Viessmann VITOCAL 350-A, Installation And Service Instructions Manual

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31
Heating circuit
Minimum flow rate
Heat pumps require a minimum heating
water flow rate (see specification on
page 246), which
must be maintained.
To ensure the minimum flow rate, install
an overflow valve.
Systems with small water volumes
For systems with small water volumes
(for example, heating systems with radi-
ators), use a heating water buffer cylin-
der to prevent excessive heat pump
cycling (starting/stopping).
Systems with large water volumes
Systems with large water volumes (for
example, underfloor heating systems)
can operate without a heating water buf-
fer cylinder. In these heating systems,
install an overflow valve at the heating
circuit distributor of the underfloor heat-
ing system that is furthest away from the
heat pump. This safeguards the mini-
mum flow rate, even in sealed heating
circuits.
In conjunction with an underfloor heating
system, install a temperature limiter
(accessory, order no. 7151 728 or
7151 729) (for connection, see
page 92).
Heating water buffer cylinder oper-
ated in parallel
Applications for a heating water buffer
cylinder:
■ Bridging power-OFF periods:
At peak times, heat pumps may be
switched off by your local power sup-
ply utility, subject to your electricity tar-
iff. A heating water buffer cylinder sup-
plies the heating circuits even during
this power-OFF period.
■ Constant flow rate through the heat
pump:
Heating water buffer cylinders provide
hydraulic separation of the volume
flow in the heat pump and heating cir-
cuits. For example, the flow rate in the
heat pump circuit remains constant,
even if the heating circuit flow rate is
reduced by thermostatic valves.
■ Longer heat pump operating times
Because of the increased water volume
of the heat source and the fact that it may
have a separate shut-off facility, an addi-
tional (or larger) expansion vessel
should be provided.
Protect the heat pump in accordance
with EN 12828 [or local regulations].
Systems without heating water buffer
cylinder
To safeguard the minimum heating
water flow rate (see specification on
page 246), do
not install a mixer in the
heating circuit.
Preparing for installation
Function description for the system examples
(cont.)
5414 828 GB
Installation