Water Heating Applications Research Articles

Experimental determination of thermal conductivity of CNTs-H2O based nanofluids

Solar thermal collectors are being widely used for water heating applications in domestic, commercial, and industrial sectors. The main drawback of these collectors is their low thermal efficiency. The thermal efficiency of these collectors can be significantly increased by enhancing the heat transfer fluid’s thermal properties. This problem can be overcome by homogeneous mixing of nanoparticles in the base fluid such as water. The fluids with nanoparticles have better heat transfer efficiency and thermo-physical properties as compared to monofluid (water). In this study, the percent rise in thermal conductivity of the nanofluids is measured through experimentation by dissolving carbon nanotubes (CNTs) as nanoparticles in different concentrations (v/v %) inside the base fluid. The nanofluids are characterized by using the computer controlled thermal conductivity of liquids and gases unit, (TCLGC) by varying the CNTs sample composition from 0.01-0.05 v/v %. The results show that the inclusion of CNTs as nanoparticles significantly improves the thermal conductivity of nanofluids. Moreover, when CNTs are used at 0.05 v/v% inside a 100 ml sample solution, the highest increase in thermal conductivity is observed as 72%

Design and analysis of thermoacoustic air source heat pump water heaters

Thermoacoustic air-to-water air source heat pumps (TAWASHP) are the eco-friendly, simple, compressor less, low cost and likely looking future substitute for the existing compressor-based heat pumps. In this work, the design optimization of the 1-kW TAWASHP with helium for the temperature difference of 15 to 70 K for pumping heat from the atmospheric air to water using the linear thermoacoustic concepts was discussed. The optimized design can fit for both cooling and water heating applications without wasting the heat rejection to the surrounding atmosphere, rather supplied to the insulated hot water tank. The optimized one-fourth wavelength resonator TAWASHP shows the coefficient of performance of 1.1 to 2.34. The theoretical results are validated with the DeltaEC software results, and the results are in concurrence with each other. The DeltaEC predicts the TAWASHP can supply 1.55 to 3.35 kW of heat to water, which is equivalent to 37.3 to 80.3 kWh of heat energy per day.

Thermal Energy Storage With Horizontal Thermocline Tank for Sludge Drying Application

Solar thermal technologies can be an attractive option for the decarbonization of process heat applications; in particular, thermal energy storage is a high value proposition for continuous processes that may operate at a range of thermal conditions. A thermal-fluid model is developed to investigate the buoyant flow in a horizontal thermocline storage tank for a sludge-drying application. The process conditions and tank geometry considered are unique compared to the domestic water heating application typically considered in the literature and well suited for parabolic trough collectors. It was found that good separation of hot and cold fluids can be achieved with the long horizontal tank geometry depending on the inlet configuration. Uniform flow distribution along the length of the tank is required to establish a thermocline. Assuming desirable inlet conditions can be achieved, the tank outlet temperature predicted by the thermal-fluid model shows good agreement with the system-level performance model.

A comprehensive review of the hybrid heating systems consisting of heat pumps and solar collectors for hot water and space heating application

A comprehensive review of the hybrid heating systems consisting of heat pumps and solar collectors for hot water and space heating application

Experimental and numerical investigation of a solar thermocline system for domestic water heating applications

Experimental and numerical investigation of a solar thermocline system for domestic water heating applications

Optimal discharge pressure and performance characteristics of a transcritical CO2 heat pump system with a tri-partite gas cooler for combined space and water heating

