CO for thermal energy storage (TES) case studies

1

1

CO2 mitigation accounting for thermal energy storage (TES) case studies 2

3

4

Luisa F. Cabeza1, Laia Miró1, Eduard Oró1,*, Alvaro de Gracia1, Viktoria Martin2, 5

Andreas Krönauer4, Christoph Rathgeber4, Mohammed M. Farid6, Halime O. Paksoy7, 6

Mònica Martínez8, A. Inés Fernández8 7

8

1GREA Innovació Concurrent, Universitat de Lleida, Edifici CREA, Pere de 9

Cabrera s/n, 25001-Lleida, Spain, Phone: +34-973 003576, e-mail: 10

[email protected] 11

*Current address: Catalonia Institute for Energy Research, IREC, Jardins de les 12

Dones de Negre 1, 08930 Sant Adrià de Besòs, Barcelona, Spain 13

2KTH, Royal Institute of Technology, Dept. of Energy Technology, Stockholm, 14

Sweden 15

4Bavarian Center for Applied Energy Research (ZAE Bayern), Walther-Meissner-16

Str. 6, 85748 Garching, Germany. e-mail: [email protected] 17

6Department of Chemical and Materials Engineering, University of Auckland, 18

Auckland, New Zealand. Email:[email protected] 19

7Department of Chemistry, Çukurova University, Turkey, Phone: +90-3223386418, e-20

mail: [email protected] 21

8Department of Materials Science & Metallurgical Engineering, Universitat de 22

Barcelona, Martí i Franqués 1-11, 08028-Barcelona, Spain, Phone: +34-934021298, e-23

mail: [email protected] 24

25

26

2

Abstract27

28

According to the IPCC, societies can respond to climate changes by adapting to its 29

impacts and by mitigation, that is, by reducing GHG emissions. No single technology 30

can provide all of the mitigation potential in any sector, but many technologies have 31

been acknowledged in being able to contribute to such potential. Among the 32

technologies that can contribute in such potential, thermal energy storage (TES) is not 33

included explicitly, but implicitly as part of technologies such as energy supply, 34

buildings, and industry. To enable a more detailed assessment of the CO2 mitigation 35

potential of TES across many sectors, the group Annex 25 “Surplus heat management 36

using advanced TES for CO2 mitigation” of the Energy Conservation through Energy 37

Storage Implementing Agreement (ECES IA) of the International Energy Agency (AEI) 38

present in this article the CO2 mitigation potential of different case studies with 39

integrated TES. This potential is shown using operational and embodied CO2 40

parameters. Results are difficult to compare since TES is always designed in relation to 41

its application, and each technology impacts the energy system as a whole to different 42

extents. The applications analysed for operational CO2 are refrigeration, solar power 43

plants, mobile heat storage in industrial waste heat recovery, passive systems in 44

buildings, ATES for a supermarket, greenhouse applications, and dishwasher with 45

zeolite in Germany. The paper shows that the reason for mitigation is different in each 46

application, from energy savings to larger solar share or lowering energy consumption 47

from appliances. The mitigation potential dues to integrated TES is quantified in 48

kg/MWh energy produced or heat delivered. Embodied CO2 in two TES case studies is 49

presented, buildings and solar power plants. 50

51

52

53

Key words: CO2 mitigation potential, Thermal Energy Storage (TES), Operational CO2, 54

Embodied CO2, 55

56

3

1 Introduction57

58

According to the Intergovernmental Panel on Climate Change (IPCC), societies can 59

respond to climate changes by adapting to its impacts and by mitigation, that is, by 60

reducing Greenhouse Gas (GHG) emissions [1]. No single technology can provide all of 61

the mitigation potential in any sector, but many technologies have been acknowledged 62

in being able to contribute to such potential. Among these technologies thermal energy 63

storage (TES) is not included explicitly, but implicitly as part of technologies such as 64

energy supply (improved supply and distributions efficiency, renewable heat and power, 65

combined heat and power, concentrated solar power, etc.), buildings (more efficient 66

electrical appliances including heating and cooling devices, improved insulation, 67

passive and active solar design for heating and cooling, etc.), and industry (heat and 68

power recovery and advanced energy efficiency). 69

70

The benefits of TES may not be evident since their effects are not immediate in some 71

cases or they are only appreciable under specific circumstances. A first attempt on 72

accounting for TES potential energy savings and climate change mitigation was carried 73

out by Arce et al. [2]. In this study, an overview of the TES potential in Spain and 74

Europe was given by numerically demonstrating how TES can provide significant 75

energy and environmental benefits on national and continental scales. The sectors 76

considered were buildings (seasonal solar thermal systems, district/central heating, short 77

term solar thermal systems, and passive cold systems) and industry and transport 78

(combined heat and power, heating and cooling in industry, power stations and 79

transport, and concentrated solar power plants). Results showed how the potential load 80

reduction at the EU-level may be of 1,160,695 MWth during the next 10 years. Such 81

impact can exert a strong influence over power capacities to be installed over that 82

period. The share of Germany and Spain in this reduction is of 8% and 9%, 83

respectively. Yearly potential energy savings at the EU-level were estimated to be 7.5%. 84

Regarding electrical energy savings, Spain accounts for 20% of the overall savings at 85

the EU, which amounts to a 0.1% of the electrical energy consumption. Finally, the 86

estimated potential CO2 emissions reduction in the EU averaged 5.5% (based on 1990 87

and 2005 levels). 88

4

To enable a more detailed assessment of the CO2 mitigation potential of TES, across 89

many energy intensive sectors, the group Annex 25 “Surplus heat management using 90

advanced TES for CO2 mitigation” of the Energy Conservation through Energy Storage 91

Implementing Agreement (ECES IA) of the International Energy Agency (IEA) was 92

formed. This group focussed on the CO2 mitigation potential in several applications and 93

presented case studies with integrated TES. This potential is shown as operational and 94

embodied CO2. The aim of this paper is to present the results of the comprehensive 95

work conducted by the team members of Annex 25, carried out between 2011 and 2013. 96

