Heating Water Buffer Cylinder For Optimised Runtimes; Heating Water Buffer Cylinder For Bridging Periods When The Supply Is Blocked; Water Quality; Heating Water - Viessmann VITOCAL 300-G Technical Manual

Design information
Because of the increased water volume of the heat source and the fact
that it may have a separate shut-off facility, an additional (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.

Heating water buffer cylinder for optimised runtimes

V = Q · (20 to 25 litres)
HP HP
Q = Absolute rated heat pump heating output
WP
V = Heating water buffer cylinder volume in litres
HP
Example:
Type BW 110 with Q
WP
V = 10.2 · 20 litres = 204 litre cylinder capacity
HP
Selection: Vitocell 100-E with 200 litre capacity
3

Heating water buffer cylinder for bridging periods when the supply is blocked

This version is offered for heat distribution systems without additional
cylinder mass (e.g. radiators, hydraulic fan convectors).
Storing 100 % of heating energy for the duration of the power-OFF
periods is feasible, but not recommended, otherwise cylinders would
become too large.
Example:
Φ = 10 kW = 10000 W
HL
t = 2 h (max. 3 x per day)
Sz
Δϑ =10 K
c
= 1.163 Wh/(kg∙K) for water
P
Spec. thermal capacity in kWh/(kg ∙ K)
c
P
Φ Heat load of the building in kW
HL
t Period in h during which the supply is blocked
Sz
V Heating water buffer cylinder volume in litres
HP
Δϑ System cool-down in K
100 % sizing
(subject to the existing heating surfaces)
Φ · t
HL SZ
V =
HP c · Δ
P

3.10 Water quality

Heating water

Unsuitable fill and top-up water increases the level of deposits and
corrosion and may lead to system damage.
Regarding the quality and amount of heating water, incl. fill and top-up
water, observe the VDI 2035 [or local regulations].
VIESMANN
48
(cont.)
= 10.2 kW
Protect the heat pump in accordance with EN 12828 [or local regula-
tions].
Note
With two-stage heat pumps and heat pump cascades, the volume of
the heating water buffer cylinder can be sized for runtime optimisation
to match the highest possible rated heat pump heating output.
10000 W · 2 h
V = =1720 kg
HP
Wh
1.163 · 10 k
kg · k
1720 kg water represent a cylinder capacity of approx. 1720 l.
Selection: 2 Vitocell 100-E each with 1000 l capacity.
Rough sizing
(subject to the utilisation of the delayed building heat loss)
∙ (60 to 80 l)
V
= Φ
HP
HL
= 10 ∙ 60 l
V
HP
V = 600 litre cylinder capacity
HP
Selection: 1 Vitocell 100-E with 750 litre cylinder capacity.
■ Thoroughly flush the entire heating system prior to filling it with water.
■ Only use fill water of potable quality.
■ Soften fill water with a hardness above 16.8 °dH (3.0 mol/m
with the small softening system for heating water (see the
Viessmann Vitoset pricelist).
3 ), e.g.
VITOCAL 300-G