lecture 2 district heating supply residential buildings

Lecture 2. District Heating Supply Residential Buildings

Hongwei Li Civil Engineering Department

Building 118, room 206Technical University of Denmark

[email protected]

Lecture Content

Introduction Thermostatic valves Raidator performance LTDH supply low‐energy buildings LTDH supply existing buildings Load shifting by using thermal mass Integrated assessment

Low Temperature District Heating Supply Residential Buildings

Direct/Indirect SH and Open/Close DHW System


Single pipe system vs. Two pipe system


Hydraulic balance in radiators


Optimal distribute water in the heating system based on the actual demand

Execess flow pass through loops with less resistance

TRV valves control the flow to meet the exact demand

Thermostatic valves (TRV)


Thermostatic sensor Presetting angle valve Presetting straight valve

Thermostat with remote capillary sensor

Danfoss

TRV videos

http://radiatorcontrol.com/how_a_trv_works.aspx http://radiatorcontrol.com/gas_filled_design_works.aspx


Thermostatic valves (TRV)


Substation in residential house


∙ ∆∆∆

∆ 2

∙( ), , ,

Radiator performance


, ,

0

10

20

30

40

50

60

70

80

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1.6

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Q/Q

N

G/GN

90‐Sup

80‐Sup

75‐Sup

70‐Sup

60‐Sup

90‐Dt

80‐Dt

75‐Dt

70‐Dt

60‐Dt

Inlet temperature: 75oC Outlet temperature: 65oC Reference temperature at 20oC BS EN 442, 1997

Radiator performance


Power and mass flow rate


‐25

‐20

‐15

‐10

‐5

0

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 4 8 12 16 20 24

Mass flo

w ra

tio

Hrs

Constant Supply77oC

Ambient

Temperature oC H.Li et.al

Influence on DH network


0

100

200

300

400

500

600

700

800

900

1000

0 4 8 12 16 20 24

Pres

sure

kPa

Time hr

DHST‐50Pa/m‐LTDHDHST‐50Pa/m‐TraditionalDHST‐200Pa/m‐LTDHDHST‐200Pa/m‐Traditional

150

200

250

300

350

400

450

0 4 8 12 16 20 24

Pres

sure

kPa

Time hr

ITHE‐50Pa/m‐LTDH

ITHE ‐50Pa/m‐Traditional

ITHE ‐200Pa/m‐LTDH

ITHE ‐200Pa/m‐Traditional

Network analysis


H.Li et.al

• Initially the radiator is designed based on lower design network temperature.During the operation, the network supply temperature is high.

• Radiator is over‐dimensioned with a larger heat transfer area under designcondition.

• Building has gone through renovation, for example windows, insulation, etc, after the radiators were selected.

Radiator over‐dimension


∙ ∆ = ∙ 1 ∙ ∆

Radiator over‐dimension


H.Li

LTDH Supply Low‐Energy Building


r119 kitchen dining room

living room

bath 1

r116 techn. room

r91 bath2

hall

entrance bedroom

• Class 2015: 30+1000/A kWh• 159m2, 12 zones• Ventilation rate: 60 l/s• HE recovery efficiency: 75%.

Design supply air temperature: 16oC

• Three heating devises: - Radiator: 55/25/20oC/-12oC. P

regulator with 0.5oC deadband. - Forced Air Heating: 50/20oC/-

15oC. Total air flow 90 L/s at design condition

- Floor Heating: 3oC DT (supply/return), Weather compensatedsupply curve [‐21:35]; [‐5:27]; [35:27]. Electronic on/off valvecontrolled by thermsotat withdeadband 0.2oC

M.Brand et.al

Results: Thermal Comfort


18.0

19.0

20.0

21.0

22.0

23.0

24.0

840 864 888 912

Tair [°C]

Time [h]

Tair r11.9 RAD‐C1 Tair r11.6 RAD‐C1 Tair bedroom RAD‐C1

Tair r11.9 FAH‐C1 Tair r11.6 FAH‐C1 Tair bedroom FAH‐C1

Tair, room 119 Radiators Tair, room 116 Radiators Tair, bedroom Radiators

Tair, room 119 FAH II Tair, room 116 FAH II Tair, bedroom FAH II

Results: Water Temperature from SH Systems Tsupply=55°C


‐20

‐10

0

10

20

30

40

0.0

0.5

1.0

1.5

2.0

2.5

3.0

24 48 72 96 120 144 168 192

T outdo

or, T

return[°C]

Mass F

low [k

g/min]

Time [h]RAD‐C1 FAH‐B1‐90 FH‐C1‐4.2kW Tret RAD‐C1

Tret FAH‐B1‐90 Tret FH‐C1‐4.2kW Toutdoor

Radiator III Treturn Radiator IIIFAH II FH II

Treturn FAH II Treturn FH II Toutdoor

Network supply/return temperature


S.Werner

Existing Buildings

According to EPBD in 2012, only 3% of public buildings are enforced withdeep building renovation.

