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OPTIMISATION OF DH NETWORK DESIGNInnovative DH Breakfast Seminar, 3rd DECEMBER 2014: MARKUS EURING
OPTIMISING HEAT NETWORK DESIGNDISTRICT HEATING OPERATING HOURS
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10 days
Total costs
Heat loss costs
Co
sts
OPTIMISING HEAT NETWORK DESIGNBALANCE OF CAPITAL COSTS & OPERATIONAL COSTS
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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
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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?
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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.
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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
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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
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3) OPTIMISING FLOW/RETURN TEMPERATURES (PIPE SIZING)IMPORTANCE OF DELTA T IN A DHN
∆T
1
2
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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?
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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
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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
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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 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%
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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
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- 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
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- 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%
2X UNO 40 = 0.412 W/MK DUO 40 = 0.302 W/MK SAVINGS WITH DUO ���� 36%
2X UNO 63 = 0.506 W/MK DUO 63 = 0.360 W/MK SAVINGS WITH DUO ���� 40%
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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
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No diversity
£222k => £187k
125 --> 110140 --> 125
90 --> 75
40 --> 32
OPTIMISING HEAT NETWORK DESIGN EXAMPLE COST SAVING WITH OPTIMESED PIPE SIZING
Option 1
50 connections
Total load 1000 kW
Total network 800 m, using only single pipes
Flow/return temperature 82/71
No diversity
Option 2
Same as option 1 before but:
Flow/return temperature 80/60
Using diversity
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No diversity
.
£187k => £107k
160 --> 110110 --> 75
75 --> 63
63 --> 50
125 --> 75
OPTIMISING HEAT NETWORK DESIGN EXAMPLE COST SAVING WITH OPTIMESED PIPE SIZING
Option 2
50 connections
Total load 1000 kW
Total network 800 m, using only single pipes
Flow/return temperature 80/60
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
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Using diversity Reducing pipe sizes on no critical line
£107k => £93k50 --> 40
OPTIMISING HEAT NETWORK DESIGN EXAMPLE COST SAVING WITH OPTIMESED PIPE SIZING
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£
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- 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
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