optimisation of dh network design · innovative dh breakfast seminar, 3rd december 2014: markus...

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OPTIMISATION OF DH NETWORK DESIGNInnovative DH Breakfast Seminar, 3rd DECEMBER 2014: MARKUS EURING

OPTIMISING HEAT NETWORK DESIGNDISTRICT HEATING OPERATING HOURS

© REHAU - - 03.12.2014

10 days

Total costs

Heat loss costs

Co

sts

OPTIMISING HEAT NETWORK DESIGNBALANCE OF CAPITAL COSTS & OPERATIONAL COSTS

© REHAU - - 03.12.2014

Capital costs

Pumping costs

Pipe diameter

1) Calculating the correct heat load

2) The impact of diversity

OPTIMISING HEAT NETWORK DESIGN4 AREAS TO FOCUS ON

© REHAU - - 03.12.2014

3) Optimising the flow/return temperatures (pipe sizing)

4) Reducing installation costs

1) CALCULATING THE CORRECT HEAT LOADOPTIMISING HEAT NETWORK DESIGN

What can happen....

- Heat loads are only roughly estimated

- Or the heat load from the old boiler is assumed

=> In this case the heat loads are normally too high

What is the impact of overestimating heat loads?

© REHAU - - 03.12.2014

What is the impact of overestimating heat loads?

- An inefficient system will be installed

- High investment and operating costs

- The income for selling the heat will be less than

expected

=> The correct heat load is the basis for a efficient

District Heating network

2) THE IMPACT OF DIVERSITYOPTIMISING HEAT NETWORK DESIGN

Over capacity from

using diversity of 1

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.

© REHAU - - 03.12.2014

Using a diversity factor, you can reduce the required

load for the plant and the heat network.

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

means you only must supply for 700 kW.

1000kW x 0.7 = 700 kW

Original (w/o diversity) = 2540 kW

Actual = 1600 kW

=> diversity 0.63 = 1600/2540

2) THE IMPACT OF DIVERSITYREAL LIFE MEASUREMENTS – GERMAN HEAT NETWORK WITH 80 CONNECTIONS

1600kW

© REHAU - - 03.12.2014

Coldest days

Feb 2012 April 2012

1) + 2) CALCULATING HEAT LOAD + DIVERSITYDESIGN THE CORRECT BOILER SIZE(ES) => MODULAR POWER SEPARATION

Base load boiler

Peak load boiler

© REHAU - - 03.12.2014

3) OPTIMISING FLOW/RETURN TEMPERATURES (PIPE SIZING)IMPORTANCE OF DELTA T IN A DHN

∆T

1

2

© REHAU - - 03.12.2014

Q = f * c * ∆T

Q...= transported power

f...= flow rate

c...= thermal capacity of water

∆T...= difference between flow and return

~> same Q by 3 *∆T => Q = 1/3 f * c * 3 ∆T

∆T

2867/8600=1/3

Higher delta T

=> lower flow rates

=> Smaller pipe sizes

2

3) OPTIMISING FLOW/RETURN TEMPERATURES (PIPE SIZING)RETURN TEMERATURE IN A DHN

60 °C

60 °C

70 °C

65 °C

50 °C

60 °C

60 °C

Return temperature depends on

• Heating system (radiator, UFH, ...)

• Heat interface unit specification

• Hydraulic balance, yes or no?

© REHAU - - 03.12.2014

80 °C

60 °C

60 °C

60 °C

Power plant

Heat customer

Heat interface unit (HIU)

3) OPTIMISING FLOW/RETURN TEMPERATURES (PIPE SIZING)HYDRAULIC BALANCE

Without hydraulic balance

Hydraulic balance

• The hydraulic balance is a requirement to supply

the radiator with the proper amount of water

• In a well-balanced heating system, each radiator

© REHAU - - 03.12.2014

With hydraulic balance

• In a well-balanced heating system, each radiator

receives the correct flow of heating water to

match its performance, the return is therefore

cooler

• Hydraulic balance must also be done in DH

network

Modern systems often use flow temperatures of 80°C:

