Domestic Hot Water Storage Tank Research Articles

Domestic Hot Water Storage Tank: Design and Analysis for Improving Thermal Stratification

Experimental designs for a solar domestic hot water storage system were built in efforts to maximize thermal stratification within the tank. A stratified thermal store has been shown by prior literature to maximize temperature of the hot water drawn from the tank and simultaneously minimize collector inlet temperature required for effective heat transfer from the solar panels, thereby improving the annual performance of domestic solar hot water heating systems (DSHWH) by 30–60%. Our design incorporates partitions, thermal diodes, and a coiled heat exchanger enclosed in an annulus. The thermal diodes are passive devices that promote natural convection currents of hot water upward, while inhibiting reverse flow and mixing. Several variations of heat exchanger coils, diodes and partitions were simulated using ansys Computational Fluid Dynamics, and benchmarked using experimental data. The results revealed that the optimum design incorporated two partitions separated by a specific distance with four diodes for each partition. In addition, it was discovered that varying the length and diameter of the thermal diodes greatly affected the temperature distribution. The thermal diodes and partitions were used to maintain stratification for long periods of time by facilitating natural convective currents and taking advantage of the buoyancy effect. The results of the experiment and simulations proved that incorporating these elements into the design can greatly improve the thermal performance and temperature stratification of a domestic hot water storage tank.

Rule-based demand-side management of domestic hot water production with heat pumps in zero energy neighbourhoods

Grid saturation has been reported in electricity distribution systems with a high penetration of photovoltaic (PV) systems. This saturation is often caused by overvoltage and results in curtailing or shutting down of the PV inverters, leading to a loss of renewable electricity generation. The presented work assesses the potential of rule-based demand-side management (DSM) applied to domestic hot water (DHW) production with heat pumps in dwellings for reducing the non-renewable energy use of the neighbourhood. The studied case consists of 33 single-family dwellings connected to a single phase distribution grid in a moderate European climate. Each dwelling is designed as a net-zero energy building by adequate design of a heat pump and PV system. A detailed dynamic simulation model is implemented by use of a cross-domain Modelica library for integrated district energy assessment. The user behaviour is obtained from a stochastic model based on Markov chains and survival analysis. Different rule-based DSM control strategies are applied to the individual dwelling's DHW systems. The results show that for balancing the PV production, active thermal energy storage in the DHW storage tanks is very promising. Even with very basic control algorithms and small storage tanks of 0.3 m3, curtailing losses can be reduced by 74%. This represents a net energy saving on a neighbourhood level of 3.4%.

EXPERIMENTAL STUDY OF HOT WATER STORAGE TANKS FROM A DOMESTIC REFRIGERATOR

The extreme necessity to diversify the sources of renewable energy motivates the search for methods of recycling of thermal energy losses of equipments. Thus, these energy losses can be used as a new source of energy for water heating and storage in a Domestic Hot Water Storage Tank (DHWST). Therefore, an experimental apparatus is proposed with a cylindrical tank for liquid storage. The main objective of this experimental test is the estimation of the coefficient of comprehensive energy performance (COP) relative to the system and the analysis of the hot water storage through the stratification technique. The storage and use of this form of energy utilizes a shell and tube heat exchanger, whose function is to condensate the cooling liquid using water in countercurrent, which substitutes the refrigerator finned condenser. Thermal energy losses are collected by the thermosiphon principle, and stored as sensible heat in the tank. The results showed the full operation of the modified refrigeration system as well as the storage of hot water at satisfactory thermal levels for domestic use, since this is a commercially manufactured refrigerator.

Refrigerator COP with thermal storage

Due to the extreme necessity to diversify renewable energy sources, the search for energy recycling methods through the utilization of thermal losses from equipment has become fundamental. Thus, these losses can be used as a new source of energy for water heating and storage in domestic hot water storage tanks (DHWST). For this reason, the construction of an experimental apparatus with a cylindrical thermal storage tank is proposed, in which the objective of the study will be a survey of the coefficient of performance concerning conventional and modified refrigerators, as well as to perform an analysis of hot water, through the thermal stratification technique using a refrigerator with a modified condenser. The collected thermal loss, as per the thermosyphon principle, will be stored as thermal energy. The results showed the full operation of the modified refrigeration system, which did not reveal significant alterations in thermodynamic behavior after the modifications made on the condenser. The dynamic behavior of the thermal distribution was observed through the thermal stratification effect and temperature evolution in terms of time, showing greater variability of the modified refrigerator generating more thermal comfort to users in addition to providing domestic hot water.

