A Computationally Inexpensive Energy Model for Horizontal Electric Water Heaters With Scheduling

Abstract

Electric water heaters (EWHs) remain one of the main contributors to energy consumption in countries where they are used. EWH models serve as a step towards achieving optimised control, and can also be used to inform users of expected savings due to changes, if the model is energy-based. Various models have been proposed, but none of them include more than half of the six key features that the model presented in this paper supports: horizontal orientation; schedule control; low computational complexity; validation of the model; multinodal stratification; and multinodal standing losses. The presented model is validated against six datasets: four comprising 900 hours with multiple water usage events; and two with only standing losses. The results show that the model estimates energy consumption over ten days including usage with an error of less than 2% and 5% for schedule control and thermostat control respectively. The simulation model is simple enough to execute ten days of simulation in less than 100 milliseconds on a standard desktop machine, 150 times faster than a prominent model from literature, making it also suitable for large scale simulations or for use on mobile devices.

Saving on household electric water heating: What works best and by how much?

“…A two-node physical model of an EWH, presented in [9], is used to simulate the thermodynamic response (and therefore energy consumption) of an individual EWH. This model was validated using consumption data from a household EWH which included x days and y usage events.…”

How much energy can optimal control of domestic water heating save?

“…Subsequently, Nel et al (2016a) presented a more accurate model with the explicit purpose of modelling energy used for water heating under schedule control. Their model makes provision for horizontally mounted water heaters (the most common orientation found in South Africa) under thermostat-based and scheduledbased heating control.…”

“…Scheduling schemes need to account for the device's thermal behaviour, water draw patterns and customer comfort and convenience (Gholizadeh and Aravinthan, 2016;Roux et al, 2018). Thermal models for water heaters, and algorithms for their control, are described extensively in the literature for smart grid applications (Goh and Apt, 2004;Nehrir et al, 2007;Du and Lu, 2011;Lu et al, 2011;Diao et al, 2012;Diduch et al, 2012;Booysen et al, 2013;Boudreaux et al, 2014;Nel et al, 2016a;Kepplinger et al, 2015;Gholizadeh and Aravinthan, 2016;Zuniga et al, 2017;Ahmed et al, 2018;Hohne et al, 2018;Jack et al, 2018;Kapsalis et al, 2018;Lunacek et al, 2018;Kepplinger et al, 2019;Gerber et al, 2019). However, only rarely are the proposed models explicitly considered as a means to reduce the overall energy used for water heating, and the resulting greenhouse gas emissions.…”

Combining grid-tied PV and intelligent water heater control to reduce the energy costs at schools in South Africa

“…The building's EWH water consumption and energy usage was captured with smart water heater controllers that were retrofitted to all seven EWHs installed within the school, and simulated for the three intelligent water heater configurations discussed in Section 2. Since all the EWHs are mounted horizontally, the norm in South Africa, the EWHs are modelled using the computationally efficient two-node model proposed by Nel et al (2018).…”