Design and comparison of two different optimized solar ......Hassam ur Rehman, Janne Hirvonen, Kai 6LUHQ ³ Performance comparison between optimized design of a centralized and semi-decentralized

Design and comparison of two different optimized solar

district heating typologies for Finnish Conditions

IBPSA-Nordic

Aalto University, Finland

27th -28th September 2018

Hassam ur Rehman

School of Engineering, Department of Mechanical Engineering

HVAC group

Hassam ur Rehman PhD Student

2

Background and challenges: Finland

• Building are largest consumers of energy in Finland Two solar community concepts: Kerava (1980s) and Eko-

Viikki (without seasonal storage).

• At high latitudes there are four major challenges: The weather is extremely cold during winters The annual mismatch between irradiation and demand Losses from the seasonal storage are high-ground condition The resulting energy costs are not yet competitive

• Seasonal storage is essential in Nordic conditions. Borehole TES (BTES)

• We found that, solar district heating is influenced by Climate of the location and controls


3

Research questions and motivation

Motivation:

• Develop economically competitive, locally optimized solar community concepts (SCC) with around 90% Renewable Energy Fraction (REF) in Finnish conditions.

• Does De-centralized system configuration has any affect and influence on performance?

Design of the centralized and de-centralized solar district heating network in Nordic conditions

• Which important design variables in the system has an affect on the performance? And how much?

Influence of the design variables on the system performance


4

Methodology

• TRNSYS and TRNBuild Simulation – Solver (engine) – Component library, widely used in the simulation community – Solar district systems are designed and simulated on TRNSYS

• MOBO optimizer – Multi-objective optimization – Genetic algorithm – Optimization objectives (minimize the life cycle costs and

purchased electricity)


5

Energy system design- Centralized

• Solar thermal charge Central large warm tank

• BTES charge & discharge via large central warm tank

• Individual house has small hot tank and heat pump

Individual house heat pump takes energy from SPH return

line and charge hot tank

Provide SPH & DHW

• PV is used to provide electricity Excess sold and shortfall

imported via grid

Energy system design- Decentralized

• Hassam ur Rehman, Janne Hirvonen, Kai Siren, “Performance comparison between optimized

design of a centralized and semi-

decentralized community size

solar district heating system,” Applied Energy, vol. 229, pp.

1072-1094, 2018


6

Why De-centralized system?

Proposed/Desgined Case- Community with 100 buildings

• De-centralized solar thermal system Low temperature centralized operation (mainly space heating)

• Potentially less losses through network due to less lengths of domestic hot water piping Hot water is produced inside the houses

• Lower cost

Reference Case- Single Building • 50 kWh/m2/yr space heating and 40 kWh/m2/yr domestice hot water demands, with heat pump (3kW) • No solar thermal or photovotialcs and seasonal storage (BTES)


7

Results-Centralized versus Decentralized system

••••

••••

100

200

300

400

500

600

700

800

20 40 60 80 100

Lif

e c

ycle

co

st

(€/m

2)

Purchased energy (kWh/m2/yr)

Centralized energy system(Pareto front)

Decentralized energy system(Pareto front)

Reference single building

Design variables Types of

variables System type

Range/ Values

(total for 100

houses)

Prices (€)

ST area (m2) Continuous Decentralized 50-6000 1000―550 €/m2 Centralized 500-6000 600―550 €/m2

PV area (m2) Continuous Both systems 50-6000 450―200 €//m2 Hot tank

volume/house

(m3)

Continuous Decentralized 0.5-5/house 900―810 €/m3

Centralized 1-5/house 850―810 €/m3 Warm tank

volume (m3) Continuous

Decentralized 300-500 900―810 €/m3 Centralized 150-500

BTES aspect ratio

Continuous Both systems

0.25-5 3€/m3(excavation for insulation

and piping)

+33.5€/m(drill)+88€/m3 (1.5 m

thick insulation)

BTES borehole

density 0.05-0.25

BTES volume (m3) 10,000-70,000

Hot tank charge

set points (oC) Continuous

Decentralized 60-75 oC (for heat

pump)

Centralized 68-83 oC (for

collector)

