Product detailed description

ATTACK Z 200 SOL - solar DHW cylinder with two heat exchangers

The Z 200 SOL model is specially designed for solar domestic hot water heating systems. The 200-litre tank contains two separate heating coils located at different heights, which allows the temperature stratification of the water in the cylinder to be exploited, maximising the gain 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 under partial cloud cover), the large area of the lower exchanger allows 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 gain on a given day is not sufficient to reach the required DHW temperature (typically 55-60 °C). The entire system is controlled by a solar controller, which compares the temperature at the collector and in the cylinder and switches on the solar circuit circulation pump only when it makes sense to transfer heat (the collector is warmer than the lower part of the cylinder).

Thanks to this stratification (layering), the lower part of the cylinder can be cooler and still efficiently absorb solar heat, while the upper layer remains ready for immediate hot water draw-off thanks to boiler back-up heating.

Key features

• 200-litre capacity, grey insulation, vertical design
• Two separate heating coils (solar lower + boiler upper)
• Large-area lower heat exchanger optimised for low-temperature solar gain
• 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 adding a 6/4" electric heating element as a third (backup) heat source

Technical parameters

Installation

The Z 200 SOL cylinder is placed on a solid floor of the utility room (it is not designed for wall mounting like the smaller OKC models) close to the solar station and the 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, an expansion tank for the solar circuit, and filled with antifreeze mixture; the upper heat exchanger is connected to the conventional boiler heating circuit with its own circulation pump.

Part of the complete solar assembly is also a solar controller with two to three temperature sensors (collector, lower and upper part of the cylinder), which controls the operation of the solar circuit circulation pump. Do not forget the DHW safety valve, the expansion tank on the DHW side, and the solar circuit safety valve (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 inspection of the magnesium anode, it is advisable for a solar cylinder 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 solar circuit expansion tank, and the functionality of the solar controller and pump. Neglected maintenance of the solar circuit can reduce collector yield even with a fault-free cylinder.

Step-by-step commissioning procedure

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

Safety warnings

The solar circuit operates at higher temperatures and pressures than a standard heating circuit, especially in 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 needs practically free of charge during summer months, partially reduces boiler fuel consumption in transitional periods (spring, autumn), and in winter serves more as a pre-heating stage before boiler back-up heating. With a typical installation for a 200 l cylinder with the recommended collector area, it is possible to achieve an annual solar coverage of DHW needs 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 of usually a few years.

Who is the Z 200 SOL suitable for

We recommend the solar design to all households that have or plan to install solar collectors for hot water heating. The 200-litre capacity is suitable for a 2-4 person household with a typical collector area of 2-4 m². 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 that differ in heating method and purpose. Below is a brief overview to help you choose a related or replacement product:

• Z .. OKC / OKCV - A basic indirectly heated cylinder with one heat exchanger, connected to a boiler. The simplest and most affordable solution for DHW preparation 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 that want to make use of free solar heat as well.
• Z .. HP - One large-area heat exchanger optimised for the low outlet temperatures of a heat pump. A choice for households with a heat pump as the main heat source.
• PZO .. PLUS - Directly heated, its own gas burner, no boiler required. 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 inspection 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 especially in winter months, boiler back-up heating is still needed. For the Z 200 SOL model, we recommend having the entire solar system (collectors, controller, cylinder capacity) professionally sized by a solar technology supplier.

Frequently asked questions

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

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

Does the cylinder work without sun, for example in winter?

Yes, in that case the heating is taken over entirely by the upper heat exchanger connected to the boiler, just as if the cylinder had no solar heat exchanger at all.

How many collectors do I need for this capacity?

As a rough guide, 1-1.5 m² of collector is calculated per 50-70 l of cylinder capacity, so for 200 l approximately 3 m² of collector area, 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 at weaker sunlight.

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 solar circuit circulation pump.

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 needs will the sun cover during the year?

Roughly 50-65% of annual needs depending on location, roof orientation, collector area and household consumption; in summer months this 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 stops 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 tank, and the functionality of the controller, ideally 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 boiler with a higher temperature; for cooperation with a heat pump we recommend rather the Z HP model with a large-area heat exchanger, or consulting the suitability of the combination with our technical advisors.

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

The solar controller usually displays the collector and cylinder temperatures and the status of the circulation pump; a drop in cylinder temperature during sunny weather and a non-functioning pump are the first signs to have it checked by a service technician.

Connection to the solar station and antifreeze mixture

The solar station is a compact unit containing the solar circuit circulation pump, flow meter, solar circuit safety valve, pressure gauges and check valves - it is installed between the collectors and the lower heat exchanger of the Z 200 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 degrade slightly over time, so its regular inspection (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 offers greater storage capacity for households with a larger collector area (4-6 m²) or a higher number of people - the larger capacity can store more solar heat during the day, extending the time during which the household draws hot water without needing boiler back-up heating. If you are planning multiple 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 the capacities.

Summary

The Z 200 SOL model is the best choice for households that want to make maximum use of solar energy for hot water heating while still having the certainty of boiler back-up heating when there is not enough sun. The two separate heat exchangers and temperature stratification ensure efficient use of both heat sources in a single tank. Investing in solar DHW heating is one of the measures with a relatively quick 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 stated 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 other cylinder components (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 find the nearest service centre.