Buffer tanks are not a new invention. But the more we rely on renewable energies in our homes, the more important they become. They store heat and therefore contribute to the efficiency of photovoltaic systems and heat pump systems. You can store the heat energy temporarily, so to say, until your heating system requires it or new hot water is needed for cooking, washing or showering. The combination of a buffer tank and heat pump can also pay off with a favorable night-time electricity tariff.

On sunny days, for example, you can use the surplus generated by your photovoltaic system during the midday hours to heat the heating water in the buffer tank. You can use the stored heat energy with a time delay when you need it most.

How does it work? Almost as simple as grandma's immersion heater. The adjustable electric heating element in the buffer tank is connected directly to the photovoltaic system and converts the electrical energy into thermal energy. A buffer storage tank therefore saves real money and increases both the efficiency and effectiveness of your photovoltaic system.

The buffer tank is connected to the heat pump and heating system circuits via flow and return pipes. The heat pump heats the water in the flow of the heat pump circuit via a heat exchanger and transfers it to the buffer tank. The return line transports cool water back to the heat pump. When heating is required, the heating water is routed from the buffer tank into the flow of the heating system and distributed to the radiators and/or the panel heating. The cooled heating water is returned to the buffer tank via the return flow and the cycle starts again.

Air/water heat pumps are just as suitable as brine/water heat pumps. There are also many options for the heating system, from conventional radiators to panel heating systems such as underfloor heating, wall heating or ceiling heating. In the article "Heat pump with radiator - The guide", we have compiled a lot of useful information about heat pump-compatible heating systems.

THE BUFFER TANK AS A HYDRAULIC SEPARATOR

In old buildings in particular, the existing pipe installation is not always suitable for heat pumps due to the different volume flows, i.e. circulating water masses. If the heating water were to be piped directly from the heat pump into the heating circuit, the pressure there may be too high. On the other hand, closing the heating thermostats can reduce the flow rate to such an extent that the heat pump goes into fault mode. Efficient decoupling of the hydraulic circuits between the heat pump and the heating circuit via a separating buffer tank provides a remedy here, as it keeps the flow rate in the heat pump circuit constant. Your buffer tank acts like a hydraulic separator.

BUFFER TANK AS ENERGY STORAGE

With air/water heat pumps in particular, a defrosting process occurs on the heat pump at temperatures as low as approx. 5°C. As heat is extracted from the ambient air, the heat exchanger freezes and must be defrosted. The heat pump receives the energy required for defrosting either from the building envelope or from the buffer tank.

BUFFER TANK PREVENTS FREQUENT CYCLING OF THE HEAT PUMP

In existing buildings in particular, buffer tanks also prevent the heat pump from switching on and off frequently - known as cycling - as they already have the required hot water ready when the room temperatures drop. This improves efficiency and extends the life of the compressor. However, modern inverter heat pumps can regulate their output continuously and with the greatest possible efficiency to the desired temperature for heating and hot water. As they work in modulating mode, they ideally only switch off very rarely. One of our trained specialist partners will be happy to explain to you whether this clever technology is sufficient for your individual heat pump project or whether you need a buffer tank after all.

BUFFER TANK BYPASSES BLOCKING TIME

If you choose a low-cost heat pump electricity tariff, you enable your energy supplier to use your heat pump to stabilize the grid and avoid peak loads. This means they can take it off the grid for a while. With a buffer tank, you can easily bridge these off-peak periods and keep your home warm and cozy.

AND WHAT ABOUT UNDERFLOOR HEATING?

If you have installed underfloor heating, this will generally take over the heat storage, as already mentioned. So you don't need an additional buffer tank simply because of the utility company shut-off times. However, there may be other reasons for a buffer tank in individual cases, but this can usually be smaller. It is best to seek advice from one of our specialist partner companies in your area.

Which buffer tank is right for you depends on your requirements, the structural conditions, the existing pipes and your heating system. Please note: If you need a buffer tank, it must not be oversized. Apart from the increased space requirement, this would be inefficient because the cylinder loses unused heat energy over time, even with the best insulation.

Separate buffer tank: As described above, it decouples the hydraulic circuits between the heat pump and the heating circuit and acts as a hydraulic separator. The circuits are routed through separate heat exchangers.

Series buffer tank: Is connected in series with the heat pump and the heating system in one circuit. There is no hydraulic separation between the volume flows of the heat pump and the heating system. Advantage: lower heat retention losses due to the return flow integration. Disadvantage: only works at one temperature level and requires an overflow valve.

Stratified storage tank: Water is stored in different temperature layers. The heat pump accesses the layer with the required temperature via appropriately arranged inlets and outlets.

Combi tank: DHW and heating water are stored in one tank. The drinking water is heated using the instantaneous water heater principle.

Integrated buffer tank: The hot water tank and domestic hot water heat pumps are housed in one casing to save space.

Multifunctional storage tank: Can be fed simultaneously from different heat sources such as heat pumps, solar thermal energy, photovoltaics or solid fuel boilers.