Influence of Operation Temperatures on Performance of a CO2 Heat Pump Water Heating System

An air-to-water CO2 heat pump is used in combination with a domestic hot water storage tank, and the performance of this water heating system is affected significantly not only by instantaneous ambient air and city water temperatures but also by hourly changes in domestic hot water demand and temperature distribution in the storage tank. In this paper, the influence of operation conditions such as outlet water temperature during operation and inlet water temperature for shutdown of a CO2 heat pump on the performance of a water heating system is investigated by numerical simulation. The trade-off relationship between the system efficiency and the volume of unused domestic hot water as criteria for the system performance is clarified in relation to the operation conditions. The influence of seasonal changes in ambient air and city water temperatures on the trade-off relationship is also clarified.

Influence of ambient temperatures on performance of a CO 2 heat pump water heating system

In residential applications, an air-to-water CO 2 heat pump is used in combination with a domestic hot water storage tank, and the performance of this system is affected significantly not only by instantaneous ambient air and city water temperatures but also by hourly changes of domestic hot water consumption and temperature distribution in the storage tank. In this paper, the performance of a CO 2 heat pump water heating system is analyzed by numerical simulation. A simulation model is created based on thermodynamic equations, and the values of model parameters are estimated based on measured data for existing devices. The calculated performance is compared with the measured one, and the simulation model is validated. The system performance is clarified in consideration of seasonal changes of ambient air and city water temperatures.

Experimental analysis of a domestic electric hot water storage tank. Part II: dynamic mode of operation

In this paper, the experimental analysis of a full-scale Domestic Electric Hot Water Storage Tank (DEHWST) with a capacity of 150 l is reported. The tank is equipped with three different inlets and two different outlets of practical interest. The dynamic mode of operation of the tank has been experimentally analyzed taking into account the six possible inlet–outlet port arrangements and water draw-off flow rates of 5, 10 and 15 l/min. The analysis is based on the transient temperature distributions of the outlet and inlet water flow and on the transient temperature profiles of the water inside the tank measured by an appropriate data acquisition system. Performance parameters to evaluate the thermal stratification in the tank and the discharging energy and exergy efficiencies are defined and calculated from the experimental data. The characteristic performance of the tank with different inlet–outlet port configurations is analyzed and the best one is identified and proposed to use in practice.

Experimental analysis of a domestic electric hot water storage tank. Part I: Static mode of operation

In this paper, the experimental analysis of the static mode of operation of a full-scale Domestic Electric Hot Water Storage Tank (DEHWST) with a capacity of 150 l is reported. The main purpose of the analysis is to determine the thermal behaviour of the DEHWST for the static heating and cooling periods in order to characterize its performance. The analysis is based on experimental data taken from a tank provided by the manufacturer and equipped with an appropriate data acquisition system. The storage tank, the data acquisition system and the experimental methodology are described. Performance parameters to evaluate the energy and exergy efficiencies and thermal stratification are defined and obtained from the experimental data. The results of the analysis for different heating powers and tank pressures are shown and discussed.

Design of a PV driven low flow solar domestic hot water system and modeling of the system collector outlet temperature

The system under consideration comprises a new freeze tolerant flat plate collector connected directly to a domestic hot water storage tank. Water is circulated by means of a small 12 V DC pump, driven directly by a PV module. It is desired that the system will operate with a variable low flow to provide a relatively constant outlet temperature and promote thermal stratification in the storage tank. The rationale behind employing this operational strategy is outlined, and an overview of the benefits of employing such a system is given. In respect of controlling the flow to optimize the performance of the present system, through a thorough examination of their respective characteristics and interactions, the process of selecting the most suitable combination of system components is highlighted. Furthermore, a method for determining the degree of PV output control that is required to best meet the optimum operating condition is given. System performance is then analyzed in relation to the desired operating condition. For a given pump and hydraulic system, an algorithm for predicting the collector outlet temperature in relation to the peak PV output, degree of control, collector efficiency characteristics and irradiance is presented. Predicted and measured outlet temperatures are compared, and the results discussed.

