Design considerations for integration of two 5 MW vapour compression heat pumps in the Greater Copenhagen district heating system

Transcription

1 Design considerations for integration of two 5 MW vapour compression heat pumps in the Greater Copenhagen district heating system 3 rd International conference on smart energy systems and 4 th generation district heating, 13 th September 2017 Torben Ommen, Pernille Jørgensen, Jonas Jensen, Wiebke Markussen, Brian Elmegaard Section of Thermal Energy, Technical University of Denmark

2 Introduction Expected share of HPs in Greater Copenhagen DH system - Heat pumps are often referred to as a key technology for DH integration in the Smart Energy System. + Integration potential shared with other unit types: electric boilers and combined heat and power plants. - Target to supply CO2 neutral district heating for Municipality of Copenhagen by % of the supplied heat was classified as CO2 neutral in Optimal reduction of heat cost if 300 MW installed capacity by MW should be in operation by DTU Mechanical Engineering

3 Introduction Expected share of HPs in Greater Copenhagen DH system - Heat pumps are often referred to as a key technology for DH integration in the Smart Energy System. + Integration potential shared with other unit types: electric boilers and combined heat and power plants. - Target to supply CO2 neutral district heating for Municipality of Copenhagen by % of the supplied heat was classified as CO2 neutral in Optimal reduction of heat cost if 300 MW installed capacity by MW should be in operation by A number of barriers prevent a large-scale introduction (at least in Denmark), eg.: + High cost of the produced heat from large-scale HPs. + Limited availability of heat sources. + Lack of knowledge and experiences for SES operation. 2 DTU Mechanical Engineering

4 The SVAF project Agenda Introduction Expected share of HPs in Greater Copenhagen DH system The SVAF project Two 5 MW HPs in Copenhagen Vapour compression heat pumps in finite reservoirs Heat pumps in combined heat and power systems Economic considerations regarding serial HPs Utilisation of a geothermal heat source Suggested configuration for direct heat exchange and HPs Method Results Utilisation of waste- and sea water as heat source Two stage Ammonia heat pumps with oil-cooling Examples of 3 suggested configurations Future work in the SVAF project 3 DTU Mechanical Engineering

5 The SVAF project Two 5 MW HPs in Copenhagen - 3 rd generation DH - Two electric HP systems - Condenser design load: 5 MW + One multi-heat source configuration: Waste- and sea water (2018) + One single heat source configuration: Geothermal (2019) - Natural working fluids + Currently available units are limited. 4 DTU Mechanical Engineering

6 The SVAF project Two 5 MW HPs in Copenhagen - 3 rd generation DH - Two electric HP systems - Condenser design load: 5 MW + One multi-heat source configuration: Waste- and sea water (2018) + One single heat source configuration: Geothermal (2019) - Natural working fluids + Currently available units are limited. - The objective of this study is to give initial design suggestions for the system configuration + Later used to establish guidelines for generalised system configurations. 4 DTU Mechanical Engineering

7 The SVAF project Vapour compression heat pumps in finite reservoirs T cond Refrigerant Sink media Source media sink 3 Expansion valve 4 Condenser Evaporator Compressor 2 1 Gross Temp. lift T lift T sink T source T ( o C) T pinch T pinch T pinch Temperature variation of sink stream Temperature variation of source stream T evap (a) Principle sketch of VCHP T source Relative heat transfer (-) (b) Temperature - Heat load diagram 5 DTU Mechanical Engineering

8 The SVAF project Heat pumps in combined heat and power systems In heating systems where majority of heat is supplied by combined heat and power plants (CHP) HPs may be integrated in a number of characteristic methods. Objective: energy efficiency, heat cost etc. SF SD SR RF RD (F) T DH,Forward (D) T Demand (R) T DH,Return (S) T Source 6 DTU Mechanical Engineering

9 The SVAF project Heat pumps in combined heat and power systems 6 5 DH 70 o C - 35 o C DH 90 o C - 40 o C DH 105 o C - 50 o C CHP Stackgasses COSPelec [-] COSPelec [-] SF SD SR RF RD 0 SF SD SR RF1 RF2 RD (a) DH network temperature dependency (b) Production characteristics 7 DTU Mechanical Engineering

