Characterization of thermal stratification in a horizontally-configured electric water heater (EWH) storage tank

Published: 18 October 2023| Version 1 | DOI: 10.17632/ddmv4w434g.1


This dataset encompasses data for static heating and cooling modes, as well as dynamic water events for a horizontally-configured domestic electric water heater (DEWH) with a capacity of 150 liters. The model name of the device is "Kwikot Superline". The tank is equipped with a heating coil having a nominal power of 3 kW and insulation which provides a B-class energy rating as per South African national standards (SANS) 151, which limits standing losses to 2.59 kWh/24h. The specimen tank is located in a laboratory within the Faculty of Electrical and Electronic Engineering at Stellenbosch University, South Africa. The data were collected using a custom-built test bench designed to assist in characterizing the thermal response of the specimen tank. The test bench has the capability to emulate and control ambient temperature using a climatic chamber, emulate inlet water temperature, mimic user behavior by controlling water usage patterns, and manage electrical switching frequencies and conditions for the heating element. Additionally, a custom data acquisition module was specifically designed and built for this purpose, highlighting the capture of thermal stratification within the tank, outlet water temperature, environmental temperatures (ambient and inlet water), energy usage, and water usage. The internal stratification measurement unit was designed and built to measure three-dimensional temperature distributions within the specimen tank, with the most significant data being the stratification data in the plane of gravity. Five different vertical busses were installed in the tank to measure stratification at different longitudinal locations within the tank. Although radial temperatures were also recorded, no significant differences were observed. Environmental and operational data, such as input power to the heating element, ambient (chamber) temperature, inlet water temperature, outlet water temperature, flow rate of water discharge events, and laboratory temperatures, were also recorded. Schematics of the test bench and internal temperature measurement device are provided in the "Schematics" folder, offering a reference to sensor locations that directly correspond to those seen in the datasets. A description of the dataset structure is also provided in the "Experimental Data" folder, which describes the variables, their corresponding data types, units, and formats. Please note that all provided datasets are raw and unprocessed. Data formats: CSV, JSON, MATLAB Data


Steps to reproduce

The steps to produce the datasets are outlined in great detail in the published works in the provided related links. Summary: In order to obtain the objective for EWH control and measurement, two main systems are required. 1. A control system that is specifically designed and fitted to provide the thermostat feedback and control, as well as an environmental chamber to produce the required ambient temperatures. 2. A data acquisition module that is capable of reading an abundance of temperature data, energy data and water event data. The most useful protocol that was used to measure temperature was the "1-wire" protocol since it allowed the measurement of multiple temperature sensors on a single bus. Most of the temperature sensors applied in the test bench were DS18B20 temperature sensors that were compatible with the protocol. The DAQ module was constructed and programmed using a ARM based microcontroller. In terms of experimentation, there are a few things to consider for thermal characterisation: 1. Thermal step response and regulation - Starting from a uniform temperature and activating the heating coil until set point is reached followed by tank uniformity. 2. Thermal diffusion between layers after a water draw event 3. Effect of ambient temperature on water cooling rate One of the findings from this data is that the temperatures along the longitudinal length and radial width, don't vary significantly. Thus, when reproducing the data, one can consider reducing the number of vertical busses for smaller measurement packages. This assumes that the temperature along these lengths are uniform.


Stellenbosch University Faculty of Engineering, Stellenbosch University


Electric Power, Temperature, Energy Storage, Thermal Energy Storage, Thermal Energy, Thermostatically Controlled Loads