Ice Store: Viessmann - Germany

Ice storage system: New heat source for brine/water heat pumps

With the innovative ice storage system, Viessmann is offering a new and attractive heat source for brine/water heat pumps. Unlike geothermal probes the ice storage system does not require planning permission. It provides an extremely reliable, economic and environmentally compatible heat supply to buildings of almost any size, from single family homes to large residential or commercial buildings. The ice storage system can also be used for natural cooling in the summer months. The “cold” occurs as a kind of “natural waste product” during the regeneration phase of the ice store.

The Viessmann ice storage system simultaneously utilizes heat from the ambient air, the ground and solar energy. This is done by filling the storage cylinder with normal mains water and by burying it in the ground directly below the surface. Because there is no need to drill deep holes for geothermal probes, and the untreated mains water is completely safe for the ground water, the ice storage cylinder can be installed and operated without having to obtain planning permission.

Simple setup

A heat exchanger with polyethylene pipes transfers heat from the outdoor air and solar radiant heat to the tank contents. Geothermal heat reaches the interior via the cylinder wall. Via a second heat exchanger, the heat pump draws the energy for building and water heating.

Apart from the ice storage cylinder and a Vitocal brine/water heat pump the system also includes a solar air absorber. The unglazed absorber collects heat from the ambient air and sunlight. This energy is used primarily to heat the cylinder. If heat from the solar air absorber is provided in addition, it is also used directly as an energy source for the heat pump. The intelligent heat source management in the controller of the Vitocal heat pump determines which heat source– solar air absorber or ice storage cylinder – has the higher temperature and should therefore be used, allowing high seasonal performance factors to be achieved.

Using crystallization energy for heating

If the energy supplied from the environment is not sufficient to cover the heat demand, energy is extracted from the water bit by bit and the cylinder contents cooled down to freezing point. The freezing that occurs as more and more heat is extracted is intentional, because the phase transition from water to ice provides a further energy yield – this is why it is called an ice store. During the freezing to ice process, the heat pump extracts 93 Wh/(kg • K) crystallization energy and uses it for heating. Assuming a cylinder content of 10 m3, the additional energy yield corresponds to around 100 liters of fuel oil.

The ice storage cylinder is regenerated as the temperature rises and sunlight increases. This means that the water content is available as a heat source to an almost unlimited extent.

Cool buildings with “natural cooling”

If sized accordingly, the ice storage cylinder can absorb the heat from the building on hot summer days and in this way help to cool the rooms. To achieve this the Vitocal brine/water heat pump merely needs to be fitted with the "natural cooling” box, which ensures the heat from the rooms is removed via the heating system and transferred to the ice storage cylinder, where it can then be stored for later use as a heat source.

System packages for easy installation

For the fast implementation of heat pump systems Viessmann offers preassembled system packages for buildings with heat loads of between 6 and 17 kW. This keeps planning work to a minimum and simplifies the ordering of components. The packages include the ice storage cylinder with built-in heat exchangers, the solar air absorbers with a mounting system for the usual roof coverings and the necessary heat transfer medium for the primary circuit.

For larger properties with higher heating demand the design of the ice storage cylinder and solar air absorbers has to be project-specific. In this conjunction, Viessmann offers corresponding support with planning the system.

Advantages for trade partners

-     Simplified harnessing of several heat sources at comparatively low investment cost – outside air, solar radiation, geothermal energy are all used simultaneously as heat sources

-     Heat source management for optimum use of ice store, solar air absorbers and heat pump

-     No drilling or environmental permit required

-     Low maintenance, easily serviced ice storage cylinder