Viessmann VITOCAL 300-G Installation And Service Instructions Manual page 18

Preparing for installation
Function description for the system examples
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 88).
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 flow in the
secondary and heating circuits. For
example, the flow rate in the secon-
dary circuit remains constant even if
the heating circuit flow rate is reduced
via thermostatic valves.
■ Longer heat pump operating times
18
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.
Note
The flow rate of the secondary pump
should be greater than that of the heating
circuit pumps.
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 from
page 242), do not install a mixer in the
heating circuit.
Low loss header
When using a low loss header, ensure
that the flow rate on the heating circuit
side is greater than the flow rate on the
secondary side of the heat pump.
The heat pump control unit treats a low
loss header like a small heating water
buffer cylinder. The low loss header must
therefore be configured as a heating
water buffer cylinder in the control unit
settings (see from page 204).
(cont.)