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Air-Cooled Chiller Optimal LCC Design forMinimum Equipment Performance Standard (MEPS)

Peter Armstrong, M Tauha Ali. April 2018

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• Per capita CO2 emissions is 5 times the world average standing at about 20 tCO2/year [World Bank, 2010]

• Peak electricity generation is expected to grow from 10.6 GW in 2012 to more than 23 GW in 2020 (annual growth rate of 10%)

• Abu Dhabi allocated AED17.5 billion ($4.8 billion) to water and

electricity subsidies in 2014 [Abu Dhabi Executive Council announcement of 20 April 2014]

• Since subsidies cover close to 66% of the electricity cost [EAA, 2011], any savings from conservation or efficiency will accrue in majority to the Abu Dhabi government

• In addition, slower demand growth will lower the need for future expansion of supply/distribution infrastructure

• About 60% of the annual electricity consumption and 75% of the peak demand of the Emirate can be traced back to air-conditioning

Abu Dhabi Context: Subsidized Power

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• Peak demand of the Abu Dhabi system: 8.3 GW (overall peak generation 10.6 GW) [ADWEC]

• Total annual consumption: 47,117 GWh (84% buildings) [SCAD]• True cost of electricity: 0.32* AED/kWh (0.09 $/kWh) [RSB]• Annual subsidy paid by the government on electricity:

66% x 0.09 x 47,117,000,000 = $2.8 billion• A 20% savings on the buildings A/C consumption results in total

annual energy savings of:20% x 60% x 84% x 47,117 = 4,750 GWh

• This translates into annual subsidy savings of about 10%: 66% x 0.09 x 4,750,000,000 = $282 million

• In addition:• Peak demand will decrease by: 20% x 75% x 84% x 8.3 = 1 GW• Annual carbon emission will be reduced by about 3 MtCO2

* EAA’s chiller maintenance study (2011) suggested true marginal cost of 0.45 AED/kWh (0.12 $/kWh)

Impact of energy efficiency in Abu Dhabi (2012)

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Electrical Energy Use in Abu Dhabi (AD Island only)

Note: Electrical Load = Cooling Load/COP

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• Identify Baseline Chiller1. Baseline design has standard features typical of contemporary UAE eqpt.

• Fixed-speed condenser fans• Variable-speed screw compressors• Relatively low first cost for required capacity

2. Monitor and characterize baseline performance3. Use baseline case to validate chiller model…hence we have developed a

• Flexible component-based chiller model1. Any size condenser2. Evaporator types: DX, flooded, sprayed or falling film3. Any type compressor. Can be variable- or fixed-speed4. Variable- or fixed-speed condenser fans5. Alternative Cycle, e.g. ejector, economized, suction-line heat exchanger6. Optimal controls for e.g. fan speed, subcooling. w/these capabilities we can

• Optimize chiller design using… 1. Validated models of baseline and advanced components2. Optimal control of variable-speed fans, compressors, and subcooling3. Cost models of baseline and advanced components; scaling functions4. Annual load profile or frequency distribution (capacity fraction and Tamb)

Process for establishing GCC-optimized chiller to benchmark

Minimum Energy Performance Standard

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Selection and Instrumentation of Baseline Chiller

Baseline Chiller Characterization

Airflow by Traverse and

Calibrated flow box

Baseline chiller was operated over a wide range of conditions and capacity fraction. Comprehensive real-world data used to validate the component-based model.

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Examples of Component ModelsScrew and Reciprocating Compressor Isentropic Efficiency

Screw Compressor

1

2

3

4

5

6

15

20

25

30

0.5

0.6

0.7

0.8

0.9

1.0

Pressure RatioFrequency

Ise

ntr

opic

Eff

icie

ncy

Reciprocating Compressor

11.5

22.5

33.5

44.5

55.5

4060

80100

120140

160180

200

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

Pressure ratioFrequency

Ise

ntr

op

ic E

ffic

ien

cy

Frequency is ~proportional to loadPressure ratio is function of ambient temperature and load

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Performance Maps for >20 Modeled Chiller Designs

Example Chiller Design: Variable-Speed Screw Compressor, R-134a, Variable-Speed Condenser Fans with 1 X Condenser

