Oddgeir Gudmundsson Application Specialist Marek Brand Application Specialist Jan Eric Thorsen Director Danfoss District Heating Application Centre DK Nordborg Content Introduction Concept ID: 482582
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Slide1
Utilization of return water in district heating networks
Oddgeir Gudmundsson
Application Specialist
Marek Brand
Application Specialist
Jan Eric Thorsen
Director
Danfoss District Heating Application Centre
DK-
NordborgSlide2
Content
Introduction
Concept
Technology
Cases
ConclusionSlide3
Introduction
For district heating to maintain economic feasibility in the worlds energy structure it is important to allow the concept to develop
A clear development can be seen when considering how the network temperature levels has changed from the 1
st
generation towards the 4
th
generation district heating systems
This development has increased the network efficiency through reduced heat losses and also opened up for variety of new heat sources
At the same time the distribution pipes and the pipe insulation has been developed in effort to further reduce the distribution heat losses and to simply the process of constructing the distribution network
Similarly the control equipment and heat exchanger units have been developed to optimize the system operation
This development has occurred for the last 30 years, however majority the building stock is still the same or may have been lightly renovated through that time
New and renovated buildings generally have lower
temperature level requirements.
This fact has opened up for cascading usage of the energy supplied through the district heating networkSlide4
1G
2G
3G
4G
IntroductionSlide5
Concept
District heating schemes are operating with various temperature levels depending on the original design of the network and the connected building stock
In many cases existing buildings may require high supply temperatures and consequently have high return temperatures,
f.ex
. supply of 90-100°C and return of 40-60°C
Sufficient temperature levels vary and depend on the heating installations
New energy efficient buildings with floor heating installation only need supply temperatures of 35-40°C to fulfill their heating requirement
Domestic hot water (DHW) temperature of 45°C
is considered sufficient for everyday use. Having DH supply temperature of 50°C is sufficient for preparing DHW at 45°C via instantaneous heat exchanger solution, without risk of Legionella.
This fact gives the opportunity to utilize the return flow from existing areas in new areas and hence utilize the capacity of existing DH networks to a greater extend with minimum investment costs.Utilize further the capacity of the distribution networkIncreased efficiency at the plant due to lower return temperatureReduced heat losses in the return lineSlide6
Conceptual example of cascading energy usage in district heating
All energy classes
Newly
constructed / renovated
areas
D
D
multi-apartment
single-family
C
C
C
C
Recently build and renovated
C
C
C
C
F
F
F
F
F
F
F
Non-renovated older buildings
CHP waste incineration
CHP natural gas
Large scale solar
A
A
Low-energy
buildings
High temperature
supply, 90°C
High temperature
return, 50°C
Low temperature
return, 25°CSlide7
Utilization of return water for existing buildings
Renovation of the existing network
Low Temperature District HeatingSlide8
Low Temperature DH for existing buildings
Project supported by the Danish government
75 single-family buildings from 1997
Floor heating
Realisation
New low-temperature DH in-house substation
New DH network
Heat loss reduced from 41% -> 14%
80% of heat demand supplied
from main DH return line
Before transition average T
supply = 70-75°CAfter transition average Tsupply = 55°CSlide9
Area substation
As the
DH
return temperature can vary it may become necessary to raise the return temperature before it is supplied to the secondary network
This
can be achieved by mixing the return water with hot water from the main DH supply pipeline
Primary network
T
supply
=
90
°C
Treturn
=52°CTreturn
=26°C
S
ø
nderby
Area substation
Sønderby
low temperature DH
T
supply
=
52
°C
Sønderby
Last consumerSubstation at the consumerThermostatic bypassSlide10Slide11
Micro booster – Reduced temperature levels
Ultra-Low Temperature District HeatingSlide12
Objective: Maximum utilization of district heating return flow
Ultra-Low Temperature DH for existing buildings
Project supported by the Danish government
4 single-family buildings from before 1960
Radiators
, mix of 1 pipe and 2 pipe systems
Realization
Micro heat pump DH substation in each house to boost the supply temperature for instantaneous preparation of Domestic Hot Water
New U-LTDH network
Heat loss only 46% of the heat loss that would be experienced in a traditionally designed networkArea heat exchanger substation connected to the main district heating network regulates the supply temperatureSupply temperature kept as low as possible at all times
Area substationSlide13
For floor heating temperature levels of 30-40°C are sufficient
Domestic hot water of 45°C is sufficient for all normal
use
With instantaneous preparation of DHW there is no risk of Legionella
Micro heat pump unit boost the supply temperature to
53-55°C
and stores the water in a primary side located storage tank until DHW tapping occurs
Condenser
Evaporator
Instantaneous DHW preparation
No Legionella risk
DH side storage tank
Micro booster concept
Micro booster installedSlide14
Heat exchanger area substation
The aim of the substation is to maintain constant secondary side temperature of 40°C
As
the DH return temperature can vary
primary side supply is mixed with the return to maintain constant 45°C supply to the heat exchanger by means of a pump controlSlide15
Pump
Pressure gauge m.
afsp
.
og
studs
Temperatur
sensor
Thermometer
One-way valve,
check valve
Energy meter
Control valve
Shut-off valve, NL normally closed
M
FE
Frequency control
Heat exchanger
Expansion vessel
s
Controller
FVF
FVR
M
To
Manenvej
T2
T_outside
FE
s
Expansion vessel
Max. Flow 6 m3/h
Pump: TPE 32-80/4
Pump: Magna 40–120F with 10 m head.
30°C
HEX capacity: 70 kW
Kamstrup
energy meter NF installs them
T12
P1
M1
T21
35°C
45°C
40°CSlide16
How applicable can this be?Slide17
Low-temperature DH for existing buildings
Supported by the Danish government
8 single-family houses from 1970
With
traditional
radiators
: 70/40/20°C
How much could Tsupply be reduced without sacrificing comfort?
Numerical simulations
Many possibilities
Various refurbishment stages
Low-temperature radiators
Real measurements
Should follow real conditions
R
esults are coming soon…
70°C
4
0°C
heat output
100 %
5
0
°C
33
°C
heat output
55 %same radiatorsṁ = constantSlide18
Duration of
T
sup
over/equal certain temperature
Heating curves for radiators
Single-family-house from 1970 – results from simulation
! !
Low-temperature substation for DHW
T
supply
[°C]
hours above certain temperature [%/a
]
*Extensive renovation = low energy windows + roof insulation
=Slide19
Existing
buildings can be supplied with LTDH already today if
T
supply
is in cold periods increased
above 50
°C
Required
Tsupply to radiators depends on:desired indoor temperaturestate of the building
heating system
DH companies should be more strict in reducing Tsupply
to:reduce heat losses from DH networkintegrate more renewables
DHW
applicatoin
should
always
be changed
to low-temperature
one
LTDH for Existing BuildingsSlide20
Conclusions
There is a potential to further utilize the capacity of existing district heating network and reduce the network return temperature significantly by cascading the energy use
Studies show that with light renovation of buildings the requirements to the DH supply temperature sinks significantly
As new areas are built or building areas renovated close to existing district heating network it is possible to establish district heating network with low investment costs utilizing the remaining heat in the return pipeline from the existing DH grid Slide21
Thank you for the
attention
Contact information:
Oddgeir Gudmundsson
Application Specialist, Application Centre
Danfoss District Energy, DK-
Nordborg
og@danfoss.com