Direct-expansion Heat Pump System Research Articles

Experimental study on a direct-expansion micro-channel PV/T evaporator using water-ZnO nanofluid as the spectral beam splitter

Introducing nanofluid (NF) as the spectral beam splitter (SBS) in photovoltaic/thermal (PV/T) evaporators can significantly enhance their performance and energy flexibility. In this study, a novel direct-expansion micro-channel evaporator using water-ZnO nanofluid as SBS (i.e., NF-MC-PV/T evaporator) was manufactured. Particularly, the stability of low-viscosity water-ZnO nanofluid was first optimized and natural convection within the NF-MC-PV/T evaporator was directly formed. Further, a direct-expansion heat pump system based on the NF-MC-PV/T evaporator was developed and tested. According to the findings, adding sodium hexametaphosphate as a dispersant with the dispersion ratio of 1:5 and ultrasonic treatment for 1.5 h can achieve the optimal stability of water-ZnO nanofluid. The nanofluid's natural convection can reduce the evaporator's operating temperature and improve the PV module's temperature distribution uniformity. Specifically, the NF-MC-PV/T evaporator's operating temperature was lower than the environment temperature and a pure PV module. Besides, the PV module's temperature distribution was uniform in the direction perpendicular to the refrigerant flow with a max temperature gradient of only 4.59 °C. The typical photothermal efficiency of the NF-MC-PV/T evaporator reached 102.55 % while the heat loss coefficient was only 4.37. Moreover, the average photothermal efficiency, photovoltaic efficiency, and COP of the system were 103.58 %, 12.03 %, and 5.09, respectively.

Hybrid PV/T Heat Pump System with PCM for Combined Heating, Cooling and Power Provision in Buildings

Hybrid photovoltaic-thermal heat pump (PV/T-HP) solar energy systems are promising since they can achieve a system total efficiency greater than 80%. By maximizing the output of a PV/T system for simultaneous heating and cooling, this strategy can meet over 60% of urban households’ heating needs and around 40% of their cooling needs. In this work, a novel PV/T evaporator was designed, fabricated, and an aluminium foil encapsulated hydrated salt (HS36) PCM was integrated with the PV/T evaporator of the PV/T direct expansion heat pump system (PV/T-DXHP). Energy analysis was carried out on the PV/T-DXHP system with PCM in tropical climate regions of India for achieving net zero energy buildings. The experimental study revealed that the average PV electricity efficiency was 14.17%, which is near the PV panel’s STC value. The average thermal efficiency of the system was 104.38%, and the PV/T system’s average overall efficiency was 117.58%. The heating and cooling COPs of the system were 5.73 and 4.62, respectively. It was concluded that net-zero energy buildings are possible with the help of photovoltaic heat pump systems that use PCM and solar energy to make electricity, cool spaces, and heat water.

Economic evaluation and annual performance analysis of a novel series-coupled PV/T and solar TC with solar direct expansion heat pump system: An experimental and numerical study

Hybrid photovoltaic/thermal (PV/T) systems are proposed to harvest the two renewable forms of energy, thermal and electrical. The PV/T system generates low-temperature thermal and electrical energy, which is usually not much and might meet the demand for residential building heating and hot water. This research presents the economic evaluation and annual energy performance of a novel series-coupled PV/T and a solar thermal collector (TC) with a solar direct expansion heat pump system. A comprehensive approach was developed and utilized to evaluate the quantitative and qualitative performance of the hybrid refrigerant-based PV/T-TC system using the 1st (energy) and 2nd (exergy) laws of thermodynamics. A 0.5234 kW rating heat pump prototype system with a PV/T-TC area of 3.5 m2 was built and tested under the real conditions of Karachi, Pakistan, and a simulation model was developed via MATLAB to predict the annual energy performance. The experimental results show that the PV/T-TC system's mean daily electrical, thermal, overall energy and exergy efficiencies were 14.08%, 60.12%, 74.20%, and 18.12%, respectively. The numerical results reveal that a PV/T-TC assisted solar heat pump system can generate 303.51 kWh of electricity and 3213.12 kWh of thermal energy annually. The annual average COP of the hybrid refrigerant-based PV/T-TC system is 5.68. According to the comparison of economic performance between the PV/T assisted direct-expansion heat pump system and PV/T-TC assisted direct-expansion heat pump system, the hybrid refrigerant-based PV/T-TC assisted direct-expansion heat pump system has a payback period of 5.20 years, whereas the refrigerant-based PV/T assisted direct-expansion heat pump system has a payback period of 7.15 years. The experimental data is consistent with the simulation outcomes, with an average relative error of 3.30%.

