor comfort. The winter seasons will be characterized by shorter cold periods, with a higher average minimum temperature, while the summertime will present higher temperatures and the intensification of extreme hot periods. Therefore, building energy behaviour will be modified. The heating consumption is expected to decrease while the cooling and ventilation needs are likely to increase. The changing of the boundary conditions and needs in terms of heating/cooling energy delivered will affect the building systems, with consequences both on the indoor comfort and the overall emissions.

Consequently, countries historically characterized by a predominant cold season and low

needs in terms of space cooling will be, for example, forced to implement new systems

- 15 -

to overcome the hotter summer periods. Furthermore, the raise of the outdoor and indoor air temperatures also addresses a series of problems regarding human health. High temperatures could lead to deaths related to strokes, myocardial infarction, and pulmonary disorders, with an elevated risk for elderly people.

The actual design practice takes into consideration temperatures and climate data based on average historical survey values up to 30 years old statistics, considering climatic conditions that most probably will not occur anymore. Therefore, a new approach which considers the actual and the future climatic condition could be considered to analyse the possible changes and design in a more adaptive way. Additionally, new technologies and design approaches need to be considered to decrease the cooling energy demand. The concept of passive strategies, already present in the construction sector, is gaining popularity and relevance among the scientific society. The introduction of appropriate passive cooling solutions decreases the energy demand for the cooling season and ventilation needs without consuming energy or with low energy usage.

1.3 Objectives and research questions

In this research, the impact of climate change on an office building of new construction in the region of Stockholm (Sweden) will be studied. The variation of energy demand and comfort conditions will be analysed for the current and future climate conditions. In relation to the current climate, a typical year in accordance with the usual design practice will be considered, while for the future climate two morphed files will be analysed concerning the global warming changes. The office building under investigation will be equipped with different passive cooling strategies to decrease the cooling demand and ventilation needs for future climates. The strategies will focus on the reduction of solar thermal loads (solar thermal control techniques) to decrease the cooling loads on the building systems. Purpose of this research will be to evaluate the effectiveness and the best-suited design in the cold climate of Stockholm. To fulfil these aims, a computational study will be carried out with respect to the building energy consumption and indoor thermal comfort for the case study building. The properties of the different strategies will be preliminary calculated and analysed with the support of software (LBNL Window 7.7 and WIS) and hand calculations, while the building energy simulations will be carried out through the energy simulation software IDA-ICE. The calculation process results will be used to answer the following research questions:

- To what extent will climate change affect building energy consumption and indoor climate comfort in 50 years?

- How will the passive cooling strategies under investigation perform with respect to the current and future climate condition? To what extent will they reduce the cooling demand?

- How will a different approach and calculation process affect the building energy

demand?

- 16 - 1.4 Research Methodology

In this research study, an extensive literature review and a case study are the research methods followed to answer the previously described research questions. Among all the methods, the literature review has been selected to analyse the impact of climate change on buildings, the actual requirements in terms of energy and comfort, and the current state of the scientific literature about the passive cooling solutions and their use in buildings.

Subsequently, a case study has been selected to perform detailed calculations on the building energy usage and indoor climate comfort with respect to different climate conditions.

The literature review initially considers an in-depth report regarding climate change impacts. The definition of climate change and its general features will be captured to provide detailed knowledge about the phenomenon. Related scientific articles and publications will be analysed to assess the framework of the future climate around the globe and more in detail in Sweden, where the case study building will operate.

Additionally, building energy and indoor comfort requirements will be examined. The focus of the examination will be settled on the Swedish national requirements to evaluate the minimum required performance for new construction buildings and how these could evolve. Finally, the literature review will take into consideration extensive research on passive cooling strategies. The design concept will be explained and then descriptions of the different categories and solutions with the related results will be reported from scientific articles and journals.