Warm tank charge

set points (oC) Continuous Both systems 35-50 oC

Building

quality/configurati

on

Discrete Both systems

Type 1: space

heating demand=

25kWh/m2/yr

15,628

€/building

Type 2: space

heating demand=

37kWh/m2/yr

13,260

€/building

Type 3: space

heating demand=

50kWh/m2/yr

12,655

€/building

Centralized system • DHW in the centralized building

De-centralized system • DHW heating in the buildings

Hassam ur Rehman, Janne Hirvonen, Kai

Siren, “Performance comparison between optimized design of a centralized and semi-

decentralized community size solar district

heating system,” Applied Energy, vol. 229, pp. 1072-1094, 2018


8

Results- Cost breakdown

0

100

200

300

400

500

600

700

800

1 5 9

13

17

21

25

29

33

37

41

45

49

53

57

61

65

69

73

77

81

85

89

93

97

101

105

109

113

117

121

125

129

133

137

141

Lif

e cy

cle

cost

bre

ak

dow

n (€/

m2)

Configurations

Purchased electricity cost Borehole seasonal storage cost

Building cost Photo voltaic panels cost

Warm tank cost Hot water tank cost

Solar collector cost

Renewable energy fractionheat = 57%


0

100

200

300

400

500

600

700

800

1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89 93 97 101105109

Lif

e cy

cle

cost

bre

ak

dow

n (€/

m2)

Configurations

Purchased electricity cost Borehole seasonal storage cost

Building cost Photo voltaic panels cost

Warm tank cost Hot water tank cost

Solar collector cost



Centralized

system

Decentralized

system


9

Results- Design variable (Collectors and PV)

• Larger area of collectors

0

1000

2000

3000

4000

5000

6000

1

10

19

28

37

46

55

64

73

82

91

100

109

118

127

136

So

lar

ther

ma

l co

llec

tor

are

a

(m2)

- C

entr

ali

zed

Configurations

a

0

1000

2000

3000

4000

5000

6000

1 7

13

19

25

31

37

43

49

55

61

67

73

79

85

91

97

103

109

So

lar

ther

ma

l co

llec

tor

are

a

(m2)

- D

ecen

tra

lize

d

Configurations

b

0

1000

2000

3000

4000

5000

6000

7000

1

10

19

28

37

46

55

64

73

82

91

100

109

118

127

136

Ph

oto

vo

lta

ic p

an

els

are

a (

m2)

-

Cen

tra

lize

d

Configurations

a

0

1000

2000

3000

4000

5000

6000

7000

1 7

13

19

25

31

37

43

49

55

61

67

73

79

85

91

97

103

109

Ph

oto

vo

lta

ic p

an

els

are

a (

m2)

-

Dec

entr

ali

zed

Configurations

b

Centralized Decentralized

Collectors

PV

• Less area of collectors

Collectors

PV






10

Results- Design variable (BTES)

Large BTES volume, less depths and more boreholes


0

1000

2000

3000

4000

5000

6000

0

5000

10000

15000

20000

25000

30000

35000

40000

450001 9

17

25

33

41

49

57

65

73

81

89

97

105

113

121

129

137 S

ola

r th

erm

al

coll

ecto

r a

rea

(m

2)

Bo

reh

ole

th

erm

al

ener

gy

sto

rag

e

vo

lum

e (m

3)

- C

entr

ali

zed

Configurations

BTES volume (m3)

Solar collector area (m2)

a

0

1000

2000

3000

4000

5000

6000

0

50

100

150

200

250

300

350

1 9

17

25

33

41

49

57

65

73

81

89

97

105

113

121

129

137

So

lar

ther

ma

l co

llec

tor

are

a (

m2)

Dep

th (

m)

& N

um

ber

of

bo

reh

ole

s

Configurations

Depth of borehole (m)Number of boreholesSolar collector area (m2)

a

Large BTES volume, less depths and more boreholes

0

500

1000

1500

2000

2500

3000

3500

9600

9800

10000

10200

10400

10600

10800

1 7

13

19

25

31

37

43

49

55

61

67

73

79

85

91

97

103

109

So

lar

ther

ma

l co

llec

tor

are

a

(m2)

Bo

reh

ole

th

erm

al

ener

gy

sto

rag

e v

olu

me

(m3)