Field experimental investigation on electricity and thermal performances of a large scale photovoltaic solar-thermal direct expansion heat pump system

The comprehensive utilization of photovoltaic and solar-thermal (PVT) is an important approach to achieve the carbon peaking and carbon neutrality goals, and can realize the generation of electricity and thermal energy cleanly and efficiently. In order to satisfy the basic living demands including electricity, space heating and domestic hot water of Chinese rural residents, a large scale direct expansion PVT heat pump (DX-PVT-HP) system used plate-tube evaporator has been proposed in the present paper. An experimental platform with a solar panel installation area of 32.47 m2 is installed on the roof of a dormitory in Hefei, and its operation characteristics including electricity and thermal performance are field tested and analyzed in winter. The data indicates that during the operation of the heat pump, the cooling effect of the plate-tube evaporator on the solar panel can maximum increase the photoelectric conversion efficiency by 25.0% in comparison with that of the conventional solar panel. In the process of heating 1500 L water from 5.5 °C to 45 °C on a sunny day, the average coefficient of performance (COP) of the system reaches 4.96, and the power generation of the system is greater than the power consumption. Finally, the concept of equivalent net thermal energy is proposed to unify the output of electricity and thermal energy to evaluate the comprehensive performance of the system. The results demonstrate that it is feasible to adopt the designed PVT heat pump system to meet the basic living needs of rural residents.

Experimental and numerical investigation on a solar direct-expansion heat pump system employing PV/T & solar thermal collector as evaporator

The objective of the research is to present an investigation on the operational performance of the integrated photovoltaic/thermal system (PV/T) and solar thermal collector (TC) with a heat pump system (PVT-TC) and its potential use for generating high thermal energy and electricity simultaneously. The numerical simulation model and testing rig of the PVT-TC heat pump system have been developed to analyze the electrical, thermal, and total efficiency of the system. An experimental test was carried out under real weather conditions. The experimental results revealed that the average electrical, thermal efficiency, and coefficient of performance (COP) of the PVT-TC heat pump system are 14.08%, 66.71%, and 6.11, respectively. According to comparative analysis with the similar systems, the PVT-TC heat pump system exhibits a higher electrical and thermal efficiency, thus showing a better application potential in residential buildings. The PVT-TC system occupies 3.3278 m2 and generates an average of 0.86 kWh/day of electricity and 6.35 kWh/day of thermal energy, as a result of 86.1% of primary energy saving efficiency being obtained. In addition, the PVT-TC heat pump system is simulated using COMSOL Multiphysics® to examine the temperature distribution of the solar TC and PV/T systems. The numerical model is also verified by the experimental data, with a root mean square deviation with less than 1.53%.

Experimental study on the performance of a photovoltaic/thermal-air dual heat source direct-expansion heat pump

A new type of photovoltaic (PV)/thermal (PV/T) air evaporator based on micro heat pipe arrays (MHPAs) and a PV/T air dual heat source direct-expansion heat pump system that can achieve heating, refrigeration, and PV power generation were developed. System performance was experimentally investigated. Results showed that the MHPAs exerted a significant cooling effect on the PV modules, which were cooled by 31.6 °C under the experimental conditions, with a low longitudinal temperature difference of 2.1 °C. The increase in PV efficiency was 5.3%. The evaporator can receive heat from solar energy and air energy under appropriate ambient temperature, and the average heat collection efficiency was 106.1%. The average heating coefficients of performance (COP) of the heat pump in solar (S), combined solar and air (SA), and air (A) modes were 2.8, 2.1, and 2, respectively, under typical heating conditions during winter. Average PV efficiency values in S and SA modes were 13.3% and 6.8%, respectively. The average cooling COP was 2.2 and the average PV efficiency was 11.2% under typical cooling conditions during summer. The performance difference and control strategy in various modes and seasons were summarized. This research provides data to support the practical application of heat pump systems.

