September 22, 2011 Roy Hubbard HVAC Systems Technology
Lesson Objectives (YC-3) At the end of this session, you will understand: Understanding Chiller Energy Fundamentals Impact of VSDs (maintenance and energy) chillers pumps towers 2
Chiller Energy Fundamentals
Chiller Energy Fundamentals A chiller s energy(kw) use is dependent on both cooling load & compressor head. (lift/press diff)
Energy Usage -Constant Speed Driven Chillers Chiller Energy Analogy 5
Energy Usage -Constant Speed Driven Chillers Chiller Energy Analogy Load (weight of rock) 6
Energy Usage -Constant Speed Driven Chillers Chiller Energy Analogy Lift (height of mountain) Load (weight of rock) 7
Energy Usage -Constant Speed Driven Chillers Chiller Energy Analogy 100% Lift ENERGY 0% Load (weight of rock) (height of mountain) 8
Energy Usage -Constant Speed Driven Chillers Chiller Energy Analogy 100% ENERGY Load (weight of rock) Design Lift Lift (height of mountain) 0% 9
Energy Usage -Constant Speed Driven Chillers Chiller Energy Analogy 100% Condenser Temp. ENERGY 0% Load (weight of rock) Design Lift Lift (height of mountain) Evaporator Temp. 10
Energy Usage -Constant Speed Driven Chillers Chiller Energy Analogy 100% Condenser Temp. 85 F (29.5 C) ECWT ENERGY 0% Load (weight of rock) Design Lift Evaporator Temp. 44 F (6.7 C) LCHWT 11
Energy Usage -Constant Speed Driven Chillers Chiller Energy Analogy Cold Condenser Water Condenser Temp. 85 F (29.5 C) ECWT 70% 55 F (12.8 C) ECWT ENERGY 0% Load (weight of rock) Off- Design Lift Evaporator Temp. 44 F (6.7 C) LCHWT 12
Off-Design Energy Performance Curves Poor! % KW 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 85 75 65 55 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% % Load
Off-Design Energy Performance Curves Great! % KW 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 85 75 65 55 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% % Load
Off-Design Energy Performance Curves Poor! % KW 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 85 75 65 55 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% % Load
Off-Design Energy Performance Curves Great! % KW 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 85 75 65 55 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% % Load
Off-Design Energy Performance Curves - Average % KW 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 85 75 65 55 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% % Load
Chiller Energy Fundamentals A chiller s energy(kw) use is dependent on both cooling load & compressor head.(lift/press diff) A chiller s efficiency (kw/ton) varies little with load, but much with compressor head
Chiller Efficiency How does chiller efficiency change as load and head vary?
kw/ton vs Load/Head Design 20
kw/ton vs Load/Head Design 21
Chiller Efficiency (Constant Speed)
Chiller Efficiency (Constant Speed)
Chiller Efficiency (Constant Speed)
Variable Speed Chillers
Energy Usage -Constant Speed Driven Chillers Chiller Energy Analogy 100% Condenser Temp. 85 F (29.5 C) ECWT ENERGY 0% Load (weight of rock) Design Lift Evaporator Temp. 44 F (6.7 C) LCHWT 26
Energy Usage -Constant Speed Driven Chillers Chiller Energy Analogy Cold Condenser Water Condenser Temp. 85 F(29.5 C) ECWT 70% ENERGY Load (weight of rock) 0% Evaporator Temp. 44 F (6.7 C) LCHWT Off- Design Lift 55 F (12.8 C) ECWT 27
Energy Usage -Variable Speed Driven Chillers Cold Entering Condenser Water Condenser Temp. 85 F(29.5 C) ECWT 50% 55 F (12.8 C) ECWT ENERGY 0% Load (weight of rock) Off- Design Lift Evaporator Temp. 44 F (6.7 C) LCHWT 28
Energy Usage -Constant Speed Driven Chillers Cold Entering Condenser Water Condenser Temp. 85 F(29.5 C) ECWT 70% 55 F (12.8 C) ECWT ENERGY 0% Load (weight of rock) Off- Design Lift Evaporator Temp. 44 F (6.7 C) LCHWT 29
