HIGH PERFORMANCE CHILLED WATER SYSTEMS. EarthWise HVAC. EarthWise HVAC High Performance CHW Plants

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1 HIGH PERFORMANCE CHILLED WATER SYSTEMS EarthWise HVAC Simon Ho e: 2012 EarthWise HVAC High Performance CHW Plants Low Flow Low Temperature Systems Variable Flow Systems Variable CHW Variable CDW Chillers Piping Configurations Chiller Tower Optimization Pumping Optimization 2 1

2 LOW FLOW LOW TEMPERATURE HIGH EFFICIENCY SYSTEMS 3 Low Flow, Low Temperature High Efficiency 1.Slow the Flow 2.Drive the Chiller Harder 3.Chillers more efficient than ancillaries ~/ $ piping +/-$ air handlers +/-$ +/-$ chillers ~/ $ ductwork controls +/-$ FIRST COST & OPERATING COST COMFORT, ACOUSTICS & EFFICIENCY 4 2

3 Low Flow Low Temperature Low flow CHW and/or CDW improves system efficiency at part load Pumping power reduction more than offset slight increase in chiller power Low flow also decreases infrastructure costs Piping, valves Insulation Pumps Towers CT sizing can reduce with warm (design) condenser water and lower flows Re-invest some of the capital back into higher efficiency chillers, towers, coils and controls 5 Chiller Efficiency (Code vs Best in Class) Higher efficiencies today allow for better chiller utilization COP kw MEPS AU s 1980s 1990s 2000s 2010s 6 Note: Efficiencies at full load at AHRI (Standard MEPS) conditions water-cooled chillers 3

4 CHW Design Parameters Parameter Past/Conventional EarthWise Leaving CHW, [ o C] 6 ~ 7 4 ~ 6 CHW δt, [K] 5 ~ 7 9 ~ 12 CHW Flow, [L/s/MW] 34 ~ ~ 26 Leaving CDW, [ o C] ~ 38 CDW δt, [K] ~ 10 CDW Flow, [L/s/MW] ~ 35 Cooltools TM Chilled Water Plant Design Guide (Dec 2009) recommends 6.7 to 11.1K δt on chilled water and 6.7 to 10K δt on condenser δt Steven Taylor (ASHRAE Dec 2011), Clearly life-cycle costs will be lower, the higher the (chilled water) δt... within the range of their analysis (up to 13.9K δt) 7 CHW Plant Efficiency Chiller efficiency improvements Minimum code requirements: MEPS compliant AHRI or Eurovent certified; assurance of performance CHW Plant Ancillaries do Count! CHW pumps CDW pumps Cooling Tower fans CHW Plant System Efficiency [COP] defined by COOLING CAPACITY [kw] TOTAL POWER INPUT [kw] 8 Total Power Input includes power input of chillers and ancillaries 4

5 CHW Plant Efficiency Scale 9 Source: Thomas Hartman, 2001 CHW Plant Efficiency Conventional CHW plants spend significant portion of operational hours at part load Ancillaries power input are significant at part load % Total kw input % 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 25% 50% 70% 100% Note: Based on two screw chillers in parallel, AHRI conditions and sequenced. Pump heads at 400/250 kpa, cross-flow towers Tower Fans CDS Pumps EVP Pumps Chillers Plant Capacity 5

6 VARIABLE FLOW CHILLED WATER SYSTEMS 11 Primary only CV Design 1 2 (each) 3 Primary CV pumps 300 L/s Bypass 300 L/s 12 6

7 Primary only CV Part Load 11.7 C 11.7 C 1 2 (each) 11.7 C C Primary CV pumps 50 L/s 250 L/s Bypass 250 L/s 13 Primary secondary Design (each) Primary CV pumps 300 L/s bypass (decoupler) secondary VV pumps 300 L/s 14 7

8 Primary secondary Part load 11.7 C 11.7 C 1 2 (each) 11.7 C C Primary CV pumps 50 L/s 250 L/s bypass (decoupler) Secondary VV pumps 250 L/s 15 Variable primary Design 150 L/s (each) P Primary VV (or flow meter) pumps 0 L/s 300 L/s 300 L/s 16 8

9 Variable primary Part load 125 L/s (each) L/s L/s L/s P Primary VV (or flow meter) pumps 0 L/s 250 L/s 250 L/s 17 Variable primary System Flow < Chiller Min Flow 9.0 C 1 pump 40 L/s 9.0 C 40 L/s OFF OFF P Primary VV (or flow meter) pumps L/s 20 L/s 20 L/s 18 9

