Chris Bales Solar Energy Research Center SERC, Dalarna University College Borlänge, Sweden. Contents. Summary. Principles.

Transcription

1 Thermal Storage with the Thermo-Chemical Accumulator (TCA) Chris Bales, Dalarna University College Borlänge, Sweden Condensor / Evaporator Reactor Contents Summary Principles Solution vessel Water vessel Measurements Simulations Conclusions The work has been financed by the Swedish National Energy Agency Chris Bales 1

2 Summary The thermo-chemical accumulator (TCA) is a three phase chemical heat pump (absorption) with integral heat storage. Developed by Swedish company using LiCl/water pair. The aim of the study was to evaluate the technology principally for cooling applications Three generations of units have been tested in the lab and field. TRNSYS model has been developed. System simulations for a cooling and seasonal heat storage were performed. Results show that: The technology works and is now reliable. Current temperature lift is a limiting factor. The cost of the salt is also a limiting factor. The technology is being commericalised. Chris Bales 2

3 Principles - Charging Spridare Övre värmeväxlare Solution pumped over generator heat exchanger. To ambient C Kondensor/evaporator Gasledning Solution gets more concentrated. Condensor Spridare Pump Process can carry on until crystals form and fall down under gravity. Solid separated from solution by basket. Heat source C Generator / Reactor Undre värmeväxlare Filter Reaktor Mantel Pump Chris Bales 3

4 Principles - Discharging Spridare Övre värmeväxlare Solution pumped over reactor heat exchanger. Solution absorbs water vapour and drips onto slurry. From ambient or cooling load 5-17 C Evaporator Kondensor/evaporator Spridare Undre värmeväxlare Pump Gasledning Solid increases concentation to near saturation. Three phases present constant dt between evaporator and absorber. To heat load or ambient C Absorber/Reactor Filter Reaktor Mantel Pump Chris Bales 4

5 First Generation Quasi-Continuous Storage Use T MC,in Huvudkondensor/ T MCout evaporator Main Condenser Pump Water to slave Vatten till slavevaporator T MR,in T SE,out T MR,out Huvudreaktor Main Reactor Substans från slavreaktor Slavevaporator Evaporator Pump Slave Slavreaktor Reactor Substans T till slavreaktor SE,in T SRout Pump Pump T SR,in Chris Bales 5

6 First Generation Field Measurements (2004) Office load (6 am 10 pm) District heating (70 C during summer) Limitation of charging capacity during hot days Charging at night and early day 30 T amb P MR fjärrvärme Q charge [ C] Tute T ac,su T room P SE Q ac [W] T rumsgivare Tut SE :00 04:00 08:00 12:00 16:00 20:00 24: Chris Bales 6

7 First Generation Daily COP COP kyla [100kWh] JUL COP per dygn AUG 2004 Avgiven komfortkyla Temp [ C] Utomhus dygnsmedeltemp. T a Variation from day to day Different states of charge Gap for maintenance (vacuum pumping) Required regularly COP 0.55 before and 0.59 after gap Chris Bales 7

8 Second Generation Batch Process Two identical vessels Alternate charge / discharge Connection via switching unit Design: 10 / 18 kw max cooling / heating rate 56 / 76 kwh storage for cooling / heating Never achieved this in prototypes Tubes connected to the external Condensor / evaporator Heat exchanger Reactor Heat exchanger Salt filter basket Barrel Internal pumps 8 valves for controlling internal processes 180 mm Connection unit 2000 mm 700 mm 700 mm Chris Bales 8

9 Second Generation - Charge Temperature : : : : : : : : :00 Tci Tco Tocci Tocco 12 Power 8 4 Pocc Pc,corr : : : : : : : : :00 Chris Bales 9

10 Second Generation - Discharge Temperature 30 Tocdi Tocdo Taci Taco : : : : : : : : :00 12 Power 8 4 Pocd Pac : : : : : : : : :00 Chris Bales 10

11 Second Generation - Summary Tested at several sites in Sweden, Switzerland and Spain COP of ~0.46 Short-circuit from evaporator to reactor Loss of vacuum Corrosion and in some machines leakages Very erratic behaviour Blocked valves and pipes Long swap time of minutes Chris Bales 11

12 Third Generation Batch Process (2005-6) Reliability problems solved Tested at developing company Measured storage of 22 kwh (cold), 35 kwh (heat) Swap time of ~10 minutes Condensor / Evaporator Reactor Estimated COP of Problems with measurements Energy density: 0.9 GJ/m 3 for material (3.6 that of water for C) 0.3 GJ/m 3 for heating with respect to machine volume (1.2 that of water) 0.2 GJ/m 3 for cooling with respect to machine volume (4.7 times water for dt=10k) Solution vessel Water vessel Chris Bales 12