10 The SVAF project Economic considerations regarding serial HPs - Industrial and DH practises are different + DH focuses on cost of heat + Different taxation leads to changed trade off between investment and performance Refrigerant Sink media Source media Qcond,2 Counter Current Configuration Qcond,1 Deviation from reference system (%) COP Industrial NPV Industrial COP District Heating NPV District Heating No Series 2 3 Number of HP in series (a) T sink / T source = 20 K / 20 K T ( o C) Qevap,2 Ẇ2 Qevap,1 Ẇ Heat load (MW) Temperature variation of sink stream Temperature variation of source stream (b) Counter-current configuration 8 DTU Mechanical Engineering

11 Utilisation of a geothermal heat source Agenda Introduction Expected share of HPs in Greater Copenhagen DH system The SVAF project Two 5 MW HPs in Copenhagen Vapour compression heat pumps in finite reservoirs Heat pumps in combined heat and power systems Economic considerations regarding serial HPs Utilisation of a geothermal heat source Suggested configuration for direct heat exchange and HPs Method Results Utilisation of waste- and sea water as heat source Two stage Ammonia heat pumps with oil-cooling Examples of 3 suggested configurations Future work in the SVAF project 9 DTU Mechanical Engineering

12 Utilisation of a geothermal heat source Suggested configuration for direct heat exchange District heat return District heat supply 6 7 District heat stream (DH) Geothermal stream (GT) Heat pump 1 Heat pump 2 Geothermal supply Geothermal return Heat load ratio =,, Mass flow ratio =,, (a) Principle sketch of suggested configuration 10 DTU Mechanical Engineering

13 Utilisation of a geothermal heat source Suggested configuration for direct heat exchange Direct heat exchange Heat pump 1 Heat pump 2 District heat supply 85 C Geothermal heat source 73 C Temperature C Heat Load (MW) 7,2 (a) Tempeature heat load diagram of suggested counter-current configuration District heat return 50 C Geothermal heat source return 16 C 11 DTU Mechanical Engineering

14 Utilisation of a geothermal heat source Ammonia-water hybrid compression-absorption HP Sink Sink T 3 T 4 Mixing (adiabatic absorption) Reciever Throttling valve 4 Source Absorber Internal HEX 5 6 Desorber Mixer Pump 3 2 Source 1 7 j k Rich xr Lean xl Vapour xv Water Stream Component Compressor Liquid-vapour separator Temperature ( C) T sink,out T 5 T sink,in T source,in T 1 T source,out T 7 Absorption curve Heat source Heat sink Desorption curve Q Desorber Q Absorber Ẇ T sink T lift T source Heat Load (kw) (a) Principle sketch of the HACHP (b) Temperature - heat load diagram of the HACHP 12 DTU Mechanical Engineering

15 Utilisation of a geothermal heat source Method 1 Simple system model based on HP exergy efficiency, ǫ HP, and HEX pinch point temperature difference, T pp,hex. + Investigate optimal f Q and fm. + Investigate the influence of ǫ HP and T pp,hex on optimal f Q and fm. 2 Include the real efficiency of the HACHP. + Investigate optimal f Q and fm including HP characteristics. + Suggest a range of exergy-optimal configurations. 3 Determine the best possible design. + Apply economic analysis to a set of optimal solutions. + Investigate the limiting technical constraints. 13 DTU Mechanical Engineering

16 Utilisation of a geothermal heat source Simple model, equal heat pump efficiency + One combination of f Q and fm optimizes the system efficiency. + It is observed that this occurs when the HEX is balanced and there is no exergy destruction related to the mixing. (a) Two HPs with equal exergetic efficiency and a direct HEX with a pinch temperature difference of 5 K. 14 DTU Mechanical Engineering

17 Utilisation of a geothermal heat source Including HACHP characteristics + One combination of fq and fm optimizes the system efficiency. + The difference in HPs efficiency is low enough to favour the serial connection. + Economic analysis was applied to fq from 0.2 to 0.6 and the optimal value of fm. (a) Two HPs with realistic exergetic efficiency and a direct HEX with a pinch temperature difference of 5 K. 15 DTU Mechanical Engineering

18 Utilisation of a geothermal heat source Technical Constraints (a) High pressure of HP1 and HP2. (b) Compressor discharge temperature of HP1 and HP2. 16 DTU Mechanical Engineering

19 Utilisation of a geothermal heat source Economic analysis + The suggested design leads to total exergetic efficiency of 0.63, this is within 2 % of the theoretical economic optimum. + System COP of 6.1 [/] by use of HPs with COP of 4.4 [/] and 4.6 [/]. (a) Economic performance of the two HACHPs and HEX 17 DTU Mechanical Engineering