The case study will consider an office building recently built in the urban area of

Stockholm. The building model will be used to perform building energy simulations with

respect to the current and future climate of Stockholm. The results will also provide

information regarding the indoor climate and occupant satisfaction. Analyses between the

two climate conditions and the different implemented passive cooling strategies will be

done to assess the energy usage and indoor comfort variations. Therefore, the climate

change impact on the building, with respect to separate design configurations, will be

calculated through the building simulations results. Finally, a simplified life-cycle cost

analysis will be performed to assess the potential economic benefits of the three options

over the 50 years building lifespan.

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2 Climate Change

2.1 Introduction to climate change

Mankind has altered the Earth for millennia but only in the last century, the effects of human actions have become visible and alarming on a global scale. Nowadays, the existence and fast progress of a worldwide climate change are evident with several environmental alterations, such as changes in ice cover, sea level, ecosystems, and extreme events. Since the second half of the 20

^th

century, the issue of climate change acquired a high level of attention in political, economic, ethical, and social matters around the world. The International Panel on Climate Change (IPCC), releasing its first assessment report about climate change in 1990, reported the risks of profound changes in the Earth system given by the increase in greenhouse gas (GHG) emissions. Later, IPCC defined the climate change as: “A change in the state of the climate that can be identified (e.g., by using statistical tests) by changes in the mean and/or the variability of its properties and that persists for an extended period, typically decades or longer.

Climate change may be due to natural internal processes or external forcings such as modulations of the solar cycles, volcanic eruptions and persistent anthropogenic changes in the composition of the atmosphere or in land use.” (IPCC, 2014). The latter definition differs from the one given by the United Nations Framework Convention on Climate Change (UNFCCC) in 1992 where climate change is addressed in Article 1 as: “A change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods.” (United Nations, 1992). The United Nations underlines a difference between impacts on the Earth system which can be related to human actions and climate variability given by natural causes, that is not present in the IPCC report. Independently from which definition is chosen, the focus remains on the effects and changes on the global environment for which human actions have been scientifically proven to be a leading factor.

Several political, governmental, and scientific programs have been established since the

first identification of the problem to mitigate climate change. In 1997 the first important

action to reduce GHG emissions and the progressive worsening of the environmental

conditions is represented by the Kyoto Protocol. Entered in force in 2005 and shared

nowadays by 192 parties, this protocol is an international agreement related to the

UNFCCC ratified in 1992 which forces the members to limit and reduce the GHG

emissions with agreed individual targets. It especially commits the industrialized

developed countries among the others because they are recognized as largely responsible

for the excessive levels of GHGs in the atmosphere. Recently, another and more severe

agreement was signed during the 21

^st

Conference of the Parties (COP21) in Paris, in

December 2015. The so-called Paris Agreement formed its bases on the UNFCCC report

and for the first time united the signing members to put ambitious efforts to combat

climate change and adapt to its effects. Its principal intent is to improve the worldwide

response to climate change by limiting the global temperature rise of this century well

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below 2°C respect to the pre-industrial temperatures. In accordance with this temperature goal, the Agreement underlines a global aim regarding adaptation meant as enhance adaptive capacity, improve resilience, and reduce vulnerability to climate change.

Subsequently to these international agreements, several new national and regional policies have been established and implemented in countries all over the world. Sweden is working on the mitigation of climate change and adaptation to the new environmental adversities for several years. In 2007, the Swedish Commission on Climate and Vulnerability delivered a final report entitled “Sweden facing climate change – threats and opportunities” in which global and national climatic conditions, changes, and vulnerabilities have been assessed. The report connects to the UNFCCC and introduces a carbon dioxide tax policy. Governmental, environmental, and economic analyses were reported together with numerous proposals to better control the environmental changes and to mitigate them. In parallel, the Swedish National Board of Housing, Building and Planning (Boverket) has been working to set and update environmental goals for the built environment.

Therefore, it is evident a worldwide interest regarding these climatic issues with shared actions with the common aim of decreasing the emissions for a mitigation of the climate change. The latter, if not stop from a progressive worsening, will affect the global population on a social, economic, health and environmental scale with possibly dramatic consequences. Adaptation and reduction in vulnerability to the changing and extreme weather conditions remarked in the Paris Agreement, such as the increase of temperature, sea level, and precipitation result to be key points in the challenge against climate change.

