Utilization of return water in district heating networks

Nordic Show Room on Energy Quality Management, 27-28th August 2014, O. GUDMUNDSSON, DANFOSS A/S

28.08.2014 | 1

Utilization of return water in district heating networks

Oddgeir GudmundssonApplication Specialist

Marek BrandApplication Specialist

Jan Eric ThorsenDirector

Danfoss District Heating Application CentreDK-Nordborg


28.08.2014 | 2

Content

Introduction

Concept

Technology

Cases

Conclusion


28.08.2014 | 4

1G 2G 3G 4G

Introduction


28.08.2014 | 5

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 network Increased efficiency at the plant due to lower return temperature Reduced heat losses in the return line


28.08.2014 | 6

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

FF

F

FFF

F

Non-renovated older buildings

CHP waste incineration

CHP natural gas

Large scale solar

A

A

Low-energybuildings

High temperature supply, 90°C

High temperature return, 50°C

Low temperature return, 25°C


28.08.2014 | 7

Utilization of return water for existing buildings

Renovation of the existing network Low Temperature District Heating


28.08.2014 | 8

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 Tsupply = 70-75°C

After transition average Tsupply = 55°C


28.08.2014 | 9

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

Tsupply=90°C

Treturn=52°C

Treturn=26°C

Sønderby Area substation

Sønderby low temperature

DH

Tsupply=52°C

Sønderby Last consumer

Substation at the consumer

Thermostatic bypass


28.08.2014 | 10


28.08.2014 | 11

Micro booster – Reduced temperature levels

Ultra-Low Temperature District Heating


28.08.2014 | 12

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 network

Area heat exchanger substation connected to the main district heating network regulates the supply temperature

Supply temperature kept as low as possible at all times

Area substation


28.08.2014 | 13

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 installed


28.08.2014 | 14

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 control


28.08.2014 | 16

How applicable can this be?


28.08.2014 | 17

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

Results are coming soon…

70°C40°C

heat output 100 %

50°C33°C

heat output 55 %

same radiatorsṁ = constant


28.08.2014 | 18

Duration of Tsup over/equal certain temperatureHeating curves for radiators

Single-family-house from 1970 – results from simulation

! !Low-temperature substation for DHW

Tsu

pp

ly [

°C]

hou

rs a

bove c

ert

ain

te

mp

era

ture

[%

/a]

>50 >55 >60 >65 >70 50

non-renovated 20°C

21.4246575342466

8.13698630136986

2.86986301369863

1.25342465753425

0.222602739726027

66.0924657534247

new windows 20°C

6.83561643835616

1.78767123287671

0.23972602739726

0 0 91.1369863013699

extensive renovation 20°C

0.445205479452055

0 0 0 0 99.5547945205479

new windows 22°C

16.5034246575342

4.79794520547945

1.5958904109589

0.14041095890411

0 76.9623287671233

new windows 22°C LT rad.

1.82191780821918

0.318493150684932

0 0 0 97.8595890410959

3

8

13

18

23

Tsupply [°C]

*Extensive renovation = low energy windows + roof insulation

=


28.08.2014 | 19

Existing buildings can be supplied with LTDH already today if Tsupply is in cold periods increased above 50°C

Required Tsupply to radiators depends on:

desired indoor temperature

state of the building heating system

DH companies should be more strict in reducing Tsupply to:

reduce heat losses from DH network

integrate more renewables

DHW applicatoin should

always be changed to low-temperature one

LTDH for Existing Buildings


28.08.2014 | 20

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


28.08.2014 | 21

Thank you for the attention

Contact information:Oddgeir Gudmundsson

Application Specialist, Application CentreDanfoss District Energy, DK-Nordborg

[email protected]

mailto:[email protected]

Utilization of return water in district heating networks

Documents

Transcript of Utilization of return water in district heating networks