Hot Water Tank Research Articles

Dynamic Modelling and Validation of an Air-to-Water Reversible R744 Heat Pump for High Energy Demand Buildings

This paper presents a reversible heat pump based on CO2 as the refrigerant, able to provide heating, cooling, and domestic hot water to high energy demand buildings. The unit was developed and tested under the EU H2020 project MultiPACK, which has the main goal of assuring the market about the feasibility, reliability, and energy efficiency of CO2 integrated systems for heating and cooling and promoting a fast transition to low environmental impact solutions. Within the project, the confidence raising was performed by installation and monitoring of fully integrated state-of-the art CO2 systems in the Southern European Climate. With the aim of predicting the unit behaviour under variable load and boundary conditions, a dynamic model of the entire unit was developed with commercial software, considering actual components and the implemented control system and it was validated with experimental data, collected at the factory’s lab before commissioning. The validation against experimental data collected during operation as a heat pump demonstrated a maximum percentage difference between the experimental and predicted value of gas–cooler heat flow rate equal to +5.0%. A preliminary comparison with the experimental data in chiller configuration is reported, however further development was required to achieve a satisfactory validation. Lastly, the numerical model was utilized to simulate a typical operation in heat pump configuration with the system coupled with a hot water tank storage for the production of domestic hot water and space heating; the model predicts higher COP when operating in domestic hot water operation due to the lower water inlet temperature.

Unconstrained melting of phase change material in cylindrical containers inside hot water tanks: Numerical investigation and effect of aspect ratios

In this study, a numerical model with variable mushy zone constants was developed based on the enthalpy-porosity method for the unconstrained melting of phase change material (PCM) encapsulated in cylindrical containers inside hot water tanks. In particular, a method for dynamically determining mushy zone constants was established. Mushy zone constants were explicitly calculated for each element in the solid region and updated at each iteration in the solution procedure of the model. The model showed satisfactory performance, with a mean absolute relative error of 5.2% between experimental measurements and numerical results. Based on this model, the unconstrained melting process of PCM and the influence of the aspect ratio of the cylindrical container were investigated. Results showed that contact melting accelerated the heat transfer of PCM at the bottom region and further enhanced the natural convection of liquid PCM at the side region. Moreover, the aspect ratio exerted little influence on the heat transfer coefficient at side wall surfaces. The correlation between the total melting time and aspect ratio was also calculated. The peak total melting time occurred for an aspect ratio of 5.49, and the smallest total surface area corresponded to an aspect ratio of 2. Clearly, larger total surface areas do not necessarily result in shorter total melting time. Further analysis indicated that flatter containers likely to be preferable to slenderer containers in practical designs. In addition, increasing the percentage of the bottom surface area to the total surface area can increase the average heat transfer coefficient of latent heat storage units.

Operation performance study and prediction of photovoltaic thermal heat pump system engineering in winter

An array arrangement strategy of photovoltaic thermal modules and a connection form of refrigerant pipeline were innovatively proposed by author’s research group. Subsequently, the photovoltaic thermal heat pump system engineering was designed and constructed, and then the performance study of system heating in continuous operation and stage operation in winter was carried out in January 2021. During the system operation, the average coefficient of heating performance of the system was 2.95 in daytime stage operating, 2.55 in nighttime stage operating and 2.07 in continuous operating. To conduct the application simulation of photovoltaic thermal heat pump system, first the prediction model of system heating performance based on back propagation neural network was established and verified according to the operational parameters, then 12 cities of typical climate zone in China were selected to conduct operation simulation and performance prediction to analyze the regional applicability of the system, finally the performance prediction of system heating under variable working conditions was carried out to guide the design calculation of engineering application of photovoltaic thermal heat pump system engineering. It can be concluded that the system was more suitable for engineering application in cities of cold zone and hot summer and cold winter zone than that in severe cold zone. Besides that, the integration and operation optimization of system should be carried out to reduce the average temperature of the circulating hot water tank so that the energy efficiency of hot water system can be improved by 42%.