The transcritical CO2 heat pump holds promise for achieving carbon neutrality in buildings, primarily due to its high energy efficiency in hot water heating. However, using it for space heating often leads to efficiency losses. A heat pump equipped with a tri-partite gas cooler can address this issue by providing both space heating and hot water while maintaining lower refrigerant temperatures at the gas cooler exit. Nonetheless, there is limited research on the characteristics of a CO2 heat pump system designed for simultaneous space and hot water production. This work fills this gap by analyzing the impacts of operational and system configuration, considering the variation of space heating to hot water production loads. A theoretical model is presented and verified with the experiments. Results show that under the specified conditions, the heat load ratio has minimal influence on the optimal discharge pressure. Increasing the water outlet temperature from 60 °C to 80 °C leads to a nearly 14% decrease in maximum COP, with a corresponding 12.2% increase in the optimal pressure. A 10 K rise in water inlet temperature results in approximately a 21% decline in maximum COP. Evaporation temperature has little impact on the optimal discharge pressure, while maximum COP increases by roughly 63% with a rise in evaporation temperature from -10 °C to 10 °C. Space heating water temperature notably affects the optimal discharge pressure. Integration of an IHX enhances system COP but has marginal impact on the optimal discharge pressure. These findings offer insights for designing and optimizing transcritical CO2 heat pumps for simultaneous space and water heating applications.

Investigation of graphene-perovskite integration for enhanced absorption of solar thermal absorber for industrial heating applications

Advanced materials are critical for enhancing the efficiency of solar absorbers. Hence, the present study looks at the unique interaction between graphene and perovskite materials, a combination that has the potential to change the landscape of solar energy harvesting. The Graphene–Perovskite Integrated Solar Absorber (GPISA) structure harvests more than 98 % in UV and VIS regions ranging from 200 nm and goes up to 4000 nm of the solar spectrum using the Finite Element Method (FEM). Not only does it boast a broader absorption range from 200 to 4000 nm, covering virtually the entire solar spectrum, but it also achieves an impressive average absorption of 95.50 %. Additionally, the comprehensive analysis of its performance, encompasses optimized parameterization, exhaustive mapping of electric and magnetic field intensities, and in-depth investigation of both transverse magnetic (TM) and transverse electric (TE) field behaviors. This correlates to a weighted absorption rate of more than 97 % in the AM1.5 solar spectrum, as well as endurance to varied incoming angles (0°–80°) without considerable absorption loss, making it suitable for real-world direct sunlight absorptance. The GPISA is significantly more cost-effective due to its 3240 nm thickness. Overall, GPISA's exceptional combination of broad absorption, high efficiency, and compact design firmly positions it as a frontrunner in the advancement of efficient, high-performance solar energy harvesting. GPISA has efficient uses in solar induction systems as well as solar air, water heating, and other industrial heating applications.

Hybrid Technologies for Water Heating Applications: A Review

The over-reliance on fossil resources necessitates the development of a sustainable energy system. Renewable energy and efficient hybrid water heating technologies are viable net-zero energy options. The economic benefits of these hybrid technologies offer a promising prospect for widespread adoption in developing countries as a means of increasing the hot water production. These hybrid technologies are becoming increasingly popular for domestic thermal applications in remote areas to compensate for energy shortages. This paper provides an overview of hybrid renewable water heating technologies with a focus on hybrid configurations, optimization techniques, mono-particle, and hybrid nanofluids and modelling. This paper also highlights the prospects for increasing the economic attractiveness and public acceptance of such systems.

Evaluations of heat pump water heater with liquid-separation condensation from perspectives of performance enhancement and heat exchange area reduction

Heat pump water heater (HPWH) offers great potential to reduce energy consumption in water heating applications. But its performance enhancement and/or initial cost deduction are the main challenges to promote market penetration. In this paper, a heat transfer improvement technology, i.e., liquid-separation condensation (LSC), is implemented to HPWH and screen to achieve the maximized COP (E-HPWH) or reduced condenser area (R-HPWH). A model of HPWH with LSC is developed and validated, and its predictions are in good agreements with tested results from the baseline (B-HPWH) with an average deviation of 4.92 % at most. By using this validated model, E-HPWH and R-HPWH are obtained by adjusting the path arrangement and separation efficiencies. With the same heat transfer area, the COP of E-HPWH reaches 4.48, which is 7.43 % higher than that of B-HPWH, and the heating time is shortened by 13.1 %. With the same COP of B-HPWH being 4.17, the heat transfer area of R-HPWH is reduced by 22.2 % and heating time is shortened by 4.1 %. Then transient heating-up process of three HPWHs are comparatively investigated. Results indicate that E-HPWH has the highest compressor power as well as pressures and temperatures at the inlets of condenser and evaporator, followed by R-HPWH and B-HPWH. E-HPWH and R-HPWH overperform B-HPWH in terms of heat capacity before 4220s, due to the increased mass flowrate. Compared to B-HPWH, E-HPWH and R-HPWH have averagely 15.02 % and 7.29 % higher COP before 2790s and 1860s, respectively. Their states are less differentiated as the water temperature increases.

