Water is a real quick-change artist: it can be liquid, solid or gaseous. When the temperature falls below zero degrees and water solidifies into ice, energy is released, the so-called heat of crystallization - and it's quite something: "When the physical state changes, the same energy is released that is needed to move a liter of water from zero to 80 degrees Celsius," say the experts at heating technology manufacturer Viessmann. This means that heat can also be obtained from cold.
The so-called ice storage heater uses this effect. This is a heat generation system that uses renewable energy sources from the environment: geothermal energy, air and sun. The ice storage heater essentially consists of two parts: a water tank buried in the ground and a brine-water heat pump, which are connected to each other and work together to provide energy. This creates a cycle that causes the water in the tank to continually liquefy or solidify and produce heat with every change in physical state.
In most cases, the system is supplemented with solar air absorbers, which absorb heat from the surrounding air and are usually located on the roof or outside walls of a building. The advantage of this triple construction: Thanks to the additional heat source, the ice storage can be made smaller, which reduces costs. However, that's not a bargain: "For a typical single-family home you have to expect at least 17,000 euros plus VAT," says Wolfgang Rogatty, spokesman for Viessmann Climate Solutions SE.
Depending on the type and size of the building, the costs for ice storage heating systems can add up to well over 100,000 euros. The range of sizes ranges from ten cubic meters capacity (10,000 liters) to the four-digit cubic meter range, says Rogatty: "With a volume of 1,700 cubic meters, the ice energy storage in a leisure center in Lindlar is the largest in Germany to date."
The heart of every ice storage heater is the storage container buried in the ground. It is filled with water, which serves as the primary energy source and carrier medium. Inside this tank is a spiral system of many small pipes through which a freeze-proof liquid called brine circulates. They serve as heat transfer surfaces and contain an extraction and a regeneration heat exchanger, which enable the functional cycle of the water - and can also provide cooling in addition to heat. In this respect, the system is suitable for all buildings with high cooling or heating requirements, ranging from residential buildings to municipal buildings.
After connecting to the heat pump and the solar air absorbers, the ice storage heating system can be put into operation. In order to generate heating heat, the heat pump gradually removes its energy from the water via the extraction heat exchanger. This causes the temperature to drop and causes the water to gradually freeze and the crystallization energy can be used via the heat pump - for heating or hot water preparation, for example. Conversely, the regeneration heat exchanger ensures that heat from the ground, the solar air absorbers and other available heat sources is supplied to the water in order to thaw solidified water and keep the process of physical state change going.
If you are interested in an ice storage heater, you should keep a few special features in mind. Since this only works in combination with a heat pump, the property should be as well insulated as possible to avoid losses in efficiency. There must also be enough space on the property to bury the ice storage: "With a cistern with 12,000 liters, you need a garden area of 16 square meters," says Christof Lehner, head of development and quality management at the Austrian heating manufacturer Ecotherm.
In addition, ice storage heating still has exotic status in Germany. The number of manufacturers is very manageable: the majority of the products come from Viessmann or Ecotherm. As a result, there are only a few installation companies that can design, dimension and install the systems correctly. This is particularly important given that ice storage is not a standard solution.
The fact that the market for private individuals is still in its infancy may also be due to the high costs of ice storage heating systems. Rogatty knows that things have already made a lot of progress in the commercial sector: "There are now several thousand systems of all sizes in operation in Germany alone." They offer a number of advantages: Thanks to the crystallization process, they are space-saving, as the storage volume can be reduced by up to six times compared to other heating systems such as geothermal collectors. In addition, no approval is usually required for the installation itself and putting an ice storage heating system into operation is uncomplicated and low-maintenance.
This article first appeared on Capital.de.