Parametric studies of heat pump water heater using low GWP refrigerants

A storage heat pump water heater (HPWH) comprises a vapor compression system and a hot water tank. It can lead to more than 70% energy saving, compared with electric resistance heating. HPWH usually uses a wrapped-tank coil as the water heater. The wrapped coil has a strong interaction with the water tank and impose a new challenge for the engineering design and simulation study. Based on the US DOE/ORNL Heat Pump Design Model (HPDM), i.e., a public-domain, component-based thermal system modelling platform, a segment-to-segment wrapped-tank coil model coupled with a one-dimensional stratified water tank model were developed, which facilitates modeling and design HPWHs having various configurations and components. The hardware-based design model was used to evaluate refrigerants having lower global warming potentials to replace R-134a, including R-1234yf, R-1234ze, R-290, R-513A and R-450A, when effects of compressor size, refrigerant charge on 24-hour uniform energy factor (UEF) and first-hour rating (FHR) were investigated. In the drop-in replacements, R-1234ze achieved the best UEF, and R-290 resulted in the lowest UEF. When downsizing the compressor to maximize the UEFs, the UEFs of R-134a, R-290, R1234yf, R-450A and R-513A ascended to the range of 4.4 to 4.53, with R-513A having the highest UEF. The R-1234ze ended up having the lowest UEF of 4.27. Refrigerants having larger volumetric vaporization heat led to higher FHRs if using the fixed-size compressor, that R-290 resulted in the highest FHR.

Performance of a shallow solar pond coupled with a heat pump cycle for thermal energy in net zero-energy buildings

Refrigerant evaporation, in heat pumping systems, is a particularly complex process. Since the evaporator is subjected to environmental conditions, several factors weigh in on overall system performance, mainly, the additional energy input from the surroundings. This renders the evaporation process especially susceptible to gaps and fluctuations of said energy availability, particularly in solar-assisted setups. Despite the, comparatively, high heat flux associated to this source, these occurrences make them suitable mostly for low-to-medium thermal requirements, especially in regions with more extreme climates. The present work introduces a novel evaporator design, based on solar ponds. The proposed evaporation device incorporates a short-term, passive, thermal storage solution to compensate for gaps in energy availability. A mathematical-thermal model is developed and a performance assessment is conducted based on real seasonal atmospheric and operation conditions. For this study R134a, R152a, R1234yf and R1234ze(E) were used as working fluids. The proposed heat pump configuration is evaluated for hot water production at 55 °C, indoor air heating at 18–22 °C and a combined simultaneous scheme. The results show that this configuration performs well under moderate climate conditions. For hot water production during spring, highest outlet temperature of 68.54 °C for the R1234yf working fluid, were reached and maintained after the first 13 h. Internal thermal capacitor reached an average temperature of 61.88 °C for R1234yf. During winter, these temperatures decrease almost by a third, with 40.6 °C for R1234yf working fluid. However, daily average outlet temperature of 64.8°Care reached within the first 15 h of operation. Despite a lower thermal storage, with average capacitor, the system yielded consistent average outlet temperature of 20.7 °C. For a simultaneous operation scheme, desired outlet water temperature, is reached within the first 16 h of operation, whilst the indoor air temperature reaches comfort levels within the first 12 h. Despite employing part of the energy absorbed to maintain a stable comfort condition within the dwelling, instead of compensating the heat loss of the hot water tank, both goals are achieved. The inclusion of an inner thermal capacitor that collects and stores energy at a much higher rate provides the refrigerant with an additional heat source. This results in a more effective overall energy absorption of the evaporator, which exceeds the rate at which heat is dissipated from the tank/dwelling to the environment. This heat loss buffer lessens, considerably, the thermal demand during periods with lower energy availability, resulting in achievable outlet conditions.

