Sizing According To Continuous Output; Application; Determining The Required Dhw Cylinder, Example 1 (With Constant Flow Temperatures); Determining The Required Dhw Cylinder, Example 2 (With A Fixed Heat Source Temperature Differential) - Viessmann Vitocell 300-H Technical Manual

Sizing
(cont.)

4.3 Sizing according to continuous output

Application

Sizing according to continuous output is employed if hot water is to
be continuously drawn from the DHW cylinder. This sizing method is
therefore mainly used for commercial applications.

Determining the required DHW cylinder, example 1 (with constant flow temperatures)

Requirements:
■ Continuous output in l/h or kW
■ DHW outlet temperature in °C
■ Cold water inlet temperature in °C
■ Heating water flow temperature in °C
The DHW cylinder "Specification" is used to determine:
■ Capacity and number of DHW cylinders
■ Flow rate on the heating water side
■ Delivery head of the circulation pump for cylinder heating
The DHW cylinders are sized in the same way.
The following example illustrates the calculation procedure.
Example:
For production purposes, a factory requires 2700 l/h DHW at 60 °C.
The boilers deliver a heating water flow temperature of 90 °C. The
cold water inlet temperature is 10 °C.
4
Continuous output
DHW outlet temperature
Cold water inlet temperature
Heating water flow temperature
Required cylinder type
Calculating the number and size of the DHW cylinders
Procedure:
1. Select Vitocell 300-V, type EVIA-A
2. Refer to the specification for cylinder banks in the Vitocell 300-V
datasheet.
3. In the table, find the line for "Continuous output from 10 to 60 °C"
and Heating water flow temperature "90 °C".
4. In the column Cylinder capacity = 500 l and Number of cylinders =
3, a continuous output of 3033 l/h is specified.
Selected DHW cylinders:
3 x Vitocell 300-V, type EVIA-A, each with 500 l capacity.
The continuous output of the selected DHW cylinders must be at
least equal to the required continuous output.
Calculating heating water flow rate
A heating output of 162 kW is required for the calculated continuous
output (see table "Specification" in the datasheet for the DHW cylin-
der). The required heating water flow rate is stated in the table col-
umn for the selected DHW cylinder: 9.0 m
pump for cylinder heating for a heating water flow rate of 9.0 m
Calculating the pressure drop on the heating water side
The total flow rate of 9.0 m
heating water flow and return lines (e.g. valves, bends) as well as
the boiler when calculating the pressure drop in the complete sys-
tem.

Determining the required DHW cylinder, example 2 (with a fixed heat source temperature differential)

Requirements:
■ Required continuous output in kW or in l/h (conversion required)
■ DHW outlet temperature in °C
■ Cold water inlet temperature in °C
VIESMANN
24
= 2700 l/h
= 60 °C
= 10 °C
= 90 °C
= Stainless steel, vertical
3 /h, i.e. size the circulation
3
/h must be taken into account for the
Where several cylinders are connected in parallel, the total pressure
drop is equal to the pressure drop of an individual cylinder. The pres-
sure drop of the DHW cylinder on the heating water side for the head
of the circulation pump for cylinder heating is calculated as follows:
As the 3 cylinders are connected in parallel, each cylinder has a
heating water flow rate of 3.0 m
the diagram "Pressure drop on the heating water side" in the data-
sheet for "Vitocell 300-V, type EVIA-A". For a heating water flow rate
of 3000 l/h, read the pressure drop off the straight line of the cylinder
with a capacity of 500 l: 90 mbar (9 kPa)
9.0 6.0
A
3.0 6.0
A Heating water flow
B Heating water return
Result:
Total heating water flow rate = 9.0 m
Heating water flow rate per cylinder = 3.0 m
Pressure drop on the heating water side of the DHW cylinder =
90 mbar (9 kPa)
Sizing the circulation pump for cylinder heating
The circulation pump for cylinder heating must therefore deliver a
heating water flow rate of 9.0 m
on the heating water side of 90 mbar (9 kPa) for the 3 cylinders, plus
the pressure drop of the boiler, the pipework between the cylinders
and the boiler, and the individual pressure drop values of fittings and
valves.
The following rule of thumb applies: If the available boiler heating
output ² (to DIN 4701) or Φ
K
tinuous output ² or Φ
cyl
for cylinder heating to suit the transfer of the boiler heating output. If,
on the other hand, the boiler heating output is greater than the con-
tinuous output ² or Φ
3 /h.
cyl
can be sized to suit the continuous output as a maximum rating.
■ Heating water flow temperature in °C
■ Heating water return temperature in °C
3
/h (see following diagram). Refer to
3.0
9.0
B
3 /h
3 /h
3
/h and overcome the pressure drop
(to EN 12831) is lower than the con-
K
, it is sufficient to size the circulation pump
cyl
, the circulation pump for cylinder heating
cyl
DHW heating