Energy and exergy analysis of a novel multi-fluid heat exchanger for sustainable space and water heating application

Energy and exergy analysis of a novel multi-fluid heat exchanger for sustainable space and water heating application

Thermal energy storage materials designed from recycled Tetra Pak waste and paraffin waxes with enhanced photothermal conversion efficiencies

The phase change material (PCM)-integrated solar water heaters have great potential to save energy by utilizing renewable resources and to extend working hours even after sunsets. The PCM composites fabricated with recycled waste products lead to the circular economy which would contribute significantly to the sustainable development goals. In this work, Tetra Pak waste (TP) was used to prepare a form-stable PCM composite by mixing with paraffin wax (PW) and expanded graphite (EG) to integrate with solar water heaters. Two different PWs with melting points of 44 (RT44) and 64 (RT64) were used in the lower and higher temperature ranges of domestic water heating applications, respectively. The prepared composites exhibited enhanced thermal conductivity (1.1–1.15 W/m.°C), heat storage capacity (98.5–105.6 J/g), and photothermal conversion efficiency (85% and 55% for composites with RT44 and RT64, respectively). The numerical analysis conducted on a validated model helped to estimate the optimum composite thickness for specific solar exposure time. The fabricated PCM composite promoted the recycling of TP waste into useful products and was efficient in maintaining a higher nocturnal water temperature in the solar water heater.

Performance enhancement of flat-plate and parabolic trough solar collector using nanofluid for water heating application

Flat plate solar collector (FPSC) and parabolic trough solar collector (PTSC) are widely used for residential solar water heating (SWH) applications. This work studied two different solar collector systems. Nanofluid and its influence on the residential solar water heating (SWH) systems were investigated. The two SWH systems were designed, installed, tested, and compared at varying mass flow rates (mf) of 0.47, 1.05, and 1.75 kg min−1 in ambient environmental conditions. The comparative study was conducted according to thermal efficiency (ηth), useful energy gain (QU), stored energy (QS), outlet hot water temperature (To), and difference temperature (ΔT) between the cold inlet and hot outlet water from the collectors. The analysis of outcomes showed that the PTSC was more efficient than FPSC. The FPSC and PTSC systems performance were investigated using two different types of nanofluids. Carbon nanotubes in water and ethylene glycol were utilized. A remarkable improvement in the average thermal efficiency 64.1 % and 80.6 % of FPSC and PTSC systems using ethylene glycol nanofluid were obtained respectively. The total reduction in CO2 emissions was 31.26 kg/day and 39.28 kg/day for the FPSCs and PTSCs, respectively in the presence of ethylene glycol nanofluid. A significant saving in CO2 release is owing to the renewable clean energy of solar collectors.

Optimal utilisation of low-grade solar-air source for heat pump water heating using a dual-source evaporator with forced convection

This research utilises a Direct Expansion Modified Solar-Air dual-source Heat Pump (SAHP-MDX) for water heating applications. Unlike conventional dual-source heat pumps, which rely solely on natural convection for extracting ambient thermal sources during partial sunshine and dusky hours, the SAHP-MDX incorporates a dual-source evaporator adapted with forced convection, effectively removing the dual-source energy throughout the day. The system operates in three distinct modes: Solar-Air source Natural Mode (SANM), Solar-Air source Forced Mode (SAFM), and Air-source Forced Mode (AFM). This study investigates the performance of the SAHP-MDX under various ambient (solar radiation and ambient temperature) and operational conditions (water tank temperature). The average daily Coefficient of Performance (COP) of SAHP-MDX is approximately 3.22, with average COP values of 3.51, 3.16, and 2.99 in SANM, SAFM, and AFM, respectively. The average heating times of SAHP-MDX in SANM, SAFM, and AFM cycles are 163, 177, and 197 min, respectively. Furthermore, the daily power consumption analysis reveals that the SANM, SAFM, and AFM heating cycles contribute 45.89%, 20.57%, and 33.54%, respectively. Considering these findings, the proposed SAHP-MDX system demonstrates the promising potential for water heating applications throughout the day, particularly in regions characterised by diverse ambient and operational conditions.

