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Hydrocarbon Refrigerant Performance in UAE Air-Cooled Chillers

Peter Armstrong, Masdar Institute, October 2014 Research Sponsors: Tabreed Executive Affairs Authority

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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

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Electrical demand in Abu-Dhabi (2010)

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Contribution of cooling to electrical load (2010)

AC Pumps & Fans

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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 = 293.1 kWh thermal At 50% efficiency, 1 mmBTU of gas = 146.5 kWh electricity In Abu-Dhabi, 1 kWh of electricity 0.7 kg CO2

Ad

apte

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rom

: Th

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• 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 air-conditioned 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.

Strategic importance of cooling

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• 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 cost-effective 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 Tamb)

Motivations for

Minimum Equipment Performance Standard

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• Instrumentation and characterization of baseline chiller 1. Redundant airflow by calibrated anemometer traverse and 2. Calibrated flow box

Baseline Chiller Characterization

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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 Tfluid from Tsurf

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Screw and Reciprocating Compressor Maps Top: volumetric efficiency – Bottom: isentropic efficiency

• Screw Compressor

3.03.5

4.04.5

5.05.5

6.0

50

100

150

2002

4

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x 10-4

Pressure RatioFrequency

Refr

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rate

/Fre

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2000.4

0.6

0.8

1.0

Pressure RatioFrequency

Isen

tro

pic

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1.5

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4.5

5.56

16

18

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x 10-4

Pressure Ratio

Frequency

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requency

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Pressure RatioFrequency

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• Reciprocating Compressor

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Performance Maps for >20 Modeled Chiller Designs

Economized Variable-Speed Screw Compressor, R-134a, Variable-Speed Condenser Fans with 1 X Condenser

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Control Impact

• Control Options 1. Variable Speed Condenser Fans 2. Optimal Subcooling (shown) 3. Variable Speed Compressor

0.25 0.3 0.35 0.4 0.450.25

0.3

0.35

0.4

0.45

1/COP--normal operation

1/C

OP

--w

ith

op

tim

al X

sc

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• 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

Candidate Chiller Designs

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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 137597.96 0 Base Date - 137597.96

Residual Cost 4127.94 20 SPV20 = 0.3769 1555.82

Replacement cost 2460.00 Every 5th SPV5 = 0.7835 642.47

Electricity cost 84114.08 Annual ErgUPV20 =14.959 1258262.51

Non-energy O&M 7987.38 Annual UPV20 =12.4622 99540.30

SPV - Single Payment Present Value Factor UPV - Uniform Present Value Factor ErgUPV - Modified Uniform Present Value Factor

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Life-Cycle Cost, Screw, R-134a at $0.08/kWh

Case Name Case

#

Condnsr

Size X

SEER SEER

Imprv%

Equipmnt

Cost ($)

Energy

(MWh/y)

Saving

($/y)

LCC

($)

Base case 1 1.0 2.806 -- 137598 465.65 -- 796597

Oversize Condenser 2a 1.3 2.921 4.076 143489 447.42 1459 780732

Oversize Condenser 2b 1.5 3.010 7.253 147938 434.16 2519 769369

Oversize Condenser 2c 1.8 3.012 7.307 155534 433.94 2537 776792

Optimal SubCooling 3a 1.3 3.061 9.055 143489 426.99 3093 756284

Optimal SubCooling 3b 1.5 3.116 11.01 147938 419.48 3694 751795

Optimal SubCooling 3c 1.8 3.138 11.80 155534 416.51 3931 755927

Variable-Speed Fans 4a 1.0 3.097 10.35 185161 421.97 3494 792426

Variable-Speed Fans 4b 1.5 3.226 14.95 195502 405.10 4844 782696

Variable-Speed Fans 4c 1.8 3.275 16.71 203098 399.00 5332 783069

Optimal SubClg+VSpd Fans 5a 1.0 3.217 14.59 185161 408.57 4567 776386

Optimal SubClg+VSpd Fans 5b 1.5 3.295 17.40 195502 394.65 5681 768321

Optimal SubClg+VSpd Fans 5c 1.8 3.328 18.54 203098 392.79 5829 772049

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Life-Cycle Cost, Recip, R-134a at $0.08/kWh

Case Name Case

#

Condnsr

Size X

SEER SEER

Imprv%

Equipmnt

Cost ($)

Energy

(MWh/y)

Saving

($/y)

LCC

($)

Base case 1 1.0 2.806 -- 137598 465.65 -- 796597

Oversize Condenser 6a 1.3 4.708 67.75 163086 277.58 15046 597305

Oversize Condenser 6b 1.5 4.847 72.70 167535 269.63 15682 592288

Oversize Condenser 6c 1.8 4.903 74.68 175131 266.57 15927 596305

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Life-Cycle Cost, Screw, NH3 and Butane at $0.08/kWh

Case Name Case

#

Condnsr

Size X

SEER SEER

Imprv%

Equipmnt

Cost ($)

Energy

(MWh/y)

Saving

($/y)

LCC

($)

Base case 1 1.0 2.806 -- 137598 465.65 -- 796597

Base case @ Ammonia 7a 1.0 3.187 13.42 137598 410.11 4444 730123

Base case @ Butane 8a 1.0 2.843 1.189 137598 461.273 351 791351

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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