ENERGY MANAGEMENT IN A CHILLED WATER PLANT USING THERMAL STORAGE The Tenth International Conference on Thermal Energy Storage ECOSTOCK 2006 Stephane Bilodeau,, PE, Ph.D. sbilodeau@groupeenerstat.com
Scope Overview of the project Storage Approach Operating Schematic Implementation Results Monitoring Results Economical Results Conclusion
TES Project in IBM Bromont
TES Project in IBM Bromont Chilled Water Production Optimisation using Thermal Energy Storage Dismantling 2 Old Chillers (1000 tons each) Over a total of (7000 tons) of installed capacity in the Plant Using Thermal Storage to reduce Peak Load as well as improving plant efficiency Integrated in a closed loop using water-glycol solution as a thermofluid (250 l/s or 4000 usgpm) Improved control strategy To secure the chilled water supply to the plant To simplify operation
TES to Improve the Performance of the Facility Novanergy works to maximise efficiencies 17 000.0 Fluctuations In Energy Consumption 2950.0 16 500.0 16 000.0 Novanergy works to reduce this... 2450.0 15 500.0 15 000.0 1950.0 14 500.0 Série1 Série2 14 000.0 1450.0 13 500.0 13 000.0 950.0 12 500.0 12 000.0 2004-06-02 2004-06-03 2004-06-04 2004-06-05 2004-06-06 2004-06-07 2004-06-08 2004-06-09 2004-06-10 450.0 2004-06-11
Storage approach The Preferred Storage Approach Partial storage In the partial-storage approach, the mechanical equipment runs to meet part of the peak period cooling load, and the remainder is met by drawing from storage. The equipment is sized at a smaller capacity than the design load. Partial storage e systems may be run as load- leveling or demand-limiting operations. In a load-leveling leveling system, the equipment is sized to run at its full capacity for 24 hours on the severe days. The strategy is most effective where the peak cooling c load is much higher than the average load. Partial-storage load-leveling leveling operating strategy In a load-leveling leveling system the equipment runs at its full capacity for 24 hours h on the design day. When the load is less than the equipment output, the surplus s energy is stored. When the load exceeds the capacity, the additional requirement is discharged from storage. A load-leveling leveling approach minimizes the required equipment and storage capacities c as well as GHG emissions for a given load.
Operating Schematic Plant Vech2 Discharge MCP2 Vref 1 2 Ech2 MCP1 NV1 Charge & Discharge 4 3 Po (VFD) Cooling Tower
Operating Schematic 1 MCP2 Chilled Water Plant Load Vech2 2 Ech2 Vref MCP1 Discharge NV1 Charge & Discharge 3 4 Po (EFV)
Energy Efficiency The recharge is driving the energy efficiency of the process: NV1: : High Efficiency Compressor Operation Charge the cold storage tank at low outside temperature Reducing part load improves kw/ton Free cooling: : night free cooling may be moved to follow day loads NFC: by charging the system directly with a cooling tower at night during mid season QFC: by precooling the cold side to improve overall efficiency [Quasi-Free Cooling approach] Energy recycling: exploiting plant energy rejection DER: Direct recovery of rejected energy (condenser side) IER: Using the differential between the Part load and the nominal operating condition of heating or cooling equipments to recharge at high efficiency eliminating part load operation (reducing energy consumption and equipment wear)
Implementation
Operation 2 Storage Tanks PCM with 30 F and 40 F melting point Useful capacity respectively of 2226 tons-h and 1995 tons-h
LOG(p),h-DIAGRAM Q SGHX : 0 [kw] 2 5 4 T 2 : 39.7 [ C] T 4 : 26.5 [ C] T 5 : 26.5 [ C] Q C : 4348 [kw] T C : 28.5 [ C] 3 T 3 : 39.7 [ C] Thermodynamic cycle with TES W : 597.7 [kw] m : 23.14 [kg/s] Q E : 3780 [kw] T E : -1.5 [ C] 7 6 X 6 : 0.19 [kg/kg] T 7 : 2.0 [ C] 8 1 T 8 : 3.0 [ C] T 1 : 3.0 [ C] REFRIGERANT : R134a COP : 6.324 COP* : 6.364 η CARNOT : 0.703
