1

Implication of low temperature district heating on network investment costs, primary energy savings and 

cost benefits

Ambrose Dodoo, Leif Gustavsson and Nguyen Le Truong

Linnaeus University, Sweden

This presentation is based on an on-going project on:

Low temperature district heating and new energy efficient building blocks

Project partners include Växjöbostäder, Växjö Energi AB and Växjö Municipality

The presented results are preliminary

2

Implication of low temperature district heating on network investment costs, primary energy savings and cost benefits

We consider three types of exploitation of a development area in Växjö, in southern Sweden Low exploitation Medium exploitation High exploitation

We consider two different energy performance of buildings Swedish building code (BBR 2015) Passive house criteria

We consider three temperature levels for district heating network 80/40oC 65/30oC 50/20oC

Project site in southwest of Växjö

Växjö

Växjö is a city of about 65 000 inhabitants

District heating system (DHS)

o ~ 185 MWpeak and ~ 630 GWhheat/year

o ~ 98% of production based on biomass

o 2 CHP plants and several boilers

Measured temperature in DH-network in 2013

3

Project site

A new developed area in Torparängen, Växjö

Planning of ≈ 250 apartments/houses,

– 125 apartments

– 125 row houses and small houses

4, 6, 8 or 10 story-buildings

Different building frames – Concrete

– Wood

• Different heat supply options– District heating

– Electric heat pumps in each building

3D models of different exploitation alternatives

Low exploitation of townhouses and villas,9010 m2 heated floor area

Medium-exploitation of apartment buildings and townhouses, 23 540 m2 heated floor area

High-exploitation of apartment buildings, 29 350 m2 heated floor area

4

Buildings heat demand

Simulated based on current Swedish building code (BBR) and passive house criteria (Passive)

Used for the design and calculation of district heat options

• For apartment buildings:

Building typeSpace heating load (kW / building)

BBR Passive

o 6 storeys, 24 apartments 54.5 27.8

• For row houses:

House typeSpace heating load (kW / house)

BBR Passive

o 2 stories, 6-13 houses/row, 140 m2/house

4.34-6.20 1.80-2.42

0

100

200

300

400

500

600

700

800

900

1000

0 1000 2000 3000 4000 5000 6000 7000 8000

Hea

t d

em

an

d (

kW)

Hour

High

Medium

Low

0

100

200

300

400

500

600

700

800

900

1000

0 1000 2000 3000 4000 5000 6000 7000 8000

Hea

t d

em

an

d (

kW)

Hour

High

Medium

Low

Profiles of total space and hot water demand for the different exploitation areas – hour by hour simulations

BBR Passive

5

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Hea

t d

eman

d (

MW

h)

Space heating

Hot water

Scenario of building exploitation

mediumlow high

0

500

1000

1500

2000

2500

3000

Hea

t d

eman

d (

MW

h)

Space heating

Hot water

Scenario of building exploitation

mediumlow high

Annual space and hot water demands for the different exploitation areas

BBR Passive

Layout of district heat distribution network: Low exploitation of townhouses and villas 

BBR Passive

6

Layout of district heat distribution network: Medium‐exploitation of apartment buildings and townhouses

PassiveBBR

Layout of district heat distribution network: High‐exploitation of apartment buildings

7

0

50

100

150

200

250

Dis

trib

uti

on

lo

sses

(M

Wh)

Scenario of building exploitation

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

mediumlow high

0

50

100

150

200

250

Dis

trib

uti

on

lo

sses

(M

Wh)

Scenario of building exploitation

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

mediumlow high

Local network heat losses for different alternatives and options

BBR Passive

0

500

1000

1500

2000

2500

3000

Dis

tric

t h

eat

use

(M

Wh)

Distribution losses

Hot water heating

Space heating

Scenario of building exploitation

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

mediumlow high

0

500

1000

1500

2000

2500

3000

Dis

tric

t h

eat

use

(M

Wh)

Distribution losses

Hot water heating

Space heating

Scenario of building exploitation

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0o C

50/2

0oC

mediumlow high

Local network heat losses, space and hot water heating demands for different exploitations

Local network losses: 3.9-20.1% in alternatives with BBR standard

7.4-31.8% in alternatives with passive criteria

BBR Passive

8

Primary energy use for local network losses

A biomass-based DHS using the heat load duration curve of Växjö is used for calculation

0

20

40

60

80

100

120

140

160

180

200

0 50 100 150 200 250 300 350

Dis

tric

t h

eat

load

(M

W)