The Influence of Return Loop Flow Rate on Stratification in a Vertical Hot Water Storage Tank Connected to a Heat Pump Water Heater

A temperature-controlled hot water heat pump was simulated using heating in a vertical, domestic hot water storage tank. The influence of the return loop flow rate on stratification was investigated experimentally. The return loop is the water line that supplies a long line of consumers with hot water, and returns colder water to the middle of the hot water storage tank. The return temperature is a function of the length of the loop, insulation, and ambient conditions. Temperatures were measured as a function of time at different vertical locations on the centerline of the storage tank. The temperature distributions in the tank were compared for different return flow rates. A return flow rate of three tank volumes per day was identified as preferable, although good results were also obtained for less than three tank volumes per day.

Introducing advanced testing methods for domestic hot water storage tanks in Jordan

In Solar Domestic Hot Water (SDHW) systems the usage of hot water storage tanks is absolutely essential, and, the thermal behaviour of these tanks has a large influence on the efficiency of the entire system. To assess this influence, as well as to improve the quality of the storage tanks, it is very important to determine its parameters. Through a technical co-operation project between the Royal Scientific Society (RSS) in Amman and the Technical University of Munich (TU) (sponsored by the Forschungszentrum Karlsruhe), work was carried out: • — to apply a new development in storage testing to the existing facility at the RSS • — to examine its applicability • — to examine its reproducibility to local storage tanks made in Jordan. This paper presents the above referenced work including a description of the storage test facility and the applied ‘dynamic system testing’ procedure, which is based on the transient system simulation TRNSYS and the program for dynamic fitting DF. Through the testing of two storage tanks, it became evident that another test sequence was needed to determine the thermal vertical conductivity in the storage tanks. A new test sequence was proposed and tested to determine this parameter, which has a profound influence on the determination of certain other parameters.

Thermal performance of a residential desuperheater/water heater system

A residential desuperheater/water heater system was tested in a laboratory under controlled environmental conditions. The desuperheater, integrated to a thermal storage system, was installed in the Dual-Air Loop Test Facility at The Center for Energy Studies, The University of Texas at Austin. The major components of the system consisted of the refrigerant compressor, domestic hot water (DHW) desuperheater, thermal storage tank with evaporator/condenser coil, DHW storage tank, DHW circulating pump, space conditioning water circulation pump, and indoor heat exchanger. Although measurements were made to quantify space heating, space cooling, and domestic water heating, this paper only emphasizes the desuperheater/water heater performance of the unit. The desuperheater system was tested over a range of outdoor conditions to determine parameters such as desuperheater rate and DHW temperatures. The desuperheater rate decreased with entering water temperature, since the heat transfer between the water and refrigerant decreased as the entering water temperature increased. In addition, the desuperheater coefficients of performance decreased with entering water temperature. The DHW tank first-hour rating, F, was 52.9 gal/h. The recovery efficiency and energy factor were 0.74 and 0.77, respectively.

Performance prediction of a multi-tank domestic hot water solar plant

SYNOPSIS Poor stratification in Domestic Hot Water (DHW) storage tanks strongly reduces the performance of solar collectors. As stratification disturbances are frequent particularly in medium-large size plants, it is more realistic to consider fully mixed tanks. Multi-tank storage systems can work well even if stratification is not assured, provided that suitable connections in the tanks allow different thermal levels in every tank, forming a kind of forced stratification. Three control strategies of multi-tank systems have been simulated and compared with single-tank. Annual results demonstrate that multi-tank is a good solution in the absence of stratification. Different performances of multi-tank systems are also discussed.

Failures of Domestic Hot Water Storage Tanks★

sometimes attempt to explain fail ure by saying it is due to the chemicals in water. This bit of information often disturbs consumer, and he usually concludes that water that will eat out a galvanized-iron tank will most certainly ruin his stomach. If water supply is not chemically treated, or at most is only chlo rinated, plumber sometimes points to a nearby trolley line or transformer, which, he says, leaks electricity into pipes and destroys water tank. Tank manufacturers also have their

Failures of Domestic Hot Water Storage Tanks

sometimes attempt to explain fail ure by saying it is due to the chemicals in water. This bit of information often disturbs consumer, and he usually concludes that water that will eat out a galvanized-iron tank will most certainly ruin his stomach. If water supply is not chemically treated, or at most is only chlo rinated, plumber sometimes points to a nearby trolley line or transformer, which, he says, leaks electricity into pipes and destroys water tank. Tank manufacturers also have their