Collaboration and in-depth research in many disciplines and sectors, such as the built environment, are required and needful for this purpose.

2.2 Main consequences

Climate change has several consequences on the natural environment and weather

conditions, like average temperature increase, intense precipitations, and sea-level

increase (in connection with sea-ice cycle) among the others. The global rise of average

temperature is the foremost and most detectable aspect which many other effects are

connected to. Measurements of the global mean surface temperature proved an almost

linear increase since the late 19

^th

century, with calculated warming of 0.85°C (0.65 to

1.06°C) over the period 1880-2012 (IPCC, 2013). The last three decades showed a

successive and progressive increase of the temperature higher than any other previously

recorded, escalading with the warmest decade at the beginning of the 21

^st

century. Recent

data showed a further increment over the second decade. Seven years of the decade 2010-

2019 appear in the top ten warmest years since 1880 where 2016 and 2019 showed the

highest average temperature increase of 0.99 and 0.94°C respectively (NOAA, 2020) as

shown in Figure 1.

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Figure 1 – Global average annual surface temperature increase from 1880 to 2019, Source: (NOAA, 2020)

This increase of the Earth surface temperature can be related both to human activities and natural causes, such as the amount of solar energy, and it is directly connected to the expansion of the “greenhouse effect” (NASA, 2020). The latter is a result of the increase of trapped heat into the atmosphere instead of being radiated towards the outer space. The reduction in the radiative potentials of the Earth is due to the increase of certain gases concentrations in the atmosphere, such as water vapour, nitrous oxide, methane, and carbon dioxide. The first one is defined as a “feedback” gas respect to climate change because of its physical and chemical response to the increase of temperature. It increases its concentration with the warming of the Earth surface and atmosphere, increasing the presence of clouds and the precipitations. The other three gases are treated as “forcing”

climate change because the increment of their presence in the atmosphere reduces the radiative abilities of the planet and thus increment the so-called “greenhouse effect”.

Those gases can be both produced by human activities and natural causes, like respiration, volcano eruptions, deforestation, burning fossil fuels, soil cultivation practices, and biomass burning among the others. In the Fifth Assessment Report by IPCC, it was concluded that the human actions since the beginning of the industrial era are the major responsible for the increment of the “greenhouse effect” and the subsequent climate change with a probability higher than 95%.

Figure 2 - Total annual anthropogenic greenhouse gas (GHG) emissions for the period 1970 to 2010 by gases: CO2

from fossil fuel combustion and industrial processes; CO2 from Forestry and Other Land Use (FOLU); methane (CH4); nitrous oxide (N2O); fluorinated gases covered under the Kyoto Protocol (F-gases); Source: (IPCC, 2014)

- 20 -

In Figure 2 it is possible to observe the increase of the aforementioned gases since 1970 in connection to fossil fuel combustion, industrial processes, deforestation, land usage, and other human activities. The greatest contribution of human processes is given by the release of carbon dioxide. Its emissions due to fossil fuel combustion and industrial processes resulted to contribute to the increase of the GHG emissions by 78% only between 1970 and 2010.

Consequently, the increase in temperature affects indirectly another important natural process like evaporation and precipitation. As mentioned before the change in the surface and atmospheric temperature relates to a higher amount of water vapour concentration which leads to an increment of the precipitations. In this case, the analysis and prediction of the phenomenon it is not easy as with the temperature, but it has been statistically proven that annual global precipitation has increased since 1900. The modification of the rainfall cycle also induced the increment of the short and extreme episodes all around the globe.

The warming of the Earth surface and atmosphere also prompted the alteration of the sea- ice cycle and the increase of the sea level on a global scale. Since the beginning of the 20

^th

century, it has been observed a sea-level rise rate higher than the two previous millennia, with an increase up to 0.19 m (0.17 to 0.21 m) between 1900 and 2010, as can be seen also in Figure 3 (IPCC, 2014).

