With ZSBR ... / ZBR ... boilers, domestic hot water is produced by means of indirectly heated cylinders. ZSBR boilers are heating appliances with an integrated three-way valve for connecting an indirect cylinder. ZBR boilers are heating-only appliances with the following options for heating domestic hot water:
- with a pump integrated in the boiler (accessory) and an external three-way valve (supplied on site)
- with a heating pump and a cylinder charging pump outside the appliance. With this arrangement, provided the mixing valve in the heating circuit is controlled appropriately, the heating circuit and the hot water cylinder can be supplied at the same time.
A cylinder temperature sensor with a coded connector can be connected to the Heatronic 3 control unit without any additional accessories. Using the cylinder temperature sensor, the hot water temperature in the indirect cylinder can easily be set on the Heatronic 3 unit.
ZWBR combi boilers heat domestic hot water instantaneously by means of a plate heat exchanger. Thanks to the enlarged heat transfer surface of the plate heat exchanger, the heating return is always cooled sufficiently and the water is heated in economical condensing mode.
Choosing a hot water cylinder
Selection criteria:
- required comfort (number of people, usage), size of the NL coefficient
- available boiler output
- available space
Hot water comfort
The performance factor to DIN 4108 indicates the number of fully supplied flats with 3,5 occupants, a standard bath and two further draw-off points. Larger baths, for example, require a higher NL coefficient, and fewer occupants a lower one.
Cylinder charging output of the boilers:
Charging the cylinder´
The ECO button lets you choose between two cylinder charging functions: 14,7 26,2 39,1 Comfort mode: The water in the cylinder is heated to the set temperature as a priority. The boiler then switches back to heating mode. ECO mode: The boiler alternates at ten-minute intervals between heating the water in the cylinder and heating mode until the water in the cylinder reaches the set temperature. The boiler then switches to continuous heating mode.
Space requirements
Junkers condensing boilers allow a variety of combinations and installation options with Junkers hot water cylinders. The specific space requirements depend on the cylinder actually chosen.
Connecting the cylinder to the cold water supply
The connection to the cold water supply must be made in accordance with DIN 1988, using suitable fittings or a complete safety group. The safety valve must be type-tested and set so that it prevents the cylinder's permissible operating pressure from being exceeded by more than 10%. If the static pressure of the installation exceeds 80% of the opening pressure of the safety valve, a pressure regulator must be fitted upstream of this valve. This means that with Junkers cylinders of the SO ... and ST ... series, a pressure reducing valve must be fitted from an operating pressure of 8 bar upwards. This assumes that a safety valve with an opening pressure of 10 bar is fitted. Where a non-return valve is used, the safety valve must be fitted between the non-return valve and the cylinder connection (cold water).
To prevent water loss through the safety valve, we recommend additionally fitting an expansion vessel that is permitted and approved for drinking water.
The discharge pipe must not be shut off and must discharge freely and visibly into the drain. Its sizing depends on the size of the cylinder.
To prevent contact corrosion on the cylinder's connection threads, it is advisable to use brass or bronze threaded fittings for the connections. In combination with copper pipework, an unfavourable water composition and high water hardness can lead to the pipes furring up as a result of electrochemical processes. To prevent this, we recommend electrical isolation using insulating components or insulating threaded fittings.
Connecting the cylinder to the boiler
To ensure trouble-free and optimised operation, only connecting pipes with the lowest possible resistance may be used on the hot water side.
The following accessories are available:
- ST 65 E: accessory no. 1161
- ST 120/160: accessory no. 615/2
If the connecting pipes are to be installed on site, we recommend the following minimum sizes:
Where corrugated hoses are used, the increased water resistance must be taken into account in the sizing (thermal expansion 20 K). Pipes should be kept as short as possible. Pipes, connections and threaded joints must be insulated against heat loss in accordance with the applicable regulations. An effective air vent must be installed at the highest point between the hot water cylinder and the Junkers condensing boiler to prevent malfunctions caused by air entering the system.
Secondary circulation connection
All Junkers cylinders (except the ST 65 E) are fitted with a secondary circulation connection. If no circulation pipe is connected, the connection must be capped. For the ST 120-2 E and ST 160-2 E cylinders, accessory ZL 102/1 is available, consisting of a plastic dip tube and threaded fittings. In view of cooling losses, circulation is permitted only with a time-controlled or temperature-controlled circulation pump.
Connecting two cylinders in parallel
Connect the cylinders to the heating and to the hot water diagonally (Tichelmann system). This balances the pressure losses. Connect only one cylinder temperature sensor.
Hot water expansion vessel
To prevent water loss through the safety valve, we recommend additionally fitting an expansion vessel that is permitted and approved for drinking water. It must be installed in the cold water supply between the cylinder and the safety group. The following table serves as a rough guide to sizing the expansion vessel. Different sizes may result where the usable volume of individual vessel types differs. The figures relate to a cylinder temperature of 60°C.
Overheating / flow limitation
Junkers hot water cylinders are optimised for maximum performance (NL number). With short draw-offs in quick succession, the set temperature may therefore be exceeded and heat may stratify in the upper part of the cylinder. This overshoot is inherent in the design and does not affect comfort.
This temperature overshoot can be reduced by connecting a circulation pipe with a time-controlled or, where possible, time- and temperature-controlled circulation pump. To make the best possible use of the cylinder capacity and to prevent premature mixing, we recommend setting the cold water inflow to the cylinder as follows:
Hot water from the ZWBR boiler
The ZWBR combi version of the boiler forms a single unit consisting of a heating section and a hot water section. A plate heat exchanger is provided for heating hot water instantaneously.