10 VPF - Advantages Less capital...more space Energy efficient Pumping savings during most operating conditions, down to minimum flow Pumping kw {Flow} 2.0 to 2.8 Improves reliability of system with manifold arrangement Separates pumping duty from cooling duty Not operating pumps to start chillers Chillers can fully realize its maximum capacity Over-pumping during part load to fully load chillers before bringing on the next chiller 19 VPF Chiller Lab Test 50% Flow in 30 sec Capacity Control with Water Flow Compensation 1, , L/s 1, Water Temp [degf] Evaporator W ater Flow Water Flow [gpm] 38 L/s 60 Evap Entering W ater Temp C C 40 Evap Leaving W ater Temp :00:00 0:10:00 0:20:00 0:30:00 0:40:00 0:50:00 Time (hour:min:sec) 20 10

11 VPF Chiller Selections Flow range-ability Ratio of minimum to design flow rates Aim for 1:2 ratio as a minimum Better ratios with larger centrifugal chillers than smaller screw type due to HX combinations available Higher velocities (high number of passes) will have higher design δp but also better range High design δp does not mean high energy consumption as chiller plant runs at part load most of the time Low flow designs may have poorer range-ability unless piped in series Consult manufacturers with experience 21 VPF System Considerations 22 System level Controls, not stand alone loops Basic operation Enable plant Control pumps Start lead chiller Start and stop lag chillers Vary flow to demand with dynamic reset Manage chiller and bypass operation at low flow Managing lead-lag Transient flows Sequence of Operation System integrator with experience 11

12 SYSTEM LEVEL CONTROLS Variable primary Controls 1 40 L/s 2 OFF 3 OFF Primary VV pumps P (or flow meter) P 23 System Options and Analysis No one ideal flow or temperature for all jobs There is a trend of lower operating costs with lower flows up to a certain point Need comprehensive analysis, not spreadsheet 24 12

13 Full Load System Input kw System kw Tower Fans CDS Pumps EVP Pumps Chillers Parallel AHRI Parallel AHRI, VPF Low Flow CHW Low Flow CHW & CDW 25 Note: Based on two screw chillers in parallel, sequenced. AHRI conditions compared to Low Flow CHW 5.5/15.5C; Low Flow CDS 28/36C. Pump heads at 400/250 kpa, cross-flow towers 75% Load System Input kw System kw Tower Fans CDS Pumps EVP Pumps Chillers 50 0 Parallel AHRI Parallel AHRI, VPF Low Flow CHW Low Flow CHW & CDW 26 Note: Based on two screw chillers in parallel, sequenced. AHRI conditions compared to Low Flow CHW 5.5/15.5C; Low Flow CDS 28/36C. Pump heads at 400/250 kpa, cross-flow towers 13

14 50% Load System Input kw System kw Tower Fans CDS Pumps EVP Pumps Chillers Parallel AHRI Parallel AHRI, VPF Low Flow CHW Low Flow CHW & CDW 27 Note: Based on two screw chillers in parallel, sequenced. AHRI conditions compared to Low Flow CHW 5.5/15.5C; Low Flow CDS 28/36C. Pump heads at 400/250 kpa, cross-flow towers 25% Load System Input kw System kw Tower Fans CDS Pumps EVP Pumps Chillers 20 0 Parallel AHRI Parallel AHRI, VPF Low Flow CHW Low Flow CHW & CDW 28 Note: Based on two screw chillers in parallel, sequenced. AHRI conditions compared to Low Flow CHW 5.5/15.5C; Low Flow CDS 28/36C. Pump heads at 400/250 kpa, cross-flow towers 14

15 Variable Condenser Flow (VCF) 29 System efficiency of VCF improvements are less compared to VPF on CHW Tower static head remains constant Chiller power increases due to higher lift at low flow Less or not effective on lift sensitive chillers (VSD) Possible Improvement on system efficiency especially at low loads < 50% - requires system level optimization controls Care with centrifugal chillers with surge limit and loss of VSD benefit More sensitive with single stage centrifugals Check unloading at various condenser flows and temperatures CHILLER PIPING & CONFIGURATIONS 30 15

16 Parallel - Parallel COP Chillers 6.1 System o C 29.4 o C, 59 L/s 34.6 o C 20 kw 29.4 o C, 59 L/s 20 kw 12.2 o C 25 kw 1100 kw COP o C, 47 L/s 12.2 o C 25 kw 34.6 o C 1100 kw 6.7 o C, 47 L/s COP K Waterside Lift o C Note: Based on two screw chillers in parallel, sequenced at AHRI conditions. Pump heads at 400/250 kpa, cross-flow towers. System COP includes chillers, pumps & tower fans Series - Parallel COP Chillers 6.3 System o C 29.4 o C, 62 L/s 34.7 o C 21 kw 29.4 o C, 57 L/s 19 kw 15.5 o C 28 kw 1080 kw 10.1 o C 1020 kw COP 6.8 COP o C 5.5 o C, 52.4 L/s 24.6 K 29.2 K Waterside Lift 10.1 o C 5.5 o C 32 Note: Based on two screw chillers in series evap low flow, parallel cond. Pump heads at 400/250 kpa, cross-flow towers. System COP includes chillers, pumps & tower fans 16

