Construction and Installation Center
Buffer tanks come in various sizes and differ in terms of materials, insulation technology, and installation methods (typically available in vertical or horizontal configurations). While we won't delve into those specifics here, we will explore the different functions that modern buffer tanks can perform—because the possibilities are quite extensive!
Traditional Buffer Tank
Originally, buffer tanks were used to prevent heat pumps from short cycling. Short cycling occurs when a heat pump turns on and off repeatedly within a short period. This happens, for example, when the heat generated cannot be transferred to the heating system all at once. Instead of a smooth, steady flow, heat is delivered in short bursts. Using a buffer tank solves this problem.
Thanks to this large-volume storage tank for central heating water, heat is effectively buffered, allowing the heat pump to run continuously. The heat can then be gradually released from the buffer tank into the heating system. This is more efficient and also helps extend the lifespan of the heat pump.
Heat Storage
The original function of the traditional buffer tank has since been expanded to include heat storage. By installing a larger vessel that holds a significant volume of central heating water, a considerable amount of heat can be stored. Consequently, the buffer tank is now primarily transforming into a kind of "thermal battery." Of course, it still serves to prevent the heat pump from short cycling.
This ample heat storage capacity (essentially storing hot central heating water) is intended for later use. After all, the times when a heat pump runs happily on free solar energy (for instance) don't always coincide perfectly with when the occupants actually need heating. Just as unused electricity can be fed into the grid or stored in a home battery, this capability is used to store heat. After all: Store it when you have it, so you can use it when you need it!
Heat Exchanger
A customer might be using or considering multiple heat sources. For example, a heat pump combined with solar thermal collectors or PVT (Photovoltaic Thermal) panels. Ideally, all these heat sources should be able to store their energy in one central location. For this purpose, you can install a buffer tank equipped with one or more internal heat exchangers.
The buffer tank connects to the heat pump via standard ports. Additionally, the piping from the solar thermal collectors (which contain a refrigerant fluid) can be connected directly to the heat exchanger inside the buffer tank. This allows the refrigerant to transfer its heat smoothly to the heating water within the buffer tank. In this way, an excellent "thermal hub" is created.
Stratified Storage
There is also the stratified buffer tank. Here, heat is stored in multiple temperature layers (stratification), creating distinct thermal zones that are kept as separate as possible. This makes it possible to supply central heating water to different heating distribution systems (e.g., low-temperature floor heating and high-temperature radiators) simultaneously. Stratified buffer tanks can also offer additional functions, which leads us directly to the next type of buffer tank.
Domestic Hot Water
Originally, buffer tanks were exclusively for central heating water. Therefore, for domestic hot water, you needed a different type of storage tank. That said, these two functions can indeed be combined. Particularly with stratified buffer tanks, adding a (stainless steel) heat exchanger is one option for heating domestic water, especially in the upper part (the hottest zone) of the tank. In this case, fresh domestic water flows through the coil, as it must be strictly separated from the central heating water inside the buffer tank.
Another variant involves adding a dedicated additional tank specifically for domestic hot water inside the top of the buffer tank, known as a "tank-in-tank" system. Buffer tanks that can additionally provide domestic hot water are sometimes referred to as "combi buffer tanks" or "sanitary buffer tanks."
By integrating these two functions, you only need to install one (potentially slightly larger) vessel instead of two separate tanks. Of course, it is crucial that the domestic hot water can be heated to a sufficiently high temperature to prevent Legionella bacteria growth. For central heating water (used in low-temperature systems), lower temperatures are perfectly sufficient.
Hot Water Cylinder (Boiler Vessel)
Strictly speaking, this is not a buffer tank, but for the sake of completeness, the hot water storage cylinder or boiler vessel should not be omitted here. This type of storage tank is specifically designed for heating domestic hot water, entirely independent of the central heating system.
Again, via a heat exchanger, heat from the piping of the heat pump, solar thermal collectors, or PVT panels is transferred to the domestic water. During this process, the drinking water never comes into contact with the refrigerant or the system water (heating water).
An independent hot water cylinder allows you to separate domestic hot water storage from central heating water storage. This is useful if the cylinder is better suited for installation in a different location, for example. Or it might be considered the optimal solution if a buffer tank is already installed. Another possibility is that the customer simply doesn't require a buffer tank at all, and a dedicated hot water cylinder is entirely sufficient for their needs.