Figure 3 - Global sea level increase from 1880, Source: (NASA, 2020)

The thermal alterations of the planet affect the level of the oceans because they are the

biggest heat sink absorbing around 90% of the atmospheric heat (see Figure 4). The

increase of this heat associated with emission given by human activities thus brought to

two main processes: thermal expansion and melting of the ices. In the first case, the ocean

water expands and increases the sea level absorbing and storing the heat in excess. In

parallel, the higher temperatures induce the melting of ices, such as glaciers and ice

sheets.

- 21 -

Figure 4 - Energy accumulation within the Earth’s climate system between 1970 and 2010, Source: (IPCC, 2014)

2.3 Climate change in Sweden

Effects and consequences of the ongoing climate change are already visible nowadays in the natural environment and human society. As stated before, it is certain that changes in the weather and natural processes will continue to affect us with increasing force over the next decades. However, the impacts of global climate change are expected to have different results and consequences on a local scale. The pre-existent environmental, morphological, and social conditions will bring to different evolution and outcomes regarding the changes in the climate conditions for each specific geographical location.

Sweden is a Scandinavian country located in Northern Europe characterized by a

differentiated climate between south-north and coastal-inland areas. Köppen

classification identifies the south and coastal areas with a warm temperate and humid

climate (Cfb), the central and eastern part as continental with warm summers (Dfb) and

the northern regions with a continental subarctic climate (Dfc). Swedish climate is

relatively mild during the winter in relation to its northerly latitude because of a

significant maritime influence given by its proximity to the North Atlantic, the Baltic Sea,

and the prevalent south-western to western wind (SOU, 2007). The predominant winds

across the country introduce relatively warm and moist air that, together with the

commonly present low-pressure areas and weather fronts, move in line with the North

Atlantic Polar Front. The unstable low-pressure areas induce changeable weather

conditions and make the climate rich in precipitation all over the year. Most of the

- 22 -

country, under cold temperate/continental and subarctic climate, is usually covered by snow during the winter period. The western-coastal area is the richest in precipitation due to its close connection to the ocean, while the southern part can suffer from long periods of dry weather when the low-pressure areas are pushed away from high-pressure fronts coming from the south. In relation to these high-pressure areas, a small portion of the southern region is characterized by a semi-arid climate where the amount of precipitation is equalized by the evapotranspiration. Consequently, climate changes are strictly related to the location of the city or area within the Swedish country, with the possibility of the complex and different evolution of the weather and environmental conditions like surface temperatures, sea level, and precipitation.

2.3.1 Different Climate Scenarios

The severity of the consequences due to climate change underlines the need for intervention on the environment and human activities. As mentioned before, the ongoing changes will greatly affect human health, natural environment, biodiversity, economy, and human society. It is possible to detect and collect data about the changes that occurred in the past and calculate trends for the climatic conditions of the planet. On the other hand, the intrinsic nature of climate changes is denoted by the continuous variation of the processes, substance concentrations, and nature and human reactions to those. Therefore, it is more complex to estimate and develop trend for future changes in the climatic conditions, always containing a certain amount of uncertainty due to mainly three causes:

- Variation in natural processes. In the previous chapter and in accordance with the UNFCCC definition of climate change, the climate can change and adapt to the variation of natural processes. These processes can be divided into internal and external. In the first case, natural entities, and processes inside the atmosphere deviate from their previous behaviour, such as the interaction between oceans and atmosphere or volcano eruptions. Conversely, natural external processes are related to the interaction of the Earth with outer corps and processes, such as changes in receiving solar energy due to variation of the orbit.

- Limited knowledge about Earth system processes. Understanding of terrestrial processes results still now quite complex and full of uncertainties. The lack of a complete comprehension is thus reflected in the approximated and incomplete representation of the processes when they are reproduced on climate models.