17 Series Counter-flow COP Chillers 6.4 System o C 31.7 o C 28.0 o C, 75.5 L/s 25 kw 15.5 o C 28 kw 1200 kw 10.1 o C 1000 kw COP 6.4 COP o C 31.7 o C 5.5 o C, 52.4 L/s 26.0 K 26.2 K Waterside Lift 10.1 o C 5.5 o C 33 Note: Based on two screw chillers in series evap low flow, counter-flow cond. Pump heads at 400/250 kpa, cross-flow towers. System COP includes chillers, pumps & tower fans Parallel Configuration Large Capacity Plants COP Chillers 6.6 System o C 28.0 o C, 349 L/s 116 kw p 30.5 K 36.0 o C 5.5 o C Waterside Lift 16.5 o C 4 off 2.5MW, COP o C, 217 L/s 113 kw p 34 Note: Based on two duplex centrifugal chillers in series evap low flow, counter-flow cond. Pump heads at 400/250 kpa, cross-flow towers. System COP includes chillers, pumps & tower fans 17

18 Parallel Configuration Large Capacity Plants COP Chillers 6.9 System o C 28.0 o C, 344 L/s 115 kw p 16.5 o C 26.0 K 36.0 o C 2 off 5.0 MW, COP K 31.5 o C 5.5 o C, 217 L/s 115 kw p 10.0 o C 5.5 o C Waterside Lift 35 Note: Based on two duplex centrifugal chillers in parallel evap low flow, counter-flow cond. Pump heads at 400/250 kpa, cross-flow towers. System COP includes chillers, pumps & tower fans Series Series (counter-flow) Large Capacity Plants COP Chillers 7.4 System o C 31.6 o C 28.0 o C, 340 L/s 113 kwp 15.5 o C 127 kw 5.5MW, p COP o C 23.2 K 23.8 K 10 o C 33.8 o C 31.6 o C 4.5MW, COP K 29.8 o C 5.5 o C, 238 L/s 12.7 o C Waterside Lift 10 o C 7.7 o C 5.5 o C 36 Note: Based on two duplex centrifugal chillers in series evap low flow, counter-flow cond. Pump heads at 400/250 kpa, cross-flow towers. System COP includes chillers, pumps & tower fans 18

19 Summary of EarthWise Chiller Plant Configurations Low flow CHW and CDW improves system COP Series connection improves performance at full and part load Use variable flow to improve pumping efficiency VPF with Series chillers maximizes pump savings Potential savings with variable condenser water flow at low loads Couple with overall chiller, pump and tower sequencing strategy Include optimal tower water control 37 CHILLER, TOWER AND PUMPING OPTIMIZATION 38 19

20 Chiller Tower Optimization Wet-bulb Condenser water temperature Heat Rejection Load Tower Design Cooling Load Condenser water temperature Chiller design 39 Condenser water control At Part Load Hot? 29ºC minimizes tower fan power, increases chiller power Cold? 15ºC minimizes chiller power, increases tower fan power Wet-bulb + 3K approach? Assumption that Load WB... Not always true! Approach is not fixed Optimized? Dynamic reset based on load & ambient to minimize system energy 40 20

21 Chiller Tower Optimization energy consumption, kw total chiller tower optimal control point condenser water temperature, C Note: Chiller at 50% Load, ambient 10ºC WB CTO comparisons 1,200,000 CHW Plant Annual Energy Cons [kwh] 1,000, , , , ,000-15C 18C 20C 22C 25C CTO ~ 6% Towers Pumps Chillers 2 3 yr payback 40% ROI CT Minimum Temp Set Point [ºC] 42 Sydney Commercial Office Application; BCA Class 5 schedules 2,200 kw cooling, water-cooled screw chillers, VAV, Econ cycle, 21

22 Chiller Tower Optimization RH T T TRACER SYSTEM LEVEL CONTROLS F F 43 Pumping Optimization Variable Flow CHW systems System Level critical valve reset Keeps critical valve near fully open Dynamic reset of δp set point Minimizes pumping power Better coil and temperature control Air Handling Units Better acoustics TRACER SYSTEM LEVEL CONTROLS VFD VV CHWP Control Valves Pressure Differential Controller or Transmitter 44 22

23 Questions or Comments Simon Ho e: 45 23