-

Dec

entr

ali

zed

Configurations

BTES volume (m3)Solar collector area (m2)

b

0

1000

2000

3000

4000

5000

6000

0

50

100

150

200

250

300

350

1 7

13

19

25

31

37

43

49

55

61

67

73

79

85

91

97

103

109

So

lar

ther

ma

l co

llec

tor

are

a (

m2)

Dep

th (

m)

& N

um

ber

of

bo

reh

ole

s

Configurations

Depth of borehole (m)

Number of boreholes

Solar collector area (m2)

b






11

Results- Design variable (Hot tank set point)

• Higher setpoint- Collector


• Lower setpoint- Heat pump

0

10

20

30

40

50

60

68


12

Results- Distribution operating temperature

• Centralized network has 40 % higher losses compared to decentralized network – Decentralized system has 400 m length of heating network, where as centralized system

has 4000 m length for 100 buildings

0

100

200

300

400

500

600

700

0

10

20

30

40

50

60

70

Centralized district heating system Decentralized district heating network

Lif

e cy

cle

cost

(€/

m2)

Dis

tric

t te

mp

era

ture

(oC

)

Operating temperatures of the network

(4000 m)

Life cycle cost of the system

Purchased electricity = 28 kWh/m2/yr

Collector area= 3750 m2

Photovoltaic area= 5912 m2

Building demand = 50 kWh/m2/yr

BTES volume = 22000 m3

Hot tank volume = 151 m3

Warm tank volume = 179 m3

Purchased electricity = 28 kWh/m2/yr

Collector area= 462 m2

Photovoltaic area= 5854 m2

Building demand = 37 kWh/m2/yr

BTES volume = 10342 m3

Hot tank volume = 238 m3

Warm tank volume = 355 m3






13

Results-Economic sensitivity





100

200

300

400

500

600

700

800

900

1000

20 30 40 50 60

Lif

e cy

cle

cost

(€/

m2)

Purchased electricity (kWh/m2/yr)

Reference (Pareto Front)-

Centralized system

25% increase in Electricity price

(Pareto front)

25 % decrease in PV price

(Pareto front)

25 % decrease in collector price

(Pareto front)

100

200

300

400

500

600

700

800

900

1000

20 25 30 35 40

Lif

e cy

cle

cost

(€/

m2)

Purchased electricity (kWh/m2/yr)

Reference (Pareto Front)-

Decentralized system

25% increase in electricity price

(Pareto front)

25% decrease in PV price (Pareto

front)

25% decrease in collector price

(Pareto front)

Parameter Value Trend Reference

Electricity price 25 % Increase Peak oil news, “Trends In The Cost Of Energy,” 2013. [Online]. Available: http://peakoil.com/alternative-

energy/trends-in-the-cost-of-energy. [Accessed 2018].

Collector and photovoltaic 25 % Decrease J. Sanchez, “PV Market Trends,” 2012. [Online]. Available: https://www.homepower.com/articles/solar-

electricity/equipment-products/pv-market-trends.

[Accessed 2018].

Decentralized Centralized


14

Summary

22.11.2017 14

• Community energy system is better both technically and economically compared to single building heat pump system.

• Community sized solar district heating systems for higher latitudes can achieve renewable energy fraction of 57-90%.

• Decentralization can reduce the life cycle cost by 35% and losses in the network by 40% compared to centralized system.

• Number of boreholes and volume of storage increased when the performance improved, on the other hand the depth of the boreholes decreased.

• The set points are sensitive to the system typology and the hydraulic connections.

• The Pareto fronts are more sensitive to the electricity price in worst performance cases, and more sensitive to the component prices in best performing cases.

Thank you


Hassam ur Rehman

PhD Candidate

Department of Mechanical Engineering

Aalto University, Finland

Reference Hassam ur Rehman, Janne Hirvonen, Kai Siren, “Performance comparison between optimized design of a centralized and semi-decentralized community size solar district heating system,” Applied Energy, vol. 229, pp. 1072-1094, 2018

Documents

Design and comparison of two different optimized solar ......Hassam ur Rehman, Janne Hirvonen, Kai 6LUHQ ³ Performance comparison between optimized design of a centralized and semi-decentralized