highlights  Models for individual components of tankless gas water heaters are developed.  Experiments are conducted to determine calibration parameters for heat cell model.  Simulation for different configurations and scenarios are conducted.

Domestic hot water production is responsible for a significant part of domestic energy consumption; instantaneous gas heating devices are widely used because they don't require reservoirs, therefore have a competitive use/consumption ratio compared to other technologies. However, users' perception of comfort is severely affected by sudden changes in temperature outside the desired temperature. The instability of the water temperature with overshoots and undershoots is the most common disadvantage, which occurs mainly due to sudden changes in the water flow requested by users and the response delays inherent to the heating system. Traditional heat cell power controllers have difficulties in responding to these problems in a timely manner, as they don't have the capacity to anticipate the effects of sudden variations in water flowrate.In this work, predictive control strategies were developed which, due to its predictive nature, allows anticipating and correcting the negative effects of sudden variations of water flowrate in the temperature. A comparative analysis of model based predictive controllers (MPCs), with and without adaptive function, with traditional controllers used in the tankless gas water heaters (TGWHs) was carried out. Tests in a simulated environment demonstrated better performances in the stabilization of temperature during sudden changes in water flowrates.

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An innovative methodology and a virtual test bench are proposed to support the design of water heaters' control strategies. This platform allows to speed up the development and evaluation of control systems even before the existence of prototypes or real test environments. By simulating the environmental conditions and the state of the different device components, it will be possible to detect and correct possible initial errors in the control system design which can be time consuming and costly due to subsequent modifications to the system or equipment components. The architecture of the proposed system establishes four operating modes, open loop data acquisition, real time simulation, hardware-in-the-loop simulation, and test of the complete real system, the incorporation of these functionalities in the same platform is not reported in the literature for domestic water heaters. The virtual test bench was designed to accommodate different water heaters including, but not limited to, gas, electric and heat pumps, for instantaneous hot water production or including hot water storage. The prototype of the virtual test bench is described emphasizing the hardware-in-the-loop methodologies and embedded control. The particular case study of a tankless gas water heater is presented implementing the different operation modes in the virtual test bench. The water heater models, control strategies, simulation and experimental data are presented and discussed.