4th International Conference on Smart Energy Systems and 4th Generation District Heating Aalborg, 13-14 November 2018
Model predictive control of a heat booster substation for ultra-low temperature district heating
4th International Conference on Smart Energy Systems and 4th Generation District Heating 2018
#SES4DH2018
Kevin Michael Smith1, Corentin Latou2, Jan Eric Thorsen3, Svend Svendsen1 (1) Technical University of Denmark
(2) Ecole Centrale de Nantes (3) Danfoss Drives A/S
Components Storage tank Heat pump to storage tank Circulation heat pump Heat exchanger for DHW Ultra-low temperature district heating (ULTDH) Supply: 40°C, return: 25°C Domestic water Hot water: 55°C, cold water: 10°C Circulation loop Forward: 55°C, return: 50°C
4th International Conference on Smart Energy Systems and 4th Generation District Heating 2018 #SES4DH2018
Model Predictive Control (MPC) Optimal equipment scheduling
Applied system dynamics
Smooth differential equations (smaller solver tolerance)
Forecasted energy needs
Minimise cost function (e.g. energy cost + discomfort)
Allows constraints (e.g. max. set-points)
Re-initialisation of states
4th International Conference on Smart Energy Systems and 4th Generation District Heating 2018 #SES4DH2018
The process of model identification accounts for 70% of the effort for implementing an MPC controller (Henze, 2013).
System model Modelica language in Dymola
GUI for equation-based system modelling
Modelica Buildings Library from LBNL
Open-source component library
(e.g. stratified tank, HP, pumps, heat ex., etc.)
JModelica Open-source simulation and optimisation
4th International Conference on Smart Energy Systems and 4th Generation District Heating 2018 #SES4DH2018
Component validation with real data
Input known parameters to component models
Heat exchanger
Stratified tank model
Heat pump model
Test data to validate models
Default parameters for pumps and valves
4th International Conference on Smart Energy Systems and 4th Generation District Heating 2018 #SES4DH2018
Tank validation – Upper level
4th International Conference on Smart Energy Systems and 4th Generation District Heating 2018 - #SES4DH2018
0
10
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0 7200 14400 21600 28800 36000 43200
T [C
]
Time [s]
01-31: Temperature #1
T tank top #1 (S6) #1 #1 #1
Ideally mixed layers may cause numerical diffusion
Tank validation – Lower level
4th International Conference on Smart Energy Systems and 4th Generation District Heating 2018 - #SES4DH2018
0
10
20
30
40
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0 7200 14400 21600 28800 36000 43200
T [C
]
Time [s]
01-31: Temperature #5
T tank #5 (S8) #5 #5 #5
More layers improves convergence with actual data
Large heat pump validation
4th International Conference on Smart Energy Systems and 4th Generation District
Heating 2018 - #SES4DH2018
40
50
60
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28800 32400 36000 39600 43200
T [C
]
Time [s]
Simulation results: condenser temperature
T L-HP cond (measure) Condenser (SIM1) Condenser (SIM2)
Error measurement/simulation results (working time) SIM 1 SIM 2
Condenser mean absolute error [C] 0,27 0,86 Evaporator mean absolute error [C] 1,63 0,80
System model Library includes six versions of booster station
4th International Conference on Smart Energy Systems and 4th Generation District Heating 2018 #SES4DH2018
System model
4th International Conference on Smart Energy Systems and 4th Generation District Heating 2018 #SES4DH2018
System model Modified tank model to include third port (circulation HP)
4th International Conference on Smart Energy Systems and 4th Generation District Heating 2018 #SES4DH2018
MPC of a booster station Optimise
When to charge tank
Condenser and evaporator flow rates
Heat source for circulation heat pump
Middle tank
Return
DH Supply (not included yet in model)
Based on energy costs
4th International Conference on Smart Energy Systems and 4th Generation District Heating 2018 #SES4DH2018
Cost function
𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 𝑐𝑐 = � 𝑃𝑃𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 ∗ 𝑝𝑝𝑝𝑝𝑝𝑝𝑐𝑐𝑝𝑝𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 𝑑𝑑𝑐𝑐𝑡𝑡
0+ � 𝑃𝑃𝐷𝐷𝐷𝐷 ∗ 𝑝𝑝𝑝𝑝𝑝𝑝𝑐𝑐𝑝𝑝𝐷𝐷𝐷𝐷 𝑑𝑑𝑐𝑐
𝑡𝑡
0
DH tariffs based on production weighted price from HOFOR
4th International Conference on Smart Energy Systems and 4th Generation District Heating 2018 #SES4DH2018
0,00
0,05
0,10
0,15
0,20
0,25
264 266 268 270 272 274 276 278 280 282 284 286 288
[DKK
/kW
h]
[h]
DH production weighted average cost: 12-01-2016
Electricity price
4th International Conference on Smart Energy Systems and 4th Generation District Heating 2018 #SES4DH2018
0,000
1,000
2,000
3,000
4,000
264 266 268 270 272 274 276 278 280 282 284 286 288
[DKK
/kW
h]
[h]
Spot/load-based tariff 12-01-2016
Spot/Load-based tariff Spot/Load-based tariff (consumption prognosis)
Average costs 2 [DKK/MWh] Actual energy 810 35,2% System 150 6,5% Taxes 1340 58,3% Total 2300 100,0%
Method from Ulbig & Andersson (2010) ; Data from Nordpool (spot price and load) & Danish energy statistics 2015 (https://ens.dk/en)
Reference case: DHW Tapping Profile Pseudo-random Python library Shifted load profile for a 14 apartments Profile 1: 1413 L/day Profile 2: 1397 L/day
4th International Conference on Smart Energy Systems and 4th Generation District Heating 2018 - #SES4DH2018
0
100
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0 7200 14400 21600 28800 36000 43200 50400 57600 64800 72000 79200 86400
Flow
rate
[L/h
]
Time [s]
DHW pattern
Profile 1 (14 flats) Profile 2 (14 flats)
Simulation/Optimisation Compile as FMU in Jmodelica for optimisation
Issue in JModelica with block of code (Buildings Lib.)
Successful simulation, once removed everywhere
4th International Conference on Smart Energy Systems and 4th Generation District Heating 2018 #SES4DH2018
Simulation
4th International Conference on Smart Energy Systems and 4th Generation District Heating 2018 #SES4DH2018
Next steps
• Add DH supply as potential circ. HP source • Optimise controls in JModelica • Test MPC with real data (offline) Thank you for your attention.
4th International Conference on Smart Energy Systems and 4th Generation District
Heating 2018 - #SES4DH2018
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