The details of each application are discussed; nevertheless numbers are hard to compare 97

since TES is always designed in relation to its application, and each technology impacts 98

the energy system as a whole (e.g. national, or EU level) to various extents. 99

100

101

In order to incorporate eco-objectives into the design process of a product, additional 102

properties than the well characterized engineering properties are needed. These 103

properties (like embodied energy or CO2 footprint) include measures of the energy 104

committed and carbon released into the atmosphere when a material is extracted or 105

synthesised. 106

107

Embodied energy is the energy, excluding bio-fuels, that is used in making 1 kg of 108

material from its ores and feedstock in an industrial production plant. The CO2 footprint 109

is the sum of all the contributions per unit mass of usable materials existing in a plant. 110

In transport and in most industrial processes, there is a correlation, known as CO2 111

factor, between CO2 emissions and the energy consumption: 112

113

footprint ≅ 0.08Energy consumption

114

A commonly used value is a carbon footprint of 500 g CO2/kWh of electricity 115

production, coming from a developed country with an energy mix of 75% fossil fuel, 116

and a conversion efficiency of 38%, giving an oil equivalence of 7 MJ [3]. 117

118

Due to the low precision of the eco-attributes related to energy and carbon footprint, it is 119

accepted that there is an elevated uncertainty (of about 10 - 20% [3]) for decision 120

making. 121

5

The CO2 mitigation potential accounting is commonly carried out by counting the 122

energy used/saved and translating that to tons of CO2 using the CO2 emission factor. 123

But the CO2 emission factor depends on the country and on the year under investigation. 124

Usually, these issues are not considered, and authors only mention the country or group 125

of countries where the CO2 emission factor is used for, but scarcely the year. In this 126

article, the CO2 mitigation potential is shown using the operational and the embodied 127

CO2. Operational CO2 refers to the mitigated CO2 during the operation phase of the 128

component/application while the embodied CO2 refers to the CO2 released into the 129

atmosphere when the component/application is made. 130

131

Moreover, another key issue is the fact that CO2 emissions influence is rarely 132

considered when TES is studied in different applications. 133

134

135

2 OperationalCO2accountinginTEScasestudies136

137

A variety of technologies has been assessed in terms of the energy savings, and 138

resulting CO2 mitigation potential from integrating TES. The details of each application 139

are further discussed below, followed by a summarizing assessment. 140

141

In the examples discussed below, different TES technologies are used, sensible heat 142

storage and latent heat storage with phase change materials (PCM). In this section, each 143

technology is assessed in their respective country. More detail in these technologies can 144

be found elsewhere [4]. 145

146

2.1 Refrigerationapplications147

148

A model to estimate the potential Spanish and European impact when using TES for 149

cold production, in terms of energy consumption and CO2 emissions reduction, was 150

developed in a previous publication [5]. Table 1 shows all the cases analysed and the 151

electricity savings due to the implementation. The total energy demand for cold 152

applications in Spain and Europe was calculated, and after that the energy reduction and 153

therefore CO2 emissions mitigation was determined assuming a full implementation of 154

6

the PCM (phase change materials) TES systems (Figure 1). Two scenarios have been 155

studied, the low and the high scenario. The low scenario accounts for the lowest factors 156

of electricity savings, while the high scenario accounts for the highest values of energy 157

savings found in the literature. 158

159

Table 1. Potential electricity savings related in the maintenance of low temperature 160

sensitive products [5]. 161

Cases analysed Sector Authors Electricity savings

Domestic

refrigerators

Domestic and

commercial

sector

Azzouz et al.

[6]

During normal working

conditions, 10-30% COP

Domestic freezer Gin et al. [7] During defrost cycle by 8%, and

by 7% during door openings

Domestic

refrigerator

(refrigerator and

freezer)

Subramaniam

et al. [8]


conditions by 8%

Refrigerated trucks

(PCM on the walls)

Cold in road

transport

Ahmed et al.

[9]

Daily average reduction of the

heat flux from the ambient to the

refrigerated truck of 16.3%

Refrigerated trucks

(novel refrigeration

system

incorporating

PCM)

Liu et al. [10]


conditions between 6 and 38%,

depending on the chosen scenario

Industrial

refrigeration Cold in

industry

Cheralathan

et al. [11]


conditions, 6-20% SEC (kW/TR)

Refrigeration

plants

Wang et al.

[12]


conditions, 4-8% COP

162

1

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1

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ure 2. Distr

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CO2 emissi

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[5].

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he cold stor

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include th

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rage and co

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to 22%. Ev

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he capital co

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t TES syste

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ize that the

hours and

become mu

ount instea

come to alle

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system co

of a therm

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are of the p

f 1 MW. T

em used wi

field [13].

n of PCM-T

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domestic c

therefore p

ch higher

d of the e

eviate the pe

simulation

onsidered

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without therm

ng intermitt

power plant

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ith a parab

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produced w

because he

energy mix

eak load an

for a TES

is presente

gives the s

ances in the

mal storage

ent cloud c

t by as muc

es the sup

bolic trough

ms is barely

be much

me of the en

with higher

ere the mar

x factors b

nd hence imp

S unit used

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system abil

amount of

undergoes

cover. Add

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pplementary

h solar colle

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ure 3.

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large

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for a

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deliv

load

Supp

fuel

(MW

Solar

216

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221

ummary of t

results of th

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much as 47%

more meagr

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Table

able

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(MWh)

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required

Wh)

r share (%)

ure 4. Tota

oudy day f

the results o

hese simula

ion of energ

% to levels

re on cloud

mal energy s

ge tank as a

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16.4

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47.6

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for: left – sy

obtained by

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over 70% o

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buffer betw

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9

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on a sunny

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he ability to

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lts obtained

ay

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16.82

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nd Edgar [13

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day. The im

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3] are prese

f storage ca

er plant can

mprovemen

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a constant p

and energy

l and Edga

Cloudy

em w/o

TES

8.40

5.78

4.3

red to the lo

ystem with

ented in Tab

apacity, the

n be increas

nts in solar

cover, the

power outp

y demand (F

ar [13].

y day

System w

TES

8.49

15.51

35.4

oad on a pa

h storage [1

ble 2.

solar

ed by

share

main

put by

Figure

with

artly

3].

