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DISTRICT HEATING & HEAT NETWORKSPRESENTATION

LEARNING OBJECTIVESAGENDA

- What is district heating? - Understand basic principles

and advantages of DH

- Potential heat sources – What options are available and

the benefits of CHP

- Pipe materials and properties – Selecting appropriate

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- Pipe materials and properties – Selecting appropriate

pipe materials for each individual project

- Installation and design – What key data is needed to size

a pre-insulated pipe network

- Biogas / Anaerobic digestion – How it works and what

feedstocks can be used

REHAU WORLDWIDETHINK GLOBALLY – ACT LOCALLY

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6 CONTINENTS 174 LOCATIONS OVER 15,000 EMPLOYEES

REHAU DIVISIONS

FURNITURE, HOUSEHOLD APPLIANCES,

HOSES AND INDUSTRIAL DEVELOPEMENTS

UNLIMITED POLYMER SOLUTIONS

Industry

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EXTERIOR, WATER MANAGEMENT, AIR

MANAGEMENT & SEALING

WINDOW AND CURTAIN WALLING

TECHNOLOGY, BUILDING TECHNOLOGY,

CIVIL ENGINEERINGBuilding

Solutions

Automotive

Hot water or steam is centrally produced

- Transported via insulated pipe network

- Connected to individual properties via a heat interface unit

WHAT IS DISTRICT HEATING?DEFINITION

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- Connected to individual properties via a heat interface unit

- Heat metered

- Heat delivered via conventional heating systems

More efficient to produce energy locally - minimise losses

Community based heat sources (e.g. central biomass plant)

maximise benefits of renewables

Future proof – easy to change fuel source

WHAT IS DISTRICT HEATING?BENEFITS

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Minimise maintenance using one central plant – no individual

gas checks required

USE OF DISTRICT HEATINGAUSTRIA COMPARED TO EUROPE

Percentage of Houses Supplied by District Heating

40%50%60%70%80%90%

100%

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0%10%20%30%40%

Icela

nd

Denmar

k

Estoni

a

Poland

Sweden

Slovak

ia

Finlan

d

Hunga

ry

Austri

a

Germ

any

Nethe

rland

s

UK

Austria: District Heating now nearly 11%

Lack of district heating (DH) experience in Austria -> Higher

cost to install as perceived as ‘higher risk’

Lack of awareness of DH and historically poorly conceived

schemes

WHAT IS DISTRICT HEATING?POTENTIAL BARRIERS

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Community acceptance required – once installed, closed

network, no possibility to switch provider

Control of tariffs for varying usage from end users

HEAT SOURCE OPTIONSOFF-SITE & ON-SITE HEAT GENERATION

Waste heat from power stations

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Waste heat from power stations

Energy from Waste (EfW) plants

On-site CHP (fossil fuel or renewable)

Central boiler (fossil fuel or renewable)

COMBINED HEAT AND POWERBASIC PRINCIPLE

Energy in 100%

Heat losses 70%

Useful electricity 30%

Traditional power plant

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Useful heat 55%

Useful electricity 30%

Heat losses 15%

Energy in 100% +

Combined heat & power plant (CHP)

CHP offers the following benefits:

- Produces both heat and electricity on site

- More efficient use of energy - 80-90% efficient

- Cost savings of 15-40% compared to traditional

COMBINED HEAT AND POWERHOW IT WORKS

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- Cost savings of 15-40% compared to traditional

methods (gas boilers and national grid)

- Responsive heat supply – heat can be stored

Not fuel source dependent - powered either using fossil fuels or renewable sources (such as biomass or biogas).

Biomass district heating schemes work well because:

• Biomass boilers are often bulkier than traditional boilers, hence

typically located in external plant room, not individual houses

BIOMASS CHPINTRODUCTION

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• Require regular wood chip or pellet deliveries to only one

central plant

• Can be located discreetly on site extremes

PRE-INSULATED PIPEWORKOPTIONS FOR PIPE MATERIALS

Steel pipe with PU

foam

Polymer pipe with

PU foam

Polymer pipe with PEX

foam

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(closed cell - bonded)(closed cell - bonded) (closed cell – non-bonded)

PRE-INSULATED PIPEWORKSTEEL PIPES

Advantages:

- Strong material – resistant to impact damage

- Larger diameter sizes available

- Capable of withstanding higher flow temperatures / pressure

Disadvantages:

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Disadvantages:

- Only straight lengths possible

- Joints required every 6-12m

- High installation costs

- Corrosion problems (therefore warning systems are required)

- Specialist welding required

λ ≈ 0.024 W/mK

Closed cell insulation:

Advantages:

- Excellent thermal insulation

- No water ingress if outer jacket punctured

- No thermal expansion (self-compensating)