- Variation in future GHG emissions and other air pollutants concentrations. As mentioned before, the emissions are mainly related to human activities and thus, completely dependent on the factors managing those activities. The level of industrialization, the increment in the global population, the development of economy and technology and the implementation of dedicated policies characterize considerably the amount of GHG emissions and their future trends.

Therefore, the human actions from now on will determine the rate of increase in

GHG emissions and pollutant concentrations as well as the climate response to

that, resulting in a difficult issue of prediction based on probabilistic assumptions.

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Since it is not possible to forecast or predict with reasonable certainty the climate variation due to external natural processes, only the internal one can be considered for the future GHG and air pollutants concentration to predict the climate response. GHG emissions, as mentioned above, need to be evaluated in relation to variation in human society with the input related scenarios. Socio-economic scenarios are indeed implemented in climate studies to obtain predictions on how the future emissions may be in relation to a range of variables such as socio-economic change, technological development, energy and land use, and climate policies implementation. The resulting data from studies about these possible climate future developments will be included in the climate models used in this master thesis.

In the climate research area, the International Panel on Climate Change has developed, for several years, detailed procedures, models, and sets of scenarios to facilitate the future assessment of climate change. In 1990 the IPCC published in the First Assessment Report (AR1) a new approach to climate change scenarios developed with the name of SA90.

Over the years different approaches have been explored and published until the final release in 2013 with the Fifth Assessment Report (AR5) of a new procedure using future emission models to forecast the impact of GHG emissions on climate change. There are four emission models defined as “Representative Concentration Pathways” (RCPs) which provide information on possible development trends for the main forcing agents of climate change. They are named after the level of radiative forcing (RF) reached in 2100, where RF is meant as the additional energy absorbed by the Earth system in relation to the increase of the “greenhouse effect”, expressed in Watts per square meter (W/m

²

). It can further be identified as the balance between the energy entering the atmosphere and the amount leaving towards the outer space in comparison with the pre-industrial levels.

The total RF is governed by both positive forcings from GHG and a negative one from aerosols, where CO

2

has the dominant effect and an increment of RF reflects a global temperature increase. RCPs are time and space dependant trends of GHG and air pollutants concentrations due to human actions with the possibility to provide quantitative data about these pollutants over time. The name of these models reflects two important features. They are “representative” because they are meant to represent a large set of scenarios available in the literature, both with and without active climate policy. On the other hand, the choice of “concentration pathways” underlines the intrinsic feature of being consistent sets of projections of the RF governing factors, where the concentrations are the main output which can be used as input to climatic models.

The four pathways are respectively named RCP2.6, RCP4.5, RCP6.0, and RCP8.5, where

the number corresponds to the RF value achieved in 2100, as mentioned before. For

example, the RCP4.5 represents the emission model where the concentration of GHG

reached in 2100 will generate an RF equal to 4.5 W/m

²

, compared to the pre-industrial

level. The GHG concentration in the atmosphere increases in the range between 720 and

580 carbon dioxide equivalents in 2100. Together with these emission data, useful to

assess the future effect on a global and local climate, these models also include economic,

demographic, energy, and climate policy considerations which directly and indirectly

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affect the future emissions. In Table 1 follows brief descriptions of the four scenarios provided by IPCC in the AR5.

RCP2.6

RCP4.5

CO2 emissions increase by 2020

CO

2

emissions increase by 2040

- More powerful climate policies - Low energy intensity

- Oil usage reduction

- Population increases to 9 billion - No significant change in the area of

pasture

- CH

4

emissions reduced by 40%

- CO

2

emissions culminate in 2020, negative in 2100

- The CO

2

content in the atmosphere culminates around 2050, then

moderate decrease to circa 400ppm in 2100

- Powerful climate policies - Lower energy intensity

- The extensive forest planting program - Population slightly below 9 billion - Larger harvests changed consumption

