Hydrocarbon Refrigerant Performance in UAE Air-Cooled Chillers

Transcription

1 Hydrocarbon Refrigerant Performance in UAE Air-Cooled Chillers Peter Armstrong, Masdar Institute, October 2014 Research Sponsors: Tabreed Executive Affairs Authority 1

2 Motivation for Efficient Cooling Efforts Inefficient use of fuel (oil depletion) Impact on Economic Health Reduced disposable income Cost of subsidies Reduced exports Infrastructure cost of Generation and T&D capacity growth Impact on Environment GWP and ODP Opportunity to combine: Introduction of new refrigerants More stringent equipment performance standards EAA Comprehensive Cooling Program Six DSM Projects Six R&D Projects R&D-1a: GCC-Specific Advanced Chiller 2

3 Electrical demand in Abu-Dhabi (2010) 3

4 Contribution of cooling to electrical load (2010) AC Pumps & Fans 4

5 Adapted from: The Economist Subsidy Cost of fuel in oil power plant: 100 USD/barrel cost of fuel 13 cents/kwh 125 USD/barrel cost of fuel 16 cents/kwh Cost of fuel in gas power plant: 5 $/mmbtu 5 cents/kwh 10 $/mmbtu 10 cents/kwh Cost and emissions of Peakers in Abu- Dhabi: 22 $/mmbtu 15 cents/kwh Emissions: 7 kgco2/kwh 1 liter of oil has 10 kwh thermal energy 1 Barrel of oil has 155 liters = 1550 kwh thermal At 50% efficiency, 1 barrel of oil = 775 kwh electricity 1mmBTU of natural gas = kwh thermal At 50% efficiency, 1 mmbtu of gas = kwh electricity In Abu-Dhabi, 1 kwh of electricity 0.7 kg CO2 5

6 Strategic importance of cooling The energy required by buildings for AC approaches 60% of the total energy used in the Emirate The problem is more acute during summer periods when up to 70% of the peak demand can be traced back to buildings cooling systems Not only is the AC load a significant burden on the grid, but airconditioned buildings are often perceived to be uncomfortable (mainly because of low performance building envelope & AC equipment) Beyond the huge ecological impact of inefficient cooling, the economic cost to the national economy (energy subsidies) is staggering The GCC, and many other hot-humid regions (e.g., Singapore) share the same concerns and should combine efforts Urbanization is a global trend A/C an urban necessity. 6

7 Motivations for Minimum Equipment Performance Standard UAE cooling climate is extreme 1. Long cooling season >8 months; 12 months in many buildings 2. Very high peak, max-daily, and July-August mean temperatures 3. High humidity High performance chillers are rarely used because of subsidized electricity rates. Moreover some measures that could be costeffective in UAE, e.g. 2-stage positive displacement compression, are not available anywhere because they are not cost-effective for A/C application in countries of equipment origin. To optimize chiller design requires 1. Flexible component-based chiller model 2. Validated models of baseline and advanced components 3. Optimal control of variable-speed fans, compressors, and subcooling 4. Cost models of baseline and advanced components; scaling functions 5. Annual load profile or frequency distribution (capacity fraction and T amb ) 7

8 Baseline Chiller Characterization Instrumentation and characterization of baseline chiller 1. Redundant airflow by calibrated anemometer traverse and 2. Calibrated flow box 8

9 Baseline Characterization Refrigerant- and air-side temperatures Chilled water supply stratification 5% heat balance achieved over a wide range of operating conditions Validation is crucial to test model assumptions Heat balance is crucial to identify and correct instrumentation errors Fluid exit temperature is Not uniform Good thermal bond, pipe conductivity (copper) and insulation are essential to estimate T fluid from T surf 9

10 Screw and Reciprocating Compressor Maps Top: volumetric efficiency Bottom: isentropic efficiency x 10 Reciprocating Compressor Refrigerant Volume Flow Rate /Frequency Refrigerant Volume Flowrate /Frequency Screw Compressor x Frequency Pressure Ratio Frequency Pressure Ratio Isentropic Efficiency Isentropic Efficiency Frequency Pressure Ratio 4 20 Frequency Pressure Ratio 10

