CLESS 2S: high-stratification thermal storage with DHW production
CLESS 2S is the CLESS configuration combining technical heat storage, instantaneous domestic hot water production and solar thermal integration.
The system uses special compensation chambers to manage water flows between the heat generator, storage tank and heating circuit, supporting thermal stratification and reducing mixing between hot and cold water.
Patented compensation-chamber system
CLESS operation is based on dynamic water-flow management between the heat generator and the heating circuit.
Generator and heating circuit with the same flow rate
The compensation chambers allow direct thermal-flow exchange between the heat generator and the heating circuit.
The generator produces more energy than required
Excess heat is transferred to the storage tank and hot water is directed towards the upper section of the buffer tank.
The heating system requires stored energy
The heating circuit can use the hot water stored in the upper section of the tank, where thermal stratification concentrates the available heat.
Instantaneous domestic hot water production
CLESS 2S includes a dedicated domestic hot water heat exchanger positioned in the upper section of the storage tank.
The internal design concentrates heat around the DHW heat exchanger, allowing domestic water to be heated instantaneously as it passes through the exchanger.
Removable DHW heat exchangerThe domestic hot water heat exchanger can be removed to facilitate maintenance and possible replacement over time.
Domestic hot water is therefore not stored directly inside the main technical storage volume, but is heated through the dedicated heat exchanger.
CLESS 2S for biomass and gas boilers
REQA identifies CLESS 2S as the DHW-equipped configuration intended particularly for systems using biomass heat generators and gas boilers.
The flow-management system allows heat to be transferred towards the heating circuit without necessarily heating the entire storage volume beforehand, while excess thermal energy can be stored inside the buffer tank.
Heat generator protection and return-flow management
The compensation chambers help prevent the heat generator from directly receiving the coldest water stored at the bottom of the buffer tank.
The system instead manages the return flow from the heating circuit, helping reduce sudden thermal variations affecting the generator.
Integrated solar thermal heat exchanger
CLESS 2S also includes a dedicated heat exchanger for the solar thermal circuit.
Energy produced by solar collectors can therefore be transferred to the storage tank and used together with the main heat generator.
Three versions: CLESS 600, 800 and 1000 2S
CLESS 2S is available in three different sizes. The commercial designation identifies the model, while the actual useful volume is shown in the technical table.
| Specification | CLESS 600 2S | CLESS 800 2S | CLESS 1000 2S |
|---|
| Useful volume | 510 l | 738 l | 945 l |
| Energy class | C | C | C |
| Heat loss | 112 W | 130 W | 144 W |
| DHW heat exchanger surface | 3 m² | 3 m² | 4 m² |
| DHW production 10/45 °C with storage at 70 °C | 1.5 m³/h | 1.5 m³/h | 2 m³/h |
| DHW heat exchanger pressure drop | 295 mbar | 295 mbar | 584 mbar |
| Solar heat exchanger surface | 2.5 m² | 2.5 m² | 3 m² |
| Solar heat exchanger pressure drop | 73 mbar | 191 mbar | 313 mbar |
| Empty weight | 203 kg | 224 kg | 250 kg |
| Max. buffer tank operating pressure | 3 bar | 3 bar | 3 bar |
| Max. DHW heat exchanger operating pressure | 3 bar | 3 bar | 3 bar |
| Max. solar heat exchanger operating pressure | 10 bar | 10 bar | 10 bar |
| Max. operating temperature | 90 °C | 90 °C | 90 °C |
| REQA product code | 304.004 | 304.005 | 304.006 |
CLESS 2S dimensions
| Dimension | 600 2S | 800 2S | 1000 2S |
|---|
| Diameter without insulation | 650 mm | 790 mm | 790 mm |
| Overall diameter | 850 mm | 990 mm | 990 mm |
| Overall height | 1765 mm | 1725 mm | 2175 mm |
| Domestic cold water inlet | 3/4" | 3/4" | 3/4" |
| Domestic hot water outlet | 3/4" | 3/4" | 3/4" |
100 mm thermal insulation
The CLESS range uses 100 mm thick recycled polyester-fibre insulation, designed to reduce thermal losses.
Insulation: recycled polyester fibre
Thickness: 100 mm
Outer covering: PVC Seta Skin
Maximum operating temperature: 90 °C
When should you choose CLESS 2S?
CLESS 2S is suitable when instantaneous domestic hot water production is required in addition to technical heat storage.
- systems with biomass heat generators;
- systems with gas boilers;
- systems requiring DHW production through a heat exchanger;
- systems with solar thermal integration;
- heating systems requiring high-stratification technical storage.
Frequently asked questions about CLESS 2S
Does CLESS 2S produce domestic hot water?
Yes. It features a removable DHW heat exchanger for instantaneous domestic hot water production.
What is the difference between CLESS 1S and CLESS 2S?
CLESS 1S is designed for technical heat storage without DHW production, while CLESS 2S also includes the domestic hot water heat exchanger.
Does CLESS 2S include a solar heat exchanger?
Yes. All CLESS 2S versions include a dedicated heat exchanger for the solar thermal circuit.
What is the DHW production capacity of CLESS 2S?
With domestic water heated from 10 to 45 °C and the storage tank at 70 °C, the catalogue specifies 1.5 m³/h for CLESS 600 2S and 800 2S, and 2 m³/h for CLESS 1000 2S.
Which size should I choose?
The choice between CLESS 600, 800 and 1000 2S should take into account the heat generator output, the building's heating demand, DHW requirements, heating circuit characteristics and any solar thermal integration.
Advice and orderingCLESS 2S can be ordered in 600, 800 and 1000 versions. Contact our customer service team to check the most suitable configuration for your system and the relevant delivery times.
Correct storage sizing and system configuration must be checked by a qualified technician. Always refer to REQA technical documentation and applicable regulations.