Investigating thermal stratification in a vertical hot water storage tank under multiple transient operations

Hot water storage (HWS) tanks are one of the commonly employed sensible energy storage systems that store heat energy using water as the storage medium. Hot water tanks store thermal energy from multiple energy sources and practise several utilization methods, however, identifying the best approach to effectively utilize the stored thermal energy inside the tank from the energy efficiency point of view is critical. Present work focuses on the transient numerical investigation of a domestic, multi-sourced HWS tank. Thermal behaviour of HWS tank is analysed in three dynamic operational modes, namely charging, continuous delivery, and discharging operation. The axis-symmetric, two-dimensional model of the double coiled, vertical HWS tank of cylindrical shape is simulated using ANSYS Fluent. The numerical model is validated against the experiment data in charging mode. Influence of operating modes on the degree of thermal stratification is determined. Axial temperature evolution, dimensionless Stratification, and Richardson numbers are calculated and compared for each operational case. Results show that thermal stratification depends on the location of heating source inside the tank under the given operational mode. The degree of stratification in both the charging and continuous delivery modes is improved when the heat exchanger coil installed at the upper portion of the tank is functioning. The Stratification numbers are 0.28 and 0.32 after 30 min in the charging mode, and continuous delivery mode, respectively. The study compares thermal performance of HWS tank in different conditions and reveals the evolution of the thermal stratification with time, which are essential in designing stratified HWS tanks.

Transient CFD simulation of charging hot water tank

This paper presents characteristics of heat accumulation system operation in one of the Polish combined heat and power (CHP) plants. The heat source cooperating with this installation is cogeneration units consisting of gas engines with a total heat output of 8 MWt and total electrical power of 8 MWe. The total thermal capacity of the non-pressure hot water accumulator is 75 MWh. An important issue in the case of hot water tanks is thermal stratification caused by the difference in density between higher-temperature water, located at the top of the hot water storage tank and colder water at its bottom. The article presents the results of numerical analysis based on the axial-symmetric model of a hot water tank using Ansys Fluent R19.2 software. Simulations with the Computational Fluid Dynamics (CFD) method were carried out for the process of charging the heat accumulator lasting 10 h. The effect of mesh density on the results obtained was analysed. The results were compared with the measurement data from the CHP plant. Heat losses from the hot water tank were taken into account and the density characteristics of the heat flux lost to the environment were presented.

Design of a solar district heating system with seasonal storage in Italy

The residential sector is responsible for 26% of final energy consumption in the European Union. A key strategy to reduce household fossil fuel use is solar district heating with seasonal thermal energy storage. Although this technology has been widely applied in Northern Europe (Sweden, Denmark, and Germany), it has not been implemented in Italy. This research presents a new numerical tool, and applies it to the REPLICATE project in the Italian city of Florence, which is financed under the Horizon 2020 Smart Cities and Communities initiative. Our novel tool, which is based on a dynamic model coupled with the finite element method, has been developed to guide the design of the district heating plant and obtain a reliable estimation of performance, notably storage heat losses. The overall aim is to reduce the prediction inaccuracies that have characterized past projects. The final dynamic model is implemented in TRNSYS, and makes it possible to select the main plant parameters and define control strategies. It is linked to a detailed heat transfer model developed in COMSOL Multiphysics®, which can calculate storage heat losses and determine the optimal thickness of insulation material. Our in-depth parametric study determined the optimal volume of the hot water tank to be 3800 m3, and the size of the solar field to be 1000 m2. We also evaluated the effectiveness of the addition of a water–water heat pump. This analysis found that it is a crucial component as it can increase storage capacity and improve the performance of solar collectors by up to 124 MWh. Our results indicate that with an optimized configuration, the solar fraction of the system can reach up to 44%.