- More flexible compared to steel

PRE-INSULATED PIPEWORKTWO TYPES OF PIPE INSULATION – CLOSED CELL

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- More flexible compared to steel

- Long coil lengths possible (less joints)

Disadvantages:

- Less flexible compared to open cell

λ = 0.022 W/mK

PRE-INSULATED PIPEWORKTWO TYPES OF PIPE INSULATION – OPEN CELL

Open cell insulation:

Advantages:

- Greater flexibility

- Simpler jointing / installation (foam easily removed)

- Ideal for confined spaces

- Long coil lengths possible (less joints)

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- Long coil lengths possible (less joints)

Disadvantages:

- PU closed cell pipes have improved thermal insulation

λ = 0.043 W/mK

PRE-INSULATED PIPEWORKHYBRID SYSTEM

Possible to combine steel & polymer for large DH

schemes.

Benefits are:

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- High temperature / volume steel mains

- Cost-effective to install flexible polymer house

connections

- Can use polymer for smaller mains off ‘spines’

Most flow temperatures are ca. 80°C:

- Reduced heat losses

- Extends pipe lifespan

- Makes a safer network (no steam)

DELTA T OF DISTRICT HEATING NETWORKSIMPORTANCE OF OPTIMISING THE FLOW / RETURN TEMPERATURES

Flow / return

temperatures (C)

Heat load

(kW)

Pipe size

required

82-71 350 110mm

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Ensure return temperature is as low as possible (high ∆T):

- Reduces pipe size - > reduce capital costs

- Ensures low-grade heat can be used (e.g. Waste heat from

CHP)

82-71 350 110mm

80-60 350 75mm

80-50 350 63mm

With an operating pressure of 6 bar, the service life of the pipes is min.

30 years under the following conditions:

- Continuous operating temperature of 85°C

- Continuous operating temperature of 80°C,

- with 90°C for one month per year and 95°C for 100 hours per year

LIFESPAN OF DISTRICT HEATING NETWORKSTEMPERATURE AND PRESSURE

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Cross-linked polyethylene (PE-Xa) has the following benefits:

• Temperature resistant to +95ºC

• High chemical resistance

• Oxygen barrier

• Simple jointing process

PRE-INSULATED PIPEWORKSIMPLIFIED STEPS TO DESIGN A HEAT NETWORK

5 kW 8 kW11 kW7 kW

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1. Calculate heat

loads for each

dwelling

2. Identify heat

source & required

capacity

3. Pipe sizing (based

on flow rates &

pressure losses

4. Create bill of

materials

Biomass boiler

31kW

Zoning the area:

- Based on proximity to buildings

- Add the heat loads to form a cumulative for each

zone

- Size the pipe based on flow rates and pressure

losses

Example DH network:

PRE-INSULATED PIPEWORKZONING DIFFERENT PARTS OF THE NETWORK

Zone 1 Zone 4

Zone 2 Zone 3 Zone 5

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Example DH network:

Zone use Total Heat load

Zone 1 10 houses – each 5kW 50kW

Zone 2 15 houses – each 5kW 75kW

Zone 3 Primary school 75kW

Zone 4 Office 150kW

Zone 5 15 houses – each 10kW 100kW

Total heat load is

450kW

∆T = 10K

Plant Room

Zone 4

150 kWZone 1

50 kW

250 kW

A

B

C

D

E

PRE-INSULATED PIPEWORKEXAMPLE OF ZONING

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Zone 5

100 kW

Zone 3

75 kW

Zone 2

75 kW

450 kW 400 kW 100 kW

B D

F

∆T = 10K

Plant Room

Zone 4

150 kWZone 1

50 kW

250 kW

90 mm

A

B

C

D

E

PRE-INSULATED PIPEWORKEXAMPLE OF ZONING

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Supply pipe feeding into buildings

(32mm)

Zone 5

100 kW

Zone 3

75 kW

Zone 2

75 kW

450 kW

110 mm

400 kW

110 mm

100 kW

63mm

B D

F

Total costs

Co

sts

OPTIMAL NETWORK DESIGNBALANCE OF INVESTMENT & OPERATIONAL COSTS

The goal should be, optimal network design in order to minimize the total annual costs - sum of investment

costs and operating costs, based on a certain period of use!

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Heat loss costs

Investment costs

Pumping costs

Co

sts

Pipe diameter

OPERATING HOURS OF HEAT NETWORKS HEAT DEMANDS PLOTTED OVER ONE YEAR

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15 days

New building

Fac

tor

DIVERSITY OF HEAT NETWORKSIMPACT OF DIVERSITY FACTOR

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Old building

Renovated old building

Numbers of connections

Div

ersi

tyF

acto

r

Standard network Ring network

HEAT NETWORK GEOMETRYSTANDARD VS RING MAIN

Heat

source

Heat

source

Heat

source

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Typically a branch network (with a main distribution pipe) is used. However, a ring main offers some benefits

for certain projects:

- Allows multiple heat sources (future connections)

- Flexibility of design

- Reliability

- Redundancy

PRE-INSULATED PIPEWORKINSTALLATION

- Cover 600mm minimum 800mm with traffic loads

- 100mm of 0.8mm grade sand around the pipe

- Pipe positions:

- Besides each other

- On top of each other

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- On top of each other

Warning tape must be used!