13 TCA Unit Model Dynamic TRNSYS model Masses for reactor and condensor/evaporator Masses for bulk water, solution and crystals Simple heat exchanger model Theoretical temperature difference between reactor and codensor Based on Conde (2004) Parameters identified from data for third generation Not fully validated Theoretical COP (~0.7) Chris Bales 13

14 Function Heat source System Model Cooling Application Broad simulation study with variation of main boundary conditions Cooling load only Solar collector with backup heater Dehumidification is treated separately (ideal) Heat sink Cooling distribution Component 30 m 2 flat plate collector, efficiency as in IEA-SHC Task 26 (Weiss, 2003), at 45 C slope facing south with 12 kw auxiliary boiler. Single dry cooler (30 kw) for Stockholm, cooling tower (34 kw) for Madrid. 15 C chilled ceiling panel. Set temperature for cooling control is 1 C less than max. allowed temperature according to DIN 1946/2 (DIN, 1994). Building Office, one floor of 120 m 2, with 7.5 kw design load in Stockholm (50 W/m 2 ). TCA unit Two CW10 units with controller. Chris Bales 14

15 Cooling Application Madrid Key Figures Collector 44.6 GJ Cooling Tower GJ High COP therm Not dependent on part load Higher than measured in current prototypes Auxiliary 21.6 GJ El. 3.8 GJ Cooling 47.2 GJ COP el = 12.5 COP therm = 0.71 Low COP el Solution pumps on continuously Solar fraction ~67% Chris Bales 15

16 Cooling Application Charge Temperatures T charge [ C] Majority of time between 40 and 80 C Charge temperature dependent on state of charge Gives spread T amb [ C] Chris Bales 16

17 Cooling Application Supply Temperatures T supply [ C] T supply [ C] P cool [kw] P cool [kw] Chris Bales 17

18 Cooling Application PPD values PPD [%] T amb [ C] Overheating at low temperatures due to control strategy of cooling distribution Reacts too slowly Chris Bales 18

19 Cooling Application Collector Type and Area 80% 75% Flat Plate Vacuum tube (gross area) Solar Fraction 70% 65% 60% 55% 50% Collector Area [m 2 ] Chris Bales 19

20 Cooling Application Cooling Load Energy [GJ] Qcoll COPtherm 1000 hours PPD>20% Qcool SF Office load has sharp peak and little at night Hotel load has more even load over 24 hours Office Load (30W/m2) Office Load (50W/m2) Hotel Load (40W/m2) 0.0 Chris Bales 20

21 Cooling Application Storage for Hotel Load Solar Fraction 80% 75% 70% 65% 60% 55% 50% 45% 40% 35% 30 m2 50 m Storage Size [kg LiCl] Doubling of storage adds 13% in solar gain Both 30 and 50 m 2 fields Halving storage decreases solar gain by 25% Chris Bales 21

22 Seasonal Storage Simple feasibility simulation study for 100% seasonal heat storage for space heating Heat load as for IEA-SHC Task 26 house SFH30 Three climates: Carpentras (south France), Zürich, Stockholm Separate system models for charge and discharge Energy [MJ], Mass LiCl [kg] Qsh Qdhw Qaux,20m2 Qaux,30m2 MLiCl,20m2 MLiCl,30m2 Cost $12/kg LiCl $28000 for seasonal store 0 CA ZU ST Chris Bales 22

23 Seasonal Storage Source Temperature Proportion of space heating covered by TCA 100% 95% 90% 85% 80% 75% 70% 65% 60% CA 35/30 CA 30/25 ZU 35/30 ZU 30/25 ST 35/30 ST 30/ Heat source temperature [ C] Chris Bales 23

24 Conclusions A system with two TCA units and controller could meet the cooling demand (13 MWh) of a small office in Madrid without extra thermal storage. An extra store or larger internal store is required for significant night time loads (hotel). The machine has a storage density for cooling ~5 times that of water (dt=10k). The electrical COP is very low due to the continuous use of the solution pump. Chris Bales 24

25 Conclusions contd A cooling tower and high temperature cooling distribution system is required for the Madrid climate. The available temperature lift is relatively small and limits the application range. The heat exchangers are not optimised and cause a decrease in lift of 2 C per kw cool load. The cost of the LiCl salt makes the technology unsuitable for seasonal storage and is a significant cost for machines for cooling applications Chris Bales 25

26 Outlook The developing company, ClimateWell AB from Sweden, recently got 11 M in (Spanish) risk capital investment Expanded to ~20 people Several installations (mostly Spain) already being monitored Solar heating/cooling Trigeneration Several new installations rest of 2006 Participation in EU project on tri-generation (Polysmart) Development work in progress on: Improved heat exchangers Design changes to reduce production costs System design and control Other salts Chris Bales 26