Sample Calculation; Calculation Of The Cylinder Size Based On Water Volume; Calculation Of The Cylinder Size Based On Heat Volume - Viessmann Vitocell 300-H Technical Manual

Cylinder loading systems — Vitocell 100-L with Vitotrans 222

5.4 Sample calculation

A sports centre is equipped with 16 showers which are limited to
15 l/min.
According to design requirements, 8 showers are operated simulta-
neously for up to 30 min continuously. The drawing temperature
should be 40 °C. A max. of 100 kW boiler output is available for
DHW heating.
c = Spec. thermal capacity
1 kWh
860 l · K
n = Number of DHW cylinders
n = Number of draw-off points
Z
Φ = Heat volume in kWh available by continuous output
D
L = Continuous output in kW

Calculation of the cylinder size based on water volume

Over a period of 30 min, a total water volume V
40 °C is required.
V = n · ´ · t
ttl. Z
= 8 showers · 15 l/min · 30 min
= 3600 l
Of the 3600 l, the 100 kW connected load can deliver a water vol-
ume V over a period of 30 min.
D
L · t
V =
D
c · ΔT
100 kW · 0.5 h · 860 l · K
V =
D
1 kWh · (40 – 10) K
5
=1433 l
This means that the DHW cylinder must make the following water
volume available at a temperature of 40 °C:
3600 l – 1433 l = 2167 l

Calculation of the cylinder size based on heat volume

Over a period of 30 min (as per calculation), a total water volume of
3600 l at a temperature of 40 °C is required. This corresponds to a
heat volume of Φ .
ttl
Φ = V · ΔT · c
ttl. ttl.
1 kWh
= 3600 l · 30 K ·
860 l · K
The connected load can, over the drawing period of 30 min, provide
a heat volume of Φ .
D
Φ = L · t
D
= 100 kW · 0.5 h = 50 kWh
This means that the DHW cylinder must store a heat volume of Φ
Φ = Φ – Φ
cyl. ttl. D
= 126 kWh – 50 kWh = 76 kWh
VIESMANN
32
at a temperature of
ttl
= 126 kWh
Φ = Total heat demand in kWh (for production and demand)
ttl
Φ = Usable heat volume of the total cylinder volume in kWh
cyl
Φ = Usable heat volume of a single DHW cylinder in kWh
cyl.
ind.
t = Time in h
T = Cylinder storage temperature in °C
a
T = Cold water inlet temperature in °C
e
ΔT = Temperature differential between draw-off temperature
and cold water inlet temperature in K
= Draw-off rate per draw-off point in l/h
´
V = DHW heated by continuous output in l
D
V = Total draw-off volume in l
ttl
V = Usable cylinder capacity in l
cyl
At a storage temperature of 60 °C, the required cylinder volume V
results.
2167 l · (40 – 10) K
V =
cyl.
(60 – 10) K
The calculated number n of Vitocell 100-L with a volume of 750 l
each results from the following:
1300 l
n = = 1.73
750 l
Selected cylinder loading system:
2 Vitocell 100-L, each with 750 l capacity, and 1 Vitotrans 222 heat
exchanger set with a heating output of 120 kW (in accordance with
max. available boiler output according to the sample calculation, i.e.
100 kW).
Each individual Vitocell 100-L DHW cylinder with 750 l cylinder
capacity stores the following heat volume Φ
Φ = 750 l · (60 – 10) K ·
cyl. ind.
= 43.6 kWh
This results in the calculated number of cylinders n.
Φ
cyl.
n =
Φ
cyl. ind.
76 kWh
= = 1.74
43.6 kWh
Selected cylinder loading system:
2 Vitocell 100-L, each with 750 l cylinder capacity, and 1
.
cyl
Vitotrans 222 heat exchanger set with a heating output of 120 kW (in
accordance with max. available boiler output according to the sam-
ple calculation, i.e. 100 kW).
(cont.)
=1300 l
:
cyl. ind.
1 kWh
860 l · K
DHW heating
cyl