5. rehau how to optimise heat network design

BEST PRACTICE IN HEAT NETWORK DESIGN Alexandra Ivanchuk, Applications Engineer – 14th June 2016, REHAU DH Workshop, Manchester

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20,000 employees worldwide – experts in polymer

manufacturing

Since 2000, involved in thousands of district heating

projects across Europe

Manufacturer of district heating pipes & fittings

Largest UK stock of district heating pipe

REHAU’s experience of district heating

2 June 2016 / Rowy 2642/ BT GB

REHAU are the only UK-

manufacturer of PE-Xa district

heating pipe. Production started

in May 2012. Est. 30% reduction

in CO2 from UK manufacturing.

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District heating pipe materials: steel (EN 253) or polymer (EN 15632)

Steel pipe with PU foam Polymer pipe with PU foam Polymer pipe with PEX foam

(bonded) (bonded) (non-bonded)


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Advantages:

- Very large diameter sizes available

- Capable of withstanding higher temperatures / pressure than polymers

- Strong material – resistant to impact damage

Disadvantages:

- Only straight lengths possible

- Joints required every 6-12m

- Expansion/contraction joints required

- High installation costs

- Corrosion problems (therefore warning systems are required)

- Specialist welding required

λ ≈ 0.022 W/mK

Steel district heating pipes


>75% of the failures in steel

district heating pipes were due

to on-site welding.

Source: German CHP & District

Heating / Cooling Association,

2013

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Advantages:

- More flexible compared to steel

- No water ingress if outer jacket punctured

- No thermal expansion (self-compensating)

- Long coil lengths possible (less joints)

Disadvantages:

- Steel has higher temperature / pressure limits

- Less flexible compared to non-bonded polymer

pipes

λ = 0.0216 W/mK

Polymer – PU insulation

(bonded)


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Advantages:

- Highly flexible

- Ideal for house connections / congested

installations

- Long coil lengths possible (less joints)

Disadvantages:

- Steel has higher temperature / pressure limits

- Lower insulation performance compared to PU

foam

λ = 0.043 W/mK

Polymer - PEX insulation

(non-bonded)


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Optimising heat network design – a balancing act

Total costs

Heat loss costs

Investment costs

Pump & pumping costs

Cos

ts

Pipe diameter

June 2016 / Rowy 2642/ BT GB

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4 key design areas to focus on

10 June 2016 / Rowy 2642/ BT GB

Correct heat loads

Diversity

Installation costs

Pipe sizing

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1. Calculating the correct heat load

11 June 2016 / Rowy 2642/ BT GB

Only roughly estimated or the old boiler load is

used

Pipes & plant will be oversized

leading to higher heat losses

Income from selling the heat

is less

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It is unlikely for every heat customer to use their peak

load at the same time. This is described as diversity.

The diversity factor is the ratio / percentage of the peak

load really used.

For a heat load of 1MW, a diversity factor of 0.7 means

you only need a 700 kW plant.

1000kW x 0.7 = 700 kW

2. The impact of diversity

12 June 2016 / Rowy 2642/ BT GB

Diversity factor in

the example on

the left

/ 13 June 2016 / Rowy 2642/ BT GB

Coldest days

Original – no diversity (1)

= 2,540 kW

Designed diversity of 0.85

= 2,160 kW

Feb 2012 April 2012

Real life measurement

of diversity from a

German DH network

with 80 connections

Actual = 1,600 kW => diversity 0.63 = 1600/2540

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Example diversity for heat network

14 June 2016 / Rowy 2642/ BT GB

= 10 houses = 5 houses = 1 house

Plant

0.9 0.9

0.9 0.9

0.9

0.70 0.75 0.79 0.83

1

1

0.96

0.96

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- Installing in soft-dig areas saves time & cost

- Polymer pipes reduce the installation costs due

to number of joints and time taken per connection

- Innovative use of tees / secondary spines

- Twin pipes instead of single pipes (where possible)

3. Reducing installation costs

15 June 2016 / Rowy 2642/ BT GB

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Trench routing optimisation

16 June 2016 / Rowy 2642/ BT GB

- Less big tees off header pipe

- More opportunity to use DUO

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2x UNO 25 = 10.9 W/m DUO 25 = 7.6 W/m

Heat loss reduction with DUO 30%

2x UNO 40 = 16.6 W/m DUO 40 = 11.6 W/m


2x UNO 63 = 19.5 W/m DUO 63 = 13.1 W/m


Data at 80/50°C using RAUTHERMEX pipe.

