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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3
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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