Design energy flexibility characterisation of a heat pump and thermal energy storage in a Comfort and Climate Box

The energy transition requires flexible resources in which heat pumps are considered as a key technology. In this context, the smart combination of a heat pump, thermal storage and control system into a single product was introduced by the International Energy Agency as a Comfort and Climate Box.This paper proposes a quantification methodology to rate the design flexibility potential of such a Comfort and Climate Box. The methodology is based on several separated charging and discharging cycles of thermal energy storages. The procedure examines several climatic conditions and heat pump operational schedules to consider operational efficiency as well. The methodology provides three reported flexibility metrics, namely the flexibility provision efficiency, average charging time and average discharging time. The method allows a fair and easy design flexibility comparison among Comfort and Climate Boxes of different manufacturers, types of heat pumps and independent from the heat emission system in use. Applying the flexibility rating procedure to several combinations of a water/water heat pump providing space heating and/or domestic hot water showed the ability of the methodology for design flexibility rating purposes. The methodology can be used without dynamic simulation software and validation against dynamic simulations showed deviations below 1 % in the reported metrics when time steps of five seconds were used. Furthermore, results also showed insights in the flexibility provision efficiency and the side-effects of activation of a possible back-up heater. Finally, the methodology has been made available through an open source script.