Numerical simulation of the melting and solidification processes of stearic acid/carbon fiber composite phase change material for solar water heating applications

Phase Change Materials (PCMs) are one of the most promising materials for storing thermal energy and supplying stored energy for Domestic Hot Water (DHW) applications. This paper presents a detailed numerical analysis to describe transient heat transfer in a phase-change composite thermal energy-storage system. The composite was composed of 92.5 % stearic acid, 7.5 % carbon fiber, and a heat transfer fluid (ethylene cellulose). Numerics were implemented using ‘The Integrated Computer Engineering and Manufacturing code for Computational Fluid Dynamics’. The results were validated using experimental data and demonstrated acceptable agreement and an accurate representation of this specific transient heat transfer problem. The difference between the simulation and experimental results was so small that we considered the simulation results reliable. When the phase change heat storage process is about 800 s, the heat is transferred to the entire phase change heat storage tank, and when the phase change heat storage process is about 10800s, the temperature of all composite phase change materials reaches the phase change temperature. When the phase change heat storage process is about 8 h, the temperature of the composite phase change material in the whole phase change heat storage tank reaches 90 ℃. The temperature tends to be stable after the phase transition heat release process for about 500 s, and there is no large fluctuation in temperature with the passage of time. When the phase change heat release process reaches 7200 s, the cold-water inlet temperature is 15 ℃, 20 ℃ and 25 ℃, and the outlet temperature is 25.8 ℃, 30.8 ℃ and 35.7 ℃, respectively, indicating that the application of composite phase change materials in phase change heat storage water tank has a good effect.

Experimental analysis of the air-to-water ejector-based R290 heat pump system for domestic application

The aim of this study was to analyze and compare the performance of an 8 kW ejector-based R290 heat pump system for hot water heating applications that operates with two different expansion devices: a throttling valve and a two-phase ejector. The vapor compression system was designed to compare the unit operating in direct expansion and ejector-based working modes under similar operating conditions. The test results were assessed for overall system performance measured by COP and heating capacity and for single-component operation. The ejector mode allowed operation at the same range of ambient temperatures as direct expansion mode with the potential to completely replace the expansion valve. The COP of ejector system was up to 2.6, which was 38% higher than direct expansion when working under similar conditions for an ambient temperature of −12.8°C. Moreover, the COP in direct expansion mode decreased significantly along the decrease of ambient temperature, whereas for the ejector mode this decrease was considerably smaller.

Experimental investigation of the solar latent heat thermal energy storage system integrated with salt hydrate phase-change materials

To achieve rational utilization of renewable energy sources, a solar latent heat thermal energy storage system for hot water application was developed in this study. The feasibility of the salt hydrates using in the solar heating was assessed and the comparative experimental investigation was conducted under various operating conditions. It shows that the higher flow rate and radiation accelerate the melting process of the phase-change material. The time taken for the storage medium to reach phase transition was reduced by approximately 48.9%; meanwhile, the collector efficiency was enhanced by approximately 10.2% as the flow rate increased from 10 g/s to 30 g/s. The accumulated charging energy increased by approximately 10.9% when the radiation increased from 850 W/m2 to 920 W/m2, resulting in a prolonged heat release process. The test results suggest the promising potential of the salt hydrates for the solar water heating applications.