In Denmark, new building growth rate is 1% per year.

75% of existing buildings in Denmark were built before 1979.

Large potential for energy saving:The annual building energy consumption and the peak heating load for

existing buildings can be over 3 times higher than low energy buildings


Feasibility to use LTDH for existing buildings

Original radiators were over‐dimensioned.

Original DH network has enough capacity redundancy for higher mass flow operation

Building subjected to renovation including windows and building envelope

Varying network supply temperature and use higher network supply temperature during peak winter hours.

Convert IHEU unit to DHST unit to reduce network dimension.

Apply high efficient heat exchanger for IHEU and special designed tank for DHST.


Pro & Con to supply LTDH to existing buildings

Advantages Improved quality match Improved thermal comfort Redced heat loss Reduced utility cost

Disadvantages Increase peak supply temperautre which can be a limitation for renewable based DH supply Increased mass flow rate cause hydraulic balancing problem For direct connection system: network pressure level For indirect connection: temperture drop at HE


Case 1: Existing building with renovation

• Typical building from 1906 in an urban area• Existing energy consumption = 146 kWh/m2

• Existing SH‐consumption = 133 kWh/m2

• Renovation measures:– New energy efficient windows with solar shading– Insulation of facade, roof and floor– Mechanical ventilation system with heat recovery– Low temperature district heating (55/25°C)


M. Harrestrup et.al

Renovation measures


U value(W/m2.K)and Infiltration (h‐1)

Existing Renovated

Facade 1,34 0,16

Window 2,9 1,28

Roof 0,2 0,13

Horizontal division betweenground floor and basement

1,5 0,3

Infiltration 0,5 0,05

Annual heating consumption


Load duration curve


Case 2: Existing building with flexible DH operation


Typical 1970s single‐family house in Denmark

Construction U‐value [W/m2K]External wall 0.31

Roof 0.33Floor 0.4

Creep basement 0.42

EUDP project

Results


Case Peak power [kW] for ‐21°C

Energy demand for SH [MWh/year]

Temp. for SH

Flow rate [L/min]

Temp. for SH

Flow rate [L/min]

Temp. for SH

Flow rate

[L/min]

Peak power [kW] for 0°C

Tout = ‐21°C Tout = 0°C Tout = 0°C1 5.8 10.49 70/40/20 2.75 60/29/20 1.47 50/34/20 2.84 3.23

2 5.0 8.3 65/35/20 2.36 60/26/20 1.16 50/29/20 1.87 2.79

3 4.5 7.55 65/32/20 1.93 52/25/20 1.31 50/26/20 1.47 2.51

Case Measures Overall window U‐value [W/m2K]

1 No measures 2.52 New glazing, old frames 1.43 New low‐energy windows (frame included) 0.9

Daily DH load variation


L. Ingvarson et.al

Time constant


∑∑

Building time constant

Type of building Time constant (hrs)

Light weight 15‐20

Normal building 50‐100

Heavy buildings 100‐250

Building time constant


Building under-heating Building over-heating

Load shifting approach


+ ‐ exp Δt/τ)

Simple building dynamic equation

Introduce a heating load ratio and discrete the equation

<1: load reduction (under heating)>1: load increase (over heating)

The room temperature becomes

∑ ∑ exp

x ratio variation for different type of buildings


-24

-22

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

-5 5 15 25 35 45 55

x ra

tio

Hours

Type 1 x ratioType 2 x ratioType 3 x ratioType 4 x ratioType 5 ratioOutside Temperature

oC

-12oC reference

H.Li et.al

Room temperature at different reference temperatures


-25

-20

-15

-10

-5

0

19.6

20.1

20.6

21.1

21.6

0 10 20 30 40 50 60

oC

Hours

-12oC room temperature

-10oC room temperatureOutside temperature

21oC

Future energy system


Site climiate characterization

Building shape/orientation

Envelope insulation: floor/roof/wall

Thermal bridge treatment

Energy efficient glazing

Shading and wind protection

Heat recovery ventilation

Energy efficient appliances

Energy efficient building

Solar thermal

PV

Geothermal

Bioenergy

Wind

Industrial waste

Inineration

Building Code


Integrated design approach for building energy reduction


K.Sperling et.al

Cost curves for heat savings and district heating supply


End of lecture


lecture 2 district heating supply residential buildings

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