Using Water-Cooled Chillers to Exceed ASHRAE Minimum Efficiency Standard by > 50%

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1 Using Water-Cooled Chillers to Exceed ASHRAE Minimum Efficiency Standard by > 50% Presented by Scott McDonough Product Manager Carrier Corporation 2015 Carrier Corporation Version 1.1

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3 GREEN DONE EASY Designing for 50% Energy Savings: Weather Determinants of Chiller Energy Consumption Variable Speed Screw Chillers Chiller Plant Design Results: Test Data Energy Analysis GDE Basic Building Blocks 4

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10 LIFT (PRESSURE DIFFERENCE) Lift = SCT less SST Saturated temperatures are surrogates for pressures 95F 85F To condense, refrigerant must be warmer than the leaving condenser water. SCT = 95F + 2F approach = 97F (35C + 1.1C = 36.1C) 44F 54F To boil, refrigerant must be colder than the leaving chilled water. SST = 44F 2F approach = 42F (6.7C - 1.1C = 5.6C) Lift is Based on Leaving Graphic: Carrier Corp. 11

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17 23XRV VFD SCREW CHILLERS AquaEdge 23XRV chiller with Greenspeed intelligence Simple Capacity Control Surge Free Operation Few Moving Parts Not part of the for credit presentation Positive Pressure Variable Orifice 175 to 550 Ton ( kw) Shaft Seal Guide Vanes IGV Actuator Solenoids Slide Valve Purge 48

18 VARIABLE EVAPORATOR FLOW Not part of the for credit presentation 58F 1000 gpm (63 l/s) 500 gpm (31.5 l/s) Flow rate reduced 50% in 35 seconds. 23XRV quickly shed the load and stabilized at the new condition. 44F 52

19 VARIABLE CONDENSER FLOW OPERATION Not part of the for credit presentation Lvg Cond Temp Condenser flow Ent Cond Temp 23XRV Operation at as condenser water flow reduced by 50% in 30 seconds.

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21 OPERATION RANGE Not part of the for credit presentation Future Load: No penalty for over sizing 100% Wide, Flexible Operational Envelope Elevated Condenser: Scaled Tower Reduced Flow Dirty Tubes 23XRV provides 10 F safety factor! Stability: 10% Load / 95F Economizer Operation: 10% Extreme Zone 40F (4.4C) 53F (11.7 C) Chilled Fluid Temperature Chilled Water Reset: 95 F (35 C) 85 F (29.4C) 55 F (12.8C) Inverted Start: 57

22 IDEAL FAN LAWS Not part of the for credit presentation Centrifugal Equipment Governed by Ideal Fan Laws Capacity ~ rpm Lift ~ rpm 2 Power ~ rpm 3 1.Speed required to match the given capacity condition is 75% 2.Speed required to match the given lift condition is 86% Speed 2 = Lift Speed = Lift = % 3. The operating speed is the greater of 1. and 2. which is 86% 4. To unload to 75% load at 86% rpm, the IGV must close 5. Minimum speed for a centrifugal chiller is a function of lift a. Operating below this speed could cause the chiller to surge b. Operating above this speed results in exponential power costs 58

23 MECHANICAL UNLOADING Not part of the for credit presentation If the centrifugal compressor must operate at 84% speed to develop sufficient head, how do we limit the capacity to 60% Hot gas bypass? Inlet guide vanes? Variable diffuser? Inlet Guide vanes in a centrifugal compressor create a pressure drop of 1% to 13% in their wake. This increases the head requirements on the compressor thereby increasing power. 60

24 Variable Speed Screw Advantages In Efficient Water Cooled Chiller Plants More Robust Operating Envelope Simpler Operation and Maintenance More Efficient More flexible

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26 BASIC SERIES COUNTER FLOW DIAGRAM Series Counter flow 60F (15.6 C) 95F (35 C) CH-2 44F (6.7 C) 85F (29.4 C) CH-1 52F (11.1 C) 90F (32.2C) Upstream chiller (CH-2) cools 60F 52F (15.6 C 11.1 C) Downstream chiller (CH-1) cools 52F 44F (11.1 C 6.7 C) Evaporator water flows thru CH-2 and then CH-1 Condenser water flows thru CH-1 and then CH-2 One pass heat exchangers for water side pressure drop 22