10

From results presented in Table 2, the mitigation of CO2 emissions in a CSP plant when 221

TES is implemented can be calculated as a function of the fuel used for hybridation 222

(Table 3). Since the supplementary fuel requirement is reduced by 43%, CO2 emissions 223

will be also reduced by 43%. 224

225

Table 3. CO2 emissions (tCO2) in a 1 MW output CSP plant with and without TES. 226

Variable Emission factor of

the fuel considered,

tCO2/TJ

System w/o TES System with TES

Supplemental

fuel required

(MWh)

--- 12.58 7.18

CO2 emissions

(tCO2)

Coal

(94.6-96.1 [14])

4.28 – 4.35 2.45 – 2.48

Natural gas

(56.1 [14])

2.54 1.45

Oil

(73.3-77.4 [14])

3.32 – 3.51 1.89 – 2.00

227

2.3 Mobileheatstorageinindustrialwasteheatrecovery228

229

Transport of heat by truck, train or boat, “heat on wheels”, is a promising supplement to 230

the currently used systems of piped thermal energy distribution or of use of waste heat 231

from industry (Figure 5). The concept requires that the heat can be stored in a material 232

with a high energy density, i.e. a large amount of heat per unit of weight and volume. 233

Mobile energy storage systems transported by truck may bridge the gap between heat 234

source and demand site in cases where a pipeline-bound connection cannot be realized 235

cost effectively. 236

237

11

238

Figure 5. Schematic description of the heat on wheels concept [15]. 239

240

Based on this result ZAE Bayern and its partner Industrieanlagen Hoffmeier GmbH 241

have developed and built a prototype of a mobile storage based on an open sorption 242

system, working with a packed bed of zeolite as adsorbent. A pilot plant with a waste 243

incineration plant as a heat source and an industrial drying process as demand site was 244

built (Figure 6). The system has been operated for about 50 cycles so far and the test 245

period is still running. 246

247

248

Figure 6. Principle of Mobile Sorption Heat Storage in Industrial Waste Heat 249

Recovery [15]. 250

251

LargeScaleCHP Utility

GBiomass

heat

Heat on wheels

Heat on wheels

Heat Carrier Return, 45 ◦C

Boiler(supple‐mental heat)

T [◦C] < T_mp

Accumulator

Charging Accumulator

DischargingAccumulator

Heat Carrier Supply, 90 ◦C

Heat Supply

Transport

Heat Demand

Small ScaleCHP Utility

MobS MobS MobS

Waste Heat

Charging station

Trans- port

Discharging station

User

12

Table 4 contains the necessary parameters to estimate the potential CO2 mitigation 252

achieved by this mobile sorption heat storage. 253

254

Table 4. Parameters for CO2 mitigation accounting. 255

256

The energy savings are equal to the amount of substituted gas (2.62 MWh) accounted as 257

the energy content per storage (2.91 MWh) times the storage efficiency (90%). 258

Multiplied with the corresponding CO2 emissions factor, 530 kg CO2 savings per 259

storage can be achieved. However, CO2 emissions due to auxiliary electric energy (85 260

kg CO2) and. the fuel consumption of the truck (29 kg CO2), have to be subtracted, thus 261

the total amount of CO2 mitigation per container is 416 kg CO2. Considering annual 262

storage handling, the amount of CO2 mitigation per storage container per year will be 263

437 t CO2. 264

265

If 10 to 100 mobile heat storage systems could be established in Germany in the 266

medium term the potential CO2 mitigation in Germany would be around 4,000 – 40,000 267

tons CO2 per year. This range refers to the physical potential of CO2 mitigation while 268

the other applications studied in this paper refer to technical potentials, as defined in [1]. 269

270

Storage

Energy content per storage [MWh] 2.91

Storage efficiency 0.9

Boundary conditions

Distance [km] (one way) 10

Auxiliary electric energy / cycle [MWh] 0.11

Specific fuel consumption truck [l/100km] 55

Annually number of storage handling 1,051

CO2 emission factors

gas [kg CO2/MWh] 202

electricity [kg CO2/MWh] 773

fuel (diesel) [kg CO2/l] 2.64

13

Similarly, the transport of excess heat from a large-scale biomass- based combined heat 271

and power plant to local smaller “boiler-based” utilities has been studied by the Swedish 272

District Energy System. Initially, the market for heat transportation with truck (train or 273

boat) was assessed by considering statistics on cities with population and connected to 274

district heating systems. Other assumptions were that the single household on average is 275

occupied by 2.5 persons and utilizes 20 MWh of heat per year. 276

277

Here, the market results show that smaller cities (between 200 and 10,000 inhabitants) 278

with district heat already in place, generate a yearly heat demand of about 11 TWh. If 279

the total demand would be provided by energy transport from the large CHP utility, the 280

additional biomass-based power generation in these plants would amount to about 7 281

TWh. The effect on CO2 mitigation on such scenario can be analysed as follows: 282

283

1. CO2 mitigation is obtained through replacing heat and electricity generated by 284

green alternatives. This is due to: 285

a. Replacing heat from an oil-based boiler (approximately 300 g/kWh) by 286

heat from biomass CHP. 287

b. Replacing electricity from EU average mix (approximately 350 g/kWh), 288

with zero CO2-emission power from biomass CHP. 289

For this case, the expected CO2 mitigation is 5.8 Mt/year, which is about 10% 290

of the present Swedish total annual CO2-emissions. 291

292

2. CO2 mitigation is obtained through the generation of electricity only since heat 293

is normally generated in a local, smaller-scale biomass boiler. 294

For this case, the expected CO2 mitigation is 2.4 Mt/year for Sweden. 295

296

2.4 Passivesystemsinbuildings297

298

It is well known that the use of latent heat storage in building passive systems could 299

reduce the energy consumption of the HVAC systems. These reductions have been 300

analysed both experimentally and numerically. 301

302

In summer, during daytime the sunshine and high temperatures result in a heat wave 303

penetrating the walls of the buildings (Figure 7). PCM absorbs the excess of heat 304

3

3

3

3

3

3

3

3

3

3

3

3

3

3

3

3

3

3

3

3

3

throu311

reduc312

and 313

temp314

proce315

comf316

312

313

314

315

316

Table319

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320

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of 23325

324

Table326

consi327

ugh its melt

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the coolin

peratures be

ess to both

fortable, clo

F

e 5 shows

ormance of

ntify the ene

m the energy

mated. Acco

38 g/kWh is

e 5 present

idering a se

ting proces

ak. During

g system c

ecome lowe

internal and

osing the cy

Figure 7. Op

s measured

f different c

ergetic bene

y consumed

ording to the

s used for th

ts CO2 emi

et point of

s, delaying

most of the

consumes l

r, the PCM

d external e

ycle and bein

perating pr

d data of e

cubicles loc

fits of using

d in each cub

e Spanish e

his estimatio

issions and

24 ºC durin

14

the heat w

e day the r

less energy

M releases th

environment

ng ready fo

rinciple of

energy con

cated in Pu

g PCM [16]

ubicle, the C

electricity pr

on.

d electrical

ng 90 days

wave penetra

oom tempe

y. During

he stored he

ts, keeping

r another da

PCM in bu

nsumption

uigverd de

].