3) OPTIMISING FLOW/RETURN TEMPERATURES (PIPE SIZING)IMPORTANCE OF OPTIMISING TEMPERATURES & EFFECTS ON PIPE SIZING

Flow / return temperatures

(C)

Heat load (kW) Pressure loss (Pa/m) Pipe size required

82-71 450 192 110mm

80-60 450 175 90mm

© REHAU - - 03.12.2014

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 biogas CHP)

80-60 450 175 90mm

80-50 450 202 75mm

3) OPTIMISING FLOW/RETURN TEMPERATURES (PIPE SIZING) IMPORTANCE OF OPTIMISING THE FLOW / RETURN TEMPERATURES

Flow / return

temperatures (C)

Pipe size (mm) Temperature drop (°C)

Heat losses

RAUTHERMEX (F&R)

% heat loss saving

82-71 110 0.94 39.4 kW -

80-60 90 1.01 27.4 kW 30%

© REHAU - - 03.12.2014

80-60 90 1.01 27.4 kW 30%

80-50 75 1.14 21.5 kW 45%

Increased delta T -> Reduced heat losses -> operational costs savings!Assumptions:

10°C soil temperature

1,000m distance

0.8m installation depth

1.0 W/m*K soil conductivity

3) OPTIMISING FLOW/RETURN TEMPERATURES (PIPE SIZING) VARIABLE FLOW TEMPARTURE REDUCES HEAT LOSSES

© REHAU - - 03.12.2014

- Polymer pipes reduce the installation cost due to number of

joints and time/cost of connections

- Backfilling costs can be reduced by installing in ‘soft-dig’

areas

- Optimised pipe trenching can reduce costs

4) REDUCING INSTALLATION COSTSCONSIDER AT DESIGN STAGE

© REHAU - - 03.12.2014

- Optimised pipe trenching can reduce costs

UNO pipe:

- Higher cost doing 2 separate pipe runs

DUO pipe:

- Lower cost than 2 x UNO pipes

- Heat loss is lower!

HEAT LOSSESUNO VS DUO RAUVITHERM

2X UNO 25 = 0.308 W/MK DUO 25 = 0.227 W/MK SAVINGS WITH DUO �� 35%



© REHAU - - 03.12.2014

OPTIMISING HEAT NETWORK DESIGN EXAMPLE COST SAVING WITH OPTIMESED PIPE SIZING

Starting point

50 connections

30 kW per house => 1,500kW

Total network 800 m, using only single pipes

Flow/return temperature 82/71

No diversity

Option 1

Same as option starting point before but:

20 kW per house = 1,000 kW

© REHAU - - 03.12.2014

No diversity

£222k => £187k

125 --> 110140 --> 125

90 --> 75

40 --> 32


Option 1

50 connections

Total load 1000 kW



No diversity

Option 2

Same as option 1 before but:


Using diversity

© REHAU - - 03.12.2014

No diversity

.

£187k => £107k

160 --> 110110 --> 75

75 --> 63

63 --> 50

125 --> 75


Option 2

50 connections

Total load 1000 kW



Using diversity

Option 3

Same as option 2 before but:

50 Total network 800 m, using DUO pipes

Reducing big Tee connections

Reducing pipe sizes on no critical line

© REHAU - - 03.12.2014

Using diversity Reducing pipe sizes on no critical line

£107k => £93k50 --> 40


Price starting point 222k£

After optimising the following:

- Correct loads 187k£

- Diversity+ temperatures 107k£

- Using DUO pipes

- Optimised trenching

Summary

50 connections

20-30 kW per house => 1-1.5 MW

Total network 800 m 93k£

© REHAU - - 03.12.2014

- Critical path

⇒ cost saving = 129k£ (58%)!!!

We reduced the capital costs more than 50%

from the original design provided.

Email: [email protected]

Phone: 01989 762538

Follow us @REHAUrenewables

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Industry

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THANK YOU FOR YOUR ATTENTIONANY QUESTIONS?

optimisation of dh network design · innovative dh breakfast seminar, 3rd december 2014: markus...

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