Water Heater Load Research Articles

Effect of Full Implementation of Domestic Solar Water Heaters on the Electricity Peak Load in Libya

Electricity plays an important role in the contemporary life, and it has become indispensable nowadays. Reducing the peak electricity load and increasing the load factor have been considered as one of the main tasks that have to be accomplished by both electricity generation-side and demand-side managements.The residential sector of Libya consumes over 31% of the total sold electricity, and 29.8% of that is delivered to the electric water heating load. This is an inefficient way of electricity utilization. Usually, the electricity supplier in Libya used to increase the local generation capacity or import electricity from neighboring countries. Both solutions did not resolve the problem. This work attempts to investigate the effect of replacing electric water heaters in the residential sector of Libya by solar water heaters on reducing the electricity peak load and increasing the load factor. The results show that on average 3% of the peak load demand can be saved. This is equivalent to 149.5 MW of reduced power. The study also revealed that the annual amount of energy saved is up to 2.55TWh, and the load factor is improved by 2% (i.e. from 65% to 67%). This saved energy is equivalent to a power plant with a nominal capacity of 448 MW considering a load factor of 0.65.

Energy and Conventional Exergy Analysis of an Integrated Transcritical CO2 (R-744) Refrigeration System

This study analyses the performance of an integrated transcritical CO2 (R-744) refrigeration system operating in winter conditions within a supermarket in Trento, north Italy. This system fulfils multiple functions, providing the heating (for domestic hot water and space heating), cooling, and freezing capabilities for the supermarket. Energy analysis reveals that the average value of the total coefficient of performance, total COP, over the entire study period is calculated at 2.47. Notably, the medium-temperature (MT) compressor rack exhibits the highest power consumption, especially in sub −5 °C conditions. The auxiliary (AUX) compressor rack and the gas cooler (GC) fan contribute significantly to the electrical power usage. The air conditioning (AC) heating load is consistently high, averaging 41.6 kW, while the domestic hot water (DHW) heating load remains stable at approximately 5 kW. The refrigeration demands include an average MT cooling load of 25.86 kW and a low-temperature (LT) freezing load of 10–15 kW, with an average of 13.76 kW. The current study also delves into exergy analysis, disclosing an overall system exergy efficiency of 22.4%. The AUX compressor rack is identified as the primary exergy destructor, followed by the GC, AC coils, MT compressor rack, and the ejector. The LT compressor rack has the highest exergy efficiency, followed by the MT and LT expansion valves.

A simplified control method for a water heating load coupled to a hybrid energy system to improve inverter longevity

In this paper, the temperature characteristics of an inverter is determined through experimental validation. The experiment involves testing under two load scenarios. The first of which considers a low inverter load, which represents a baseload at approximately 18% of the maximum rated power of the inverter. The second includes an energy intensive water heater load, which increases the loading on the inverter to above 85%. The aim of this paper is to ensure that the operating limits with respect to the inverter temperature is maintained to at least 10% below the upper limit of the device. The experimental results indicated that the rate of change of the inverter temperature was 2.988 °C/min when loaded above 85% and −1.277 °C/min after returning to the 18% rated output power level. This indicated that if the inverter is subjected to a high load of above 85% for a certain amount of time and the operating temperature has reached its acceptable maximum limit, roughly twice the amount of time is necessary to cool the components down enough for another high loading event. A basic fuzzy logic control method is proposed to maintain the inverter temperature within acceptable limits to improve overall inverter longevity.

New Evacuated Tube Solar Collector with Parabolic Trough Collector and Helical Coil Heat Exchanger for Usage in Domestic Water Heating

Buildings represent approximately two-thirds of the overall energy needs, mainly due to the growing energy consumption of air conditioning and water heating loads. Hence, it is necessary to minimize energy usage in buildings. Numerous research studies have been carried out on evacuated tube solar collectors, but to our knowledge, no previous study has mentioned the combination of an evacuated tube solar collector with a parabolic trough collector and a helical coil heat exchanger. The objective of this paper is to evaluate the thermal behavior of an innovative evacuated tube solar collector (ETSC) incorporated with a helical coil heat exchanger and equipped with a parabolic trough collector (PTC) used as a domestic water heater. To design the parabolic solar collector, the Parabola Calculator 2.0 software was used, and the Soltrace software was used to determine the optical behavior of a PTC. Moreover, an analytical model was created in order to enhance the performance of the new model of an ETSC by studying the impact of geometric design and functional parameters on the collector’s effectiveness. An assessment of the thermal behavior of the new ETSC was performed. Thus, the proposed analytical model gives the possibility of optimizing ETSCs used as domestic water heaters with lower computational costs. Furthermore, the optimum operational and geometrical parameters of the new ETSC base-helical tube heat exchanger include a higher thermal efficiency of 72%. This finding highlights the potential of the heat exchanger as an excellent component that can be incorporated into ETSCs.