PERENCANAAN JARINGAN PIPA AIR BERSIH DAN AIR KOTOR PEMBANGUNAN GEDUNG GUEST HOUSE EXINDO GRUP

In the construction of a building, a plan is needed in terms of structure, architecture and Mechanical Electrical and Plumbing (MEP) so that the functions and objectives of building construction run according to plans and needs. The purpose of this thesis is to meet the needs of clean water and plumbing installation needs in building construction. Guest House Exindo Group. In this plan, it takes data on planning drawings for plumbing installation projects as well as a list of unit prices for building materials and labor in the East Java region in 2020. The planning stages carried out for clean water and dirty water pipelines are determining the water installation scheme used, calculating the number of building occupants. , calculating the amount of water demand, calculating the capacity of ground water tanks and roof tanks, calculating IPAL and septic tanks and calculating the dimensions of the pipes used. From the results of this planning is obtained the number of room occupants as much as 401 people with clean water needs of 69.109 m3/ day, the volume of black water generated at 45.72 m3/ day, and the volume of grey water by 16.32 m3/ day. The dimensions of the clean water pipe are ½ inch – 2 inch, the dimensions of the hot water pipe are ½ inch – 1 ¼ inch, the dimensions of the dirty water pipe are 2 inch – 4 inch, and the dimensions of the hydrant pipe are 3 inch – 6 inch. The capacity of ground water tank is 25 m3, the capacity of roof tank is 12 m3, the capacity of hot water tank is 4 m3, the capacity of septic tank is 50 m3 and the IPAL’s capacity is 20 m3. Then the cost required for all installation work of clean water and black water systems for the construction of the Exindo Group Guest House Building is Rp 2.403.791.328.

Models for predicting heavy metal concentrations in residential plumbing pipes and hot water tanks

Abstract Supply water is an important source of human exposure to heavy metals through the oral pathway. Due to stagnation of water in plumbing systems, exposure concentrations of heavy metals from tap water can be higher than water distribution systems (WDS), which is often ignored by the regulatory agencies. In this study, concentrations of a few heavy metals (arsenic (As), chromium (Cr), copper (Cu), mercury (Hg), manganese (Mn), magnesium (Mg), zinc (Zn) and iron (Fe)) and water quality parameters were monitored in WDS, plumbing pipe (PP) and hot water tanks (HWT). Multiple models were trained for predicting metal concentrations in PP and HWT, which were validated. Heavy metal concentrations in HWT were 1.2–8.1 and 1.4–6.7 times the concentrations in WDS and PP respectively. Concentrations of As, Cr, Cu, Hg and Zn were in the increasing order of WDS, PP and HWT. Concentrations of Cr and Fe were higher during summer while Cu and Zn were higher in winter. The models showed variable performances for PP and HWT (R2: PP = 0.61–0.99; HWT = 0.71–0.99). The validation data demonstrated variable correlation coefficients (r: PP = 0.45–0.99; HWT = 0.83–0.99). Few models can be used for predicting heavy metals in tap water to reduce the cost of expensive sampling and analysis.

Comprehensive methodology for identifying tariff zones of efficiency of hydrogen-thermal accumulation system at the NPP

In countries with developed nuclear energy, there are problems associated with non-uniformity of the daily electricity load, due to the economically justified need to load nuclear power plants with a maximum installed capacity utilization factor. This is due to the cheapness of nuclear fuel compared to organic and, at the same time, high investment compared to thermal power plants, as well as the presence of technological limitations on maneuverability. Most organic fuel thermal power plants are switched to half-peak mode, which negatively affects their efficiency and reliability.In addition, the ever-increasing requires on the level of safety negatively affect the economic competitiveness of nuclear power plants. Improving safety through the introduction of passive heat removal systems of the reactor core is provided for in new NPP projects. These systems have several disadvantages: maintenance costs; a significant increase in capital investment; emergency cooling mode.To solve these problems, the authors developed a system of hydrogen-thermal accumulation, which, when combined with a nuclear power plant, allows one to accumulate cheap energy during the hours of a decrease in load in the power system due to electrolysis of water to produce hydrogen and oxygen, and thermal accumulation of hot water in heat-insulating tanks. Thanks to the use of hot water tanks, investment in the accumulation system is significantly reduced. Thanks to the use of a hydrogen-oxygen steam generator, the opportunity to generate an additional main steam and to use it in the additional steam turbine unit appears, which will allow to avoid costly modernization of the main equipment of the nuclear power plant and reducing its lifetime. The presence of a low-power steam turbine unit as part of the accumulation system ensures uninterrupted autonomous power supply to consumers of the NPP own needs due to the possibility of using the energy of the reactor residual heat, when the station is completely blackout. The method of combining the hydrogen complex with thermal accumulators is completely new and has no analogues.The economic efficiency of the developed energy complex has been investigated. The accumulated net present value was determined depending on the off-peak electricity tariff for the three options of the half-peak electricity tariff, taking into account possibility to refuse expensive heat exchangers of the passive heat removal systems. It is shown that the use of the proposed scheme is advisable in regions with off-peak electricity tariffs in the range 0–0.32 cents/kW·h, 0–0.8 cents/kW·h and 0–1.25 cents/kW·h, respectively, depending on the forecast dynamics of the half-peak electricity tariff. The average payback period of the accumulation system for given conditions is equal to 3–15 years.

