Utilising the potential of HEMS

Mr Wehrmaker, what is the current situation regarding energy and housing in Germany?

Wehrmaker: Rarely has this issue been discussed as much in this country as it has in the last 20 months; it seems to have finally reached the centre of society. We have no choice but to reduce our energy consumption and use renewable energy sources - we have known this for a long time, and yet we are nowhere near where we could be. Buildings account for around 35% of total energy consumption in Germany. Almost 40% of this is consumed in detached and semi-detached houses and a good quarter in apartment blocks (source: dena, 2023). It is worth taking a closer look at this 25%.

What makes the multi-family sector so interesting?

Wehrmaker: Energy management in multi-family dwellings has a crucial role to play, which is currently not given enough attention in the public debate.

Multi-unit energy management, or Home Energy Management System (HEMS), focuses on coordinating and controlling energy flows in multi-unit buildings.

What does this mean in practice? Firstly, to reduce the energy consumption of buildings, while at the same time maximising the share of renewable energy in the energy that is still required. Another benefit of HEMS is the integration of buildings into the electricity grid, so that they can be used as a grid-supporting component to stabilise the grid. However, this is a major challenge for existing buildings and grids.

And how do we get there, what does that look like in concrete terms?

Wehrmaker: The first step is not always to install a PV system or a heat pump, but to create transparency about the energy balance of a building. This can be achieved continuously and automatically during operation using intelligent measuring technology both in the apartments and in the plant room (e.g. heating system or electricity meter). With the help of transparency, a reduction in the flow temperature can often be achieved without much effort and with the greatest possible safety. Savings of 10 to 15% are possible. In turn, this transparency provides a reliable basis for later expansion, e.g. conversion to a heat pump, as the exact heat demand in the building is known.

Optimised, holistic energy management also makes a significant contribution to the various goals of the energy transition - by promoting the integration of renewable energy sources, enabling more widespread electromobility and thus relieving the pressure on the electricity grid. This benefits us all in the form of potentially lower grid charges and, ultimately, the environment.

Mr Wehrmaker, what do you need for a HEMS, a home energy management system?

The interaction of several components is important for a functioning HEMS, which must be finely tuned to each other in order to be fully effective.

Wehrmaker: As I said, the first necessary step is smart or multi-metering, for example, which continuously provides data on the energy flows in the building, together with the integration of essential local components such as PV systems, heat pumps or charging infrastructure. What happens to the consumption and building data is then crucial: How is it read and interpreted, what conclusions can be drawn about the energy status of the building, and how can this knowledge be used to control the building? Building owners and operators should also actively involve occupants. The installation of smart meters allows them to monitor their energy consumption in real time and see, for example, when enough PV power is available. This creates awareness of individual energy consumption and helps to identify inefficient behaviour. To do this, residents need the knowledge and recommendations to take action, otherwise even the best data visualisation is useless.

What other potential does the use of a HEMS offer?

Wehrmaker: In order to implement the energy transition quickly and at all levels, we need to focus not only on saving energy, but also on integrating renewable energy over time. There is a huge potential for this, especially in apartment blocks, thanks to local energy generation and storage, and the ability to shift certain loads.

Another example is the real-time control of energy consumption: for example, the supply of renewable energy is interlocked with heat pumps or the charging of electric vehicles in such a way as to maximise the purchase of (in-house) energy from renewable sources. This clearly shows how finely tuned all the components need to be - between generation and timing of consumption, but also between technical infrastructure and people. This provides a high level of security, especially in times of energy volatility. In terms of electricity costs, but also in terms of grid stability. Just as the building can be used to store electricity, it can also be used to choose the optimum time to charge electric cars or run washing machines or heat pumps.

In terms of energy supply and grid stability, are there any other benefits that HEMS can bring to the community?

Wehrmaker: If it is not possible to use renewable or locally generated energy, the HEMS and its transparent information offer another advantage: the use of dynamic tariffs. When there is a surplus of renewable energy in the grid, electricity prices on the exchange are generally very favourable. This is where the HEMS comes in, automatically shifting the charging process to particularly favourable times, taking into account the user's requirements. The same applies to the heat pump, which can run at a higher speed during periods of surplus electricity to store heat in the building.

Using buildings to store electricity sounds interesting. How realistic is this at the moment in Germany?

Wehrmaker: We have so much untapped potential today. It's worth thinking bigger and in a networked way. I have just mentioned that suitably equipped buildings can also be used as storage facilities. This is a great opportunity, especially in densely populated areas. Keyword: networking of controllable loads.

It is also conceivable to combine several HEMS and make them available to the grid operator as controllable loads.

Heat pumps and charging infrastructure, in particular, can generally reduce electricity consumption, reduce loads and thus respond to the intermittency of renewable energy generation without compromising user comfort.

At peak times, for example, such HEMS mergers can also make an important contribution to the overall stability of the grid and the supply of energy - an aspect that is well worth considering.

 Mr Wehrmaker, thank you very much for this informative interview.