20 Utilisation of waste- and sea water as heat source Agenda Introduction Expected share of HPs in Greater Copenhagen DH system The SVAF project Two 5 MW HPs in Copenhagen Vapour compression heat pumps in finite reservoirs Heat pumps in combined heat and power systems Economic considerations regarding serial HPs Utilisation of a geothermal heat source Suggested configuration for direct heat exchange and HPs Method Results Utilisation of waste- and sea water as heat source Two stage Ammonia heat pumps with oil-cooling Examples of 3 suggested configurations Future work in the SVAF project T ( o C) Refrigerant Sink media Source media Q cond,2 Q evap,2 Ẇ 2 Counter Current Configuration Q cond,1 Q evap,1 Ẇ Heat load (MW) Temperature variation of sink stream Temperature variation of source stream 18 DTU Mechanical Engineering

21 Utilisation of waste- and sea water as heat source Two stage vapour compression heat pumps - Heat exchanger network on the sink side influences COP, investment and part-load operation. - Generic recommendations needed to limit amount of feasible configurations. - Recommended configuration is different for different heat sink temperature, sink temperature glides and source temperatures. M 19 DTU Mechanical Engineering (a) Principle sketch of the VCHP - Integration with heat sink not fixed

22 Utilisation of waste- and sea water as heat source Examples of 3 suggested configurations - Configuration # 1 (a) Principle sketch of configuration # 1 20 DTU Mechanical Engineering

23 Utilisation of waste- and sea water as heat source Examples of 3 suggested configurations - Configuration # 2 21 DTU Mechanical Engineering (a) Principle sketch of configuration # 2

24 Utilisation of waste- and sea water as heat source Examples of 3 suggested configurations - Configuration # 3 22 DTU Mechanical Engineering (a) Principle sketch of configuration # 3

25 Utilisation of waste- and sea water as heat source Examples of 3 suggested configurations Configuration # 3 Temperature [ C] DTU Mechanical Engineering Heat load [kw] Subcooler HP 1 Oil cooler low pressure HP 1 Subcooler HP 2 Oil cooler low pressure HP 2 Desuperheat low pressure HP 1 Oil cooler high pressure HP 1 Desuperheat low pressure HP 2 Oil cooler high pressure HP 2 Condenser HP 1 Condenser HP 2 Desuperheat high pressure HP 1 Desuperheat high pressure HP 2 District heating water (a) Temperature heat load diagram of configuration # 3

26 Utilisation of waste- and sea water as heat source Comparison of 3 suggested configurations Table: Key Indicators for optimised configuration at DH temperatures 80/50 Share HP 1 System COP Swept Volume UA [/] [/] [m 3 /h] [W/K] Configuration # (4364/1550) 1481 Configuration # (4362/1538) 1619 Configuration # (4311/1642) Well designed heat exchanger network on the sink side has limited influences to COP and investment. - Performance during part-load operation may be significantly changed (ongoing). - Yearly performance and investment characteristics needed to evaluate the optimal solution (ongoing). 24 DTU Mechanical Engineering

27 Future work in the SVAF project Agenda Introduction Expected share of HPs in Greater Copenhagen DH system The SVAF project Two 5 MW HPs in Copenhagen Vapour compression heat pumps in finite reservoirs Heat pumps in combined heat and power systems Economic considerations regarding serial HPs Utilisation of a geothermal heat source Suggested configuration for direct heat exchange and HPs Method Results Utilisation of waste- and sea water as heat source Two stage Ammonia heat pumps with oil-cooling Examples of 3 suggested configurations Future work in the SVAF project 25 DTU Mechanical Engineering

28 Future work in the SVAF project Future work in the SVAF project - Validation of HP models with real plant data with extensive test programme. - Generic mapping of performance of potential configurations of heat pumps. - Decision support tool for heat pump selection. - HP design for large-scale application (eg. 40 MW). - Detailed knowledge of heat pumps for part load and dynamical operation. - The use of heat pumps in Smart Energy System operation. Tlift (K) Tsource,out<0 C -2.0%< rpv <9% LP HACHP VS. LP R717 HP R %< rpv <19% 0.5%< rpv <17% HP HACHP VS. HP R717 R600a Tsink = 20K (c) Tsource = 10K T sink,out ( C) 37%< rpv <78% (a) Example of Working Domain analysis 26 DTU Mechanical Engineering

29 Future work in the SVAF project Thank you for your attention This research project is financially funded by EUDP (Energy Technology Development and Demonstration). Project title: Experimental development of electric heat pumps in the Greater Copenhagen DH system - Phase 2. If questions, new ideas or interest in new projects: tsom@mek.dtu.dk 27 DTU Mechanical Engineering