Exergoeconomic and exergoenvironmental analysis of the evacuated tube heat pipe; a experimental study

In this paper, the effect of the different parameters such as solar radiation, and ambient temperature on thermodynamic performance of a Water-in-glass evacuated tube heat pipe (ETHP) is studied, including energy, exergy, environmental, economic analysis, and sustainability index. The ETHP system is evaluated under the 4E criteria; energy, exergy, economic, and environment. The energy, exergy, environmental, enviroeconomic, exergoenvironmental, exergoenviroeconomical analysis and sustainability index of the ETHP system is calculated. There are 4 collectors each collector 57 pipes as a total of 108 pieces pipes, a hot water tank, a heat exchanger, and a pump in the system. The water is used as a working fluid due to economic, and common use in the system. In the result of this experimental study, we calculated energy and exergy efficiencies of the EHTP system as %60.74 and %40.72, respectively. In addition, the environmental, exergoenviromental, enviroeconomic, and exergoenviroeconomic values of the EHTP system are found 5958.01 kgCO2/day, 5564.72 kgCO2/day, 0.7448 $/day and 0.6958 $/day, respectively. Also, the sustainability index of the system is found as 1.687.

Planning level sizing of heat pumps and hot water tanks incorporating model predictive control and future electricity tariffs

Heat pumps and hot water tanks in local energy systems require sizing to increase on-site renewables self-consumption; decrease costs through variable electricity pricing; and utilise low-cost wind power. While detailed tools can capture these mechanisms, planning-level tools lack functionality and miss these benefits. In this paper an open-source planning-level modelling tool, PyLESA, is presented and applied to a sizing study to demonstrate the capturing of these benefits at the planning-level. Specific aims of the study were to investigate: (i) model predictive control vs. fixed order control, (ii) existing and future wind-influenced electricity tariffs, and (iii) optimal cost size combinations of heat pump and hot water tank. The lowest levelized cost of heat for the existing tariffs was for a time-of-use tariff, 750 kW heat pump and 500 m3 hot water tank combination. For the future wind-influenced tariff a 1000 kW heat pump and 2000 m3 hot water tank was cost optimal and showed model predictive control benefits over fixed order control with levelized heat costs reducing 41 %, and heat demand met by renewables increasing 18 %. These results demonstrate PyLESA as capable of capturing flexibility benefits at the planning stage of design and quantify the advantage of combining flexible tariffs with model predictive control.

Model predictive control for a heat booster substation in ultra low temperature district heating systems

District heating systems may support an increased penetration of stochastic renewable energy technologies and a reduction in centralized combined heat and power plants to reduce carbon dioxide emissions. Ultra low temperature district heating minimizes transport heat losses while enabling the utilization of low-grade surplus heat. Local heat booster substations can heat water to useable temperatures using a heat pump and a hot water tank for storage and flexible operation. This paper proposes a hybrid model predictive control strategy in which an existing heat booster substation is modelled and its charging schedule optimized in real-time over a 24-h forecasted prediction horizon. This enables load shifting whereby scheduling of the heat pump minimizes operation costs. The realisation of energy flexibility can support greater utilization of renewable energy sources and surplus heat in energy supply systems to reduce primary energy consumption. The linear hybrid model predictive controller was successfully implemented in a real 22-flat multifamily building in Copenhagen to verify the control strategy. A comparison of the proposed model predictive control scheduling to the standard rule-based control showed average savings of 23 % on the electricity costs.

