A methodology is proposed for the flexibility analysis of aggregates of home devices for hot water production (known as water heaters or boilers ), for the purposes of providing services for the electrical system, such as secondary and tertiary frequency control. Both the more traditional heating technology, with simple resistance (resistive boilers), and the more modern systems equipped with an inverter Heat Pump (HP) are considered. It is assumed that the devices are controlled remotely by an aggregator. External factors that influence the thermal and electrical dynamics of water heaters are considered: room temperature, cold water temperature, consumption profiles. Flexibility, defined by the variation in power that can be obtained compared to the basic profile (absorption is greater for ‘downward’ services, and lower for ‘upward’ services) and by the permissible duration of the variation, is calculated using a dynamic model of water heaters specifically developed and instantiated according to a Monte Carlo approach to represent the aggregate.

The methodology was applied, with granularity of a quarter of an hour, to hypothetical aggregates of respectively resistive and HP boilers, on the basis of the current installed capacity for resistive water heaters and a 2030 scenario for HP ones, corresponding to a typical four-month period.

Based on the simulation, the power values available for regulation in HP water heaters (approximately 1% of the installed power) are lower than power values available for resistive boilers (4% and 2% of the installed power, upwards and downwards respectively); the difference between the two technologies can be explained by the reduced temperature range that can be set in HP water heaters. Furthermore, as regards the recovery times of the initial reference temperature following upward regulation, the recovery times of HP water heaters (up to 20 minutes) are shorter than those of resistive boilers (up to 60 minutes) due to the greater efficiency of water heating in HPs. On the other hand, following downward regulation, shorter recovery times are observed for electric boilers (up to 600 minutes) due to the lower assumed volume (up to 100 liters) compared to that of HP water heaters (200 liters, recovery time up to 800 minutes).