PRE-INSULATED PIPEWORKINDIRECT CONNECTIONS

Indirect connections:

• Each house needs a heat interface unit (HIU) off the DH network

• Individual house metering monitors & control and then bills based on

the amount of heat used

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the amount of heat used

• ‘Smart metering’ – no site readings

• Typically operated by Energy Supply Companies

Direct connections can also be used (no HIUs required) but each property

is not isolated, therefore not normally preferred.

SPECIAL APPLICATIONS – ANAEROBIC DIGESTIONINTRODUCTION

District heating

Solid waste for

fertilizer

1. Cow manure is heated to

produce methane

2. Methane generated sent to CHP

unit for electrical generation.

3. Excess heat from CHP fed back

into fermenter and used for

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CHP supplies

electricity to grid

Fermenter Biogas powered

CHP

Liquid animal

waste

into fermenter and used for

district heating

4. Solid waste reused as fertiliser

BIOGAS / ANAEROBIC DIGESTIONPOSSIBLE FEEDSTOCKS

Organic substances which can be used in anaerobic

digestion systems:

- Animal waste (e.g. cow / pig manure)

- Unused crops (leaves, stalks) & grass cuttings

- Slaughterhouse waste

- Food waste

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- Food waste

SPECIAL APPLICATIONS - UTESUNDERGROUND THERMAL ENERGY STORAGE

In district heating networks with renewable

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energy sources (e.g. solar thermal), excess

heat is wasted in the summer.

COMBINING DISTRICT HEATING WITH UTESUNDERGROUND THERMAL ENERGY STORAGE

Using underground thermal energy storage with intelligent controls, optimum use of all energy sources can be

achieved.

The excess heat in summer can then be efficiently stored and then utilised in winter with an increased efficiency.

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0

100

200

300

400

500

600

700

800

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Hea

t re

qu

irem

ent

MW

h/m

on

th

Heat requirement Available solar energy

Summer

storage

Use heat

in winter

COMBINING DISTRICT HEATING WITH UTESTYPICAL SCHEMATIC

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Source: Drake Solar Landing Community

Live operation data can be found here: www.dlsc.ca

Bioenergy village, Effelter, Germany

- 160 kW Biogas plant

- Uses DH CHP system to deliver heat to 36 houses, fire

station and restaurant

DISTRICT HEATING & HEAT NETWORKS CASE STUDIES

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- Additional wood chip biomass boiler for peak demands

- System produces 1.1 million kWh/a

- CO2 saving of 370,000 kg/a

Much Fawley Farm AD plant, Herefordshire

- AD plant fed by slurry, maize & silage

- RAUVITHERM pipework connects hot water from CHP to

chicken sheds

ANAEROBIC DIGESTION CASE STUDY

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- 2,500m of pipework in total (75 UNO & 32 DUO)

Braedstrup District Heating & Solar Park, Denmark

CASE STUDY

DISTRICT HEATING & UNDERGROUND ENERGY STORAGE

System description

-1,400 homes

- DH network owned by community

- 6MW system (3,800 MWh/a)

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Heat sources:

- 16,000m² solar collectors

- Heat pump

- Peak heating through district heating network

Heat storage:

- 2,500m³ buffer tank(hot water)

- 50 PE-Xa probes at 50m deep

Solar Storage & District Heating, Crailsheim, Germany

CASE STUDY

DISTRICT HEATING & UNDERGROUND ENERGY STORAGE

System description

- 260 dwellings, school, sports hall

- 4100 MWh/a with network temperatures flow/return

65/35°C

Heat sources:

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Heat sources:

- 7,300m² solar collectors with 5,1MW peak output

- 750 kW heat pump

- Supplementary heating through district heating

network

Heat storage:

- 100m³ high temperature peak load storage (hot water)

- 480m³ buffer storage (hot water)

- 43,200m³ ground-source probe underground storage

(80 PE-Xa probes)

SUMMARY

- Understand the pros and cons of DH networks and they can be best utilised.

- Use the benefits of on-site generation with CHPs to reduce demand on fossil fuels and increase

system efficiencies

- Selecting appropriate pipe materials for each individual project, based on pros and cons of steel and

polymer

© REHAU

polymer

- Designing a well-sized DH system is vital for ensuring highest possible energy efficiencies and low

pressure losses.

- Understand how anaerobic digestion works and the potential of producing energy from waste (and

reducing landfill)

Building Solutions

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