A storage tank is a storage device that stores energy received from an external heat source by transferring it to the water, thus ensuring system balance in the face of varying demand. Unlike a water heater, it does not have a coil; heat transfer is generally achieved through an external heat exchanger and a circulation pump. This simplifies connecting a single tank to multiple heat sources, improves hydraulic balance, and reduces undesirable temperature fluctuations in the domestic hot water.

In hotels, sports facilities, student residences, and social housing, where instantaneous consumption is high and demand patterns are irregular, a storage tank can meet peak consumption, thus avoiding frequent boiler or heat pump starts and stops, and improving equipment efficiency and lifespan. It absorbs the variable solar energy production during the day and transfers it to nighttime use. It compensates for time lags between production and consumption in heat recovery and exchange systems, thereby optimizing comfort and energy efficiency.

In a coil-free system, the heat source forms the primary circuit and transfers heat to the water in the storage tank via a plate heat exchanger. A booster pump ensures a rapid temperature increase in the water level at the top of the tank. Three-way valves and temperature sensors intelligently manage the filling and emptying process. Solar collectors charge the tank during the day, while the heat pump or boiler only activates when needed. A domestic hot water circuit and a thermostatic mixing valve provide a comfortable and reliable supply of hot water, ensuring optimal resource utilization.

Surfaces in contact with drinking water benefit from a double-layer hygienic enamel coating and cathodic protection for increased durability. Surface preparation prior to enameling enhances coating adhesion and its glass-ceramic properties. The selection of fittings, flanges, and blind plugs made of materials compatible with water chemistry reduces the risk of corrosion; where necessary, the use of stainless steel components and suitable seals improves hygiene and durability. Appropriate water treatment and periodic anodic inspection significantly extend the coating's lifespan.

To achieve good thermal stratification within the tank, it is best to use inlet and outlet diffusers along with a suitable internal hydraulic system. Hot water inlet at the top and return at the bottom minimizes mixing, thus ensuring thermal comfort during circulation. High-performance thermal insulation reduces heat loss due to stagnation and guarantees more efficient use of heat from renewable sources. Thermal bridges should be minimized in pipes and fittings, and points where thermal bridges form should be carefully insulated. Safe and stable operation is ensured by the design of an expansion vessel, a safety valve, and an appropriate check valve configuration.

The sizing takes into account daily and hourly peak consumption, the target domestic hot water temperature, the network inlet temperature, the type and power of the heat source, the heat exchanger capacity, circulation requirements, on-site measurements, and water analysis. This data determines the tank volume, connection diameters, and control strategy. During operation, periodic checks and replacements of the anodes, tests of the safety equipment, verification of the circulation and mixing valve settings, a visual inspection of the tank interior, and scheduled thermal disinfection are carried out. These measures ensure hygiene and efficient, long-lasting operation.