Product detailed description

ATTACK Z 300 SOL - solar DHW cylinder with two heat exchangers

The Z 300 SOL model is specially designed for solar domestic hot water heating systems. The 300-litre tank contains two separate heating coils placed at different heights, which allows the temperature stratification of the water in the cylinder to be used to maximise the yield from solar collectors even at low solar radiation intensity.

How a solar cylinder with two heat exchangers works

The lower heat exchanger with a larger heat transfer area is connected to solar collectors (flat-plate or vacuum tube) via a solar station with a circulation pump and antifreeze heat transfer fluid. Since the solar circuit supplies heat at a variable and often lower temperature (especially in the morning, evening or with partial cloud cover), the large area of the lower heat exchanger enables efficient heat transfer even at a small temperature difference.

The upper, smaller heat exchanger is connected to a conventional heat source - a gas, electric or solid fuel boiler - and serves to reheat the upper layer of water if the solar yield on a given day is not sufficient to reach the required DHW temperature (typically 55-60 °C). The whole system is controlled by a solar controller, which compares the temperature at the collector and in the cylinder and switches on the circulation pump of the solar circuit only when it makes sense to transfer heat (the collector is warmer than the lower part of the cylinder).

Thanks to this stratification, the lower part of the cylinder can be cooler and still effectively absorb solar heat, while the upper layer remains ready for immediate hot water draw-off thanks to reheating from the boiler.

Key features

• 300-litre capacity, grey insulation, vertical design
• Two separate heating coils (lower solar + upper boiler)
• Large-area lower heat exchanger optimised for low-temperature solar yield
• Supports temperature stratification of water in the cylinder
• Enamelled steel tank with magnesium anode
• Rigid PU insulation with low heat losses
• Built-in sockets for solar and boiler temperature sensors
• Ready for the addition of a 6/4" electric heating element for a third (backup) heat source

Technical parameters

Installation

The Z 300 SOL cylinder is placed on a solid floor of the utility room (it is not designed for wall mounting like the smaller OKC models) near the solar station and boiler, so that the pipe runs of both the solar and boiler circuits are as short as possible and thermally insulated. The lower heat exchanger is connected to the solar station with a circulation pump, expansion vessel of the solar circuit and antifreeze filling, the upper heat exchanger to the conventional heating circuit of the boiler with its own circulation pump.

A complete solar assembly also includes a solar controller with two to three temperature sensors (collector, lower and upper part of the cylinder), which controls the operation of the circulation pump of the solar circuit. Do not forget the DHW safety valve, the expansion vessel on the DHW side and the safety valve of the solar circuit (rated for higher temperatures and pressures than a standard heating circuit). Entrust the installation of the solar system and the cylinder to a company experienced in solar technology.

Maintenance and service life

In addition to the standard annual check of the magnesium anode, it is advisable to check once a year (preferably in spring before the season) the concentration and condition of the antifreeze fluid in the solar circuit, the pressure in the expansion vessel of the solar circuit and the functionality of the solar controller and pump. Neglected maintenance of the solar circuit can reduce the yield of the collectors even with a flawless cylinder.

Step-by-step commissioning procedure

1. Place the cylinder on a solid floor of the utility room near the solar station and boiler
2. Connect the lower heat exchanger to the solar circuit (collectors, solar station, expansion vessel, antifreeze fluid)
3. Connect the upper heat exchanger to the boiler heating circuit
4. Fit the solar and boiler temperature sensors into the relevant sockets of the cylinder
5. Connect the cold and hot water piping with the DHW safety valve (max. 0.6 MPa)
6. Fill the solar circuit with antifreeze fluid and vent it
7. Fill and vent the cylinder and the boiler heating circuit
8. Set and test the solar controller, check the switching of the circulation pump
9. Pressure test, leak check and hand over documentation to the user

Safety warnings

The solar circuit operates at higher temperatures and pressures than a standard heating circuit, especially in the summer months during so-called stagnation (collectors without heat draw-off), so it must be equipped with its own safety valve rated for these conditions and antifreeze fluid resistant to high temperatures. The DHW safety valve (0.6 MPa) must always remain functional. Entrust work on the solar circuit, the controller's electrical installation and the pressurised part of the cylinder to a company experienced in solar technology.

