Vaillant auroSTOR VIH S 400

Product detailed description

Vaillant auroSTOR VIH S 400 – bivalent solar domestic hot water cylinder with a capacity of 400 litres

The auroSTOR VIH S 400 model expands the range of Vaillant bivalent solar cylinders with a larger-capacity yet lower and wider variant, suitable primarily for buildings with limited ceiling height in the technical room or for households with a higher number of occupants. Just like the smaller 300-litre model, it works on the principle of two separate heat exchangers located inside the tank – the lower, cooler solar exchanger connected to roof-mounted thermal collectors, and the upper backup heating exchanger connected to an auxiliary heat source (gas boiler, heat pump, or an optional electric heating coil). Thanks to this arrangement, solar energy is utilised even at lower radiation intensity, since the water in the lower part of the tank is the coldest and heat transfer from the solar circuit is therefore most efficient there.

The 400-litre capacity is suitable for family houses with 5 – 7 occupants or for households with several bathrooms that want to maximise the share of solar heating in their total domestic hot water consumption. The lower, wider design (a height of only 1,470 mm compared to 1,775 mm for the 300 and 500-litre models) also fits better into boiler rooms with a lower ceiling, for example in the basement of an older building.

Technical characteristics

Lower and wider design compared to the 300 l model

While the 300 and 500-litre models of the auroSTOR VIH S range have a height of 1,775 mm and a diameter of 500 mm, the 400 l model within the same product line is designed the opposite way – it has a lower height of only 1,470 mm, but a larger tank diameter (650 mm). This ratio of dimensions is an advantage precisely in spaces with limited ceiling height, such as low basements, garages or older technical rooms, where a taller cylinder would not fit. The trade-off for this advantage is a larger floor space requirement – when planning the installation, we therefore recommend measuring the actual available space in the boiler room in both directions (height and floor area) in advance and comparing it with the dimensions of both design types within the VIH S range.

Principle of dual-circuit heating

As with all models of the auroSTOR VIH S range, heating here also takes place in two separate circuits. The solar exchanger in the lower part of the tank (heat exchange surface of 1.5 m², heat transfer fluid flow rate of 300 l/h) takes heat directly from the roof collectors via the solar controller and pump station. Since the lower part of the tank is always the coldest (this is where the cold inlet water is drawn from), the solar circuit can efficiently transfer heat even at lower collector temperatures, which in practice extends the daily and seasonal duration of usable solar gain. The upper backup heating exchanger (0.7 m², flow rate 900 l/h) only heats the upper “ready-to-use” part of the volume to the required temperature when solar energy is not sufficient, thereby saving the energy needed for backup heating compared to heating the entire large volume at once.

Installation

Given that the weight of the filled cylinder exceeds 550 kg, a sufficiently load-bearing masonry or concrete floor is essential. During installation, access must be ensured to all four groups of connections – the solar circuit (R1"), the backup heating circuit (R1"), the cold/hot water distribution (R1") and the optional circulation (R¾"). The solar circuit must be equipped with components specifically certified for solar applications (expansion vessel, safety valve, and a venting system resistant to high temperatures and possible short-term boiling of the fluid during summer system stagnation). We recommend entrusting the connection of the solar circuit to a certified technician experienced with thermal solar systems.

Who the 400 l model is suitable for

• family houses with 5 – 7 occupants and several bathrooms,
• buildings with limited ceiling height in the boiler room, where a taller 300/500 l cylindrical cylinder would not fit,
• households with a sufficiently large roof area for 3 or more solar collectors,
• households planning to combine the system with a heat pump or photovoltaics in the future.

Optional accessories and extensions

Like the other models in the auroSTOR VIH S range, the 400-litre version also allows the installation of an optional electric heating coil in the upper part of the tank via a flanged connection – either a classic switchable version with an output of 2/4/6 kW, or an intelligent version with consumption regulation of 0.5 – 3.5 kW designed to work together with a photovoltaic power plant. This combination allows domestic hot water preparation to be covered almost year-round from renewable sources in practice – solar collectors during the transitional season and summer, photovoltaic surplus in other cases, with the boiler or heat pump as the final backup.