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Control Impact

• Control and Part-Load Efficiency Measures1. Variable Speed Condenser Fans2. Variable Speed Compressor3. Optimal Subcooling (shown)

improvement is greatest when COP is worst—i.e. at high ambient and high capacity fraction

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 Variable-Speed Motors for • Compressors, Fans, Pumps• PM compressor motor

• 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

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 Base Date - 137597.96

Residual Cost 4127.93 20 SPV20 = 0.3769 1555.82

Refrigerant

replacement cost

2460.00 Every 5th SPV5 = 0.7835 642.47

Electricity cost 10333.62 Annual ErgUPV20

=14.959

154580.64

Non-energy O&M 7987.37 Annual UPV20 =12.4622 99540.30

SPV - Single Payment Present Value FactorUPV - Uniform Present Value FactorErgUPV - Modified Uniform Present Value Factor

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Electrical Load = Cooling Load/COP (Σ of 8760 hours)

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

Capacity Fraction

1/C

OP

(kW

e/k

Wt)

Tx = 45 oC

Tx = 40 oC

Tx = 35 oC

Tx = 30 oC

Tx = 25 oC

Tx = 20 oC

Te = 5 oC

Te = 3 oC

Te = 1 oC

Te = -1 oC

At each hour of the year, COP is evaluated from the design-specific performance map (below) based on ambient temperature and load from the AD typical load profile (right) to compute annual electricity use of the chiller design in question.

,

, /

c Hourly

c Hourly Hourly

QSCOP

Q COP

,

,

,  ,  ,

,  ,  , / , ,

c Hourly

c Hourly

Q Tx w DHI DNISCOP

Q Tx w DHI DNI COP Tx Te CF

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Life-Cycle Cost of Alternative Designs, $0.089/kWh

Case Name Case

#

Condnsr

Size X

SEER SEER

Imprv%

Equipmnt

Cost ($)

Energy

(MWh/y)

Saving

($/y)

LCC

($)

Base case Screw Compressor (SC) 1 1.0 3.350 -- 137598 116.764 -- 393917

Optimal Condenser Size_SC 2b 1.5 3.746 11.827 145591 91.732 2215 368862

Optimal Subcooling_SC 2c 1.5 3.836 14.503 145591 87.643 2577 363449

Variable-Speed Fans_SC 2d 1.5 3.895 16.256 148808 81.274 3141 358270

Optimal SubClg+VSpd Fans_SC 2e 1.5 3.904 16.517 148808 80.472 3212 357208

Retrofit Cases

Replace Screw by Recip 3b 1.3 4.966 48.217 161801 50.996 5820 331326

Optimal Subcooling_Recip 3c 1.3 5.069 51.307 161801 47.245 6152 326361

Variable-Speed Fans_Recip 3d 1.3 5.220 55.802 168225 42.334 6587 326355

Optimal SubClg+VSpd Fans_Recip 3e 1.3 5.262 57.062 168225 40.463 6753 323878

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Discussion

• Simplistic analysis will bear only low-hanging fruit1. Performance does not come cheaply but…2. The investment pays handsomely over life of MEPS chiller

• High Equipment Performance Target is Justified1. Manufacturers have a variety of off-the-shelf design options2. Options evaluated to date are all very cost-effective3. SEER can be raised from 3.5 to 5.2 at only ~60% cost increase.4. While at same time we see 18% drop in Life Cycle Cost

• Engagement of UAE Manufacturer SKM1. Manufacturing and AHRI testing capabilities2. Component cost data3. Competition among component suppliers

Electricity Savings at full penetration 2 billion aed/year

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Outlook

• Additional Chiller Design Options1. Economized Compressors (Screw or Reciprocating)2. Test all promising combinations for alternative refrigerants

• Other Candidate A/C Equipment for MEPS1. Dedicated Ventilation A/C (accounts for 20% cooling energy)2. Efficient FCU and Passive Chilled Beams or ACB3. High Temperature Chilled Water System (separate sensible/latent)4. Harmonize Building and Equipment Standards

MEPS puts immediately stop to future legacy energy problem

Enforcement is simple. Administrative cost is very low.

Electricity Savings at full penetration 2 billion aed/year

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Thank You!

