HFO for Residential HPWH Applications: Opportunities and Challenges - Kashif Nawaz Bo Shen Ahmed Elatar Van Baxter Omar Abdelaziz - Heat Pumping ...

HFO for Residential HPWH Applications:
 Opportunities and Challenges

 Kashif Nawaz
 Bo Shen
 Ahmed Elatar
 Van Baxter
 Omar Abdelaziz
ORNL is managed by UT-Battelle, LLC
for the US Department of Energy

Presentation contents

 • Importance of heat pump water heaters (HPWH)

 • Status of refrigerants for HPWH application

 • Significance of thermodynamic properties

 • Performance evaluation and validation

 • Major challenges and opportunities

2

Heat Pump Water Heating Systems
 Water heating accounts for more than 10% of all residential
 and commercial site energy use in the United States.

 Residential end-use energy by different
 applications (US EIA, 2013)

 Annual Energy Consumption of Various Water Heating Technologies.

 Energy Star Water Heater Market Profile, D&R International, 2010
3

Heat Pump Water Heating Systems
 • HPWH technology has been validated and proven to be successful
 through lab and field experiments.
 • While the technology is mature, there are obvious opportunities to
 further enhance the performance of the systems.
 • Hybrid configuration assist to meet the
 demand when HP can not provide
 sufficient heating.
 • The overall system performance depends
 on several factors including
 • Tank thermal stratification
 • Condenser design
 • Compressor
 • Working fluid

4

Historical Development For Alternative
 Refrigerants
 • Kigali amendment (2016) to the Montreal Protocol emphasized
 phase-down of HFCs (80% reduction by 2047).
 • Subsequent emergence of HFOs (or unsaturated HFCs) – 4th
 generation of fluorine-based refrigerants.
 • Alternative refrigerants have low GWP, but are mildly flammable
 (A2L, A3 gases) and are expensive.

 Refrigerant GWP100
 CO2 1
 R-22 1760
 R-134a 1300
 R-410A 1924

5

Alternative Refrigerants for HPWH

 • Hydrofluoroolefins (HFOs)
 – Fluorinated propene isomers
 • R-1234yf (CF3CF = CH2)
 • R-1234ze (CF3CH = CHF)
 – GWP < 4
 R290 R1234ze(E)
 – Mildly flammable
 • Hydrocarbons (HCs)
 – Propane and Isobutane
 – GWP

Alternative Refrigerants for HPWH

 R134a R1234yf R12234ze(E) R290 R600a
 Formula CH2FCF3 CF3CF=C2 CHF=CHCF3 C3H8 C4H10
 CAS number 811-97-2 754-12-1 29118-24-9 74-98-6 75-28-5
 Molecular mass (g/mol) 102 114 114 44 58
 ODP 0 0 0 0 0
 GWP100 1300a

Performance Evaluation Criteria for HPWH
 ( )
 n
 The First Hour Rating (FHR) is a measure of Mk cp (Ts − Ti ൯
 =෍
 the available hot water capacity of the water Wi
 k=1
 heater (in gallons).
 Time during Volume
 Draw Flow rate
 test
 number (gals/L) (GPM/LPM)
 (hh:mm)
 1 00:00 15.0 (56.8) 1.7 (6.5)
 2 00:30 2.0 (7.6) 1 (3.8)
 3 01:40 9.0 (34.1) 1.7 (6.5)
 FHR greater or FHR less Draw pattern for 4 10:30 9.0 (34.1) 1.7 (6.5)
 equal to (gals) than (gals) 24-hr UEF
 0 20 Point of use 5 11:30 5.0 (18.9) 1.7 (6.5)
 6 12:00 1.0 (3.8) 1 (3.8)
 20 55 Low usage
 7 12:45 1.0 (3.8) 1 (3.8)
 55 80 Medium usage
 8 12:50 1.0 (3.8) 1 (3.8)
 80 Max High usage
 9 16:00 1.0 (3.8) 1 (3.8)
 10 16:15 2.0 (7.6) 1 (3.8)
 11 16:45 2.0 (7.6) 1.7 (6.5)
 12 17:00 7.0 (26.5) 1.7 (6.5)
 Total volume drawn per day: 55 gallons (208 L)

8

Hydroflouroolefins as Refrigerants for HPWH
 • 46-gallon water tank
 • Heat pump T-stat at the top: on at 115 °F, off at 125 °F.
 • Electric element at the top: on at 110°F, off at 125 °F.