Product Refrigeration Load Analysis On Contact Plate Freezer On Compressor Performance At PT. Trimitra Makmur, Tarakan, North Kalimantan

Contact plate freezer (CPF) is a cooling machine unit for freezing products which of course will maintain product freshness. In Order to runs smoothly, one thing that must be considered of the cooling system is the cooling load on the freezer contact plate. The cooling load is the amount of heat absorbed per unit time. The refrigeration cycle at PT. Trimitra Makmur uses a combined refrigeration cycle (multi-stage cycle), uses two cycles of vapor compression using two single-stage compressors. The two compressors used have the same power of 55.92 kW. The cooling load on the contact plate freezer consists of product heat load, water heat load, internal heat load, and transmission heat load. In The contact plate freezer, infiltration or heat load from the outside air are not counted because during production the contact plate freezer door is closed tightly so that the air exchange value is very small and can be neglected. In this study, the average total load on contact plate freezer 1 was 23.07079 kW, so that the average total load on the three contact plate freezers at PT. Trimitra Makmur is 69.21237 kW. The results of data collection and calculations show that the COP (Coefficient of Performance) value for the high-stage cycle is 4.33, so that the high-stage compressor power used is 1/4.33 of the cooling capacity of the contact plate freezer. Whereas in the booster cycle, a COP of 6.49 was obtained, so that the booster compressor power used was 1/6.49 of the cooling capacity of the contact plate freezer. 

Heat Utilization Characteristics of Two Sensible Heat Storage Vegetable Oils for Domestic Applications

The heat utilization characteristics of two different sensible heat storage vegetable oils for domestic applications are evaluated. Heat utilization is the heat delivered to the cooking fluid/load. The two sensible heat storage vegetable oils are sunflower oil, and Roki oil (a blend of palm oil and sunflower oil). The heat utilization characteristics of the two heat storage materials are experimentally determined in water heating experiments using 1.0, 1.5, 2.0, and 2.5 kg water loads. The stored heat in Roki oil and sunflower oil is used to heat up the water during cool down/heat utilization tests. The reason for the research is that new insights into the utilization of a locally available vegetable oil (Roki oil) in Uganda, as a sensible thermal energy storage material, is determined. Additionally, a new storage pot is designed, tested, and compared with Roki oil and sunflower oil as sensible thermal energy storage materials. The highlights of the work are that average heat utilization values are dependent on the water heating load. The average heat utilization efficiency increases with the increase in the water heating load; Roki oil shows higher heat utilization and higher average heat utilization efficiency values as compared to sunflower oil; the average heat utilization and average heat utilization efficiency values increase with the increase in the water load for both Sunflower oil and Roki oil. The results suggest that Roki oil is a potential heat storage material for domestic applications since it shows better heat utilization characteristics than sunflower oil during heat utilization.

Impact of recent district heating developments and low-temperature excess heat integration on design of industrial energy systems: An integrated assessment method

One of today’s biggest challenges is taking effective measures to mitigate negative effects and consequences of human-made climate change such as sector coupling and excess heat valorization. In this work, sector coupling of residential and industrial heat supply are considered in an optimization-based design and operation evaluation for industrial energy supply systems with the aim of minimizing costs and determining the impact of on-going developments and progresses in district heating systems. The developed method is applied to a use case with a superstructure for the industrial energy system including a biomass-fired steam generation unit, two heat pumps and various thermal storages, generic industrial load profiles for steam, hot water and excess heat and simulation-based district heating load profiles. The most relevant results reveal that depending on the district heating setting total annual costs, including fuel costs and annualized investments, increase between 2 and 39% compared to no additional district heating supply by the industrial energy supply system. However, the lowest cost increase does not coincide with the lowest additional energy amount. Thus, synergies such as corresponding temperature levels between energy supply for all domains have been identified as crucial criteria for economic success. Also, unit integration for excess heat recovery occurs always combined with thermal storages adapting the temporal occurrence of excess heat. Results for the evaluated use case highlight the importance and relevance of combined considerations for sector coupling measures. Thus, methods, as presented in this work, can contribute crucial information for future assessments. However, further development of the model, e.g. a larger set of generation technologies, and further use cases with other temperature levels, demand profiles are identified as relevant next steps.

