Optimizing Chilled Water Plant Performance David Herman, PE, LEED AP Principal EnerG Associates, LLC
Optimizing Chilled Water Plant Learning Objectives Performance Review the design and operating characteristics of each equipment component of a chilled water plant Understand how the design characteristics and operation of each equipment component effects overall chiller plant efficiency Learn how to evaluate strategies to optimize chilled water plant performance based on existing chilled water plant design and operation Review actual operating data from central chilled water plants before and after implementation of optimization strategies 3/6/2014 2
Optimizing Chilled Water Plant Performance Benchmark the existing equipment Ensure proper preventive maintenance Optimize operation of existing equipment Evaluate possible capital retrofits 3/6/2014 3
A Typical Chiller Plant 3/6/2014 4
A Typical Chiller Plant What is the average total kw/ton for an existing chiller plant including chillers, cooling towers and pumps? Approx. 1.0 kw/ton What is an optimized total kw/ton for a chiller plant? Approx. 0.8 1.0 kw/ton (lower with capital investment) 3/6/2014 5
Benchmarking Pumps What is one of the most useful diagnostic tools for benchmarking pumps? The Pump Curve 3/6/2014 6
Benchmarking Pumps Example: TACO Model #TA1538 HP 75 GPM 1400 HD 140 IMP 12.5 RPM 1750 3/6/2014 7
Benchmarking Pumps 3/6/2014 8
Benchmarking Pumps How can pump impeller size be confirmed? By deadheading the pump 3/6/2014 9
Benchmarking Pumps 3/6/2014 10
Benchmarking Pumps 3/6/2014 11
Benchmarking Pumps Why is it important to use the same gauge to measure suction and discharge pressures? To avoid gauge error since the differential pressure is needed 3/6/2014 12
Benchmarking Pumps Example: Measured Suction P: 9 psig Measured Discharge P: 58 psig Measured ΔP: 58 psig Measured ΔP: 134 head To convert psi to head, multiply by 2.31 Deadhead: 163 3/6/2014 13
Benchmarking Pumps 3/6/2014 14
Benchmarking Chillers Basic Formulas 1 ton = 12,000 Btuh GPM = Q / (500 x ΔT) Tons = GPM x ΔT / 24 3/6/2014 15
Benchmarking Chillers What ΔT is the basis of the rule of thumb of 2.4 GPM/ton for evaporator flow? ΔT = 10 degrees 3/6/2014 16
Benchmarking Chillers Tag # Manuf Model # Nom Tons #1 Trane CVHE090R00 925 #2 Trane CVHE090R00 925 #3 Trane CVHE 050 F BC 515 Evaporator GPM Ent Temp Lvg Temp Temp Diff 1,350 58.4 42.0 16.4 1,350 58.4 42.0 16.4 750 58.5 42.0 16.5 Condenser GPM Lvg Temp Ent Temp Temp Diff 1,800 99.9 85.0 14.9 1,800 99.9 85.0 14.9 1,000 100.0 85.0 15.0 FLA kw kw/ton Refrig Charge Starts Hours 927 666 0.72 R 123 1,111 34,236 927 666 0.72 R 123 1,131 25,575 526 382 0.74 R 11 1170 2,276 > 21935 3/6/2014 17
Benchmarking Chillers Barrel Nom Tons Rated Flow Rated PD FT Rated Temp Diff Evap 515 750 8.1 16.5 Cond 1,000 9.7 15.0 Meas Ent P Meas Lvg P Meas Diff P Meas PD FT Meas Flow 84 80 4 9 801 78 68 10 23 1,543 Meas Ent T Meas Lvg T Meas Temp Diff Tons Amps kw kw/ton 54.0 40.0 14.0 467 440 315 0.67 80.0 89.0 9.0 3/6/2014 18
Benchmarking Chillers Measured Flow = Rated Flow * (Rated PD/Measured PD)^0.5 kw = (3)^0.5 *V * A * PF / 1000 3/6/2014 19
Ensure Proper Maintenance Pumps Chillers Cooling Towers 3/6/2014 20
Optimize Pump Operation Over pumping results in: Flow problems Energy penalty 3/6/2014 21
Optimize Chiller Operation Lower condenser water temperature set point For every one degree drop in condenser water temperature, chiller efficiency will increase 2% Consider the trade off between lower compressor energy and increased cooling tower fan energy 3/6/2014 22
Optimize Chiller Operation What is the typical location of the differential pressure sensor controlling the pump variable speed drive? Somewhere along the chilled water supply and return piping What is the optimum location? 3/6/2014 23
Optimize Chiller Operation Relocate differential pressure sensor controlling pump variable speed drive Optimum location is across the chilled water supply and return piping at the farthest chilled water coil 3/6/2014 24
Evaluate Capital Retrofits Install variable speed drive on existing chiller(s) Significant energy savings in chiller energy use is possible (up to 30% in some applications) 3/6/2014 25
Optimizing Chilled Water Plant Performance Benchmark the existing equipment Ensure proper preventive maintenance Optimize operation of existing equipment Evaluate possible capital retrofits 3/6/2014 26
To download a copy of this presentation, go to www.energengineers.com 3/6/2014 27