patterns and resulting in lower area requirements for agricultural production

- Stabilized CH

4

emissions - CO

2

emissions increases and

culminates around 2040, still positive in 2100

- CO

2

content decreases to circa 600ppm in 2100

RCP6.0 RCP8.5

CO

2

emissions increase by 2060 Continued high emissions of CO

2

- Great dependence on fossil fuels - Lower energy intensity than in RCP8.5 - Increase of arable land area, a decrease

of the pastures

- Population increases just below 10 billion

- Stabilized CH4 emissions - CO

2

emissions culminate in 2060

(75% higher than today), then decreases to a level 25% over the current one

- No additional climate policies - High energy intensity

- Energy efficiency technological development continues, but slowly.

Still great dependence on fossil fuels - Population increases to 12 billion.

- CH

4

emissions are increasing sharply - CO

2

emissions are three times higher

in 2100 than today

Table 1 – RCP Scenarios descriptions, Source: (IPCC, 2013)

As can be seen from the descriptions above, the RCP2.6 represents the best scenarios, in which the CO

2

emissions decrease and reach the lowest value among the possible scenarios. On the other hand, the RCP8.5 reflects a continuous increment of the emissions, reaching a GHG concentration three times higher in 2100 in comparison to the actual one. In Figure 6 it is underlined the annual GHG emissions in terms of CO

2

-eq for each scenario until 2100, with the range of possible emissions in terms of 10-90%

percentile, and median values.

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Figure 5 - GHG emission pathways 2000-2100 for all AR5 scenarios, Source: (IPCC, 2013)

In relation to the values of GHG emissions showed above it is then possible to evaluate the global mean variation in temperature and sea level. In Table 2 are reported the global values related to the increase of mean surface air temperature and mean sea level. These values are results of projections reported in AR5 by IPCC and indicate the variations in the period 2046-2065 and 2081-2100 in relation to the starting values relative to the period 1986-2005.

Scenario 2046-2065 2081-2100

Global Mean Surface Temperature Change

[°C]

RCP2.6 1.0 1.0

RCP4.5 1.4 1.8

RCP6.0 1.3 2.2

RCP8.5 2.0 3.7

Scenario

Global Mean Sea Level Rise [m]

RCP2.6 0.24 0.40

RCP4.5 0.26 0.47

RCP6.0 0.25 0.48

RCP8.5 0.30 0.63

Table 2 - Projected change in global mean surface temperature and global mean sea level rise for the mid- and late 21st century, relative to the 1986–2005, Source: (IPCC, 2013)

2.3.2 Main Consequences in Sweden

In relation to what is stated in the previous paragraphs, the consequences of climate change are many and will affect each local area in different ways depending on specific environmental, morphological, and social conditions. In this study case, the building under analysis is in Stockholm city and the future climate scenario selected is RCP4.5.

The latter pathway is chosen as the “medium” case scenario, according to (SMHI, 2020).

Subsequently, through an online tool provided by the Swedish Meteorological and Hydrological Institute (SMHI), it is possible to extract diagrams about several different parameters for different regional areas of Sweden, seasons, and climate change scenarios.

The raise of mean air temperature represents one of the predominant effects that will be

faced in the following years, with consequent socio-economic and health risks related to

- 26 -

over-warming periods. In the following figures (Figure 6, Figure 7, and Figure 8) the estimated change in the average air temperature [°C] in Stockholm county is shown on a yearly basis and for the winter and summer periods. The graphs report the average temperature for the period 1961-2100 comparing the predicted values with the statistical data acquired by different meteorological stations (between 1961-1990). The bars show historical data derived from observations, where the red bars demonstrate temperatures over average and the blue bars temperatures below that average. The black curve illustrates the predicted trend of temperature in accordance with the climate scenario RCP4.5. Lastly, the grey area indicates the range of temperature fluctuation related to the predicted values by SMHI with the RCP4.5 input data.