Monitoring Results Peak Shaving (kw) Reduction of Peak loads Up to 1 250 kw Compressor s efficiency improvement Average kw/tons improvement from 0.9 to 0.5 kw/tons «Free cooling» during mid season Solar Rad. Temperature (C) Nbr Hrs Nbr Hrs Global Dry Bulb Wet Bulb Amplitu de Std Tmp Wet Bulb Twb<10C (50F) Twb>18C (64F) Jan 5,66-10,9-11,5 12,8 2,7 11,3 741,0 0,3 Feb 8,9-10,7-11,5 14,0 2,3 11,3 671,4 0,7 Mar 12,72-3,3-4,8 12,2 2,3 23,4 732,1 2,2 Apr 16,16 3,6 1,0 12,0 1,6 33,8 698,1 13,4 May 18,4 11,1 7,6 14,0 1,7 45,7 506,7 102,2 Jun 19,76 16,2 13,1 14,2 1,0 55,6 108,5 220,3 Jul 19,93 18,3 15,4 13,6 1,1 59,7 37,9 289,6 Aug 17,04 16,8 14,4 13,4 1,1 57,9 67,9 257,7 Sep 12,7 12,2 10,1 13,7 1,3 50,2 352,6 142,7 Oct 8,79 6,6 4,7 12,1 1,7 40,5 632,9 39,4 Nov 4,84 0,1-1,0 9,2 1,8 30,2 705,0 0,9 Dec 4,25-8,1-8,7 10,5 2,6 16,3 737,9 0,1 Global 12,6 1,8 5992,0 1069,4
Monitoring Results Reduction in energy consumption (kwh) Reduction of part loads Performance increase by more than 15% Reduction of winter consumption Improvement of winter free cooling by extending from September to May with a «Quasi Free Cooling» with storage at nignt : + 3000 hrs Allowing for Higher return temperature from the Free cooling Exchanger Reduction in condensing temperature Recharge at night/lower outside temperatures (with average daily amplitude, it represents an improvement of 15 % to 21% in kw/tons); Condensing temperature optimization is a net thermodynamic improvement of more than 10% over the year.
Monitoring Results General results Energy production and storage for the chilled water loop Before (2004) After (2005-2006) Chiller water Production 18 728 tons-h/day 37 537 tons-h/day Daily Consumption 16 706 kwh/day 15 572 kwh/day Average Instaneous Consumption 696 kw 648,8 kw Average Production (MCP + VFD Chiller) -- 1564,1 tons Average Production (before) 780,3 tons -- Free Cooling 750 tons (for 90% of time) 945 tons (average) Total Chilled Water Production 1455 tons 2509 tons Efficiency 0,892 kw/tons 0,415 kw/tons Efficiency (including Free Cooling) 0,478 kw/tons 0,259 kw/tons
Energy Management Consumption (kwh) 800000 700000 600000 500000 400000 300000 200000 Reduction in energy consumption Novanergy MCP1+MCP2 : Improvement in operating conditions for all the chillers in the plant Reduction of 6 % in the overall electrical energy consumption of the Plant 2400 2100 1800 1500 1200 900 600 Free Cooling (number of hrs) 5 300 MWh per year 45 % in GHG Emissions for Ch.Water 1500000 1000000 kwh Energy consumption for Chilled Water 100000 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 300 0 500000 Month Reduction in consumption Free Cooling Hrs 0 January February March April May Mois June July August September October November December
Economic Analysis Comparison with standard design (Common Chillers) ) show an important improvement in the Return on Investment with the Novanergy system. Interest Rate: 4%; Present Worth Factor: 3% Marginal energy cost: : 0,0253 $/kwh No Cost reduction considered (due to the elimination of a 1000 tons chiller) The dollar value of the kwh savings was $134,400. Additional savings from peak load shaving (kw) was $162,400 for a grand total of $296,800. The net present value NPV = $3.9 M. M Payback with 400 k$ in grants : 3,7 years The Life Cycle Cost Analysis do not consider the impact of maintenance cost reductions as well as the future price fluctuations of the energy sources which would seriously improve the numbers.
Conclusion TES Implementation Results in: Reduction of the Peak Load Reduction of the Energy Consumption Simplification the operation and the maintenance It Follows loads from 100 tons to 2500 tons; It Reduces the Stop and Start to a minimum It Reduces unefficient part loads to the mechanical units and corrects the original «Overdesign» Chilled water supply more stable and safe In case of power shortage or mechanical failure, two pumps are sufficient to operate the chilled water plant Reduction in refrigerant needs (½ of the original design) Reduction in GHG emissions by 45 %