Phoenix Convention Center Phoenix, Arizona Package DX Units: Performance Optimization Strategy and...

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Package DX Units: Performance Package DX Units: Performance Optimization Strategy and Field Optimization Strategy and Field TestsTests

Package DX Units: Performance Package DX Units: Performance Optimization Strategy and Field Optimization Strategy and Field TestsTests

Michael West, PhD, PEAdvantek Consulting Engineering, Inc.

[email protected]

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EXPERT POWERED :: CLIENT DRIVENEXPERT POWERED :: CLIENT DRIVENEXPERT POWERED :: CLIENT DRIVENEXPERT POWERED :: CLIENT DRIVEN

Energy Exchange: Federal Sustainability for the Next Decade

Unitary equipment is ubiquitous. 60% of US commercial space is cooled with RTUs (DOE) 54% of commercial building cooling primary energy consumption (EIA) Total annual installations over 300,000 units Estimated 1.6 million legacy units operating at low efficiency levels

100,000 units at DoD facilities / 20,000 buildings100,000 units at USPS facilities / 30,000 buildings500,000 units at 65,000 “big box” retail stores

2ROOFTOP PORTABLE PAD MOUNT

RTU – Rooftop packaged air-conditioner UnitDOE – U.S. Department of Energy

EIA – Energy Information AdministrationUSPS – United States Postal Service

Background


Background

Unitary Efficiency Standards 6 – 11 12 – 20 21 – 60

Tons Tons TonsSEER

All 13 11.2 11 9.9 9.6All 14 10.3 10

50% Savings Beyond

90.1

All 15 12.8 12.3 11.3 10.9

- 18 - - -DOE High Performance

RTU Challenge

ASHRAE Climate

Zone

ASHRAE Standard

11.5

11.4 11.2 10.4

11.2

Adv

ance

d En

ergy

Des

ign

Gui

des

30% Savings Beyond

90.1

1,213

3-5

> 60 Tons

IEER90.1

189.1 11.8

5 Tons <

ASHRAE Standard 90.1-2010 Energy Standard for Buildings Except Low-Rise Residential BuildingsASHRAE Standard 189.1.-2009 Standard for the Design of High-Performance Green Buildings

Energy efficiency of unitary systems is much less than that of central plants.

Typical large RTU efficiency IEER 11 = 1.09 kW/Ton.

New chiller plant efficiency 0.5 kW/ton = IEER 24

Central plants can be over twice as efficient as typical unitary equipment.


“ How much cooling you get for the electricity used”Btuh per Watt (MBH per kW)

EER – Energy Efficiency Ratio Full Load @95F Ambient

IEER – Integrated Energy Efficiency Ratio Weighted Full Load & Part Load @95, 81.5, 68, and 65F Ambient

SEER – Seasonal EER Part Load @82F Ambient x 0.875 (Cyclic Performance Load Factor)

IPLV – Integrated Part-load Value Legacy rating (no longer standard)

Performance Ratings

ANSI/AHRI Standard 340/360-2007


Efficiency and Dehumidification• Energy saving goals continue to rise

IEER - Integrated Energy Efficiency Ratio 10.0 to 13.0 EER – Energy Efficiency Ratio 9.7 to 11.7 Single-zone VAV and DDC requirements of Energy Standard 90.1-2013,

Green Standard 189.1-2014, and LEED

• Dehumidification needs are increasing Reduced sensible loads means lower SHR

- Lower lighting Watts / sqft- Higher insulation R-values- Heat reflective / low-e glass- often addressed with energy intensive reheat

Part-load requirements of IAQ Standard 62.1-2013 s.5.9 (< 65%rh)

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OverviewFacilities struggle with RTU limitations.1. Basic unitary equipment cannot optimally match varying

conditions. Occupant diversity Changes in ambient conditions from morning, to afternoon, to evening Variations in weather from day to day Seasonal differences between early, mid, and late summer

2. Energy managers have no easy way to operate and monitor units for maximum energy efficiency.

3. HVAC technicians rely on indirect indicators of performance. Visual coil inspections Refrigerant pressures Manufacture date on nameplate Occupant complaints

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• Package unit design is a compromise in energy efficiency and dehumidification. Controls cannot adjust operation to match climate. Loads drastically differ in

Florida, California, Arizona, Illinois, … In many applications at part-load – latent capacity is inadequate. Expensive

reheat or hot-gas bypass is used for dehumidification. Current designs maximize efficiency at AHRI rating points only.