CO2 emissio

roduction sh

energy sav

per year (c

ating the bu

erature rema

night time

eat through

again the ro

aily use.

uildings [15

and compa

Lleida (Sp

ns to the atm

hare, a CO2

vings for di

cooling dem

uilding, and

ains comfor

, when ou

its solidific

oom temper

5].

ares the en

pain) in ord

mosphere c

2 emission f

ifferent cub

mand). The

d also

rtable

utdoor

cation

rature

nergy

der to

can be

factor

bicles,

study

15

presents the performance of a cubicle with traditional constructive system without 326

insulation (REF), with 5 cm of polyurethane (PU), with polyurethane and PCM 327

(RT27+PU), a system without insulation but with high thermal mass (Alveolar) and the 328

same system with PCM (SP25+Alveolar). The constructive systems of the different 329

cubicles are detailed in Castell et al. [16] 330

331

Table 5. CO2 emissions to the atmosphere due to the electricity consumption in 332

each cubicle [16]. 333

Electricity

consumption

(kWh/year·m2)

CO2 emissions

(kg/year·m2)

CO2 savings

(kg/year·m2)

Reference 29.3 7.0 0.0

PU 14.3 3.4 3.6

RT27+PU 12.2 2.9 4.1

Alveolar 15.8 3.8 3.2

SP25+Alveolar 13.1 3.1 3.9

334

335

Moreover, the same experimental set-up was used to test the energy performance of a 336

ventilated double skin facade (VDSF) with macro-encapsulated panels with PCM inside 337

its air cavity. This system was designed to reduce the heating demand during the winter 338

season. The VDSF acts as a solar collector during the sunny hours and once the PCM is 339

melted and the solar energy is needed by the building heating demand, the heat stored is 340

discharged to the inner environment as a heating supply. According to de Gracia et al. 341

[17] the electrical energy required by the heat pump to maintain a set point of 21 ºC 342

during heating season is reduced by 20.6% due to the use of this VDSF. 343

344

Table 6 quantifies the amount of CO2 emissions that would be saved due to the use of 345

PCM in this active system. An energy mix of 238 g CO2/kWh is also considered in this 346

case. 347

348

349

350

16

Table 6. CO2 emissions to the atmosphere due to the energy consumed in each 351

cubicle [17]. 352

Energy

consumption

(kWh/year·m2)

CO2 emissions

(kg/year·m2)

CO2 savings

(kg/year·m2)

Reference 191.8 45.6 0.0

VDSF 152.1 36.19 9.4

353

Moreover, the thermal performance of a single family house with and without PCM, 354

impregnated in the gypsum board, was numerically investigated in 10 different cities 355

around the world with different climates [18]. The paper discusses the influence of the 356

climate in the potential that PCM can provide for energy savings. Table 7 presents the 357

energy savings achieved under the different climate conditions. 358

359

Table 7. Electricity consumption of the house and the energy savings provided by 360

the PCM [18]. 361

362

Country Energy per year

(no PCM) [GJ]

Savings per

year (with

PCM) [GJ]

Savings per

year (%)

Bogota 8.39 2.60 31

Quito 7.27 2.40 33

San Francisco 14.62 1.90 13

Auckland 13.64 1.50 11

Brisbane 14.00 1.40 10

Montreal 110.00 1.10 1

Madrid 27.50 1.10 4

Stockholm 45.00 0.90 2

Kuala Lumpur 15.00 -0.30 -2

Singapore 20.00 -0.40 -2

363

These savings in the electrical energy needed to achieve thermal comfort conditions 364

during the whole year (set point of 20 ºC for heating and 23 ºC for cooling) represent 365

17

reductions in the amount of CO2 emitted to the atmosphere. According to IEA [19] the 366

worldwide CO2 emissions per kWh from electricity generation present slight variation 367

during the last 20 years, presenting a value of 564 gCO2/kWh for 2010. Moreover, the 368

IEA report also provides the energy mix of each country. Table 8 presents the amount of 369

CO2 that has been saved at the different analysed locations if considering a global 370

worldwide energy mix and a country ratio. One can see that for some locations, the 371

amount of CO2 saved is very different depending on the chosen CO2 emission factor. 372

373

Table 8. CO2 reduction from space heating and cooling considering a global 374

worldwide energy mix [18]. 375

City (Country)

CO2 reduction

[kgCO2/year·m2]

Worldwide

energy mix

CO2 reduction

[kgCO2/year·m2]

Country energy

mix

Bogota

(Colombia) 1.59 0.50

Quito (Ecuador) 1.47 1.01

San Francisco

(USA) 1.16 1.08

Auckland (New

Zealand) 0.92 0.24

Brisbane

(Australia) 0.86 1.28

Montreal

(Canada) 0.67 0.22

Madrid (Spain) 0.67 0.28

Stockholm

(Sweden) 0.55 0.03

Kuala Lumpur

(Indonesia) -0.18 -0.24

Singapore

(Singapore) -0.25 -0.22

376

18

A similar experimentation was carried out in a 4 m2 floor area test cabin in Adana, with 377

cooling and heating loads 2391 W and 665 W, respectively [20,21]. In this case, two 378

microencapsulated PCM - Micronal 5001 (melting point 26 °C and latent heat 110 379

kJ/kg) and Micronal 5008 (melting point 23 °C and latent heat 110 kJ/kg) – were used 380

to produce sandwich panels with insulation material Izopan. The south facade of the test 381

cabin was lined with sandwich panel. Total amount of PCM used was 3.5 kg. The tests 382

were carried out with PCM only, insulation only and sandwich panel linings. In 383

summer, day-time temperature in the cabin was reduced by 2.5 °C in the case of using 384

