Modeling of Air-Source Integrated Heat Pumps - Oak Ridge National ...

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Feb 23, 2016 - →10-coefficient AHRI compressor map at rated inlet superheat;. Y represents the ... x. ) (. ,. , max evap s ia a h hm. Q. -. = x x. ) exp(. 1. NTU.
2016 ACEEE Hot Water Forum – Heating Water with Integrated Heat Pumps

Modeling of Air-Source Integrated Heat Pumps -simulation-driven design Bo Shen, Keith Rice, Oak Ridge National Laboratory

February 23, 2016

ORNL is managed by UT-Battelle for the US Department of Energy

Contents 1.

Air-Source Integrated Heat Pumps (AS-IHPs) – Reasons – Operation modes and components

2.

Modeling ASIHPs with ORNL Heat Pump Design Model (HPDM) – Component and system modeling – Building energy simulation

3.

Simulation Case Studies

4.

Summary

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Conceptual Installation of ASIHP – 3-ton Rated Cooling Capacity

1.1 Reasons For Single-Unit ASIHP 1. Maximize use of highly efficient but costly variablespeed compressor, blower, fan, and pump – Recover waste heat for water heating in cooling season • Dual useful outputs from single power input

– Provide dedicated WH capability in shoulder months

2. Meet both high and lower capacity loads efficiently using speed modulation Objective: Provide >50% annual energy savings for HVAC/WH functions 3 Presentation_name

1.2 Various Components Variable-Speed Flow Movers-compressors, fans and pumps

Air-to-refrigerant HXs

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Water-to-refrigerant HXs

1.3 Multi Operation Modes Possible Single-Function Modes:

Multiple operation strategies and component states, e.g. speed, HX states.

1.

Space cooling mode (SC)

2.

Space Heating Mode (SH)

3.

Dedicated Water Heating Mode (DWH)

Combined Modes: 4.

SC + Water Heating Mode with Full Condensing (SCWH)

5.

SC + Water Heating with Desuperheating (SCDWH)

6.

SH + Water Heating with Desuperheating (SHDWH) SCWH Mode

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SCDWH Mode

SHDWH Mode

2.1 Variable-Speed Compressor Modeling Y  C1  C2Te  C3Tc  C4Te  C5TeTc  C6Tc  C7Te  C8TcTe  C9TeTc  C10Tc 2

2

3

2

2

10-coefficient AHRI compressor map at rated inlet superheat; Y represents the compressor mass flow and power use rates. Linear interpolation between speed levels. Mass flow rate adjustment for actual inlet superheat levels.

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2.2 Advanced Heat Exchanger Modeling • Segment-to-segment modeling approach  a , k , ha , k ,o m  r , k , Pr , k ,i , hr , k ,i m

kth segment

Consider phase change  r ,k , Pr ,k ,o , hr ,k ,o m

 a ,k , ha ,k ,i m

Dry Coil Analysis Heat Transfer

Wet Coil (Dehumidification) - Heat & Mass Transfer

Q max  Cmin (Th,i  Tc,i )

Q max  m a (ha,i  hs ,evap )

  1  exp( NTU )

 *  1  exp( NTU * )

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2.3 System Modeling - Component-Based Flexible Modeling Platform for Vapor Compression Systems Component-Based Component Library (component models with standard interfaces)

Plug-&-Play

Component models have standard interfaces to the solving framework, and generic connections to each other.

Configuration Text File

Flexible Solving Framework

……...

Automatically connect components into required system configuration by user input file. 8 Presentation_name

2.4 Extensive Connectivity Component Library (component models with standard interfaces)

Generate Performance Curves Configuration Text File

Curve-Fitting Program

Flexible Solving Framework

……...

ORNL Building Equipment Model

All connected.

Generate Performance Tables

Parametric Runs 9 Presentation_name

3. Specific Issues Rated to AS-IHP Development Four Simulation Case Studies 3.1 Convert Compressor Working Envelope to IHP Operation Constraints 3.2 Optimize combined efficiency

3.3 Optimize efficiency with SHR constraint 3.4 Solving competing demands 10 Presentation_name

3.1 Operation Constraints in DWH Modes Discharge Temperature [F], WH, 25 HZ, Fixed Charge, 5.3 SGPM Discharge Sat Temp [F], WH, 25 HZ, Fixed Charge, 5.3 SGPM 130 130 140 0 24 0 0 23 20 23 20 2 2 130 0 120 120 21 0 0 2 190 180

170

100

EHWT [F]

EHWT [F]

110

160

150

90

110

120

100

110

90

100

80

90

140

80

130

120

70 25

30

35

40

45

50

55

60

65

Outdoor Temperature [F]

-Discharge temperature constraint

110 70 75

80

70 25

30

35

40

45

55

60

65

70

Outdoor Temperature [F]

-Discharge saturation temp constraint

Convert compressor working envelope to equipment operation constraints. 11 Presentation_name

50

75

3.2 Optimize Combined Efficiency SC EER 8.0

Combined EER (SC+WH)

7.0

8.0

6.5

7.5

6.0 5.5

7.0

5.0 4.5 4.0 5

10

15

20

25

Increasing Subcooling

WH EER 8.0

6.5 6.0 5.5 5.0

7.5

Increasing Water Flow

Increasing Water Flow

Increasing Water Flow

7.5

7.0

4.5

6.5 4.0

6.0

5

10

15

20

Increasing Subcooling

5.5 5.0 4.5

Total delivery efficiency is the target.

4.0 5 12 Presentation_name

10

15

20

Increasing Subcooling

25

25

3.3 Optimize Efficiency with SHR constraint

Balance optimum efficiency with acceptable comfort. 13 Presentation_name

3.4 Competing Demands of SHDWH Mode Supply Air Temp [F], SH + WH 130 125 120 120

115

Water EWT [F]

110 105

110

100 100

95 90 90

80

85 20

30

40

50

60

Ambient Temp [F]

-initial design at fixed compressor speed and water flow rate

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WH function in SHDWH mode may take away too much heat from space heating. -- increase compressor speed and lower water flow rate at low ambients to compensate Presentation_name

3.5.1 Predicted Annual Energy Savings in 5 U.S Locations (TRNSYS using HPDM performance maps) - For 242 m2 (2600 ft2) well-insulated house Location Atlanta

% Energy Savings Versus Baseline HP w Electric WH 53.3

Houston

54.7

Phoenix

46.7

San Francisco

60.9

Chicago

46.0

US average

52.3

Baseline: Electric Resistance WH; HP (13.0 SEER/8.0 HSPF) Presentation_name

3.5.2 Predicted WH Savings in 5 U.S Locations

Location Atlanta

% WH Energy Savings Versus Electric WH with 0.90 EF 70.0

Houston

75.7

Phoenix

72.2

San Francisco

69.4

Chicago

62.4

US average

69.9

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4. Summary 1. Simulations indicate ASIHP able to achieve annual energy savings > 50% in numerous US climate zones. 2. Demanding to design an ASIHP, e.g.

• operation constraints at different speed levels • balance between efficiency & service/comfort requirements. • competing demands of WH & space conditioning An effective & flexible modelling tool is indispensable for the design process. 17 Presentation_name

Discussion

Bo Shen, , Keith Rice [email protected] Visit our website: www.ornl.gov/buildings

Follow me on: hpdmflex.ornl.gov Follow us on Twitter: @ORNLbuildings

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