The Use of Solar Water Heaters in Iraq An Economic Study

The Iraqi electrical system suffers from an increased electrical load for the available generation, which leads to the separation of a large number of consumers, especially during the peak load period. The water heating load represents a great value, so reducing water heating consumption can reduce the cut-off times. Solar water heaters possess many benefits. Therefore, they are used in many countries in the world today. The climate of Iraq is mostly hot and sunny. This makes using a solar water heater is convenient for consumers, especially in urban areas. For studying the use of solar water heaters in the residential sector, three consumers were selected in Mosul city in northern Iraq. Each consumer differs from the others by the value of their consumption of electrical energy (high, medium, and low). Electricity tariffs for the residential sector in Iraq vary, depending on consumption. The information for the three consumers was obtained from a previous questionnaire. In addition to obtaining their needs for hot water, the results of using solar water heaters on the roofs of the three houses of consumers showed a decrease in electricity consumption and a noticeable saving in the electricity bill. The payback period of the solar water heater system was calculated for each consumer. Reducing consumption reduces the gap between generation and load, resulting in reduced programmed shedding times for consumers. For these benefits and environmental features, it is necessary to generalize the use of solar water heaters in the residential sector in Iraq.

Hybrid thermochemical sorption seasonal storage for ultra-low temperature solar energy utilization

The effective upgrading and utilization of low or ultra-low temperature heat (below 50 °C) could meet a significant fraction of space and water heating loads. To fulfill this goal, hybrid sorption thermal energy storage (TES) to recover ultra-low grade solar heat below 50 °C is investigated, aiming to address the issue of winter heating in severe cold regions. A water-based solar photovoltaic-thermal (PVT) system is integrated to provide heat and electricity for a sorption TES system. Composite ammonium chloride is used for thermodynamic prediction in terms of weather conditions in different places. It is demonstrated that when water temperatures increase from 31.4 °C to 51.2 °C, energy efficiencies of hybrid sorption TES system under theoretical and selected working conditions in Hangzhou increase from 0.52 to 0.57 and from 0.33 to 0.38, respectively. The overall exergy efficiencies of hybrid TES with the PVT system under theoretical and selected working conditions increase from 0.059 to 0.062 and from 0.046 to 0.057, respectively. The overall exergy efficiency of the hybrid system in Helsinki is 0.55, which is 4.3% higher than those in Hangzhou. One remarkable fact is that hybrid sorption TES integrated with the PVT system is quite promising especially for severe cold regions.

Non-linear grey-box modelling for heat dynamics of buildings

This paper introduces a non-linear grey-box (GB) model based on stochastic differential equations that describes the heat dynamics of a school building in Denmark, equipped with a water-based heating system. The building is connected to a local district heating network through a heat exchanger. The heat is delivered to the rooms mainly through radiators and partially through a ventilation system. A monitoring system based on IoT sensors provides data on indoor climate in the rooms and on the heat load of the building. Using this data, we estimate unknown states and parameters of a model of the building’s heating system using the maximum likelihood method. Important novelties of this paper include models of the water flow in the circuit and the state of the valves in the radiator thermostats. The non-linear model accurately predicts the indoor air temperature, return water temperature and heat load. The ideas behind the model lay a foundation for GB models of buildings that use different kinds of water-based heating systems such as air-to-water/water-to-water heat pumps. Such GB models enable model predictive control to control e.g. the indoor air climate or provide flexibility services.