PCM only and 0.6 °C when only using insulation. Cooling loads were reduced by 7 % 385

as a result of using PCM in the summer operation, which accounts for energy saving of 386

186 kWh/year. In winter, the average temperature inside the cabin was increased by 1.6 387

°C with PCM only, 1.3 °C with only insulation and 2.2 °C with sandwich panel 388

(insulation together with PCM). Under these conditions, heating loads were reduced by 389

10% and 23% when PCM and sandwich panel were used, respectively. Energy 390

conserved for heating was 292 kWh/year. 391

392

Calculating the heating using coal and air-conditioning using electricity produced from 393

coal, the CO2 mitigation in the cases presented in Table 8 was 0.5 ton/year as average. 394

395

2.5 AquiferThermalEnergyStorage(ATES)forasupermarket396

397

This was the first ATES project in Turkey and in Mediterranean climate. The gross area 398

for the building was 1800 m² and 1400 m² of this area was air-conditioned. The peak 399

loads for cooling and heating were 195 kW and 74 kW, respectively. The ATES system 400

(Figure 8) contained two groups of wells - each at 100 m depth - connected to HVAC 401

system [20,22]. In the cooling mode, groundwater from the cold well was used to cool 402

down the condenser of the HVAC system and at the same time storing this waste heat in 403

the aquifer through the warm well. Cooling with groundwater at around 18 °C - instead 404

of outside summer air at 30-35 °C - decreased consumption of electricity significantly. 405

The stored heat was recovered from the warm well in the heating mode, when it is 406

needed in winter. The total energy that was stored in this operation is 0.4 MWh. A 407

conventional system with air cooled condenser consumes 898 kWh/day to meet the 408

peak cooling demand of 2400 kWh/day. The average COP is 2.67 for such a system. 409

The ATES system started operation with cooling mode in August 2001. Using 410

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

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424

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In 20432

m2 a433

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em was 118

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007 two sep

at Cukurov

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own-sized,

t was requi

vestment of

y. Total an

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CO2 mitiga

Figure

ouseappl

ment in com

es, and orn

e address th

food produc

parate green

a Universit

as heated a

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making the

ired for dr

heat pump

nnual electr

suming that

ation.

e 8. ATES s

lications

mmercial gr

amental pla

e need for s

tion for all,

nhouses with

ty (Turkey)

and cooled

19

age COP o

ause of 60%

e system m

rilling of th

. With this

rical energy

electricity i

system for s

reenhouses

ants. It is a

sustainable

in combine

h polyethyl

) research

by ATES

of 4.18, whi

% higher CO

more econo

he wells w

performanc

y conserva

is produced

supermark

aims at ens

an issue tha

energy serv

e.

ene covers,

farm were

technique

ich was alm

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omically vi

was cancelle

ce ATES sy

ation introd

d with coal,

ket [22].

suring susta

at will beco

vices, conse

each havin

used [20,2

and the ot

most 60% h

ump of the A

iable. The

ed out wit

ystem cons

duced by A

this would

ainable grow

ome increas

ervation of

ng an area o

23]. One o

ther one w

higher

ATES

extra

h the

umed

ATES

mean

wth of

singly

water

of 360

of the

with a

4

4

4

4

4

4

4

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4

4

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matic diagra

Figure 9

peratures in

ths in this

ES system op

very and co

In this heat

5 °C. Heat

peratures w

atoes). Tota

ed was reco

perature ins

ing. The pr

ght- was 40

ation of AT

itionally, it

eating system

e ATES gre

m summer to

mer. Greenh

am of the A

9. Schemati

n the green

climate. W

perated dur

old storage.

t storage pr

t stored wa

were below

l energy sto

overed for c

side the gre

roduct yiel

% higher th

TES system

t was pos

m and no co

enhouse. Th

o heat the gr

house was th

ATES system

ic diagram

nhouse vari

Winter air co

ring 2005-20

Total energ

ocess, grou

as recovered

11 °C (m

ored in the c

cooling of th

eenhouse e

ld of tomat

han those f

m in 2005-2

sible to c

20

ooling. Two

he basic co

reenhouse -

he “solar co

m is shown

of the ATE

ied betwee

older than

006 for 70 d

gy stored in

undwater tem

d in winter

minimum t

cold well d

he greenho

exceeded 30

toes in the

for the conv

2006, no f

cool the gr

o wells- a co

oncept of th

- as well as

ollector” to

in Figure 9

ES system f

n 40-60 °C

10 °C is th

days storing

the warm w

mperature i

r to heat th

emperature

during heat r

use for 32

0°C, the A

e ATES gr

ventional gr

fossil fuel f

reenhouse

old and a w

e ATES sys

the cold sto

store heat i

.

for greenho

C about 6

he source f

g heat and f

well in this p

increased fr

he greenhou

allowable

recovery wa

days in spr

ATES system

eenhouse-in

reenhouse.

for heating

in a perio

warm well –

stem utilize

ored in wint

in sunny da

ouse [23].

hours/day

for cooling

for 138 days

period was

rom 18-20

use, when i

e for grow

as 76.0 GJ.

ring 2006. W

m was use

n terms of

During the

was consu

od when u

– were

ed the

ter for

ays. A

for 5

. The

s heat

103.9

°C to

inside

th of

Cold

When

ed for

f fruit

e total

umed.

under

4

4

4

4

4

4

4

4

4

4

4

4

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475

476

477

478

This 484

simu485

20% 486

cove487

heati488

annu489

iterranean c

m the harves

oil No.6. F

pumps for

heating and

h/year.

sidering tha

d be saved i

07 m2 in 200

be reduced

ordingly 163

rgy manage

idered, imp

is harveste

ing through

gration a PV

ecting heat.

concept w

ulations. Th

of the ann

r about 20

ing/electrici

ual CO2 miti

climate con

st was incre

For the ATE

groundwate

cooling we

at greenhou

in every gre

05. With in

by 5 millio

3 million U

ement in

plementing t

ed instead o

seasonal st

VT-panel as

This concep

Figure 10.