A scalable phase change material-based system enhanced by multi-walled carbon nanotubes and fins for efficient solar water heating applications

Phase change material (PCM)-based harvesting and storage systems are promising solutions to solar energy's intermittence and non-uniformity issues. Previous efforts have focused on the absorption, conversion, and storage capability of PCMs. However, efficiently utilizing the stored thermal energy within PCMs remains challenging. Herein, we devise a facile and scalable PCM-based system with heat transfer and light absorption enhancement simultaneously by fins and multi-walled carbon nanotubes (MWCNTs) for solar water heating applications. Photothermal conversion experiments demonstrate that the water temperature of the PCM-based system with MWCNT and fins is up to 79.0 °C under the stationary condition, which is increased by 58.6 % and 55.2 % compared to the original composite and the MWCNT-doped one, respectively. Furthermore, numerical simulations indicate that fins act as a bridge between PCM and water, facilitating rapid heat transport and improving the thermal energy storage pattern, enabling efficient solar water heating. The water temperature can keep above 40.0 °C for 51 min at a flow rate of 11.34 l/h under ambient cooling conditions, and the maximum thermal efficiency is up to 89.2 %, which is higher than most flat plate and tubular solar collectors, demonstrating the superiority of the proposed system.

Design and Fabrication of Hybrid Charging Station

A solar collector is a device that transforms solar radiation from the Sun into heat, which is then transferred to working fluid. The use of solar collectors reduces energy costs over time as they do not use fossil fuels or electricity like in traditional waterheating. As well as in domestic settings, a large number of these collectors can be combined in an array and used to generate electricity in solar thermal power plants. There are a number of different types of solar collector designs that use the energy of the sun to heat working fluid. Parabolic dish reflector provides a better alternative way in order to generate higher temperatures with better efficiency. The parabolic dish reflector is a solar energy collector designed to capture the sun’s direct solar radiation over a large surface area and focus or “concentrate it” onto a small focal point area, increasing the solar energy received by more than a factor of two. In the present project we will do the design & development of Parabolic Dish collector with automatic solar trackingfor water heating application. Keywords: Solar energy, water heating application, parabolic dish collector, automatic solar tracking.

Preliminary characterization and thermal evaluation of a direct contact cascaded immiscible inorganic salt/high-density polyethylene as moderate temperature heat storage material

The present work assesses the direct contact cascaded immiscible phase change material (PCM) for solar heat storage systems (SHSS) in water heating applications. The direct contact cascaded immiscible PCM uses ternary salt mixture (TSM) and high-density polyethylene (HDPE). Improvement on phase behavior and thermal properties are obtained for the direct contact cascaded immiscible TSM/HDPE. The plasticity effect of HDPE leads to a stable phase transition of the mixture with the lowest supercooling degree by 0.9 °C. The initial thermal decomposition temperature for TSM and HDPE is above 400 °C, which is suitable for moderate temperature operation of SHSS. The immiscibility between TSM and HDPE leads to a multistep phase transition between 110.2 and 139.6 °C. The phase behavior during the liquid-solid transition demonstrates the lowest temperature gradient of 13.9 °C, implying a steady phase transition. It allows the stored heat can be released effectively without causing significant volume expansion of the TSM. Moreover, the enthalpy of fusion for TSM/HDPE is increased, making it favorable as solar thermal energy for water heating applications in SHSS.

Performance evaluation of an enhanced self-storing evacuated tube solar collector in residential water heating application

Phase change materials (PCMs) offer higher levels energy storage density than conventional hot water tanks commonly used with solar hot water systems. The present study aims at investigating the integration of a selected PCM within the structure of an evacuated tube solar hot water system to create some compact thermal storage capacity. Then conventional solar water heater is compared with this novel PCM-based self-storing design. The results show that the proposed self-storing design can maintain the collector output temperature at around 63 °C after 15 h of not receiving any sunlight. That is whilst the output temperature of the normal collector drops down to ambient temperature in the same period. The obtained energy storage efficiency is 57 % and 75 %, and overall thermal efficiency is 49 % and 72 %, for the normal and the self-storing collectors, respectively. For the small-scale system used in this study, the proposed design helps reduce the size of the hot water storage tank required to supply the hot water demand by 55 %. The study also shows that the same design can even yield better performance at larger scales used in practical applications.