Day

53 MW Wood powder boiler

92 MW Wood chips boiler

40 MW CHP-BST

System:

o ~ 185 MWpeak

o ~ 630 GWhheat/year

The changed primary energy use is considered as marginal

0

50

100

150

200

250

Pri

mar

y en

erg

y u

se (

MW

h)

Scenario of building exploitation

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

mediumlow high

0

50

100

150

200

250

Pri

mar

y en

erg

y u

se (

MW

h)

Scenario of building exploitation

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

mediumlow high

Primary energy use for local network losses

BBR Passive

9

0

100000

200000

300000

400000

500000

600000

Inve

stm

ent

cost

s (€

)

Substations

Network

Scenario of building exploitation

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

mediumlow high

0

100000

200000

300000

400000

500000

600000

Inve

stm

ent

cost

s (€

)

Substations

Network

Scenario of building exploitation

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

mediumlow high

Investment costs for local network and substations

BBR Passive

District heat production costs of annual local network losses

• Using biomass-based district heating system for all the scenarios

• Including capacity cost, fixed and variable O&M costs of each district heat production unit

0

20

40

60

80

100

120

140

160

180

200

0 50 100 150 200 250 300 350

Dis

tric

t h

eat

load

(M

W)

Day

53 MW Wood powder boiler

92 MW Wood chips boiler

40 MW CHP-BST

• Based on marginal cost calculation

10

0

1000

2000

3000

4000

5000

6000

7000

Dis

tric

t h

eat

pro

du

ctio

n c

ost

s (€

)

Scenario of building exploitation

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

mediumlow high

0

1000

2000

3000

4000

5000

6000

7000

Dis

tric

t h

eat

pro

du

ctio

n c

ost

s (€

)

Scenario of building exploitation

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

65/3

0oC

80/4

0oC

50/2

0oC

mediumlow high

District heat production costs of annual local network losses

BBR Passive

Cost implication of reduced supply/return temperatures in local network with 80/40oC as baseline

The difference in annual district heat production cost relative to the baseline is calculated.

The net present value of the cost difference is calculated assuming different real discount rates and lifetimes

6% and 30 years

3% and 40 years

The net present value of the cost difference is compared to difference in investment costs

11

-10000

-5000

0

Yea

rly

cost

s (€

)

Scenario of building exploitation

65/3

0oC

50/2

0oC

65/3

0oC

50/2

0oC

65/3

0oC

50/2

0oC

mediumlow high

0

20000

40000

60000

80000

100000

120000

Inve

stm

ents

(€)

-10000

-5000

0

Yea

rly

cost

s (€

)

Scenario of building exploitation

65/3

0oC

50/2

0oC

65/3

0oC

50/2

0oC

65/3

0oC

50/2

0oC

mediumlow high

0

20000

40000

60000

80000

100000

120000

Inve

stm

ents

(€)

Changes of initial investment costs (read) and yearly district heat production costs (green) with 80/40oC as baseline

BBR Passive

-90000

-80000

-70000

-60000

-50000

-40000

-30000

-20000

-10000

0

10000

NP

V (

€)

Scenario of building exploitation

65/3

0oC

50/2

0oC

65/3

0oC

50/2

0oC

65/3

0oC

50/2

0oC

mediumlow high

-90000

-80000

-70000

-60000

-50000

-40000

-30000

-20000

-10000

0

10000

NP

V (

€)

Scenario of building exploitation

65/3

0oC

50/2

0oC

65/3

0oC

50/2

0oC

65/3

0oC

50/2

0oC

mediumlow high

Increased investment cost minus net present value of reduced local network heat losses with 80/40oC as baseline

Discount rate of 6%

Lifetime 30 years

BBR Passive

12

-60000

-50000

-40000

-30000

-20000

-10000

0

10000

20000

30000

40000

NP

V (

€)

Scenario of building exploitation

65/3

0oC

50/2

0oC

65/3

0oC

50/2

0oC

65/3

0oC

50/2

0oC

mediumlow high

-60000

-50000

-40000

-30000

-20000

-10000

0

10000

20000

30000

40000

NP

V (

€)

Scenario of building exploitation

65/3

0oC

50/2

0oC

65/3

0oC

50/2

0oC

65/3

0oC

50/2

0oC

mediumlow high

Increased investment cost minus net present value of reduced local network heat losses with 80/40oC as baseline

BBR Passive

Discount rate of 3%

Lifetime 40 years

Not so far considered in the analysis

District heat production benefits of operating CHP-plants at lower district heating temperatures

Reduced distribution heat losses in the whole distribution system due to reduced supply/return temperatures

Implications of investment cost for internal distribution of heat in buildings due to different supply/return temperatures