Dhw Circulation Pipes; Connection Of The Dhw Circulation Pipe With Cylinder Banks - Viessmann Vitocell 100-H Technical Manual

Installation — DHW cylinders

6.2 DHW circulation pipes

For reasons of hygiene and convenience, DHW circulation pipes are
installed in DHW heating systems. Observe the applicable standards
and rules. As a fundamental principle, "gravity circulation systems",
which used to be commonly used, are no longer permissible nowadays
for hygiene reasons. DHW circulation pipes or DHW circulation sys-
tems must always be fitted with appropriate pumps, hydraulically
adjusted and thermally insulated in accordance with the applicable
regulations. Take the applicable standards and regulations into
account (e.g. DVGW Codes of Practice W551/W553 and DIN 1988/
TRWI).
The flow rate of the circulation system is determined according to the
scale of the pipework, the thermal insulation and the targeted or
required maximum temperature differential between the cylinder outlet
(DHW) and the DHW circulation inlet (DHW circulation).
Depending on the type of DHW heating system, there are various con-
nection options for the DHW circulation pipe. Virtually all DHW cylin-
ders are fitted with connections for the DHW circulation pipe in the
upper third of the cylinder. The exception to this is DHW heating sys-
tems in continuous operation such as freshwater modules or combi
cylinders with an integral DHW indirect coil (Vitocell 340-M/360-M).
They have a "threaded DHW circulation fitting", which means that the
DHW circulation line is routed partially into the heat exchanger. If this
is not the case, the DHW circulation pipe can also be connected to the
cold water inlet of the DHW cylinder.

6.3 Connection of the DHW circulation pipe with cylinder banks

■ Connect the DHW circulation pipe with detachable fittings.
■ Install the cylinder banks with DHW circulation according to the dia-
grams below to ensure that each individual cylinder is heated evenly.
In conjunction with boilers or district heating systems without a return
temperature limit on the heating water side and for operation on the
heating side with saturated steam up to 1 bar (0.1 MPa) pressure and
a DHW circulation pipe:
WW
Z
6
KW
VIESMANN
32
(cont.)
Connecting to the cold water inlet is also an option for DHW cylinders
where, due to the ratio of the draw-off rate and/or the flow rate of DHW
circulation to the cylinder capacity, continuous mixing of the DHW cyl-
inder content must be expected. This applies, for example, to very
small DHW cylinders. Connecting to the cold water inlet may also be
advisable in the case of extremely high DHW circulation flow rates. In
poorly insulated pipework or very widely branched systems in partic-
ular, extremely high flow rates may be necessary. It is then important
to ensure that high flow velocities cannot lead to any settling inside the
DHW cylinder. The resulting mixing in the standby part may lead, in
some cases, to extremely long heat-up times and fluctuating outlet
temperatures (DHW). In this case too, connecting the DHW circulation
pipe to the cold water inlet may be advantageous in terms of the oper-
ating characteristics of the DHW heating system.
In conjunction with district heating systems with a return temperature
limit on the heating water side and/or several DHW circulation pipes:
WW
Z
KW
DHW heating