Electric Storage Water Heaters Research Articles

Peer-to-peer energy trading for demand response of residential smart electric storage water heaters

Environmental concerns and emission reduction targets are driving a transition from fossil fuel to renewable-based electricity generation. However, intermittent and distributed renewable generation brings challenges for the grid operation, as the low voltage distribution grid increasingly becomes constrained during high residential solar PV generation. The electrification of water heating presents a large opportunity to address this challenge by intelligently responding to electrical network conditions. Smart water heaters with thermal storage can soak up excess PV as a thermal battery, which facilitates maximum renewable generation and solves local grid problems. However, the centralized operation of electricity markets tends to impede the benefits of the localized distributed energy resources (DER). In such a scenario, peer-to-peer (P2P) energy trading allows neighbouring prosumers to trade energy between themselves with minimum interference from electricity grid operators. This research develops a P2P energy trading framework, using advanced, multi-zone electric storage water heaters with autonomous and aggregated control. The financial benefits identified in this research are forthcoming due to new participation in the electricity market ancillary services, demand management and P2P energy trading. Simulated results have identified that up to 92% of household water heating energy can originate from their own rooftop PV. At the electricity grid level, P2P energy trading demonstrates an increase in the aggregated PV self-consumption from 39% to 83%, importantly allowing the remaining 17% to target grid support in periods of supply shortfall. Average retail consumer energy savings of AUD$369/annum are identified, which include 17% of savings that are attributed to P2P energy transactions, delivering a capital payback of <3 years.

Detailed evaluation of electric demand load shifting potential of heat pump water heaters in a hot humid climate

Heat pump water heaters (HPWH) are a proven method of reducing water heating energy use over prevailing electric resistance systems (ERWH). Both technologies lend themselves to enhanced control for peak load reduction. Laboratory tests were conducted in Central Florida using the CTA-2045 standard to evaluate load shifting strategies with connected water heaters. Four HPWHs from three manufacturers, including two different tank volumes, were tested alongside an ERWH in a garage-like environment. Tests aimed to shift energy use away from utility peak load periods to off-peak times when excess renewable energy resources are often available. Two load-shifting strategies were shown effective, Shed and Critical Peak, with variation by manufacturer. Beyond draw volume, other factors influenced HPWH load shifting: Florida winter conditions, which increase the energy used per draw, provided the greatest challenges to complete load shift. Inlet water temperature had a large impact on the success of load reduction. Ground temperatures in which water pipes were buried largely determined inlet water temperatures. HPWH efficiency setting: Heat pump water heaters often default to a “hybrid” mode that may use some electric resistance heat to minimize risk of running out of hot water. Operational mode can impact load shifting potential.

Demand–Response Control of Electric Storage Water Heaters Based on Dynamic Electricity Pricing and Comfort Optimization

Electric Storage Water Heaters (ESWH) are a widespread solution to supply domestic hot water (DHW) to dwellings and other applications. The working principle of these units makes them a great resource for peak shaving, which is particularly important due to the level of penetration renewable energies are achieving and their intermittent nature. Renewable energy deployment in the electricity market translates into large electricity price fluctuations throughout the day for individual users. The purpose of this study was to find a demand–response strategy for the activation of the heating element based on a multiobjective minimization of electricity cost and user discomfort, assuming a known DHW consumption profile. An experimentally validated numerical model was used to perform an evaluation of the potential savings with the demand–response optimized strategy compared to a thermostat-based approach. Results showed that cost savings of approximately 12% can be achieved on a yearly basis, while even improving user thermal comfort. Moreover, increasing the ESWH volume would allow (i) more aggressive demand–response strategies in terms of cost savings, and (ii) higher level of uncertainty in the DHW consumption profile, without detriment to discomfort.

Control optimization of PV powered electric storage and heat pump water heaters

Domestic rooftop photovoltaic (PV) systems are typically installed without energy storage and power generated in excess of the building electric load must be exported to the grid or curtailed. In this paper the use of excess PV electricity for water heating is investigated, with the hot water storage tank acting as a low-cost thermal battery. A 3.6 kWp PV system installed on a domestic house with a 315 L storage hot water heater is analysed. It is shown that advanced control of the water heater is critical to make effective use of local intermittent PV power. Without appropriate controls the excess PV power can only reduce the grid energy consumption of an electric storage water heater by approximately 13%. However, with appropriate control, savings of purchased grid electricity above 80% can be achieved for electric storage water heaters. Similarly, using a heat pump, the consumption of purchased grid electricity for water heating can be reduced by close to 90% by making use of excess PV power. The use of excess PV electricity for water heating purposes can also significantly reduce export PV electricity, thereby also assisting the voltage and frequency stabilisation of the electrical distribution network.