Operating economics and payback

Solar DHW heating can cover the vast majority of hot water demand practically free of charge in the summer months, partially reduce boiler fuel consumption in transitional periods (spring, autumn), and serve mainly as water preheating before boiler reheating in winter. With a typical installation for a 300 l cylinder with the recommended collector area, it is possible to achieve annual coverage of DHW demand by solar energy in the range of approximately 50-65%, depending on location, roof orientation and household consumption, which, at current energy prices, represents a noticeable annual saving and a payback period typically of a few years.

Who is the Z 300 SOL suitable for

We recommend the solar version to all households that have or plan to install solar collectors for hot water heating. The 300-litre capacity is suitable for a larger household or a household with a higher number of collectors (4-6 m²), where a larger volume of solar heat needs to be accumulated. Thanks to savings on water heating from fossil or electric sources, the investment usually pays back within a few years.

How to navigate the ATTACK Z / PZO cylinder range

The ATTACK brand offers several types of hot water cylinders, which differ in the method of heating and intended use. Below is a brief overview to help you orient yourself when choosing a related or replacement product:

• Z .. OKC / OKCV - Basic indirectly heated cylinder with one heat exchanger, connected to a boiler. The simplest and most affordable DHW preparation solution if you already have or plan to have a boiler.
• Z .. OKC ENTR HV 2,2 - Same principle as OKC, plus a built-in 2.2 kW electric heating element - a choice for cottages, summer operation without a boiler, or as a backup in case of boiler failure.
• Z .. SOL ▸ this is the product you are currently viewing - Two heat exchangers - boiler and large-area solar. A choice for households with solar collectors who want to make use of free solar heat as well.
• Z .. HP - One large-area heat exchanger optimised for the low output temperatures of a heat pump. A choice for households with a heat pump as the main heat source.
• PZO .. PLUS - Directly heated, with its own gas burner, requires no boiler. A choice for cottages, workshops and premises without central heating.

For all indirectly heated variants (OKC, ENTR, SOL, HP), the heating output can be supplemented or backed up with an ATTACK TH electric heating element (2/2.5/4.5/6 kW outputs) via a 6/4" flange, which is available in our range as a separate product.

Common mistakes when choosing and installing a solar system

The most common mistake with solar systems is undersizing the collector area relative to the cylinder capacity (or vice versa), a poorly set or completely missing solar controller, and neglecting the annual check of the antifreeze fluid, which loses its frost protection and heat transfer properties as it degrades. Another common mistake is expecting the solar system to completely replace the boiler - in reality, it is a supplementary source that significantly reduces costs, but boiler reheating is still needed, especially in the winter months. For the Z 300 SOL model, we recommend having the sizing of the entire solar system (collectors, controller, cylinder capacity) professionally prepared by a solar technology supplier.

Frequently asked questions

Do I also need to buy solar collectors and controls separately?

Yes, this cylinder is prepared for connection to a solar circuit; the collectors themselves, the solar station, the controller and sensors are ordered separately according to the size and orientation of the roof.

Does the cylinder work even without sunshine, for example in winter?

Yes, in that case the upper heat exchanger connected to the boiler takes over heating exactly as if the cylinder did not have a solar heat exchanger at all.

How many collectors do I need for this capacity?

As a rough guide, 1-1.5 m² of collector area is used per 50-70 l of cylinder capacity, so for 300 l approximately 5 m² of collector area is needed; the exact calculation depends on the type of collector and roof orientation.

Why does the solar heat exchanger have a larger area than the boiler one?

The solar circuit operates at a variable and often lower temperature than the boiler; the larger heat transfer area compensates for the lower temperature difference and ensures efficient heat transfer even with weaker sunshine.