was analyse

is showed t

nual heating

0% of the

ity generati

igation as sh

nditions pro

eased furthe

ES system 3

er circulatio

ere 7.6 and

uses in Turk

eenhouse. T

ntroduction

on tons /yea

USD worth o

a greenhou

the closed g

of ventilated

torage. For

s a shading

pt is schema

Schematic

ed based o

that the har

g demand,

electricity

on that is r

hown in Tab

21

oduction wo

er. The conv

3 MWh of e

on. For 200

3.2, respec

key are hea

The total gre

of ATES s

ar with an

of fuel oil w

use located

greenhouse

d, stored an

this study, t

device, gen

atically illu

c profile vie

on annual

rvested exc

at the same

demand a

replaced, th

ble 9.

ould have b

ventional gr

electricity w

05-2006 ope

ctively. Tota

ated with fu

eenhouse ar

ystems in g

extra inves

would be sav

d in Nordi

concept [24

nd used at a

the means o

nerating ele

strated in F

ew of solar

energy per

ess heat co

e time as e

as well. De

hese saving

been halted.

reenhouse w

was used to

eration of t

al energy co

uel oil, 26

ea in Turke

greenhouses

tment of 28

ved per year

ic climate

4]. Here, the

a later time

of harvestin

ectricity at t

igure 10.

blind [24].

rformance

ould be used

electricity w

epending o

gs can be tr

. Thus, the

was heated

run the fan

the system,

onserved w

ton/year of

ey was more

s, CO2 emis

80 million U

r.

has also

e summer e

e, e.g. for w

ng was by w

the same tim

.

using TRN

d to cover

was generat

on the mod

ranslated in

yield

using

n coils

COP

was 36

f CO2

e than

ssions

USD.

been

excess

winter

way of

me as

NSYS

about

ted to

de of

nto an

22

Table 9. A comparison in CO2 reduction for closed greenhouse with and without 484

considering the solar blind system [24]. 485

Conventional Greenhouse

Energy Source

Biomass Fuel Oil Electricity Natural Gas

Closed Greenhouse without

solar PVT blind

-11% 74% 62% 71%

Closed greenhouse WITH

solar PVT blind

26% 83% 74% 81%

486

As shown, the values are also there for a closed greenhouse where the heat is not 487

harvested using solar PVT blinds [25]. Then, more of the annual heating demand can be 488

covered (over 50%) but no electricity is generated in the process. For this case, heat is 489

collected at much lower temperature and thus an electrical heat pump is needed to adjust 490

the temperature of the heat. Then, the closed greenhouse might even have a negative 491

impact on climate mitigation if the harvested, stored excess heat would replace heat 492

from a biomass boiler. This means the CO2 emission is not reduced in comparison with 493

the conventional greenhouses in this case. However, combining the closed greenhouse 494

with the solar blind system such that a portion of the electrical demand is provided by 495

the PVT panels, the CO2 emission can be reduced by 26% as compared to a 496

conventional greenhouse using biomass for heating. Furthermore, more than 74% CO2 497

emission reduction can be achieved in case of using fuel oil, electricity and natural gas 498

as the external energy source for heating purpose in the greenhouse. These numbers all 499

assume the EU27 Energy Mix for Power Generation. 500

501

2.7 DishwasherwithzeoliteinGermany502

503

Open adsorption systems using water as adsorbate, zeolite as adsorbent and air as heat 504

and mass carrier can be used for heating, cooling and thermal energy storage (TES). 505

Drying processes are a promising field of application for open adsorption systems, since 506

air can be dehumidified in an adsorption cycle. For example, the energy consumption of 507

dishwashers can be reduced by means of an open adsorption system [26]. Therefore, the 508

water heating phase of the main washing cycle has been used to desorb a packed bed of 509

zeolites. The common water heating phase before the drying of the dishes has been 510

23

omitted and replaced by an adsorption phase in which the dishes are dried by hot air. In 511

this context the adsorption system was used as a thermally driven heat pump and a 512

thermal energy storage system. The reduction of the energy consumption compared to a 513

conventional dishwasher from about 1.05kWh to 0.80kWh per washing cycle leads to 514

energy savings of about 24 % [26]. This innovative dishwasher is commercially 515

available since November 2009. 516

517

The assumptions made in the CO2 mitigation calculation of this system were: energy 518

savings of 0.25 kWh per washing cycle and an average of 250 washing cycles per year 519

with a dishwasher lifetime of 10 years. A CO2 emissions factor of 0.5 kg CO2/kWh was 520

considered. An annual number of 1 million installed dishwashers with zeolite drying is 521

considered in order to demonstrate the potential energy savings and CO2 mitigation due 522

to a wide application of this TES system. Calculated energy and CO2 emissions savings 523

are presented in Table 10. 524

525

Table 10. Energy and CO2 savings due to an extensive use of a sorption storage 526

system for dishwashers. Detailed boundary conditions are given in the text. 527

Savings After 1st year After 10 years (cumulative

value)

Energy 62.5 GWh 3,440 GWh

CO2 emissions 31,250 tons 1.7 megatons

528

Today, some dishwashers with zeolite drying only consume around 0.73 kWh of 529

electricity per cycle and, hence, lie 10% below the limits for the top-grade energy 530

efficiency class A+++ [27]. 531

532

In a recent study by Santori et al. [28], a silica gel was investigated as an adsorbent 533

material for the drying stage of a dishwasher. Tests of an optimized prototype showed 534

an electric power consumption of 0.636 kWh corresponding to a reduction of energy 535

consumption of about 40% compared with the standard cycle of an energy class A 536

standard dishwasher (1.08 kWh according to [28]). 537

538

24

Therefore, assuming higher energy savings of 0.4 kWh per washing cycle and 250 539

cycles per year, the cumulative energy and CO2 emission savings after 10 years would 540

be approx. 5,500 GWh and 2.8 megatons per 1 million dishwashers, respectively. 541

3 EmbodiedCO2accountinginTEScasestudies542

543

The embodied energy is the energy that must be committed to produce a unit mass of a 544

material from whatever it is made from. It includes the embodied energy involved in the 545

extraction, primary production, transformation, transport to its place of use and 546

recycling [29]. Similarly to operational CO2, to translate the embodied energy into 547

embodied CO2 in any application, the energy mix factor should be used. 548

549

3.1 Buildings550

551

By using the CES Selector software the relation between the embodied energy vs. the 552

CO2 footprint of the primary production of several typical building materials can be 553

plotted as shown in Figure 11 [30]. The same type of data can be obtained for the 554

processing and recycling of the materials. But usually, more data is necessary to assess, 555

compare and select different materials, and e.g. water usage in its production (Figure 556

12). 557

558

Jiao et al. [31] analysed different type of buildings and the materials involved. They 559

reported that more than 90% of a building is concrete (Figure 13). The remaining 10% 560

of materials, are brick, wood and steel among some others. 561

562

5

5

5

5

5

5

564

565

566

567

F568

569

Figure

Figure 12.