Studies on active thermal insulation technology based on heat sink principle

Based on the principle of heat sink, the active thermal insulation technology was proposed in this article. An artificial low temperature zone was created during the adiabatic process, and the heat amount that needs to be blocked could be reabsorbed by this zone, then redistributed and recycled within the thermal equipment, without any energy loss, the thermal insulation could be achieved. To verify the effect of this technology, a heat sink device was designed and a new type electric storage water heater was converted. The device’s heat reallocation ability and equivalent thermal resistance were studied, along with the experimental method, the rationality of new type water heater was verified. The results show that an artificial low temperature zone was constructed within the water heater cavity, reduced internal and external temperature difference from 60 °C to 10.5 °C, the thermal insulation was improved. Besides that, according to exergy calculation, the heat reallocation function of heat sink device enabled the energy matching more reasonable, which is beneficial to enhance the thermal efficiency and achieve energy-saving.

Automatic testing system to evaluate the energy efficiency of electric storage water heaters

Background: The energy efficiency of electric storage water heaters is a concern for enterprises and customers because it is beneficial for energy saving. To decrease the workload of testing personnel and improve the testing efficiency, an automatic testing system for evaluating the energy efficiency performance of electric storage water heaters has been designed. Methods: The complete testing system includes a water supply subsystem, hot water outlet subsystem, hardware subsystem, and software subsystem. An application program was developed using Visual Basic to acquire the sensor data and transmit it in real time to a database server. The energy efficiency evaluating process was controlled by the application software,by combining the data acquisition technology, communication technology, and program logical control technology. Results: The designed system can run automatically and achieve reliable tests, two important parameters including the standing loss per 24 h and the hot water withdrawal rate were obtained. Conclusion: This system can be applied to evaluate the energy efficiency grades of electric storage water heaters.

Assessment of Mechanical Properties, Residual Stresses and Diffusible Hydrogen of Longitudinal Weld in Electric Water Heater Tanks

The core technique of electric storage water heaters is the manufacture of the tanks, and the welding technique is the key technology of the tank manufacture. A company producing water heaters received feedback from its after-sales that a large quantity of water leakage from the tanks was found in the market. A follow-up on the manufacturing site by the researchers showed that the position of the water leakage defects mostly happens in the welds of the tanks. Series of experiments were conducted to investigate the mechanical properties, residual stress, and diffusible hydrogen content of the longitudinal weld of the tank. Results of the mechanical properties showed that both the micro-hardness and the tensile strength of the welds are higher than the base metal. There are higher residual compressive stresses in the weld center and the adjacent-weld zone. Vertical residual compressive stress decreases first and then increases (149 MPa–28 MPa–134 MPa) from the weld ends to the middle, whilst the transversal stress decreases continuously (332 MPa~240 MPa) from the weld center to the heat affected zone. After enameling, the longitudinal welds’ peak micro-hardness of coarse grained region reduces by 30.9 HV1, and the average micro-hardness of the HAZ reduces by 5 HV1. The average vertical residual compressive stress difference of the same test points reduces from 270.6 MPa to 20.4 MPa. It proves that enameling can improve the mechanical property of the longitudinal welds.

Financial measures Serbia should offer for solar water heating systems

Hot water consumption is an important segment in the energy consumption in households in Serbia, where majority of households heat water with electric resistance storage water heaters. A more appropriate alternative is installation of solar water heating (SWH) systems in households. The current number of installed SWH systems in Serbia is negligibly small – only about 0.1% of all households. Serbia has recently adopted feed-in tariffs for generating electricity from renewable energy sources (RES), but it did not provide any incentive for SWH installations. It is generally accepted that best form of SWH incentive is a direct subsidy to reduce high upfront costs. The aim of this work is to suggest the level of the subsidy which Serbian government should offer in order to reach the level of SWH deployment comparable to that of more developed countries. After financial analysis of SWH installation in six Serbian cities, followed by contingent valuation survey among household owners in Serbia, it is concluded that 20% subsidy is justified already by CO2 mitigation potential of SWH systems, while 50% subsidy, which lowers equity payback period to 5.5–6 years, generates most interest among household owners.

Assessment of energy efficiency in electric storage water heaters

Nowadays there are several ways of supplying hot water for showers in residential buildings. One of them is the use of electric storage water heaters (boilers). This equipment raises the water temperature in a reservoir (tank) using the heat generated by an electric resistance. The behavior of this equipment in Brazil is still a research object and there is not a standard in the country to regulate its efficiency. In this context, an experimental program was conducted aiming to collect power consumption data to evaluate its performance. The boilers underwent an operation cycle to simulate a usage condition aiming to collect parameters for calculating the efficiency. This 1-day cycle was composed of the following phases: hot water withdrawal, reheating and standby heat loss. The methods allowed the identification of different parameters concerning the boilers work, such as: standby heat loss in 24 h, hot water withdrawal rate, reheating time and energy efficiency. The average energy efficiency obtained was of 75%. The lowest efficiency was of 62% for boiler 2 and the highest was of 85% for boiler 9.

Transient and Rate-Dependent Performance of Conventional Electric Storage Water Heating Systems

Electric resistance water heaters are relatively simple and are therefore one of the most common water heating configurations. Due to constraints on the allowable instantaneous electrical power draw, most electric water heating systems incorporate a sizable thermal storage component. The inherently unsteady storage component therefore has an overwhelming impact on the system behavior. In this investigation, a residential-scale electric storage water heater was tested across a range of flow rates for both powered and nonpowered discharge processes as well as for charge processes with no throughflow. The flow dynamics internal to the storage volume is shown to be strongly multidimensional and transient, especially when the internal heating elements are energized. Comparison of the measured data to the performance limits of a system with a fully mixed or a perfectly stratified storage element reveals that the conventional system operates relatively near to the fully mixed limit. As a result, there appears to be significant potential for improvements in system performance through reductions in the level of thermal mixing internal to the storage volume.

