Study on the operating performance of cross hot-gas bypass defrosting system for air-to-water screw heat pumps

Wang, Zhiyi; Yang, Hongxing; Song, Chen

doi:10.1016/j.applthermaleng.2013.06.007

Cited by 24 publications

(9 citation statements)

References 11 publications

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“…In other words, the control method would allow for extended operation of the system at higher COP. Another method used cross hot-gas bypass defrosting method to shorten defrost time [39]. Air at higher temperature is blown across the coils to melt frost on the airside heat exchanger.…”

Section: Evidences Of Negative Impacts Of Low Ambient Temperatures Onmentioning

confidence: 99%

Review of energy efficiency and system performance of residential heat pump water heaters

Willem

Lin

Lekov

2017

Energy and Buildings

152

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Energy efficiency is an essential component of water heating considerations in the overall efforts to achieve national energy saving goals. Although heat pump water heaters have been around for over three decades, this technology has only matured in recent years, in part because of improved systems and infrastructure as well as emerging energy conservation standards on water heating. The goal of this study is to provide a comprehensive and in-depth review of heat pump water heater research on system energy efficiency and performance topics. The study focuses on laboratory and field (in-situ) experiments and measurements, modeling of energy use and efficiency, technological modifications or upgrades, and control operation strategies; with emphasis on the Coefficient of Performance (COP), reliability, and energy savings. The review shows that while most of current heat pump water heater systems operate in the COP range of 1.8-2.5, there are some potential technological updates that could augment the current systems and increase COP to a range of 2.8-5.5. Issues that could dampen the adoption of these technologies are discussed. The review identified key areas for future studies that are still lacking in support of various changes suggested for increasing heat pump water heaters efficiency and performance.

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Section: Evidences Of Negative Impacts Of Low Ambient Temperatures Onmentioning

confidence: 99%

Review of energy efficiency and system performance of residential heat pump water heaters

Willem

Lin

Lekov

2017

Energy and Buildings

152

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“…Previously, several defrosting methods have been proposed for ASHP units, such as (1) compressor shut-down defrosting [7], (2) hot gas by-pass defrosting (HGBD) [8][9][10][11], (3) electric heating…”

Section: Introductionmentioning

confidence: 99%

“…In order to overcome the aforementioned problems, HGBD has been proposed to ensure heating indoors during defrosting without switching the reverse-cycle valve [21]. Although HGBD has several advantages for frost removal, it exhibits problems, including a long defrosting time and large variations in the discharge pressure and temperature, and is typically used in industrial units [9,22].Ultrasonic defrosting, which was first proposed by K. Adachi et al [23,24], is a new non-heating defrosting technology. The authors indicated that ultrasonic vibrations with an amplitude of 3.4 µm and a frequency of 37 kHz suppressed frost accumulation on a plate by approximately 60%.…”

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confidence: 99%

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confidence: 99%

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Ultrasonic Guided Wave Phased Array Focusing Technology and Its Application to Defrosting Performance Improvement of Air-Source Heat Pumps

Tan

Zhang

et al. 2019

Energies

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Previous studies have indicated that a basic frost layer negatively affects the heat-transfer efficiency and is difficult to remove using a single ultrasonic transducer. Herein, an ultrasonic phased array technology is proposed for evaporator coil defrosting. First, the dispersion curve of the guided wave in the vibration transfer plate and frosting fin is calculated, and the advance time of each ultrasonic vibrator and the ultrasonic near-field pressures under different velocities are determined through numerical calculations using the MATLAB software. Next, according to the advance time, ultrasonic array focusing is performed to remove the basic frost layer. Finally, the power consumption, heat-supply enthalpy difference, and coefficient of performance (COP) of the air-source heat pump (ASHP) unit are analysed. The theoretical analysis, numerical calculations, and experimental results consistently revealed that ultrasonic array focusing compensates for the energy dissipation and expends the effective defrosting area. Additionally, the perpendicular stress elicited by the Lamb wave and the differential transverse shear stress generated by the SH wave exceed the tensile strength and adhesion stress of the basic frost layer. The basic frost layer cracks and falls away, owing to the combination of the ultrasonic stress effect and the cavitation effect. The defrosting power consumption of the ASHP unit under ultrasonic array excitation decreases from −3.27% to 0.12%, whereas the heat-supply enthalpy difference increases from 4.47% to 10.86%. Therefore, the percentage increment of the COP is between 7.16% and 11.12%, and the power consumption of the reverse-cycle defrosting is 3–12 times that of ultrasonic array defrosting.

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“…However, taking heat away from indoor air can adversely affect indoor thermal comfort level. Wang et al (2013) presented the cross hot-gas bypass defrosting method. This method could overcome the main disadvantage of the reverse-cycle defrosting.…”

Section: Introductionmentioning

confidence: 99%

Analysis of air-to-water heat pump in cold climate: comparison between experiment and simulation

Januševičius

Streckienė

2015

Science - Future of Lithuania

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abstract. Heat pump systems are promising technologies for current and future buildings and this research presents the performance of air source heat pump (ASHP) system. The system was monitored, analysed and simulated using TRNSYS software. The experimental data were used to calibrate the simulation model of ASHP. The specific climate conditions are evaluated in the model. It was noticed for the heating mode that the coefficient of performance (COP) varied from 1.98 to 3.05 as the outdoor temperature changed from -7.0 ºC to +5.0 ºC, respectively. TRNSYS simulations were also performed to predict seasonal performance factor of the ASHP for Vilnius city. It was identified that seasonal performance prediction could be approximately 15% lower if frost formation effects are not included to air-water heat pump simulation model.

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Study on the operating performance of cross hot-gas bypass defrosting system for air-to-water screw heat pumps

Cited by 24 publications

References 11 publications

Review of energy efficiency and system performance of residential heat pump water heaters

Review of energy efficiency and system performance of residential heat pump water heaters

Ultrasonic Guided Wave Phased Array Focusing Technology and Its Application to Defrosting Performance Improvement of Air-Source Heat Pumps

Analysis of air-to-water heat pump in cold climate: comparison between experiment and simulation

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