1

Embo

died

ene

rgy,

prim

ary

prod

uctio

n (M

J/kg

)

0.1

1

10

100

11. Embod

Embodied

Soda lime glas

Concrete (

Sandstone

Marble

died energy

energy and

10

Cemen

Mineral wool_T-gl

Mine

Ceramic tile

ss

Plaster of paris

(normal (Portland ce

Brick

25

y and CO2 i

d water usa

Water usage 100

nt (ordinary Portland

lass

eral wool_SF-glass

ement))

Polyurethan

in typical b

age of typic

(l/kg)

A

O

d)

F

Low-e glas

PVC rigid

ne foam PS foam

building ma

cal building

1000

Aluminum, 6063, wr

Oak Pine

Bam

Fiberboard, med de

Cork

ss

m

aterials.

g materials

rought, T6

mboo

ensity

s.

5

5

5

5

5

5

5

5

5

5

5

5

5

570

571

572

Clem574

energ575

575

576

577

579

580

580

581

582

Fig

ments et al.

gy in a build

‐ The e

w

th

‐ The o

gure 13. Qu

[32] develo

ding wall:

embodied e

where He is

hickness of

operational

uantity of m

oped a comp

energy (per m

E

the embod

the wall.

energy (per

26

materials in

parison betw

m2) can be

HE eemb ·

died energy

r m2) can be

TEuse

n a building

ween the em

written as:

d·

[kJ/kg]; ρ

e written as

d

T ··

g in % wt. [

mbodied and

is the dens

:

[30].

d the operat

sity; and d

tional

is the

27

where T is the degree-days per year [K·s]; τ is lifetime of the building, 582

100 years; λ is the thermal conductivity. 583

‐ Therefore, the total energy of a building is: 584

useemblifetime EEE 585

586

In order to use less energy in the buildings, this Elifetime should be minimized, 587

therefore: 588

589

useemblifetime EEEMinimum 590

591

Giving an optimum thickness of: 592

593

·

··eH

Td 594

595

with a total life energy of: 596

597

·····2 elifetime HTE 598

599

Representing this for several materials, one can see that different materials give 600

different energy use during their lifetime, for a given wall thickness (Figure 14). For 601

instance a wall made with brick only; shows the highest lifetime energy, whereas the 602

inclusion of insulation materials (PU foams) reduces the required thickness and the 603

lifetime energy. 604

605

The use of PCM incorporated in the building materials makes them composite materials 606

in which there is a change the properties of the original material like density and 607

thermal conductivity. In this way, embodied energy of the composite will be also 608

different. There is not reported data on the embodied energy of materials containing 609

PCM, even though there is ongoing work to estimate it, in order to include some of 610

these materials in a figure like Figure 14. 611

6

6

6

6

6

6

6

6

6

6

6

6

6

6

6

6

6

6

6

6

613

Fi614

615

3.2 616

617

Thre622

litera623

and o624

these625

defin626

623

625

626

627

628

629

630

630

631

632

igure 14. L

Solarpo

e different

ature have b

operation li

e three TES

ned as the to

System

temperat

System 2

using mo

System

describe

Lifetime ene

owerplan

TES syste

been environ

ife [33] (Ta

S systems h

otal energy

1: Solid s

ture concret

2: Molten s

olten salts b

3: PCM sy

d system 2

ergy per un

nts

ems [33] to

nmentally a

ble 11). For

as been acc

inputs requi

ystem. Sen

te as storage

salts system

based on a m

ystem. Late

but with dif

28

nit area vs.

o be imple

analysed and

r that, the e

counted. Th

ired to mak

nsible heat

e material.

m. Heat is st

mixture of N

ent heat is

fferent mixi

optimised

emented in

d compared

embodied en

he embodied

ke it.

is stored

tored in liqu

NaNO3 and

s stored us

ing ratio.

thickness o

CSP plan

d during thei

nergy of the

d energy of

in this sys

uid media b

KNO3.

ing the sam

of a wall [3

nts found in

ir manufact

e componen

f a compon

stem using

by sensible

me molten

2].

n the

turing

nts of

ent is

high

heat;

salts

29

Table 11. Storage capacity and storage material used in each system [33]. 632

633

Solid system Molten salts system PCM system

Storage capacity (kWh) 350 600 ·103 100

Storage material High temperature

concrete

60 wt% NaNO3 + 40

wt% KNO3

46 wt% NaNO3

+ 54 wt%

KNO3

Amount of storage

material (kg) 26,757 5,500·103 2,100

634

In this analysis the working conditions (temperature gradient, thermal characteristics of 635

the TES materials, etc.) are not considered because this environmental analysis only 636

considers the quantity of the components that form the TES system and their embodied 637

energy. 638

639

In order to account for the embodied energy of these three TES systems, a database and 640

a method should be chosen. It has to be taken into account, mainly, the suitability of the 641

database with the components to be studied, the regional validity of the data, and the 642

boundaries of the collected data. In the case of embodied energy, the energy of the 643

extraction, manufacture, disposal, and transport must be considered. For that, EcoInvent 644

database has been chosen. This database provides the needed data to perform 645

environmental analysis that can be useful to determine the impact of the three case 646

studies, between all of them, Cumulative Energy Demand (CED) accounts for the 647

materials embodied energy. 648

649

Figure 15 to Figure 17 show the distribution of the most influencing components for the 650

three systems. The most influencing component in solid system is the steel tubes of the 651

heat exchanger. In the molten salts system, the storage component (KNO3 + NaNO3) is 652

the most significant in the embodied energy accounting. The same trend is observed in 653

the PCM storage system. 654

655

In all systems, the components used in the design can be divided into “storage 656

materials”, the material that stores the heat, and “container materials”, the structural and 657

building materials. Figure 18 shows the influence of them. Results show in the solid 658

6

6

6

6

6

6

6

6

6

6

6

6

syste661

(arou662

662

663

Figu665

666

666

667

Figu670

mo671

672

671

em, the sto

und 30 %). I

ure 15. Dist

ure 16. Dist

olten salts s

orage mater

In the molte

ribution of

ribution of

system (“O

tha

rial contrib

en salts syst

f the embod

soli

f the embod

Other < 5 %

n 5 % in th

30

bution to to

tems it is 70

died energy

id system [

died energy

%” includes

he total dist

otal embod

0 % and 85%

y most influ

33].

y most influ

s all the com

tribution) [

died energy

% in the PC

uencing com

uencing com

mponents th

[33].

y are the lo

CM system.