11 Performance Maps for >20 Modeled Chiller Designs Economized Variable-Speed Screw Compressor, R-134a, Variable-Speed Condenser Fans with 1 X Condenser 11

12 1/COP--with optimal Xsc Control Impact Control Options 1. Variable Speed Condenser Fans 2. Optimal Subcooling (shown) 3. Variable Speed Compressor /COP--normal operation 12

13 Candidate Chiller Designs Closer Approach Temperature/Low Pressure Drop: Condenser, Evaporator Part-Load Efficiency Measures: Optimized VFD Compressors, Fans, Pumps Advanced Cycles Throttling losses: Expander, Ejector Cycle, Liquid/Vapor HX, Subcooling Control Liquid Recycle/Injection to improve air-cooled Condenser Effectiveness 2-Stage Compressor: Economized, Liquid injected, Intercooled Compressor Types: Reciprocating, Screw, Scroll, Centrifugal Refrigerant (cycle interaction): Ammonia, Propane, Butane, R134, R410 Heat Rejection: Air-Cooled, Water Cooled, Evaporatively Cooled Optimal Condenser/Evaporator Sizes for each discrete combination Cycle/Compressor/Refrigerant/Condenser and Evaporator Sizes Work in progress 13

14 Life-Cycle Cost Assessment Template with 5% Discount Rate and 2% Fuel Escalation Rate (Costs shown are for Baseline Chiller) Cost Items Cost Element ($) Year of Occurrence Discount Factor Present Value ($) Initial Investment Base Date Residual Cost SPV20 = Replacement cost Every 5 th SPV5 = Electricity cost Annual ErgUPV20 = Non-energy O&M Annual UPV20 = SPV - Single Payment Present Value Factor UPV - Uniform Present Value Factor ErgUPV - Modified Uniform Present Value Factor 14

15 Life-Cycle Cost, Screw, R-134a at $0.08/kWh Case Name Case Condnsr SEER SEER Equipmnt Energy Saving LCC # Size X Imprv% Cost ($) (MWh/y) ($/y) ($) Base case Oversize Condenser 2a Oversize Condenser 2b Oversize Condenser 2c Optimal SubCooling 3a Optimal SubCooling 3b Optimal SubCooling 3c Variable-Speed Fans 4a Variable-Speed Fans 4b Variable-Speed Fans 4c Optimal SubClg+VSpd Fans 5a Optimal SubClg+VSpd Fans 5b Optimal SubClg+VSpd Fans 5c

16 Life-Cycle Cost, Recip, R-134a at $0.08/kWh Case Name Case Condnsr SEER SEER Equipmnt Energy Saving LCC # Size X Imprv% Cost ($) (MWh/y) ($/y) ($) Base case Oversize Condenser 6a Oversize Condenser 6b Oversize Condenser 6c

17 Life-Cycle Cost, Screw, NH3 and Butane at $0.08/kWh Case Name Case Condnsr SEER SEER Equipmnt Energy Saving LCC # Size X Imprv% Cost ($) (MWh/y) ($/y) ($) Base case Base Ammonia 7a Base Butane 8a

18 Conclusion / Outlook High Minimum Energy Performance Target is Justified 1. Manufacturers have a variety of off-the-shelf design options 2. Options evaluated to date are all very cost-effective 3. SEER can be raised from 2.8 to 4.8 at only 25-40% cost increase. Additional Design Options 1. Intercooled Reciprocating compressor 2. Flash desuperheating 3. Liquid-suction vapor heat exchanger 4. Combine design features with Reciprocating compressor 5. Test all promising combinations for alternative refrigerasnts Engagement of Manufacturers 1. Manufacturing capability 2. Component cost data 3. Review and feedback Other HVAC Equipment for MEP 1. Dedicated Ventilation A/C 2. Efficient FCU and Passive Chilled Beams or ACB 3. High Temperature Chilled Water System 4. Harmonize Building and Equipment Standards 18