• Factory controls were augmented with optimizing technology, and rigorous field tests of energy efficiency and dehumidification performance were carried out. Demonstrated advantages of optimizing RTU control technology. Technology installed on three RTUs in diverse climates. Intensive monitoring and performance analysis over two cooling seasons.

Overview


Ambient Air

Evaporator Evaporator CoilCoil

Condenser Condenser CoilCoil

CompressorCompressor

TXVTXV

Basic DX Cycle

Supply Air


Revises the traditional refrigeration cycle at a fundamental level.Improvement of evaporator refrigerant / two-phase heat transfer.Increased suction density improves compressor volumetric efficiency.Variable sensible heat ratio optimizes airside performance.

REFRIGERANT CIRCUIT

COIL HEAT TRANSFER

TXV – Thermostatic Expansion Valve

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Modified DX Cycle


Psychrometric Chart, 101.193 kPa

TechniSolve Software cc

Temperature, °F94929088868482807876747270686664626058565452504846444240383634

Hum

idity,

gr/

lb

130

128126124122

120118116114

112110108106

10410210098

96949290

88868482

80787674

72706866

64626058

56545250

48464442

40

Node2

Node1

Node3

Node7

Node8

Node9

MixBranch2

MixBranch1

Cooler2

Significance of DX ModificationReleases constraints on operating parameters.

1. Airflows, temperatures, and refrigerant can be optimized

2. Variable-Volume Constant-Temperature (VVCT)

3. Increase latent capacity as needed

4. Variable SHR (VSHR)

5. Single-Zone VAV

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Optimizing Control Technology

• Controls all operating parameters• Target is maximum EER while meeting

sensible and latent loads• Continuously adjusts:

Supply Blower Speed Condenser Fan Speed Refrigerant Charge Supply Air Temperature Coil Temperature Economizer Damper

• Continuously reports: EER, IEER, Tons Capacity Faults Diagnostics http://www.EERoptimizer.com/


RTUControllerGUI

Any Web DeviceTablet, Smart Phone, Laptop

Cloud Servers

PHP

Web

Sock

et

Data ConnectivityData Connectivity

LAN

VPN

or c

omm

erci

al W

AN Monitor Only


Optimizing Control Package

Liquid-Suction Heat Exchanger

Accumulator Bypass Damper

VariableFrequencyBlowerDrive

AdjustableThermostaticExpansionValve

VFD Condenser Fan

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Modified Package Unit


Modified Package Unit

Energy Exchange: Federal Sustainability for the Next Decade15

Site 1: Retail StoreBeaufort, South Carolina2627 cooling degree-daysClimate zone 3A Warm-Humid

Sou

th C

arol

ina

Field Tests


20-ton dual-circuitR-22 package DX unit Gas HeatManufactured 2/2003Found in “poor” condition

Fresh air intakeGas heating section

Compressors

Sou

th C

arol

ina

Field Tests


Interior is typical of a large retail storeInterior is typical of a large retail storeSetpoint 74F day, 80F nightSetpoint 74F day, 80F night

Sou

th C

arol

ina

Field Tests


Ca

lifo

rnia

Site 2: Classroom BuildingMojave, CaliforniaElevation 2500 feet

Climate zone 3B Hot-Dry 3225 cooling degree-days2597 heating degree-days

Field Tests


12½-ton dual-circuitR410a package DX unitHeat PumpInstalled 2010

Ca

lifo

rnia

Field Tests


Site 3: Electronics Development LaboratoryCape Canaveral, Florida3633 cooling degree-days, Climate zone 2A Hot-Humid