Comparative Performance of Low Global Warming Potential (GWP) Refrigerants as Replacement for R-410A in a Regular 2-Speed Heat Pump for Sustainable Cooling

Heat pumps are currently being developed to reduce the energy footprint for residential and commercial building space conditioning and water heating loads in cold climates. To mitigate the nocuous impact of greenhouse gas emissions on the environment, and to create a carbon-neutral building stock, alternate lower-GWP refrigerants must also replace the predominant use of R-410A, without re-engineering the mechanical hardware. In this paper, we analyze the performance of lower-GWP alternative refrigerants (R-32, R-452B, R-454B, and R-466A) relative to the conventional R-410A and draw conclusions on the relative performances to meet cooling loads. The simulations are accomplished using the heat pump design model, a well-known, public-domain design tool with a free web interface and downloadable desktop version to support public use and the HVAC R&D community. The contributions contain detailed, hardware-based heat exchanger and system analyses to provide a comprehensive assessment. The results of the simulation are scrutinized from the first (capacity and energy efficiency) and second laws (exergy analysis) to identify sources of systemic inefficiency, the root cause of lost work. This rigorous approach provides an exhaustive analysis of alternate lower-GWP refrigerants to replace R-410A using the same hardware. The results have practical value in engineering heat pumps in an economy that is compelled to alter by the consequences and uncertainties of climate change, to reduce its anthropogenic carbon footprint.

Effect of Full Implementation of Domestic Solar Water Heaters on the Electricity Peak Load in Libya

Electricity plays an important role in the contemporary life, and it has become indispensable nowadays. Reducing the peak electricity load and increasing the load factor have been considered as one of the main tasks that have to be accomplished by both electricity generation-side and demand-side managements.The residential sector of Libya consumes over 31% of the total sold electricity, and 29.8% of that is delivered to the electric water heating load. This is an inefficient way of electricity utilization. Usually, the electricity supplier in Libya used to increase the local generation capacity or import electricity from neighboring countries. Both solutions did not resolve the problem. This work attempts to investigate the effect of replacing electric water heaters in the residential sector of Libya by solar water heaters on reducing the electricity peakload and increasing the load factor. The results show that on average 3% of the peak load demand can be saved. This is equivalent to 149.5 MW of reduced power. The study also revealed that the annual amount of energy saved is up to 2.55TWh, and the load factor is improved by 2% (i.e. from 65% to 67%). This saved energy is equivalent to a power plant with a nominal capacity of 448 MW considering a load factor of 0.65

Energetic and exergetic performance comparison of three solar cookers for developing countries

Three different domestic solar cookers are compared experimentally during water heating experiments using different loads. The solar cookers experimentally tested using energy and exergy thermal performance parameters are: a solar box cooker without a reflector, a solar box cooker with a reflector and a parabolic dish solar cooker. The rate of heat losses is more detrimental to the performance of the parabolic solar cooker since the cooking vessel is exposed more to the ambient weather conditions. Heat losses seem to have little effect on the performance of the solar box cookers. The solar box cooker with the reflector shows the highest average energy efficiencies, which increase with the water heating load. The parabolic solar cooker shows the lowest average energy efficiencies with the lower loads, which increase to be higher than those of the solar box cooker without the reflector at the higher loads. The solar box cooker with the reflector shows the highest average energy and exergy efficiency values, which are not dependent on the water load. The parabolic dish solar cooker shows average exergy efficiencies, which increase with the water heating load. The greatest cooking potential in terms of the speed of cooking is shown by parabolic dish solar cooker. The best overall thermal performance is shown with the solar box cooker with a reflector, but its cooking speed is rather slow when compared to the parabolic dish solar cooker. The solar box cooker without the reflector shows the worst thermal performance in most of the tested parameters except for the heat losses where it shows the lowest heat loss factors for all the experimental tests.

Optimal Dispatching of Distribution Network Considering System Flexibility and User Thermal Comfort

To solve the problem that the uncertainty of distributed generation output seriously affects the safe and stable operation of distribution network, heat load, as a potential flexibility resource, can improve flexibility and eliminate system fluctuation without increasing new equipment. Therefore, an optimal dispatching model of the distribution network is proposed in this paper to improve the system flexibility while ensuring human comfort and operation economy. Firstly, the virtual energy storage model and human thermal comfort model of electric water heater (EWH) and air conditioning (AC) load are established. Secondly, a flexibility evaluation method is proposed based on the virtual energy storage of heat load. Furthermore, to decrease comprehensive operation cost and increase system flexibility, a two-stage distributed robust optimal dispatching model, which considers three kinds of flexible resources of EWH, AC and gas turbine (GT) is constructed. Then, the norm is used to constrain the uncertainty probability of wind turbine and photovoltaic output, and the column and constraints generation (C&CG) algorithm is used to solve the model. Finally, a simulation is given to verify the effectiveness of the proposed method in improving the flexibility of distribution network.

