Lead Performer: Oak Ridge National Laboratory – Oak Ridge, TN
July 5, 2023
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Lead Performer: Oak Ridge National Laboratory – Oak Ridge, TN
Partner: Rheem Manufacturing Co.
DOE Total Funding: $170,000
Cost Share: $100,000
Project Term: October 1, 2019 – September 30, 2022
Funding Type: CRADA
Project Objective
The HPWH (heat pump water heater) industry is shifting away from using high-global warming potential (GWP) refrigerant R-134a, which has a GWP of 1430, in favor of lower GWP alternatives such as R-1234yf, R-1234ze, R-516A, or propane, all with GWP values below 150. These alternative refrigerants, categorized as A2L or even A3, can be mildly or extremely flammable and are also subject to charge limits, typically set below 150 grams for propane. High-efficiency 120V HPWHs, which use over 4 pounds of R-134a, require larger heat exchangers and refrigerant charges. However, a significant portion of this charge is found in the condenser. Traditional D-shaped tubes in these systems have a substantial inner volume but limited contacting surface area, leading to up to 10% heat loss to the surrounding air. Submerged condensers eliminate heat loss but are susceptible to scaling on the water side. Moreover, the use of small-diameter tubes results in high pressure drops on the refrigerant side. Lastly, there is a lack of heat exchanger and system design tools for HPWHs featuring stratified water tanks and new refrigerants. The development of compact condensers is a crucial step in preparing for the transition to new refrigerants in HPWHs.
This project aims to accomplish the following objectives:
- Develop compact condensers to reduce charge and achieve similar heat transfer effectiveness of wrapped-tank D-shape coils.
- Development of microchannel and submerged condenser coil sizing and HPWH system design tool.
- Conduct an extended period of life test to assess the impact of water side mineral scaling.
Project Impact
This project aims to enable the use of flammable low-GWP refrigerants below established charge limits and achieve a uniform energy factor (UEF) rating exceeding 3.3, surpassing the ENERGY STAR UEF standard of 2.2. It also supports the transition from gas water heaters to high-performance HPWH and enforces HPWH market penetration by reducing manufacturing costs, particularly through decreased refrigerant expenses.
Contacts
DOE Technology Manager: Payam Delgoshaei
Lead Performer: Ahmed Elatar