Evaluation of fuel-switching opportunities in the residential sector

The aim of this paper is to analyse the impact of different natural gas and electricity end-use technologies in the residential sector, which compete among themselves in terms of energy consumption and carbon emissions. The analysis of 17 different technology options, which were chosen in order to match the consumption behaviour of a typical Portuguese family, has shown that the use of electric heat pumps, both for space and water-heating, combined with the use of a natural gas cooker, leads to the lowest energy consumption and to the lowest environmental impacts in terms of carbon emissions. Considering only the running costs, this choice is 45% more economic than having a natural gas centralised heating system combined with a gas cooker, and is 60% more economic than having an electric resistance space heater combined with an electric storage water heater and electric cooker, which is the worst case. The life cycle cost (LCC) analysis shows that the economic optimum is reached by the combination of a natural gas water heater with an electric storage space heater, and a natural gas cooker. The cost of conserved carbon (CCC) analysis shows that the combination of an electric heat pump water heater with an electric storage space heater, and a natural gas cooker is the best option in terms of environmental performance.

Appliance efficiency programs in Australia: labelling and standards

Household appliance penetration and ownership in Australia is higher than in western Europe, and close to North American levels. Most products are manufactured locally, by firms with international links and with access to both European and North American designs and technology. A significant share of the market is imported, mainly from New Zealand, Asia and Europe. Because of the relative mildness of the climate, appliances that carry an energy label (such as dishwashers, clothes washers, clothes dryers, and refrigerators and freezers) account for a greater share of household energy use than in most other developed countries. The energy efficiency of appliances in Australia increased steadily during the early 1980s, but the introduction of mandatory energy labelling in 1986 in some states saw a significant increase in the rate of change. The mandatory government energy labelling program, which is in force in most states, now includes refrigerators, freezers, room air conditioners, dishwashers, clothes washers and clothes dryers. A voluntary industry-based gas appliance energy labelling program is also in place for gas water heaters and flued space heaters. The Australian energy labelling program is widely regarded as among the most informative and salient in the world, and it may be extended to New Zealand over the next few years (many products in NZ already carry the label as the Australian and NZ markets are closely integrated). Label recognition and use is very high among recent and prospective appliance purchasers. The use of a static efficiency scale on the label, while assisting recognition and comprehension, has also reduced the competitive pressure on suppliers, as efficiency improvements have pushed many models to the top of the rating scale. In 1995, Australian energy ministers agreed to implement minimum energy performance standards (MEPS) for refrigerators, freezers, and electric storage water heaters, to take effect in 1999. The levels are relatively moderate, and the effect will be to complement the energy labelling program rather than to transform the energy efficiency of the market.

Market Analysis: A Case Study

AVORABLE electric rates in a given area are the first characteristics determining the market possibilities for electric ranges and electric storage water heaters. Adequate wiring, while applying only to specific buildings, designates the minimum electric supply equipment at the point of installation, and ranks next to rates as a market influence. Unlike electric refrigerators, food mixers and other socket appliances effected only slightly by rates, the range and water heater present a highly specialized problem to commercial marketing which is directly concerned with basic public utility operating policies, transportation of solid fuel, laws of the several states regarding trade practices, combination which have large gas property investments as well as electric operations, and several other fundamental economic factors which definitely remove these two products from the class of plug-in appliances requiring only a convenient outlet. In I931 there were slightly more than 20 million meters installed in dwelling units in the United States, yet only eight million electric meters had rates low enough to permit electric range installations. By I94I there were 25 million electric meters and 24 million (96 per cent) had rates for electric ranges. Three cents a kwh is considered favorable, and the 1941 national average was 2.2 cents per kwh. However, there are rates as low as one cent per kwh, so even though the utility industry has recognized the revenue value of this major appliance, our market study becomes more complicated because some rates are more favorable than others. The electric storage water heater found a rate market later than the range, but has been developing even more rapidly during recent years. Only 23 per cent of the electric meters were available in I935. Today approximately 70 per cent of the meters have a rate suitable for operation of a storage water heater. Domestic meters with 1.5 cents per kwh. or less rate, are considered favorable. As mentioned, the foregoing may have the deceptive appearance of simplifying the market situation from the commercial research point of view. Actually, this rapidly shifting scene on the nation's basic domestic electric rates has caused complexities requiring increased intensity in market study. For example, each of the several hundred operating utilities across the nation has its own rate and operating policy. However, each of them does not necessarily serve an identifiable geographic area. The properties vary in size from village municipal plants with a diesel driven generator, to vast business managed systems serving millions of residential and thousands of industrial customers. While rates and service conditions are widely different, even between companies adjacent to one another, they are invariably determined by public bodies; and while they change, lower rates do not always mean a ready market for appliances. Adequate wiring for ranges and water