Fresh water modules for hygienic hot water heating

The Vitotrans 353 fresh water module from Viessmann offers an alternative to a domestic hot water cylinder. The fresh water module eliminates the need for storing hot water, as it heats the water instantly. Heat is drawn from a buffer tank, which can be heated by various heating systems—solid fuel boilers, solar thermal systems, oil or gas boilers, heat pumps, and others. The modules are prefabricated units suitable for both wall mounting and installation directly on the cylinder itself.

Fresh water module design

Unlike conventional hot water cylinders, the water is not used to store thermal energy, but is heated only as needed using a powerful plate heat exchanger. This forms the basis of the compact system. Additionally, the Vitotrans 353 fresh water module requires the following components:

• Control unit
• Pipeline with safety valve
• Flow sensor
• Shut-off valves
• Water heating side: high-efficiency circulation pump

An additional check valve and a DHW circulation kit can be added to the freshwater module. Another accessory is a temperature-resistant valve for sampling germ-free water in accordance with the German Drinking Water Ordinance (only for types PBMA/PBMA-S, PBLA/PBLA-S, and PZMA/PZMA-S).

Heating of hot water using a plate heat exchanger

The freshwater module operates by indirectly heating domestic hot water using the instantaneous water heating principle. How does this process work in detail?

When a demand for domestic hot water from the tap arises anywhere in the building, fresh domestic hot water passes through the fresh water module, where it is heated by the hot heating water. At the same time, the heating water from the buffer tank cools. Both fluids flow in separate systems within the heat exchanger. They never come into contact with each other or mix, as the heating water does not meet the quality requirements for domestic hot water and has a much lower oxygen content. The process of heat transfer from one medium to the other continues as long as domestic hot water, which is drawn from the taps, is needed.

Water consumption and other key data

Vitotrans 353 freshwater modules are available in five different models, suitable for both wall mounting and installation directly on a heating water buffer tank. A distinction is made between the basic series and the series with DHW circulation. Depending on the model, the withdrawal rate ranges from 25 to 68 liters per minute. This applies to the following conditions:

• The set temperature of hot water for domestic use is 45 degrees Celsius
• The heating water flow temperature is 60 degrees Celsius
• The temperature of cold water at the inlet is 10 degrees Celsius.

Water extraction rates can also be increased by cascading up to four identical modules. This can be accomplished without the need for additional controls. Therefore, freshwater modules are also suitable for higher demand, such as in local government applications.

The maximum hot water temperature for all models is 95 degrees Celsius. This allows the fresh water module to be combined with various heating systems. The maximum hot water temperature is 75 degrees Celsius. This is high enough to prevent the formation of microbes, making this form of hot water heating particularly hygienic.

Ensures a constant outlet temperature

Carefully selected components ensure a constant faucet temperature at varying water flow rates. Highly efficient, latest-generation circulation pumps are controlled by an integrated control unit, ensuring heating water flow is always optimal for the current flow rate.

Integration into low-temperature heating systems

Freshwater modules require only low flow temperatures for optimal operation. This makes them ideal for integration into low-temperature heating systems. These modules thus complement the energy-efficient operation of heat pumps, gas or oil condensing boilers, and systems with solar backup. In systems with solar backup, the efficiency of the solar circuit can be increased, as the average temperature of this circuit can be reduced by using a cold return.