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Other EAA CCP Projects

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Load Research: Building-Level Energy by End-Use

• Motivation1. Baseline energy use needed to estimate retrofit savings2. So far baseline consumption not measured directly (models only)3. Occupants cannot manage energy use without feedback4. Submetering (A/C, DHW, Refrig, Ltg, pumps, lifts) increasingly required

• Barriers1. High cost of meter installation2. High cost/intrusiveness of data collection3. High cost of maintaining sub-metering networks

• Solution1. Wireless system2. Smart-phone based configuration and data collection3. Options to link to existing BAS/LAN4. …and Push data to Cloud

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Load Research: >500 End-Use Circuits/BuildingTy

pic

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h-r

ise

bu

ildin

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Typ

ical

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ibu

tio

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Load Research: One Aggregator per DB

Compact form

Fits easily inside

distribution panel …

No external equipment

Functionality beyond

existing end-use

metering equipment

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Load Research: Clip-on Current Sensor

Fully enclosed device

Compact

Wireless--Low-Energy

Bluetooth4 standard (FCC)

Simple configuration from

smartphone

Fast, neat, safe installation

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Load Research: Building-Level Energy by End-Use

Android App

Bluetooth connection

Wireless data download-no disturbing tenants

Automatic clock update from smart-phone

50 100 150 200 250-30

-20

-10

0

10

20

30

Sample

Am

plit

ude

data1

data2

data3

data4

data5

data6

data7

data8

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Load Research: Outlook

• Sampling and Metering plans1. Two ADCP Buildings2. Distribution riser diagrams3. RTI CCP building characteristics

• Submeter Production1. 60 Aggregator units2. 1000 Wireless CTs3. Android Application

• Submetering applications1. Baseline End-Use; Load Research2. Measurement and Verification3. Fault Detection/Diagnosis4. Feedback to Building Operator

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• Villa (231 m2)• WWR: 21.25%• Infiltration rate: 0.5 ACH• COP: 2.2

• Residential (21,571 m2)• WWR: 60%• Infiltration rate: 0.5 ACH• COP: 2.2

• Office (23,312 m2)• WWR: 70%• Infiltration rate: 0.3 ACH• COP: 2.8

• Retail (111,506 m2)• WWR: 12.5%• Infiltration rate: 0.5 ACH• COP: 2.8

Building types

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• Smart meters and time-of-use pricing have had only “a modest impact on reducing peak demand” among householders and “no impact at all on energy conservation”

• The difference between peak and off-peak rates hasn’t been large enough to encourage consumers to change behavior patterns: Peak-time electricity costs less than double the night-time low price

• Instead of cutting Ontario’s peak power consumption by 2,700 megawatts by 2010, use of electricity increased by 100 megawatts

• As far as automated meter reading is concerned, only 5 per cent of utilities reported savings; the others said their costs were the same or higher

Auditor-general of Ontario, 11 December 2014

Smart grid and energy efficiency: Smart metering experience in Ontario

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• Inform national policy on right balance of resource allocation to electricity/water demand-side management through the study of true dynamic cost and environmental impact of water

• Study sources and methods of water production and derive water production energy intensity for each hour of a typical year

• Study space/time variability of water production energy intensity; explore its causes and propose ways to attenuate and stabilize

• Case studies: • Concurrent power & water production versus power generation + RO• Cost-benefit analysis of long-term water storage• Modeling of the future impact of nuclear plants• Water-cooled versus air-cooled AC

Future work: Optimal Balance between Energy and Water Efficiency

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• Methodology: multi-objective optimization in view of minimizing life-cycle cost (conservation) and/or minimizing peak demand

• Retrofits: insulation, glazing, shading, AC, cool roof, air-tightness, demand-controlled ventilation, daylighting control

• Cost function: continuous/discrete, linear/nonlinear, single/multiple technology (e.g., insulation is single technology, AC is multiple technology: air-cooled/water-cooled etc.)

• Scope of analysis: retrofit isolation (e.g., wall insulation), retrofit with side-effects (e.g., window shading with impact on daylighting and cooling load), fully coupled retrofits (e.g., optimal mix of insulation, shading, AC), coupled retrofits with rebound effect

• Optimization: brute force, genetic algorithm, simulated annealing• Experimental: implement optimal retrofit package in pilot project

Future work: Whole Building Retrofit Optimization