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4 Discussion687

688

A summary of the operational CO2 mitigation potential of the case studies presented in 689

this paper is presented in Table 12. When the mitigation potential is due to electricity 690

savings, this potential would be very much influenced by the emissions factor, which 691

varies from country to country and from year to year due to the change of the energy 692

mix. Because of this, translating from electricity savings to CO2 emissions savings is 693

not possible and is not presented in this paper. 694

695

Moreover, due to the different reasons for mitigation, a quantitative comparison 696

between the different case studies presented can only be done for each country and not 697

in a general way as it would have been desirable in this paper. 698

699

Embodied CO2 accounting in thermal energy storage has been done only for building 700

materials and for a given case in solar power plants. If the building material is 701

considered as TES material (due to the thermal inertia that can be given by that 702

material), then aluminium and insulation materials are found as the material with higher 703

embodied energy per unit mass, but since buildings usually have much more concrete 704

than any other materials, concrete is the material introducing higher embodied CO2 in 705

most of today’s buildings. Finally, different materials give different energy use during 706

their lifetime when included in a building. This evaluation helps to account the lifetime 707

energy of materials used in buildings. 708

709

On the other hand, embodied CO2 accounting in solar power plants shown in this paper 710

shows that this method can be used to decide where efforts need to be directed to 711

decrease embodied CO2 in a storage system (or any other energy system). Most 712

researchers direct the efforts only to the storage material, while more CO2 can be 713

embedded in the container materials or other system components. 714

715

716

33

Table 12. Summary of CO2 mitigation potential. 717

Application CO2 mitigation potential due

to integrated TES

Main reason for

mitigation

Refrigeration 25-125 [kg/MWh cold

produced]

Electricity savings

Power plant with CSP 800-2000 [kg/MWh electricity

produced]

Larger solar share

Heat on Wheels –

industrial surplus heat

for industrial drying in

Germany

145 [kg/MWh heat delivered] Replacing natural gas for

industrial drying process

Heat on Wheels – CHP

heat replacing local

boilers in Sweden

300-500 [kg/MWh heat

delivered]

Generating more biomass

electricity in CHP plant,

and replacing oil in local

boilers

Indoor climate control

of buildings – passive

integration of TES

1-5 [kg/m2-year] Lowering energy demand

for indoor comfort control

(heating/cooling)

Active climate control

of Supermarket in

Turkey – Heat Pump +

ATES

950 [kg/kWh consumed] Saving electricity due to

higher COP of Heat Pump

Closed Greenhouse

with ATES (Turkey)

8 [kg/ MWh produced ] Electricity savings for

heating

Dishwasher with

zeolite

500 [kg/ dishwasher-year] Lowering energy

consumption from

appliances

718

719

720

721

722

34

5 Conclusions723

724

Thermal energy storage is one of the technologies with potential to reduce the GHG 725

emissions as being part of technologies such as energy supply, buildings, and industry. 726

727

The CO2 mitigation potential of real case studies which include thermal energy storage 728

(TES) is assessed. The CO2 mitigation potential is analysed by calculating the 729

operational CO2, which is the CO2 mitigated during the operation phase of the 730

component/application and the embodied CO2, which is the CO2 released to the ambient 731

while the component/application is made. 732

733

When performing these types of environmental analysis it is important to keep in mind 734

that they depend on the energy mix of the country and on the CO2 emission factor. It 735

should be highlighted that due to the low precision of the eco-attributes related to 736

energy and carbon footprint, it is accepted that there is an uncertainty of about 10 - 20% 737

for decision making. 738

739

The applications with TES presented in this article belong to the work performed in the 740

group Annex 25 “Surplus heat management using advanced TES for CO2 mitigation” of 741

the Energy Conservation through Energy Storage Implementing Agreement (ECES IA) 742

of the International Energy Agency (IEA). 743

744

In this paper a variety of technologies has been assessed in terms of the energy savings, 745

and resulting CO2 mitigation potential from integrating TES. Results are difficult to 746

compare since TES is always designed in relation to its application, and each 747

technology impacts the energy system as a whole to different extents. The applications 748

analysed are refrigeration, solar power plants, mobile heat storage in industrial waste 749

heat recovery, passive systems in buildings, ATES for a supermarket, greenhouse 750

applications, and dishwasher with zeolite in Germany. The paper shows that the reason 751

for mitigation is different in each application, from energy savings to larger solar share 752

or lowering energy consumption from appliances. The mitigation potential dues to 753

integrated TES is quantified in kg/MWh energy produced or heat delivered. 754

755

35

Finally, embodied CO2 in two TES case studies is presented, buildings and solar power 756

plants. It includes the embodied energy involved in the extraction, primary production, 757

transformation, transport to its place of use and recycling. Similarly to operational CO2, 758

to translate the embodied energy into embodied CO2 in any application, the energy mix 759

factor should be used. 760

761

762

Acknowledgements 763

764

The work was partially funded by the Spanish government (project ENE2011-22722 765

and ENE2011-28269-C03-02). The authors would also like to thank the Catalan 766

Government for the quality accreditation given to their research group GREA (2014 767

SGR 123) and DIOPMA (2014 SGR 1543). Laia Miró would like to thank the Spanish 768

Government for her research fellowship (BES-2012-051861). The research leading to 769

these results has received funding from the European Union's Seventh Framework 770

Programme (FP7/2007-2013) under grant agreement n° PIRSES-GA-2013-610692 771

(INNOSTORAGE). The work of ZAE Bayern in the development of the mobile 772

sorption heat storage was supported by the German Federal Ministry of Economics and 773

Technology under the project code 0327383B. ZAE Bayern thanks the Bosch-Siemens-774

Hausgeräte GmbH for the fruitful collaboration in the development of a sorption storage 775

for dishwashers. 776

777

778

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780

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