Abstract
Ejector-driven systems have the ability to operate at high efficiencies, utilizing recycled thermal energy as a power source. For a typical ejector heat pump (EHP) system, the increase of the condenser temperature reduces the coefficient of performance (COP). In addition, if the condenser temperature is higher than the critical temperature, the ejector may not function. In this situation, the condenser temperature must be reduced, and an additional heater will be utilized to heat the production water from the condenser temperature to the desired temperature. In this study, a single-stage gas-fired EHP is investigated and thermodynamically modeled to optimize the system COP for the purpose of heating water by utilizing the thermal energy from the ambient air. The effects of the high-temperature evaporator (HTE) and low-temperature evaporator (LTE) on the ejector critical back pressure and the EHP system performance are examined for a HTE temperature range of 120–180 °C and LTE temperatures of 15.5, 17.5, and 19.5 °C. Results show that an optimized COP for the EHP system exists and is dependent on HTE and LTE temperatures and the primary nozzle throat diameter. In addition, it is found that the peak EHP COP does not necessarily coincide with a large ejector COP. From this study, a maximum EHP COP of 1.31 is achieved at a HTE temperature of 170 °C and LTE temperature of 19.5 °C with a total heating capacity of 15.98 kW.
| Original language | English |
|---|---|
| Article number | 041009 |
| Journal | Journal of Thermal Science and Engineering Applications |
| Volume | 14 |
| Issue number | 4 |
| DOIs | |
| State | Published - Apr 2022 |
Funding
This material is based upon work supported by the US Department of Energy, Office of Science, Office of Energy Efficiency and Renewable Energy, Building Technologies Office. This research used resources of the Building Technologies Research and Integration Center of the Oak Ridge National Laboratory, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the US 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 nonexclusive, paid-up, irrevocable, world-wide 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.2
| Funders | Funder number |
|---|---|
| Office of Energy Efficiency and Renewable Energy, Building Technologies Office | |
| United States Government | |
| U.S. Department of Energy | |
| Office of Science | |
| Oak Ridge National Laboratory | DE-AC05-00OR22725 |
Keywords
- Back pressure
- Coefficient of performance (COP)
- Ejector heat pump water heater
- Energy systems
- Flue gas heater
- Heat pump
- Steam ejector
- Thermal systems