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    Comparison of solar assisted heat pump systems for heating residences: A review
    (Pergamon-Elsevier Science Ltd, 2023) Sezen, Kutbay; Gungor, Afsin
    Solar assisted heat pump (SAHP) systems have been a popular research topic in last decades because of their proven improved performance by integrating solar energy to system. Filling the literature gap in SAHP systems comparison in terms of performance and structure, contributes to the determination of the appropriate type. For this purpose, in order to compare the systems, 77 recent studies are reviewed. Systems are classified according to their configurations to provide an infrastructure for comparison. Considering the collector structure, the effect of solar radiation and ambient temperature on SAHP systems performance are examined, and the ambient condition ranges preferable for each system are identified. The complexity of systems is expressed with the type and number of components used, and the costs of the systems are compared taking into account the payback period. Reviewed studies reveal that, direct expansion systems should be preferred because of their utilization of solar and air simultaneously as heat source, below solar irradiation of 400 W/m2. Indirect expansion systems are more complex than direct expansion systems and this limits their preferability. However, replacing the solar-side evaporator with a solar air preheater, thereby integrating the existing solar system and air source heat pump system, can simplify the indirect expansion systems. The temperature rise problem that prevents the use of photovoltaic thermal panels in indirect systems can be eliminated with low-cost external cooling devices.
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    Effects of ambient conditions on solar assisted heat pump systems: a review
    (Elsevier, 2021) Sezen, Kutbay; Tuncer, Azim Dogus; Akyuz, Ali Ozhan; Gungor, Afsin
    Solar assisted heat pump (SAHP) systems aim to increase the performance of heat pumps by supporting with solar energy using various heating modes, whose performances depend on ambient conditions. In the literature, SAHP systems are classified by structure types, and the heating mode options are not considered as the main priority of the design but a result of the structure of the system. This paper aimed to investigate the effect of ambient conditions on heating modes, and identify the preferable ambient condition ranges for each SAHP system depends on their heating modes, by using a narrative review of 47 recent studies, that shed light on the problem. For this purpose, direct solar heating (DSH), air source heat pump (ASHP), solar source heat pump (SSHP) and solar-air source heat pump (S/ASHP) modes were stated as the basic heating modes of SAHP systems. In accordance with the literature, SAHP systems were classified as direct expansion solar assisted heat pump (DX-SAHP) and series, parallel and dual source indirect expansion solar assisted heat pumps (IDX-SAHP). Solar irradiation, ambient temperature, relative humidity and wind speed has been taken as major ambient conditions to investigate. Reviewed studies indicated that, parallel and series IDX-SAHP are preferable in high solar irradiations about 800 W/m2 with their DSH mode options. Frosting on evaporator is prevented in DX-SAHP with its S/ASHP mode, and even in the presence of frosting, unlike IDX-SAHPs ASHP mode, freezing is a factor that improves performance on flat evaporator in cold and humid conditions. This study indicates that there are obscure areas for future studies to focus on for a better comparison between SAHP types. Moreover, proposed novel designs of this paper, such as solar preheating of air in IDX-SAHP systems to add S/ASHP mode as an option, might enhance the performance and applicability of SAHP systems.
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    Performance analysis of air source heat pump according to outside temperature and relative humidity with mathematical modeling
    (Pergamon-Elsevier Science Ltd, 2022) Sezen, Kutbay; Gungor, Afsin
    The paper investigates the performance effect of outdoor temperature and relative humidity on ASHP performance above frosting conditions, with the developed mathematical model. The model results are validated with the experimental data available in literature, of four ASHPs in the 2.7 kW 5.8 kW capacity range. 4 kW capacity ASHP is taken as reference. Constant heating (CH), constant work (CW) and variable heating (VH) modes are determined as operating modes. The model results reveal that relative humidity is a performance enhancing factor above frosting conditions. In VH mode, which is the most realistic operating mode for residences, raise in outdoor temperature from 7 degrees C to 14 degrees C increases the COP value by 30%, and raise in the relative humidity from 0.6 to 1.0 provides an additional 5% COP increase. In CH and CW modes, the contribution of relative humidity to performance increases with temperature, up to 10.7% and 6.4%, respectively. Correlations giving the COP change rate with respect to ambient temperature and relative humidity are derived with higher than 0.9839 R2 values for dry and humid conditions of the CH, CW and VH operating modes. These correlations can be useful for researchers who intends to analyze ASHP performance based on ambient conditions.
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    Water droplet evaporation in atmospheric air stream
    (Aip Publishing, 2023) Sezen, Kutbay; Gungor, Afsin
    Evaporation of a water droplet in air is a natural phenomenon that causes the droplet and air properties to change over time. In this paper, time-dependent variation of air and water droplet properties in a flow is examined with the developed numerical model, in the range of conditions that concern air-conditioning and respiratory-based medical events and applications. An experimental setup is built and the model is validated with experiments carried out for 27 cases. Input parameters are chosen as the inlet air temperature, relative humidity, droplet temperature and diameter, and air-water mass mixing ratio. Output properties are determined as the outlet air temperature, relative humidity, mass droplet ratio, and droplet temperature to define the application case in the simplest way. Model results of 432 different cases are used to develop correlations with R20 values above 0.984, to present the effects of co-variation of input parameters. The results show that the latent heat demand of droplet evaporation is the main factor in the decrease of air temperature, while droplet temperature has almost no effect. As the air becomes saturated with moisture, evaporation almost stops and droplets carried by air flow remain. The droplet diameter affects only the process speed by reducing the processing time by the square of the reduction ratio. The developed numerical model and correlations allow the rapid determination of properties change in air-water stream over time, so it will provide great convenience to researchers dealing with water droplet evaporation in an atmospheric air stream.