Energy Usage -Variable Speed Driven Chillers Cold Entering Condenser Water Condenser Temp. 85 F(29.5 C) ECWT 50% 55 F (12.8 C) ECWT ENERGY 0% Load (weight of rock) Off- Design Lift Evaporator Temp. 44 F (6.7 C) LCHWT 30
Energy vs. Load & ECWT (CSD) 100% 90% 80% % Design KW 70% 60% 50% 40% 30% 20% 10% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% % Design Load
Energy vs. Load & ECWT (VSD) 100% 90% 80% % Design KW 70% 60% 50% 40% 30% 20% 10% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% % Design Load
Energy vs. Load & ECWT (CSD) 100% 90% 80% % Design KW 70% 60% 50% 40% 30% 20% 10% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% % Design Load
Energy vs. Load & ECWT (VSD) 100% 90% 80% % Design KW 70% 60% 50% 40% 30% 20% 10% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% % Design Load
Variable Speed Chillers 25-30% Savings
Chiller Energy Fundamentals A chiller s energy draw is dependent on both load and compressor head (lift/press diff) A chiller s efficiency (kw/ton) varies little with load, but much with compressor head Variable Speed on Chillers saves from both compressor head change and load change
Variable Speed Chillers 25-30% Savings 1/2 of Savings Head Change 1/2 of Savings Load Change
Variable Speed Chillers Load Savings depends on Head Reduction Head Savings does not depend on Load Reduction
Chiller Energy Fundamentals A chiller s energy draw is dependent on both load and compressor head (lift/press diff) A chiller s efficiency (kw/ton) varies little with load, but much with compressor head Variable Speed on Chillers saves from both compressor head change and load change Variable Speed saves energy on Multiple Chiller Plants and Single Chiller Plants
Variable Speed Chillers Load-based Sequencing Difference - Single vs Multiple? Load? - Heavier Chiller Loading (less variation), if using old load-based sequencing
Variable Speed CHW Pumps
Variable Speed CHW Pumps Good Savings on Pump Energy
Variable Flow Affinity Laws (VSD Control) RPM ~ Flow (GPM, CFM, etc.) RPM 2 ~ Head (ft, SP) RPM 3 ~ Ideal Power (hp) Apply only to Water hp= Flow X Head / 3960 note pump/motor/vsd efficiency not included Apply only to fixed, unchanging piping systems (flow varies, but no valves close)
Pump Energy Des. HP = GPM X Head 3960 X Pump Eff Des. kw = HP X 0.746 Motor Eff X VSD Eff
Variable Speed CHW Pumps Good Savings on Pump Energy Chiller energy Unaffected Maintain Tube Water Velocity 1.5 to 12 fps (Flooded 2P 45, 3P 67 max) Set Proper Ramp Function Time for VSD (5% to 30% per min 10% is typical)
Variable Speed CW Pumps (Variable Flow)
Variable Speed CW Pumps (Variable Flow) Good Savings on Pump Energy Chiller Energy will be higher Chiller Maintenance will be higher
Variable Speed CW Pumps (Variable Flow) Good Savings on Pump Energy Chiller Energy will be higher Chiller Maintenance will be higher Tower Maintenance may be higher
Variable Speed CW Pumps (Variable Flow)
Variable Speed CW Pumps (Variable Flow) Good Savings on Pump Energy Chiller Energy will be higher Chiller Maintenance will be higher Tower Maintenance may be higher Tower Approach may deteriorate
Variable Speed CW Pumps (Variable Flow) Dry Spots in Cooling Tower Fill destroys Approach
Variable Speed CW Pumps (Variable Flow) Good Savings on Pump Energy Chiller Energy will be higher Chiller Maintenance will be higher Tower Maintenance may be higher Tower Approach may deteriorate Piping System Maintenance will be higher Maintain Tube Water Velocity 3.3 to 12 fps Use to replace balancing valve
Cooling Towers Fans Variable Speed
Fan Affinity Laws (VSD Control)
Chiller Plant Component Energy CHWP at 160 ft head (10 deg rise) =.10 hp/t CWP at 50 ft head (10 deg rise) =.05 hp/t Tower Average =.05 hp/t (induced draft, gravity fed average) Chiller (at.6 kw/t) =.75 hp/t
September 22, 2011 Roy Hubbard HVAC Systems Technology