Numerical simulation and experimental validation of a micro-channel PV/T modules based direct-expansion solar heat pump system

This paper presents a novel solar driven direct-expansion heat pump system employing micro-channel PV/T modules as the evaporator. The system can provide both the electrical power and thermal energy used for space heating for buildings. Experimental work was carried out to investigate the performance of the system under real-life condition and numerical simulation work was carried out for the same condition as the experimentation using a two-dimensional model developed by the authors. This specialist simulation model contains energy balance calculation of individual models of components, i.e., models of the micro-channel PV/T module (evaporator), compressor, heat storage tank (condenser), electric expansion valve and testing room. The experimental and simulation results showed a good agreement each other, with the maximum error of 7.2% which is the temperature of refrigerant at the outlet of PV/T modules. The experimental average electrical, thermal and overall efficiencies of the PV/T module are 13.1%, 56.6% and 69.7%, respectively. While the simulated results are 13.7%, 55.0% and 68.7%, respectively. The average experimental and simulated COP of the system is 4.7 and 5.0, respectively. With the solar heat pump system providing energy for the room of 150 m2 in the real-life testing condition, the temperature of the room can remain at 18.5 °C which was high enough for the space heating. Comparison among the simulation and testing results indicated that the simulation model was reasonable for predicting the performance of the system and provided feasibility for analyzing the annual energy performance in the future.

Experimental investigation of a solar driven direct-expansion heat pump system employing the novel PV/micro-channels-evaporator modules

This paper aims to investigate a solar driven direct-expansion heat pump system employing the novel PV/micro-channels-evaporator modules, in terms of its solar thermal, electrical and overall efficiency, as well as coefficient of performance (COP), at the real-time operational condition. This work was undertaken through a dedicated system design, construction, field-testing and performance analysis. It was found that the novel PV/micro-channel-evaporator modules could achieve an average thermal, electrical and overall efficiency of 56.6%, 15.4% and 69.7% respectively at the specified operational condition, while average COP of the system reached 4.7. The innovative feature of the system lied in the structure of the evaporator that was made of the parallel-laid micro-channels. Such a structure created the reduced interior cross-sectional area and thus increased vapor flow velocity within the channels, while the high vapor velocity generated a higher shear stress exerted upon the liquid-vapor interface, leading to the reduced liquid film thickness, increased refrigerant evaporation rate, and increased electrical and heat outputs. The research has provided the fundamental data and experience for developing a highly efficient and practically feasible solar heat pump system applicable to the cold climatic conditions, thus contributing to significant fossil fuel saving and carbon reduction in the global extent.

Development and Evaluation of a Direct Expansion Heat Pump System

The move towards a low-carbon world, driven partly by climate science and partly by the business opportunities it offers,will need the promotion of environmentally friendly alternatives if an acceptable stabilisation level of atmospheric carbondioxide is to be achieved. This requires the harnessing and use of natural resources that produce no air pollution or GHGsand provides comfortable coexistence of humans, livestock, and plants. GSHPs are receiving increasing interest becauseof their potential to reduce primary energy consumption and thus reduce emissions of GHGs. The main objective of theresearch is to stimulate the uptake of the GSHPs. This paper describes the details of a prototype direct expansion GSHPtest rig and details of the construction and installation of the heat pump, heat exchanger, heat injection fan and watersupply system. It also presents a discussion of the experimental tests currently being carried out.

Numerical Study on a Novel Photovoltaic/Thermal Heat Pump System

A theoretical analysis of novel direct expansion heat pump system incorporating a Photovoltaic/Thermal (PV/T) solar collector acting as the evaporator is presented in this paper. Based on energy balance of each parts of the vacuum-tube-PV sandwich and the four main components of the heat pump system, mathematical models are developed to evaluate the energy performance of the heat pump and the electrical and thermal performances of the PV cells, under the climatic conditions of the City of Nottingham, UK. The simulation results indicate that the average monthly thermal and electrical efficiencies are 0.752 and 0.155 respectively, and the average monthly COP reaches 5.35

Geothermal direct expansion heat pump system

Geothermal direct expansion heat pump system

5671608 Geothermal direct expansion heat pump system : Wiggs B Ryland; Womack Jack L; Bickford William C Franklin, TN, United States assigned to Geothermal Heat Pumps Inc

5671608 Geothermal direct expansion heat pump system : Wiggs B Ryland; Womack Jack L; Bickford William C Franklin, TN, United States assigned to Geothermal Heat Pumps Inc