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28 SERIES COUNTERFLOW REDUCES LIFT 60F (15.6C) 44F (6.7C) Downstream Chiller 95F (35 C) 85F 52F (11.1 C) 90F (32.2C) SCT Pressure SAT. LIQUID Heat Rejection Reduced Lift Refrigerant Effect (29.4C) SST (Capacity) SAT. VAPOR System SST SCT Lift _ Parallel 42 (5.6C) 97 (36.1C) 55 (30.5C) SCF 42 (5.6C) 92 (33.3C) 50 (27.7C) Enthalpy Lower Lift = Less Work = Lower kw

29 SERIES COUNTERFLOW REDUCES LIFT 60F (15.6C) 44F (6.7C) Upstream Chiller 95F (35 C) 85F 52F (11.1 C) 90F (32.2C) SCT Pressure SAT. LIQUID Heat Rejection Reduced Lift Refrigerant Effect (29.4C) SST (Capacity) SAT. VAPOR System SST SCT Lift _ Enthalpy Parallel 42 (5.6C) 97 (36.1C) 55 (30.5C) SCF 50 (10C) 97 (36.1C) 47 (26.1C)

30 SERIES COUNTERFLOW REDUCES LIFT 60F (15.6C) 44F (6.7C) Upstream Chiller 95F (35 C) 85F 52F (11.1 C) 90F (32.2C) SCT Pressure SAT. LIQUID Heat Rejection Reduced Lift Refrigerant Effect (29.4C) SST (Capacity) SAT. VAPOR System SST SCT Lift _ Enthalpy Parallel 42 (5.6C) 97 (36.1C) 55 (30.5C) SCF 50 (10C) 97 (36.1C) 47 (26.1C)

31 44-54 F ( C) 44 F (6.7 C) 49 F (9.4 C) F ( C) 44 F (6.7 C) 50 F (10 C) F ( C) 44 F (6.7 C) 51 F (10.6 C) F ( C) 44 F (6.7 C) 52 F (11.1 C)

32 Var. Flow Return US Lvg DS Lvg 100% 60 F (15.6 C) 52 F (11.1 C) 44 F (6.7 C) 75% 60 F (15.6 C) 52 F (11.1 C) 44 F (6.7 C) 50% 60 F (15.6 C) 52 F (11.1 C) 44 F (6.7 C) 25% 60 F (15.6 C) Off 44 (6.7 C) Const. Flow Return US Lvg DS Lvg 100% 60 F (15.6 C) 52 F (11.1 C) 44 F (6.7 C) 75% 56 F (13.3 C) 50 F (10.0 C) 44 F (6.7 C) 50% 52 F (11.1 C) 48 F (8.9 C) 44 F (6.7 C) 25% 48 F (8.9 C) Off 44 (6.7 C)

33 Series Counterflow Dissadvantage If/when 1 chiller fails, the other chiller must be able to adapt to completely different operating parameters! Centrifugal chillers cannot be selected (or selected efficiently) to handle this type of variance. SCF Centrifugal applications should have a spare pair of chillers, which is not cost effective. Variable speed screw chillers can, however, be efficiently selected to withstand the vastly different operating parameters when a chiller s down. The emergence of variable speed screws has made designing SCF chilled water plants economically viable.

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35 MOVING THE FRONTIER Graphic based on Carrier chiller data 31

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37 USING WATER-COOLED CHILLERS TO EXCEED ASHRAE MINIMUM EFFICIENCY STANDARD BY > 50% REMEMBER TO FILL OUT AND TURN IN THE EVALUATION FORM Reminder: If you are registered in Florida, New York, or North Carolina, you must also sign the sheets in the back at the end of the session. Please print your name, include your registration number, and sign the sheet. 45