Abstract
Heat pump water heaters (HPWH) are an energy efficient method for water heating compared to conventional electric water heaters. A wrapped coil around the water tank is often used as the condenser for the heat pump for such applications. Thermal stratification, caused by varying heat transfer rate from the condenser to the water depending on the phase of the refrigerant and the wrap configuration, is often observed inside the tank, especially for HPWHs using CO2 as the refrigerant. The current study investigates the impact of the charging/discharging process on thermal stratification. A series of simulations were conducted based on the draw patterns recommended by the DOE method of test for rating water heater performance. We also analyzed the water circulation patterns during charging/discharging process. The thermal stratification was adversely affected because of the circulation even when the Heat Pump (HP) was operational. It was observed that a relatively higher charge/discharge flow rate disrupts the thermal stratification quickly and thus lowers the supply water temperature. Furthermore, the duration of charging/discharging also plays an important role. It was noticed that the back flow has insignificant effect on the supply water temperature if charging/discharging time is relatively small. However, the effect was obvious for larger water draw flow rates that last for longer time.
Original language | English |
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Title of host publication | Fluids Engineering |
Publisher | American Society of Mechanical Engineers (ASME) |
ISBN (Electronic) | 9780791858424 |
DOIs | |
State | Published - 2017 |
Event | ASME 2017 International Mechanical Engineering Congress and Exposition, IMECE 2017 - Tampa, United States Duration: Nov 3 2017 → Nov 9 2017 |
Publication series
Name | ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) |
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Volume | 7 |
Conference
Conference | ASME 2017 International Mechanical Engineering Congress and Exposition, IMECE 2017 |
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Country/Territory | United States |
City | Tampa |
Period | 11/3/17 → 11/9/17 |
Funding
This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).