Benefits of using twin pipe

17 June 2016 / Rowy 2642/ BT GB

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4. Optimising the flow / return temperatures

Modern DH systems typically use a flow temperature of ca. 80°C.

Ensure return temperature is as low as possible (high ΔT)

- Reduces pipe size -> reduces capital costs

18 June 2016 / Rowy 2642/ BT GB

Flow / return temperatures (°C) Heat load Pressure loss (Pa/m) Pipe size required

82/71 1.1MW 161 160mm

80/60 1.1MW 183 125mm

80/50 1.1MW 161 110mm

70/40 1.1MW 166 110mm

60/20 1.1MW 280 90mm

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F/R temperatures (°C)

Heat load Pipe sizing OD

(mm)

Heat losses (vs 82/71°C)

PE-Xa lifespan

(24/7 operation)

82/71 1.1 MW 160 <25 years

80/60 1.1 MW 125 10% lower >25 years

80/50 1.1 MW 110 19% lower >25 years

70/40 1.1 MW 110 34% lower >50 years

60/20 1.1 MW 90 69% lower >50 years

19 June 2016 / Rowy 2642 / BT GB

Heat loss assumptions:

10°C soil temperature

1km distance

0.8m installation depth

1.0 W/m*K soil conductivity

CIBSE Code of Practice:

Best practice would aim to achieve return temperatures <55°C for existing buildings

and < 40°C for new buildings.

Optimising the flow / return temperatures

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Project details:

75 connections

20kW per house = 1,500kW

Total network length = 950m

Flow / return temps = 82/71°C

No diversity applied

All UNO pipes

List price = £313k

Heat network optimisation – original design

20 June 2016 / Rowy 2642/ BT GB

160mm (12m lengths)

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Project details:

75 connections




No diversity applied

All UNO pipes

List price = £267k

Heat network optimisation – correct heat loads

21 June 2016 / Rowy 2642/ BT GB

125mm > 110mm 160mm > 140mm

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Project details:

75 connections




Diversity applied of 0.8

All UNO pipes

List price = £218k

Heat network optimisation – using diversity

22 June 2016 / Rowy 2642/ BT GB

160mm > 140mm 125mm > 110mm 110mm > 90mm

75mm > 63mm

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Project details:

75 connections





All UNO pipes

List price = £134k

Heat network optimisation – optimising flow / return temperatures

23 June 2016 / Rowy 2642/ BT GB

140mm > 90mm 110mm > 75mm 90mm > 63mm

House connections - 32mm > 25mm

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Project details:

75 connections





Route optimised

All UNO pipes

List price = £128k

Heat network optimisation – route optimisation

24 June 2016 / Rowy 2642/ BT GB

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Project details:

75 connections





Route optimised

Use DUO pipes if possible

List price = £123k

Heat network optimisation – use of DUO pipes

25 June 2016 / Rowy 2642/ BT GB

ALL DUO

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From these simple steps:

1) Heat load correction from 20kW to 16kW

2) Optimising the route and using DUOs

3) Changing flow temperature from 82/71°C to 70/40°C

4) Diversity factor of 0.8

Cost saving of 60% from the original design.

Heat losses reduced from 23.53kW to 8.98kW which is 63% heat loss reduction.

Heat network optimisation – conclusion

26 June 2016 / Rowy 2642/ BT GB

Can polymer be used for a large

scale heat network? REHAU

supplied 80km of RAUTHERMEX

to the bioenergy village of Lathen

in Germany of 11,000 residents.

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UK Case studies

28 June 2016 / Rowy 2642/ BT GB

- Gaunts Estate – AD plant – 1.6km network

- Soho luxury cottages – Biomass – 7km network

- Eleanor Social Housing – Gas CHP – 2km network

- Tattenhall Retirement Village – Gas – 2km network

- Dundee Social Housing – Gas CHP – 2.5km network

- Portmeirion Village – Biomass – 3km network

THANK YOU FOR YOUR ATTENTION Any questions?

Contact details:

[email protected]

07779 453529

5. rehau how to optimise heat network design

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