Operational envelope and performance enhancement of a two-bed adsorption cooling system

Along with the measures to improve the design of the adsorption cooling systems, the operating strategy selection plays an equally important role in their performance enhancement. Though several strategies such as heat recovery, mass recovery, multi-staging, etc., have been reported in the literature, their implementation in the more popular small-scale two-bed systems has not been given due attention. The present study highlights the performance enhancement of a two-bed single-stage silica gel-water adsorption cooling system through novel interventions in the operating cycle. A facility has been developed for testing a 10 kW water-cooled adsorption chiller. Passive heat recovery and two-stage operational strategies have been proposed for the enhancement of performance and operational envelopes through modifications in the chiller’s valves sequencing. An improvement of 23–42% in coefficient of performance (COP) is observed with an optimized passive heat recovery strategy, while maintaining the water level in the hot water tank. Two kinds of two-stage operations viz., conventional two-stage and reheat two-stage, show potential for performance improvement under extreme conditions, resulting in an operational envelope enhancement up to 56%. A theoretical approach based on the thermodynamic analysis of adsorbent limits has been presented to assess the maximum desorption temperature limits.

Applicability of thermal energy storage in future low-temperature district heating systems – Case study using multi-scenario analysis

With the flexibilities added from thermal energy storage (TES) technologies, low temperature district heating (LTDH) system can coordinate the heat and electricity sectors in a cost-effective manner. Such combinations have therefore become an important step to achieve a 100% renewable energy system. Despite the importance of TES has been demonstrated in previous studies, giving drastic changes compared to the current systems, the practical applicability of TES in the LTDH systems remains unknown. Furthermore, the proposed benefits of TES might deviate from the expectations considering the development of future characteristics, such as the low temperature levels and small space-heating demand. This study investigates the performances and benefits of four typical short-term TES technologies, including the use of central water tank (CWT), district heating network inertia, domestic hot water tank (DHWT), and building thermal mass, based on a case LTDH system in Roskilde, Denmark. Techno-economic analysis is conducted on a variety of scenarios, based on future changes in operation of the heat sources to the end-users. An integrated model is also developed to simulate the operation dynamics of the district heating system with regards to optimizing the use of the TES units. This study provides a performance map of the TES technologies in accordance with the transitions from current to future LTDH systems, indicating the relationships between the system characteristics and optimal TES applications. The CWT is found to be most preferable for integrating the variable renewable energy due to its ability to store heat for long periods. In the end-use side, with the improved building performances and reduced space heating demand in the future, there is less potential for the use of building inertia. In contrary, the benefit of the DHWT, which mainly comes from the reduction of bypass loss during the non-space-heating period, is increased in the future. Furthermore, raising the network temperatures for active storage is found to be infeasible under all future LTDH scenarios because this measure significantly influences the heat source efficiency.

Influence of Natural Weather Conditions in the Long-Term Fracture Energy of Glass Fibre Reinforced Cement (GRC) Modified with Chemical Additions.

The use of glass fibre-reinforced cement (GRC) in structural elements has been limited due to the reduction in the mechanical properties of the material with aging. Chemical additions have been used to modify the cement mortar formulation in order to minimise such loss, but no conclusive results have been obtained yet. Moreover, the application of accelerated aging methods in such modified GRC formulations still poses several uncertainties. An experimental campaign seeking to assess the reduction in the fracture energy of two GRCs manufactured with modified matrixes after five years of exposure to natural environment was performed. Furthermore, a comparison with results from the literature that used accelerated aging methods was performed. The results show that the use of the chemical additives might be capable of maintaining to a notable extent the mechanical properties of GRC after five years of natural aging. Regarding the accelerated aging method by means of immersion in hot water tanks, it seemed that the equivalences applied in previous research accurately match the degradation of the material after natural exposure to weather. Additionally, a digital image correlation analysis showed that aged GRCs seemed to distribute damage in a smaller area than young GRCs.