An operational optimization method of regional multi-energy system considering thermal quasi-dynamic characteristics

With the development of the energy internet technology, the operational optimization of regional electricity-heating-gas system is becoming a research hotspot. Considering the thermal system's quasi-dynamic characteristics will make the dispatching of regional multi-energy system more accurate and the flexibility and energy efficiency of electricity-heating-gas system's operation can be improved. The quasi-dynamic characteristics of regional thermal networks are analyzed here, as well as the demand side of heating system. Based on the thermal inertia characteristics, the virtual thermal energy storage models of both thermal networks and buildings considering thermal comfort index are formulated synthetically for central heating system. By comparing the operating results of different adjustment methods, quality adjustment method was found to have the most flexibility of regional heating system control. With the hot water supply network and heating load modeling considering virtual storage, an operational optimization model of regional electricity-heating-gas system was put forward with the purpose to reduce the total operating cost. Numerical result shows the effectiveness of the proposed method. Through case study, it's found that when considering virtual energy storage specialty of both the heating supply and demand side, the heating load can be shifted across the time periods under time-of-use (TOU) price, leading to the obvious economic improvement of multi-energy system operation.

Equivalent Electric and Heat-Pump Water Heater Models for Aggregated Community-Level Demand Response Virtual Power Plant Controls

Advanced control techniques may be used to establish a virtual power plant to regulate the operation of electric water heaters, which may be regarded as a “uni-directional battery” and a major component of a hybrid residential energy storage system. In order to estimate the potential of regulating water heaters at the aggregated level, factors including user behavior, number of water heaters, and types of water heaters must be considered. This study develops generic water heater load curves based on the data retrieved from large experimental projects for resistive electric water heaters (EWHs) and heat pump water heaters (HPWHs). A community-level digital twin with scalability has been developed to capture the aggregated hot water flow and average hot temperature in the tank. The results in this paper also include the “energy take” in line with the CTA-2045 standard and Energy Star specification. The data from the experiments demonstrated that changing from an EWH to an HPWH reduces electricity usage by approximately 70%. The case study showed that daily electricity usage could be shifted by approximately 14% and 17% by EWH and HPWHs, respectively, compared to their corresponding average power. Another case study showed that both EHWs and HPWHs, coordinated with PV to reduce morning and evening peaks, could shift approximately 22% of the daily electricity.

Application of Absolute Sustainability Assessment to New Zealand Residential Dwellings

One approach to supporting the implementation of sustainable activities by industry sectors is the use of climate targets. Such climate targets have potential to be used in design and rating tools for buildings and to support government regulation for the building and construction sector. In this study, the climate targets for New Zealand residential dwellings were calculated based on assigning the global carbon budget (for limiting temperature increase to 1.5 or 2.0 °C during 2018-2050) to three building typologies: detached, medium-density housing and apartments. These budgets were assigned to the pre-existing and new-built dwellings using building stock projections for the nominated period. Separately, the climate impact of new-built dwellings in each of the three residential typologies were assessed using Life Cycle Assessment methodology. For New Zealand residential buildings, new-built dwellings exceed their 1.5 °C climate targets by a factor of 6.7, 6.8 and 10.9 for detached, medium-density housing, and apartments respectively. For the 2.0 °C climate target, these factors are 4.8, 4.8 and 7.7 for detached, medium-density housing, and apartments respectively. The results show that about two-thirds of the climate impact of residential dwellings for the period 2018-2050 is associated with preexisting dwellings rather than new-builds. The operational energy used for space heating, water heating, lighting and plug loads makes the biggest contribution to the climate impact for all typologies of pre-built residential dwellings. For new-built residential dwellings, both the operational energy and the construction materials/products contribute most of the climate impact.

