EIFER, the European Institute for Energy Research, led a recent webinar on Sim4Blocks partner project progress, discussing district and urban demand response models – in particular, the FlexBox model.

The Flexbox model is a simulation model representing different sorts of flexibility options in terms of the energy use in buildings, blocks of buildings and on an urban level.

A FlexBox allows for the demand response flexibility of a consumer or prosumer (producer and consumer) to be characterised. For example, a FlexBox simulates how a heat pump device is running at a certain power level output, and determines what flexibility options are available at each time. It can then determine how the load can be increased (switched on to increase consumption, e.g. at times when a lot of renewable energy is available) or decreased (shut off to do allow load shedding) to identify how flexible a device is at a certain time. The model aims to collate several devices to assess the flexibility potential of a group of devices, which is typically a more complex task as even if the devices are similar, they each have their own local conditions and varied operating states.

The flexibility potentials determined by the FlexBox model can be used to further analyse their suitability in relation to market requirements, or to assess the flexibility potential of a block of buildings at district and urban levels. The FlexBox model is designed to be able to be replicated several times to allow an up-scaling of the flexibility potentials on a much larger cluster of buildings.

FlexBox storage representation

The storage in a FlexBox refers to the capacity of storing energy related to a certain piece of technology for example, it could represent a storage system such as a battery or a heat tank storage, as well as virtual storage options including the thermal activity of the building or the loading potential related to user characteristics.

FlexBox system control

 In order to assess the flexibility of a certain energy device, a simplified representation of the energy flexibility was implemented in the form of a storage unit, which is triggered by a system control. The system control acts based on two main elements that are in direct connection with the storage unit: the demand – the energy flowing out of the storage unit to cover a certain energy need, and the supply of energy into the storage unit – such as a heat pump. For the supply element, the control system decides what operational state (on, off, partial load) the supply system is in at a given time.

Furthermore, a FlexBox can determine the overheating and overcooling ranges of the storage unit, providing additional flexibility potentials.

FlexBox flexibility assessment example – heat pump

 If a heat pump is running and its heat storage is almost full, the potential for flexibility upward (i.e. to increase the load) is zero kW as the heat pump is already consuming at the its highest state. At the same time, there is a high potential to decrease the load (downwards flexibility) as there is a large amount of energy stored and so there is the option to turn the heat pump off. By turning the heat pump off when the heat storage is almost full, or depending on the amount of energy in the storage unit, the flexibility level will be able to be maintained for a longer period of time.

On the other side, if the heat pump is switched off and the storage is almost empty due to little demand, there is a larger potential for flexibility upwards, i.e. to pre-produce some heat that could be used at a later time when the demand is higher. In this case, the duration of this flexibility is also high as it will take some time until the storage is completely full and allows us to run our heat pump at full power during this time.

Case Study: Wüstenrot

Wüstenrot, a town in Germany, was used to test the parameters of a FlexBox model on one of its buildings. Based on HFT’s technical model of the heat pump and storage unit, EIFER’s FlexBox model was calibrated and validated and provided succesful results with an acceptable minimal error range.

The results from the case study have provided EIFER with sufficient results to contract further work in the project and take the FlexBox model to a district level, and fully understand how it can help the energy efficiency of blocks of buildings with demand response. EIFER will also be able to investigate the market integration of these flexibility potentials. Important aspects of these further studies will be the aggregation effects at different scales of the system, the control strategies of a group of devices, and the emerging market accessibility opportunities.