Investigation of the presence of Legionella pneumophila in water samples from Erzurum and surrounding provinces in Turkey.

Legionnaires' disease, which is a waterborne disease leading to pneumonia that can result in death, is one of the major health issues today. The study aims to carry out a three-year retrospective review of routine Legionella follow-up analyses in various samples taken mostly from hospitals in the province of Erzurum and nearby provinces, and to discover a the frequency of isolation of the agent and serogroups from each kind of media. The study included a total of 2,025 water samples taken from hospitals, hotels, Turkish baths and shopping malls in Erzurum,and 13 nearby cities between 2016 and 2018. Samples were filtered by 0.45 μm-diameter membrane filter paper in the Public Health Laboratory of Erzurum and examined for L. pneumophila using culture method, according to the criteria set out in ISO 11731-2. The presence of L. pneumophila was found in 65 of the 2,025 water samples taken in hospitals, and in none of 40 samples taken in hotels, Turkish baths and shopping malls. L. pneumophila serogroup 2-14 was detected in 46 (70.8%) of 65 samples found positive, whereas L. pneumophila serogroup 1 was detected in 18 (27.7%). Furthermore, both the L. pneumophila serogroup 2-14 and L. pneumophila serogroup 1 were detected simultaneously in one example (1.5%). The first three samples indicate that the highest positivity rates were in hot water taps (11.6%), hot water tanks (6.1%) and shower heads (4.8%). The Prevalence rat of L. pneumophila was found to be quite low compared to other studies conducted in the western regions of Turkey. Legionella positivity was found to be higher in the hot water systems of hospitals and related points, compared to the other sample points.

Integrating paraffin phase change material in the storage tank of a solar water heater to maintain a consistent hot water output temperature

The temperature of the hot water withdrawn for a solar water heater varies throughout a day. However, for process heat applications, constant temperature water can be required from a solar water heater. This is usually achieved by providing additional auxiliary heat input. Disadvantageously, such extra water heating incurs additional cost and, if met from fossil fuels, produces greenhouse gas emissions. An alternative approach of using a phase change material to moderate variations in the outlet temperature of hot water from the store is examined in this paper using an experimentally-validated CFD model of a solar water heater with a phase change material thermal energy storage in the hot water tank. The CFD model was solved by COMSOL Multiphysics. For a particular solar water heating system, incorporating an encapsulated paraffin wax phase change material has been shown to able to deliver up to 1200 L of hot water at a temperature of 60 °C ± 2 °C for more than 8 h.

Decarbonizing heat with PV-coupled heat pumps supported by electricity and heat storage: Impacts and trade-offs for prosumers and the grid

Heat pumps play an important role in decarbonizing the heating supply of buildings and they allow to increase the self-consumption of PV electricity, especially when supported by electricity or heat storage. In this study, we develop an open-source model to optimize PV-coupled heat pumps, with and without electricity and heat storage, and we compare their performance for three types of single-family houses with different thermal envelope quality paired with 549 electricity profiles. We analyze trade-offs between prosumer benefits and grid impacts, namely bill minimization, and maximum grid relief, depending on the type of storage and incentives for grid peak reduction (i.e., a capacity-based tariff). We conclude that the use of heat storage reduces the levelized cost of meeting the electricity demand between 13–26% compared to the baseline case without storage, in particular when heat pumps are used for both space heating and domestic hot water (DHW). Regarding total self-consumption rates, both storage technologies, namely batteries and hot water tanks (which supply both space heating and DHW) achieve similar rates ranging between 30–39%. In contrast, batteries are found to be very effective in reducing the peak demand (14–17% compared to the baseline scenario), but only if the retail tariff has a capacity-based component. Interestingly, the quality of the envelope plays a key role and heat pumps can double the power peak demand in poorly insulated houses, with thermal storage increasing the power peak demand further up to 8%, compared to the baseline, regardless of the storage technology. Thus, we conclude that policy makers should promote thermal retrofitting of the building stock to avoid the upgrading of the distribution grid.