Characterisation of the primary heat replacement element event for a horizontal electric water heater

Abstract

A statistical model is developed to understand the volume of water drawn from a horizontal water heater in relation to its primary heat replacement. An experiment is designed to obtain unbiased data that can be used to build a model. The model is a combination of linear and multivariate regression-based methods that uses the primary heating duration observed on the water heater's element heating pattern. It is determined that the relation between the primary heating event and the draw volume is linear. Testing showed that ambient temperature differences can increase the precision interval to 16% if not accounted for. Points of test data are used to expand the model and reduce the error to 6%. This method can reduce the complexity of physical models by eliminating the need to consider the complex thermodynamics within the electric water heater (EWH) caused by stratification for this early iteration of the model. Through the use of a simple linear regression model, it is found that a high volume draw at a high flow rate reduces the energy required by the heating element by distributing the concentrated energy at the top of the EWH better. This temperature profile is assumed to be a result of the positioning of the thermostat in the EWH. The ambient temperature is also found to have a significant impact on energy input of the heating element for a draw event.