Compatibility with solar collectors

The recommended ratio of solar collector area to cylinder capacity for family houses is usually around 1 m² of collector area per 50 – 70 litres of capacity, which for the 400-litre model corresponds to approximately 6 – 8 m² of collector area (typically 3 – 4 flat Vaillant auroTHERM collectors, depending on their size and roof orientation). The exact number of collectors, their tilt and orientation should be designed by a certified solar system designer, taking into account the actual hot water consumption of the household and local climate conditions. When making your decision, also consider future changes in consumption – if you are planning an extension, an attic flat for rent, or a growing family, it is worth considering a somewhat larger system than you currently strictly need, since expanding a completed solar system later is always more costly than correctly sizing it from the start.

Quality of the solar circuit piping

The actual solar gain achieved depends not only on the cylinder and collectors themselves, but significantly also on the quality of the piping installation between the roof and the technical room. An excessively long route or insufficiently insulated piping increases the heat losses of the solar circuit and reduces the overall efficiency of the system, especially when routed through unheated spaces (such as an attic or a cold corridor). We therefore recommend routing the solar piping via the shortest possible path and using quality insulation resistant to high temperatures and weather conditions if it is routed outdoors along the façade or roof.

Maintenance

Recommended maintenance includes regular checking of the concentration and condition of the antifreeze heat transfer fluid in the solar circuit (usually once every 2 – 3 years), checking the solar circuit pressure and the function of the expansion vessel, as well as an annual check of the cylinder's magnesium anode. If solar performance decreases over the years, it is also advisable to check the cleanliness of the collector surface and any shading from surrounding vegetation or buildings that may have appeared since the original installation.

Combination with pool heating

In buildings with a swimming pool, the solar system is sometimes designed so that in summer, when the hot water cylinder is quickly heated and any further solar gain would otherwise go to waste (or cause system stagnation), part of the heat is redirected to heat the pool water via a separate heat exchanger. Such a solution requires additional control and hydraulic interconnection, which needs to be designed individually taking into account the size of the pool and the solar system – it is worth consulting this already at the design stage of the solar system to avoid more extensive piping modifications later on.

Why choose this particular model

The auroSTOR VIH S 400 is an ideal choice for larger households that want to use solar energy for domestic hot water preparation, but at the same time have limited ceiling height in the boiler room, where a taller 300 or 500-litre cylinder would not fit. It combines a proven enamelled construction, a dual-circuit solar system and the possibility of further extension with electric backup heating, thus providing a long-term sustainable and flexible domestic hot water solution.

Solar circuit safety

The solar circuit operates at significantly higher temperatures and pressures than conventional heating systems. During intense summer sunshine combined with zero hot water consumption (for example, during the whole family's holiday), so-called system stagnation can occur, when the temperature in the collectors exceeds 150 °C and the heat transfer fluid may briefly boil. The solar circuit must therefore be equipped with components specifically certified for this application – a solar expansion vessel with a suitable membrane resistant to high temperatures, a safety valve rated for the pressures and temperatures of the solar circuit, and a venting system capable of handling short-term boiling of the fluid without damage. Standard heating safety components are not suitable for this purpose, and their use could lead to damage to the system.

Scope of delivery

The cylinder itself includes an enamelled tank with both built-in heat exchangers, a magnesium anode, EPS insulation, an outer casing and immersion sleeves for both the solar and backup heating sensors. The solar controller, pump station, solar circuit expansion vessel, the collectors themselves with mounting brackets, the heat transfer fluid and any electric heating coil are supplied separately according to the specific solar system design for the given building and roof.

Energy efficiency at a larger capacity

Despite the larger capacity (400 l), the standby heat loss remains at a reasonable level of 2.1 kWh per 24 hours thanks to the quality EPS insulation surrounding the entire tank. In practice, this means that even during a several-day period without any draw-off (for example, during a holiday), the cylinder does not consume an unreasonable amount of energy to maintain the temperature in the upper, heated part of the tank. Combining this with time-programmed backup heating (for example, only in the early morning and evening hours, when the likelihood of draw-off is highest) can further reduce backup heating costs during periods of insufficient sunshine.

Frequently Asked Questions