A flexibility product for electric water heater aggregators on electricity markets

Electric thermal loads, such as those for space heaters, water heaters and air conditioners, due to their association with energy storage, are deferrable. Thus, they can become an effective tool to compensate for the mismatches between power generation and power demand induced by renewable sources. Load reduction and load increase may appear to be equivalent to generation increase and generation withdrawal, but there is a significant difference in the associated post-load-control energy rebound phenomena. These phenomena can provoke undesirable post-load-control changes in the demand dynamics. The contribution of this paper is twofold. First, we define a flexibility product that load aggregators could propose that would involve a mean energy increase or decrease offer for a price and also guarantee bounds on the post-load-control deviations from normal. Second, we provide aggregators with the mathematical tools to specify the maximum load relief or increase possible under specific constraints on post-control recovery dynamics. The analysis rests on successive solutions of a linear program and exploits recent results on load control based on mean field game theory. We consider the case of aggregate electric water heater loads.

Photovoltaic systems on dairy farms: Financial and renewable multi-objective optimization (FARMOO) analysis

The aim of this study was to develop a financial and renewable multi-objective optimization (FARMOO) method for dairy farms. Due to increased global milk production and European Union policies concerning renewable energy contributions, the optimization of dairy farms from financial and renewable standpoints is crucial. The FARMOO method found the optimal combination of dairy farm equipment and management practices, based on a trade-off parameter which quantified the relative importance of maximizing farm net profit and maximizing farm renewable contribution. A PV system model was developed and validated to assess the financial performance and renewable contribution of this technology in a dairy farming context. Seven PV system sizes were investigated, ranging from 2 kWp to 11 kWp. Multi-objective optimization using a Genetic Algorithm was implemented to find the optimal combination of equipment and management practices based on the aforementioned trade-off parameter. For a test case of a 195 cow spring calving dairy farm in Ireland, it was found that when the relative importance of farm net profit was high, a PV system was not included in the optimal farm configuration. When net profit and renewable contribution were of equal importance, the optimal farm configuration included an 11 kWp PV system with a scheduled water heating load at 10:00. Multi-objective optimization was carried out for the same test case with the goals of maximizing farm net profit and minimizing farm CO2 emissions. Under this scenario, the optimal farm configuration included an 11 kWp PV system when the relative importance of farm net profit was low. This study included a sensitivity analysis which investigated the use of a 40% grant aid on PV system capital costs. This sensitivity analysis did not significantly improve the financial feasibility of PV systems on dairy farms. Moreover, it was found that load shifting of a farm’s water heating enabled the majority of the PV system’s electricity output to be consumed. Hence the use of batteries with small PV systems on dairy farms may not be necessary. The method described in this study will be used to inform policy and provide decision support relating to PV systems on dairy farms.

Parametric modeling and simulation of Low temperature energy storage for cold-climate multi-family residences using a geothermal heat pump system with integrated phase change material storage tank

A novel geothermal heat pump (GHP) system with an integrated low- to moderate-temperature salt hydrate phase change material (PCM) storage tank for buildings in cold climates is proposed in this study. The purpose of the PCM storage tank is to dampen peak heating loads and to remove annual ground thermal load imbalances on the ground heat exchanger (GHX) to assist in achieving an optimally-sized GHX. As heat is extracted from the closed-loop system by heat pumps in heating mode, a significant portion of this heat is used to solidify a salt hydrate PCM. This heat of fusion is later released back into the heat transfer fluid, storing it in the PCM tank and GHX for later diurnal and seasonal use. To examine the merits of the proposed concept, electric utility meter data on 15-minute time intervals were mined from an actual apartment building and used to estimate space heating, cooling, and hot water heating loads. Those data were used in an hourly, dynamic 20-year life-cycle simulation model in TRNSYS to design an optimum combination of GHX and PCM storage, where each component was sized to balance the annual ground thermal loads. The system simulation results show significant potential for GHX size reduction with a PCM storage tank, but the system is quite sensitive to the PCM melt temperature due to significant hysteretic nature of the salt hydrate PCM heating and cooling curves. We also find that there is no unique optimum unless other factors are considered such as installation cost and physical constraints; many combinations of GHX size and PCM mass are capable of achieving the design goal with similar annual electric energy consumption. For the cases examined here, a PCM melt temperature of 27 °C yields the most favorable economic results, and a preliminary economic analysis suggests that with typical drilling cost and PCM tank cost values, the GHX size can be reduced by over 50 %.