uniSTOR plus VIH SW 400

Product detailed description

Hot water storage tank Vaillant uniSTOR plus VIH SW 400

Vaillant uniSTOR plus VIH SW 400 is a bivalent, indirectly heated hot water storage tank with a volume of 372 liters, which, unlike the single-coil RW models, contains two separate heating heat exchangers with smooth tubular registers. This makes it suitable for simultaneous connection to two heat sources – typically a heat pump and a solar thermal system, or a heat pump and a boiler as a second (booster) heat source. The designation "SW" comes from the German "Solar-Warmwasserspeicher", i.e. solar hot water storage tank, and clearly distinguishes this model from the single-coil RW range, which is designed for only one heat source.

The volume of 372 liters is comparable to the RW 400 model (375 liters), the SW 400 tank has the same external dimensions and shape of the casing, but differs in the internal layout – instead of one large heat exchanger, it contains two smaller heat exchangers placed one above the other. The lower heat exchanger with a larger surface area is intended for the main heat source (heat pump or boiler), the upper, smaller heat exchanger is used for boosting from solar collectors.

Technical parameters of VIH SW 400

• Storage volume: 372 liters
• Height of the tank (with casing): 1502 mm
• Width (with casing): 790 mm
• Depth (with casing): 900 mm
• Empty tank weight (without water): approximately 189 kg
• Weight of the filled tank in operation: approximately 561 kg
• Heat transfer area of the lower (main) heat exchanger: 3.24 m²
• Heat transfer area of the upper (solar) heat exchanger: 1.47 m²
• Maximum operating pressure (domestic water): 10 bar
• Maximum operating pressure (heating/solar circuit): 10 bar
• Maximum temperature of heating water: 110 °C
• Maximum temperature of hot water: 85 °C
• Standby heat loss: 1.58 kWh/24h
• Energy efficiency class for water heating: B
• Integrated magnesium protective anode against corrosion
• Enamelled inner surface of the tank (enamel)

Difference between the RW and SW series

The key difference between the uniSTOR plus VIH RW and VIH SW series lies in the number and arrangement of heating heat exchangers. The RW model (e.g. RW 400) has one heating coil and is designed exclusively for connection to a single heat source, most often a heat pump. The SW model has two independent heat exchangers – a large lower one for the main source (heat pump, or optionally a boiler) with an area of 3.24 m² and a smaller upper one for solar collectors with an area of 1.47 m². This bivalent design allows solar collectors to preferentially boost the upper part of the tank on sunny days, thus saving energy from the main heat source, while the lower heat exchanger ensures reliable heating even during periods of insufficient solar radiation.

Externally, both models (RW 400 and SW 400) are very similar – they have the same external dimensions and the appearance of the white cylindrical casing, differing mainly in the number of connecting nozzles on the heat exchangers and internal layout. When ordering, it is therefore crucial to distinguish the exact type according to the purpose (one heat source vs. a combination of a heat pump and solar).

Construction and thermal insulation

The casing of the SW 400 tank is insulated with rigid PU foam with high density, applied directly to the steel tank without thermal bridges. The standby heat loss of 1.58 kWh per 24 hours is only slightly higher than that of the comparable single-coil RW 400 model, which is due to the presence of the second heat exchanger and associated connections. The tank and both heat exchangers are protected on the potable water side by a high-quality enamelled surface (enamel) and a magnesium protective anode against corrosion.

Installation and connection

The tank is installed as a free-standing unit on adjustable feet. Due to the two independent heating circuits, it is necessary to connect the main heat source circuit (heat pump) to the lower heat exchanger and the solar circuit to the upper heat exchanger separately during installation, including the corresponding pump groups, expansion vessels and regulation. We recommend using Vaillant regulation compatible with solar systems (e.g. auroMATIC in combination with multiMATIC or senzoCOMFORT), which is able to control the priority of heating between the solar and main source and optimize the use of solar energy.

When planning the technical room, it is necessary to allow space not only for the tank itself (minimum floor space 100 × 100 cm, room height at least 1700 mm), but also for additional components of the solar circuit – solar pump group, solar expansion vessel and possibly a solar regulator.

Compatible accessories

The VIH SW 400 tank can be supplemented with a solar pump group, a solar expansion vessel dimensioned according to the collector area, a set of temperature sensors for both circuits (solar and main source), safety valves for the domestic and heating water side and insulation sleeves for all connecting pipes. When combined with a Vaillant heat pump, we recommend the original connecting kit and compatible regulation that takes into account the specifics of bivalent operation.

For whom is the SW 400 model suitable

The SW 400 model is suitable for households that want to combine a heat pump with solar collectors for hot water preparation, or for buildings with an existing boiler to which a solar system is additionally installed. The volume of 372 liters will cover the needs of a household of 4 to 5 people, with the solar circuit significantly reducing the share of energy required from the main heat source in the summer months.

Frequently asked questions (FAQ)

Can I connect only a heat pump to the SW 400 tank without solar collectors?
Yes, the upper solar heat exchanger can remain temporarily unused and solar collectors can be installed at any time later without intervention in the tank.

Is there a difference between RW 400 and SW 400 visible from the outside?
The external dimensions and appearance of the casing are almost identical, the difference is in the number of connecting nozzles for the heating circuits – SW 400 has connections for two independent circuits.

How much space do I need for installation?
We recommend a minimum floor space of 100 × 100 cm for the tank itself, plus additional space for the solar pump group and the expansion vessel of the solar circuit.

Why is the maximum temperature of the heating water as high as 110 °C?
The solar circuit can reach higher temperatures than a conventional heating circuit in the summer months due to high solar radiation intensity and low demand, so the upper heat exchanger is dimensioned for a higher maximum temperature.

How often should the magnesium anode be checked in bivalent operation?
We recommend the same frequency as for RW models – at least once a year, during the service inspection of both connected heat sources.

Maintenance and service

Maintenance of the SW 400 tank includes not only the standard inspection of the magnesium anode and the safety valve on the domestic water side, but also the inspection of the solar circuit – the condition of the antifreeze fluid, the pressure in the solar circuit and the functionality of the solar pump group. We recommend performing service of both circuits together, ideally once a year before the start of the heating season, to ensure reliable operation throughout the year.

Economic and ecological benefits of bivalent operation

The combination of a heat pump with solar thermal collectors is one of the most efficient ways to prepare hot water in terms of the use of renewable energy sources. While the heat pump provides a reliable heat source independent of the weather, solar collectors can cover a large part or even the entire hot water heating demand without any electrical input, especially in spring, summer and autumn months. The SW 400 tank with its construction featuring two independent heat exchangers allows full use of this potential – the solar circuit can boost the upper part of the tank even when the main heat source is not in operation, thus significantly reducing the energy consumption from the heat pump especially during the summer season.

From a long-term perspective, this combination reduces household operating costs for hot water heating and at the same time reduces the carbon footprint compared to systems based on a single energy source. The return on investment in a solar system depends on the size of the collector area, the roof orientation, and the hot water consumption profile in the household, so we recommend consulting the design of the solar circuit with a qualified designer.

Operational Safety

Due to the two independent heating circuits, the SW 400 tank requires special attention to the correct sizing of safety valves and expansion vessels on both sides – on the domestic hot water side and on the solar and main heating circuit side. The solar circuit also requires the use of a suitable non-freezing heat transfer fluid resistant to high temperatures that can occur in the circuit during system stagnation on sunny days without heat withdrawal.