Figure 6 - Estimated change in annual average air temperature in Stockholm county compared to mean value from period 1961-1990 [RCP4.5], Source: (SMHI, 2020)

Figure 7 - Estimated change in winter average air temperature in Stockholm county compared to mean value from period 1961-1990 [RCP4.5], Source: (SMHI, 2020)

- 27 -

Figure 8 - Estimated change in summer average air temperature in Stockholm county compared to mean value from period 1961-1990 [RCP4.5], Source: (SMHI, 2020)

In the diagrams above it is possible to observe a significant increasing trend in the average mean temperature. In relation to the annual average air temperature, it is shown an increment which tends to stabilize around 2°C from 2070, with peaks of almost 3°C. From the data regarding the seasonal variation, it is possible to deduce how the change in the mean air temperature will be strictly dependent on the period of the year. For example, when the year 2070 is taken in consideration, the increase during summertime is around 2°C while it is predicted a rise in the average temperature of almost 4°C during the winter.

Another considerable change in the Swedish climate is represented by the amount and intensity of annual precipitations. According to (SOU, 2007), the average annual amount of precipitations is in the range of 600-700 mm per year. The distribution of the rainfalls is not homogeneously distributed over the country, the western regions and mountains are subjected to stronger precipitations reaching 1500-2000 mm per year. Conversely, the eastern and southern areas are the driest of the country with a precipitation intensity in the order of 400-500 mm per year. Figure 9 shows the average annual precipitation from 1860 to 2018. From the diagram, it is possible to observe a significant increase in the annual precipitations starting from 1975. Until 1920 the average precipitations had values below 600 mm per years, slightly increasing between 1920 and 1975 with amounts around and above 600 mm, while after 1975 the annual average never reached values below 600 mm per year.

Figure 9 - Average annual rainfalls in Sweden between 1860 and 2018, Source: (SMHI, 2020)

- 28 -

According to SMHI, also the precipitations over the country are expected to increase, reaching by 2100 an average annual intensity in the range of 20-60% higher with respect to the values of the period 1961-1990. In this range of increment are contained the different future climate scenarios and the intensification of the rainfalls reflects the various patterns of GHG emissions released in the atmosphere. The risk of more intense precipitations is strictly connected with short extreme events such as floods and long- term damages in relation to watercourses and lakes water levels. Short intensive precipitation can interfere with the natural flow of small watercourses, breaking the banks and increasing then the risk of floods in areas close to rivers or lakes. Many infrastructures near to watercourses, lakes or coastal areas could be damaged and thus increase the risk for the inhabitants and human health.

In association with an increment of the rainfalls, also the relative humidity is expected to increase. The SMHI does not have indexes and projections about future values, but it states anyway that the relative humidity is estimated to increase together with the air temperature and rainfalls intensity. High levels of humidity and heat, especially in a traditionally cold country such as Sweden, can provoke several problems related to human health. Among the consequences for human health, the reduction of evaporation is the major one. When the human body is subjected to high thermal loads it uses the natural mechanism of evaporation to cool itself down, but in case of co-presence of heat and high relative humidity, this mechanism is reduced or even stopped with increasing humidity levels. Higher levels of relative humidity and air temperature will thus affect the population greatly, the sensitivity to warmer weather will increase and consequently also the needs for the space cooling will be subjected to an increment. However, the values of relative humidity will not be modified from the actual ones for the analyses within this research due to the lack of information and projects related to the percentage of relative humidity increase.

Furthermore, as mentioned before, the increase of sea-level and the melting of sea-ice are

major changes which will affect many countries around the globe. SMHI collected data

and created an index in relation to the sea-ice content of the Baltic Sea and Kattegat

regions from 1957 until the present day. The climate index refers to the area covered by

sea-ice in these regions and can be visualized in Figure 10. In this diagram, it is possible

to observe a considerably decreasing trend, especially from the period 1985-1990 until

now, as an outcome of global warming. The black line shows the moving average over

this period, while the blue bars the ice extent over square kilometres. The decreasing trend

can also be noticed by the reduction in the cold winter periods in which the whole region

was covered by ice, the last reported one dates back to 1984-1987.