The impact of water treatment on refrigeration system energy efficiency

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Beryl Cox
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1 PACIA Carbon Solutions Forum 3 4 Aug 2011 The impact of water treatment on refrigeration system energy efficiency Tom Steele Technical Consultant, Nalco 1

2 Agenda Chiller (Refrigeration System) Background Chiller Efficiency Water Treatment Issues Impacting Efficiency Case Studies 2

3 Overview Chillers: Are major electricity users Used throughout industry To cool water, products, spaces Typically use a vapour-compression cycle Air-cooled or Water-cooled Condensers Efficiency depends on: Demand Response / Load Management Machine performance Tight Systems Clean heat transfer surfaces 3

4 Chillers Contribution to Australian Carbon Emissions 2-3% of total electricity 1-2% of total carbon Over 20,000 chillers 10% efficiency gain saves 570kt CO2 = $13M

5 Typical Refrigeration-Related Electricity usage Industry Sector % of Total electricity Dairy 25 Brewery 35 Confectionary 40 Chilled Food 50 Frozen Food 60 Cold Storage 85

6 Refrigeration Cycle Hot, HP Refrigerant vapour cooled to HP Liquid Electricity Drives Compressor Cool, HP Refrigerant Evaporated to LP Vapour HP LP Heat rejected to atmosphere T d T e Cool, High Pressure Refrigerant Expanded Process cooled by Latent Heat Of Refrigerant

7 A Typical Chilled Water System

8 Measuring Chiller Efficiency COP (Coefficient of Performance) = Useful Refrigeration Output (kw r ) Electrical Energy Input (kw e ) Useful Refrigeration Output (kw r ) = m x C p x (T h T c ) = Water Flow [kg/s] x Specific Heat [kj/kg C] x Water Temp in-out [C] Electrical Energy Input (kw e ) = Compressor + Ancillaries Power = V x A x PF x 3 ( 3 for 3 phase power) = Supply Voltage V x Current x Power factor Theoretical COP (Carnot Cycle) = T e T c - T e

9 Variation of COP Compressor Head Pressure Evaporator Pressure

10 Refrigeration Efficiency Improvement Manage Load Optimise Cold Set Point Use Ambient / Free Cooling Reduce cold product losses Improve Plant Condenser Evaporator Keep air out of refrigerant Minimise condensing temp Maintain cooling water flow Increase condenser size Keep condenser clean Maximise evaporating temp Keep evaporator clean Increase evaporator area Compressor VSD motor control Maintain refrigerant charge Minimise Air Ingress Minimise oil in refrigerant

11 The Challenges of Water Treatment

12 Cooling System Dynamics Evaporation =ƒ (RR x (T h T c )) Evaporation T h Losses Make-up Water Bleed T c RR Cooling Water Condenser Chiller Compressor Evaporator Liquid Refrigerant Make-up = Evaporation + Bleed + Losses Cycles of Concentration = = Make-up Bleed + Losses Dissolved Solids in Cooling Water Dissolved Solids in Make-up Water

13 Water-Related Efficiency Losses Evaporation T h Losses Make-up Water Bleed T c RR Cooling Water Condenser Chiller Compressor Evaporator Liquid Refrigerant

14 Chiller Performance Monitoring Measure Units Compressor Amps amps Compressor Volts volts Chilled Water Flow m3/h Chilled Water Temperature Into Evaporator C Chilled Water Temperature Out of Evaporator C Condenser Inlet CW Temperature C Design Load kwr Compressor discharge "Head" Pressure kpa Electricity Cost ($/kwh) $/kwh Operating Hours h/year

Case Study 1 NZ Dairy Plant Effect of Condenser Scale Chilled Water for Whole Milk Powder Production 7740 kwr (2200 RT) installed chiller capacity Seasonal

15 Case Study 1 NZ Dairy Plant Effect of Condenser Scale Chilled Water for Whole Milk Powder Production 7740 kwr (2200 RT) installed chiller capacity Seasonal operation 288 days/year Scale observed on tubes up to 3mm thick Scale analysed to be mainly calcite (limestone) Estimate the cost of loss of Chiller efficiency

16 Case Study 1 NZ Dairy Plant Effect of Condenser Scale Annual Chiller Electrical Cost ($) at full load = [(Chiller capacity kwr)/(cop kwr/kwe)](operating hrs)(elect $/kwh) Empirical Data for effect of deposition for a given scale type: Fouling Factor (m 2 o C/kW) Deposition thickness, mm (k = kw/m 2 o C) % Increase in Electrical Energy Summarising the Operating data: Refrigeration Capacity (kwr) 7740 Operating Days/year 288 Chiller Efficiency COP (kwr/kwe) 5 Electricity Cost ($/kwhr) 0.09 Thermal Conductivity of Deposit (kw/m deg C) 2.90E-03

17 Increased Cost, $/Year Case Study 1 NZ Dairy Plant Effect of Condenser Scale Annual Chiller Electrical Cost ($) at full load = $960k Effect of Calcite Deposit on Power Cost $700,000 $600,000 $500,000 $400,000 $300,000 $200,000 $100,000 $ Deposit Thickness, mm

Case Study 2 NZ Dairy Plant Effect of Chilled Water Biofilm Chilled Water for Whey Protein Concentrate 3740 kwr (1060 RT) installed chiller capacity Seasonal

18 Case Study 2 NZ Dairy Plant Effect of Chilled Water Biofilm Chilled Water for Whey Protein Concentrate 3740 kwr (1060 RT) installed chiller capacity Seasonal operation 288 days/year Loss of production due to lack of chilled water Major slime and biofilm observed in tan Estimate the cost of loss of Chiller efficiency

19 Case Study 2 NZ Dairy Plant Effect of Chilled Water Biofilm Annual Chiller Electrical Cost ($) at full load = $460k :

20 Case Study 3 NZ Dairy Plant COP Monitoring Identify the source of data - (luckily this was easily found on the process control screen):

21 Case Study 3 NZ Dairy Plant COP Monitoring Enter the data in a simple spreadsheet Date: 17/09/2010 9/04/ /04/ /04/2010 Compressor Amps amps Compressor Volts volts Chilled Water Flow m3/h Water Temperature Into Chiller C Water Temperature Leaving Chiller C Temperature Difference C Condenser Inlet CW Temperature C kw (electrical) kwe kw (refrgeration) kwr % Load % kw/ton (actual) kw/ton Condenser Inlet CW Temp. (design) C Percent Energy Wasted % #DIV/0! Condenser Pressure kpa Cost Electricity ($/kwhr) $/kwhr Number of Operating Hours hrs/year Operating Energy Cost $/year Design Energy Cost $/year Wasted Energy Cost $/year COP

22 Case Study 3 NZ Dairy Plant COP Monitoring Review the Trends:

23 Parting Thoughts Vapour Compression Liquid Chiller Plants typically have energy / carbon saving potential The potential savings can be modeled and tracked using performance monitoring Improvement in water treatment management provides a good opportunity for efficiency gains 23

24 Question Time 24

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