 Case number Wrap pattern Evaporator size* Tank insulation effectiveness (%) Condenser tube size (inches)

 1 Parallel-counter 1 Evap 90 0.31
 2 Parallel-counter 1 Evap 90 0.50
 3 Parallel-counter 2 Evap 90 0.31
 4 Parallel-counter 2 Evap 90 0.50
 Condenser wrap configurations (a)
 5 Parallel-counter 1 Evap 95 0.31
 counter flow (b) parallel-counter
 6 Parallel-counter 1 Evap 95 0.50
 flow
 7 Parallel-counter 2 Evap 95 0.31
 8 Parallel-counter 2 Evap 95 0.50
 9 Counter 1 Evap 90 0.31
 10 Counter 1 Evap 90 0.50
 11 Counter 2 Evap 90 0.31
 12 Counter 2 Evap 90 0.50
 13 Counter 1 Evap 95 0.31
 14 Counter 1 Evap 95 0.50
 15 Counter 2 Evap 95 0.31
 16 Counter 2 Evap 95 0.50

9

Analysis Strategy

 B. Shen, K. Nawaz, A. Elatar, V. Baxter, “Development and Validation of Quasi-Steady-State Heat Pump Water Heater Model Having
 Stratified Water Tank and Wrapped-Tank Condenser” International Journal of Refrigeration, 2018, 87,78-90.

10

Hydroflouroolefins as Refrigerants for HPWH
 First Hour Rating

 • FHR rating for all various cases is comparable- Medium pattern
 • R1234ze (E) has reduced FHR due to lower volumetric capacity

11

Hydroflouroolefins as Refrigerants for HPWH
 Unified Energy Factor

 • UEF is more sensitive to tank effectiveness and condenser tube size.

12

Hydroflouroolefins as Refrigerants for HPWH
 Compressor Discharge Temperature

 • Due to comparable compressor discharge temperature, no significant
 modifications are required (compressor type, lubricating oil etc.)

13

Experimental Validation

14

Opportunities

 • Alternative refrigerants can be effective drop-in-replacement
 for conventional fluids (R134a).

 • Minor to no system modification is required to acquire an
 acceptable performance.

 • Appropriate system modification can provide further
 improvement in the system efficiency.

 • Selective fluids can lead to substantial reduction in system
 volume (refrigerant charge inventory).

15

Challenges

 • Alternative refrigerants impose safety concerns. Mild to high flammability
 can be an issue requiring system redesign to meet specific requirements.

 • Often times the alternative refrigerants are expensive and substantial
 reduction in volume is required.

16

References
 • K Nawaz, B Shen, A Elatar, V Baxter, O Abdelaziz, "R1234yf and R1234ze (E) as low-GWP
 refrigerants for residential heat pump water heaters", International Journal of Refrigeration
 82, 348-365
 • K Nawaz, B Shen, A Elatar, V Baxter, O Abdelaziz, "R290 (propane) and R600a (isobutane) as
 natural refrigerants for residential heat pump water heaters", Applied Thermal Engineering
 127, 870-883
 • K Nawaz, B Shen, A Elatar, V Baxter, O Abdelaziz, "Performance optimization of CO2 heat
 pump water heater", International Journal of Refrigeration 85, 213-228
 • M. R. Ally., Vishaldeep Sharma, and Kashif Nawaz. "Options for low–global-warming-
 potential and natural refrigerants Part I: constrains of the shape of the PT and TS saturation
 phase boundaries." International Journal of Refrigeration (2019).
 • K. Nawaz, and Moonis R. Ally. "Options for low–global-warming-potential and natural
 refrigerants Part 2: Performance of refrigerants and systemic irreversibilities." International
 Journal of Refrigeration (2019).

17

Acknowledgements

 DOE Building Technologies Office, Emerging Technologies –
 Antonio Bouza, Erika Gupta (Program Managers)

 A O Smith Manufacturing –
 Steve Memory (Director, Thermal and Materials)
 Jiammin Yin (Lead Designer)

18

Kashif Nawaz
 nawazk@ornl.gov

19