Flo

rida

Field Tests


8½-ton dual-circuitR410a package DX unit9 kW-heat Installed 1/2012

Flo

rida

Field Tests


Interior zone is a precisely controlledInterior zone is a precisely controlledelectronics development laboratoryelectronics development laboratorytemperature 74F temperature 74F 1 degree-F, 45% humidity 1 degree-F, 45% humidity 5%rh5%rh

Flo

rida

Field Tests


45 Sensors on each RTU

• Compressor Amps (2)• Fan and Blower Amps• Total Unit Power• Refrigerant Pressures (4)• Refrigerant Temperatures (12)• Refrigerant Flows (2)• Air Temperatures

at thermostat, return, outdoor, coil, entering & leaving coil, unit discharge

• Air Humiditycoil entering, unit discharge, at

thermostat, outdoor• Space and Ambient CO2 level• Control point status

Performance Measurement Data available live via web linkhttp://www.tinyurl.com/CCAFS-EDL

Performance Analysis


www.tinyurl.com/CCAFS-EDL

Analysis


Four operating conditions satisfy the IEER rating criteria set forth in ANSI/AHRI Standard 340/360-2007 A, B, C, and D rating conditions 95F, 81.5F, 68F, and 65F ambient Linear interpolation between field-measured data points by section 6.2.2

“EER is determined by plotting the tested EER vs. the percent load and using straight line segments to connect the actual performance points.”

Operational IEER calculated with respect to section 6.2.2IEER = (0.020 • A) + (0.617 • B) + (0.238 • C) + (0.125 • D)

where A, B, C, and D are the interpolated / field-measured EERs (Btuh per Watt)

Accuracy Field-estimated IEER is ±4.7% or ±0.6 Btuh/Watt via sensitivity / propagation of

error uncertainty analysis All comparisons performed with data from same sensors installed in same

positions, therefore uncertainty in the baseline field-estimated IEER equally applies to the modified unit’s field-estimated IEER (high or low)

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Performance Analysis


35

40

45

50

55

60

65

70

75

80

66 68 70 72 74 76 78 80

Dry Bulb Temperature F

Rela

tive H

um

idit

y %

rh

35

40

45

50

55

60

65

70

75

80

66 68 70 72 74 76 78 80

Dry Bulb Temperature F

Rela

tive H

um

idit

y %

rh MCASB System SHR vs Space RH

y = 9E-05x2 - 0.0224x + 1.6039

R2 = 0.2827

0.40

0.50

0.60

0.70

0.80

0.90

1.00

30

35

40

45

50

55

60

65

70

75

80

SPACE %RH

CA

LC

ULA

TE

D S

HR

MCASB System SHR vs Space RH

y = 9E-05x2 - 0.0224x + 1.6039

R2 = 0.2827

0.40

0.50

0.60

0.70

0.80

0.90

1.00

30

35

40

45

50

55

60

65

70

75

80

SPACE %RH

CA

LC

ULA

TE

D S

HR

Field Test Results


Damper Position Control Signal vs RHTest Site: Beaufort, SC

0

20

40

60

80

100

40 45 50 55 60 65 70

Space Relative Humidity [%rh]

% D

am

pe

r O

pe

n

OpeningClosing

Condenser Fan Speed Signal vs OATTest Site: Beaufort, SC

0

20

40

60

80

100

50 60 70 80 90 100

Outside Air Temperature [F]

% S

pe

ed

Stage 2

Stage 1

Field Test Results


Field Test Results


Results Summary

• Efficiency increase ranged from 15% to 37%• Operational IEER raised by 1.9 to 2.9 points• Comparable improvement in EER vs IEER• CA unit showed most improvement


Economic Analysis

Technology cost basis: $4,500Discount rate: 3.0%


Economics

IEER Cost $ / Ton

Flagship Model * 18.5 25,666 2,053

Midline Model 11.4 11,857 949

Modified Base Model 13.7 14,166 1,133

Cost comparison of three 12½-ton package units.

* Flagship model with variable speed inverter scroll compressors, plenum airfoil fans, electronic expansion valves, proprietary digital controls


Conclusion

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Optimizing RTU Control Technology

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