VARICAL Modular Buffer Stores

VARICAL - The modular buffering system

For energy generation in the heating sector, a decentralised heat supply plays an increasingly important role. Often, several energy sources are used in the building, which contribute to the heat and power supply together or separately, as conditions dictate.

Since the supply of renewable energy is also very variable both throughout the day and according to the season, a good storage capacity with low heat losses and good stratification is important. When retrofitting buildings to achieve the greatest potential for climate action, maximising use of a small space is an important factor as larger volumes increase the potential for saving CO₂ and costs.

VARICAL — the modular buffer store system — has been developed for this application. It offers great advantages in terms of space requirements, ease of installation and set-up, especially with limited access.

 Areas of application

  • Solar heat
  • Biomass
  • Heat pumps
  • District heating
  • Combined heat and power
  • Power plants
  • Power-to-heat

Easy access modular system

The individual modules can be taken through 70 cm wide doors and usually also through the narrow hallways and entrances typical of existing buildings.

Space-saving installation

Compared to individual thermal stores, with VARICAL it is often possible to achieve the same large storage volumes in half the installation footprint.

Flexible integration

The five connections on each side of the tank allow use as a heating buffer or in combination with a fresh water station in a wide range of applications.

Steel pressure Tank

The modular buffer storage can be pressurised as usual for buffer stores, up to 3 bar operating pressure, so that heat generators and heating circuits can be directly connected without the need for heat exchangers and transfer losses.

Innovative heat insulation system with LE-EPS insulation and optional VIP vacuum insulation

Thanks to the heat-resistant and performant LE-EPS insulation and the joint insulation of all modules, heat losses are kept very low. The air chambers inside the insulation shells also have a good insulating effect. The heat losses can be further reduced to very low values using the optional vacuum insulation panels (VIP), which can be pushed into the air chambers.

Integrated Bypass for quick heat delivery

If the heat generator is connected on one side of the storage tank and the heating circuit on the other side of the same pipe, the water from the heat generator can flow directly into the heating circuit without any mixing losses.

Only the surplus flow passes through the slots of the charging and discharging pipe into the buffer store. This is particularly important for heat pumps, where any degree of cooling by mixing should be avoided.

Proven and well thought-out sealing system

A special sealing system has been developed and carefully tested to permanently seal the pipe ducts. It seals the individual modules at the pipe passages by means of flat and lamella seals and is based on proven long-life elastomers in combination with stainless steel sleeves.

The slats seal without pressure during filling and emptying. As the pressure increases, the sealing function increases. The sealing system was successfully tested in a pressure-change testing device at the ITW of the University of Stuttgart.

Controlled charging and discharging

The charging and discharging pipes, which extend through the entire length of the store, enable cleanly layered charging and discharging through special inlet and outlet openings for the buffer water with flow deflection.

IMPORTANT INFORMATION: VARICAL is currently only manufactured and delivered by request for larger projects with an order of 40 modules or more. Please ask when planning your systems.



VARICAL was awarded with the Innovation Award 2017 by the OTTI-symposium for thermal solar energy.

Technical data: VARICAL

No. of modules

Length w/o insulation

Length w/ insulation

Total weight empty*

Total weight filled*



*Weight indication incl. pressure profile, pipes and insulation

Individual modules

Intermediate module

End module

Tare weight (approx.)


Max. permissable tank pressure

Max. permissable temperature