Is a special controller needed?

Yes, a solar controller with temperature sensors on the collector and in the cylinder is an essential part of a functional solar system; it controls the operation of the circulation pump of the solar circuit.

Can I also add an electric heating element as a third source?

Yes, the cylinder has a free 6/4" flange ready for fitting an ATTACK TH electric element as an additional backup heat source.

How often should the solar fluid be checked?

We recommend checking the concentration of the antifreeze mixture and the pressure in the solar circuit once a year, ideally in spring before the main season.

Can the cylinder be wall-mounted like the smaller OKC models?

No, due to its larger capacity and weight, this model is designed to be placed on the floor, not wall-mounted.

What percentage of DHW demand will the sun cover during the year?

Approximately 50-65% of annual demand, depending on location, roof orientation, collector area and household consumption; in the summer months it can be practically 100%.

What happens to the solar circuit in summer when the cylinder is full and hot?

In that case, the controller limits or interrupts the operation of the circulation pump (stagnation); the collectors temporarily do not use the heat gained - the system is designed for this condition and there is no risk of damage with properly sized safety equipment.

Is annual maintenance of the solar circuit necessary?

Yes, we recommend an annual check of the concentration and condition of the antifreeze fluid, the pressure of the expansion vessel and the functionality of the controller, preferably in spring before the main season.

Can I connect a heat pump instead of a boiler to this cylinder?

The upper heat exchanger is primarily designed for a higher-temperature boiler; for cooperation with a heat pump we recommend rather the Z HP model with a large-area heat exchanger, or consultation on the suitability of the combination with our technical advisory service.

How do I know that the solar circuit is working properly?

The solar controller usually displays the temperatures of the collector and cylinder and the status of the circulation pump; a drop in cylinder temperature in sunny weather and a non-functioning pump are the first signs that a service technician should check the system.

Connection with the solar station and antifreeze mixture

The solar station is a compact unit that contains the circulation pump of the solar circuit, a flow meter, the safety valve of the solar circuit, pressure gauges and check valves - it is installed between the collectors and the lower heat exchanger of the Z 300 SOL cylinder. The solar circuit is filled with a special antifreeze heat transfer fluid based on propylene glycol, which withstands high temperatures during stagnation as well as frost in winter. The quality and concentration of this fluid degrades slightly over time, so its regular checking (usually once a year) is part of standard solar system maintenance.

Comparison of Z 200 SOL and Z 300 SOL capacities

We offer the SOL solar range in capacities of 200 and 300 litres. The smaller 200 l capacity is suitable for a 2-4 person household with a smaller collector area (2-4 m²), while the 300 l capacity provides a larger storage capacity for households with a larger collector area (4-6 m²) or a higher number of people - the larger capacity can accumulate more solar heat during the day, extending the period during which the household draws hot water without needing boiler reheating. If you are planning several collectors from the start, we recommend choosing the larger 300 l capacity right away, as replacing the cylinder later is more costly than the price difference between capacities.

Summary

The Z 300 SOL model is the best choice for households that want to make the most of solar energy for heating hot water while still having the assurance of boiler reheating when there is not enough sunshine. Two separate heat exchangers and temperature stratification ensure efficient use of both heat sources in a single tank. Investing in solar DHW heating is a measure with a relatively fast payback, while also reducing the household's dependence on fossil fuel and electricity prices.

Warranty and service

The manufacturer ATTACK provides a 5-year warranty on the cylinder tank from the date of sale, subject to the conditions specified in the warranty certificate (regular anode inspection, compliance with maximum operating pressure and temperature, installation of safety equipment in accordance with applicable legislation). A standard warranty period of 24 months applies to the other components of the cylinder (insulation, jacket, electrical components, sensors, accessories). Service and spare parts for the entire ATTACK range are provided by a network of authorised service partners in Slovakia and the Czech Republic; our team will be happy to help you choose the right part or contact the nearest service centre if needed.