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- Supplying district heating for residential buildings- LTDH-Thermal mass
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Lecture 2. District Heating Supply Residential Buildings
Hongwei Li Civil Engineering Department
Building 118, room 206Technical University of Denmark
hong@byg.dtu.dk
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
Low Temperature District Heating Supply Residential Buildings
Single pipe system vs. Two pipe system
Low Temperature District Heating Supply Residential Buildings
Hydraulic balance in radiators
Low Temperature District Heating Supply Residential Buildings
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)
Low Temperature District Heating Supply Residential Buildings
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
Low Temperature District Heating Supply Residential Buildings
Thermostatic valves (TRV)
Low Temperature District Heating Supply Residential Buildings
Substation in residential house
Low Temperature District Heating Supply Residential Buildings
∙ ∆∆∆
∆ 2
∙( ), , ,
Radiator performance
Low Temperature District Heating Supply Residential Buildings
, ,
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
Low Temperature District Heating Supply Residential Buildings
Power and mass flow rate
Low Temperature District Heating Supply Residential Buildings
‐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
Low Temperature District Heating Supply Residential Buildings
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
Low Temperature District Heating Supply Residential Buildings
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
Low Temperature District Heating Supply Residential Buildings
∙ ∆ = ∙ 1 ∙ ∆
Radiator over‐dimension
Low Temperature District Heating Supply Residential Buildings
H.Li
LTDH Supply Low‐Energy Building
Low Temperature District Heating Supply Residential Buildings
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
Low Temperature District Heating Supply Residential Buildings
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
Low Temperature District Heating Supply Residential Buildings
‐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
Low Temperature District Heating Supply Residential Buildings
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
Low Temperature District Heating Supply Residential 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.
Low Temperature District Heating Supply Residential Buildings
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
Low Temperature District Heating Supply Residential Buildings
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)
Low Temperature District Heating Supply Residential Buildings
M. Harrestrup et.al
Renovation measures
Low Temperature District Heating Supply Residential Buildings
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
Low Temperature District Heating Supply Residential Buildings
Load duration curve
Low Temperature District Heating Supply Residential Buildings
Case 2: Existing building with flexible DH operation
Low Temperature District Heating Supply Residential Buildings
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
Low Temperature District Heating Supply Residential Buildings
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
Low Temperature District Heating Supply Residential Buildings
L. Ingvarson et.al
Time constant
Low Temperature District Heating Supply Residential Buildings
∑∑
Building time constant
Type of building Time constant (hrs)
Light weight 15‐20
Normal building 50‐100
Heavy buildings 100‐250
Building time constant
Low Temperature District Heating Supply Residential Buildings
Building under-heating Building over-heating
Load shifting approach
Low Temperature District Heating Supply Residential Buildings
+ ‐ 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
Low Temperature District Heating Supply Residential 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
Low Temperature District Heating Supply Residential Buildings
-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
Low Temperature District Heating Supply Residential Buildings
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
Low Temperature District Heating Supply Residential Buildings
Integrated design approach for building energy reduction
Low Temperature District Heating Supply Residential Buildings
K.Sperling et.al
Cost curves for heat savings and district heating supply
Low Temperature District Heating Supply Residential Buildings
End of lecture
Low Temperature District Heating Supply Residential Buildings
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