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3064298_201507
20. Connecting the heating / cooling
circuit and the DHW circuit
Size calculation for air/water heat pumps:
Approx.
10 litres/kW
heating output (for A2/W35)
Air/water
heat pump
BWL-1S(B)-07
BWL-1S(B)-10
BWL-1S(B)-14
Buffer cylinder
SPU-1-200
SPU-1-200
SPU-1-200
Recommended buffer
cylinder sizing for the
BWL-1S(B)
A buffer cylinder for optimising compressor runtime is not required, thanks to
the inverter technology; therefore smaller buffer cylinders are sufficient
.
Recommended sizing for
diaphragm expansion vessel
(DEV)
Expansion vessel
size
Water content
heating system
Expansion vessel
pre-charge pressure
25 litres
235 litres
1.5 bar
35 litres
320 litres
1.5 bar
50 litres
470 litres
1.5 bar
80 litres
750 litres
1.5 bar
100 litres
850 litres
1.5 bar
140 litres
1210 litres
1.5 bar
200 litres
1600 litres
1.5 bar
Since variable flow rates can arise on the heat draw-off side depending on the load,
the minimum flow rate must be ensured to enable fault-free heat pump operation.
This is usually achieved by installing a separating buffer cylinder or a low loss header.
A buffer cylinder is essential for all systems with radiators, individual room
temperature control (thermostatic valves), multiple heat generators or heating
circuits.
For air/water heat pumps with output-dependent control in connection with 100 %
underfloor heating, there is no need to use a
buffer cylinder, provided the following
condition is met:
1 (or more) lines of the heating system (e.g. bathroom) is permanently and fully open
(requires the written consent of the operator). For this, the minimum flow rate must be
verified by means of a pressure drop calculation.
If necessary, one (or more) heated heating circuits(s) can be specifically opened fully
via output A1 during defrost mode.
The valve opening time must be < 20 sec.
Buffer cylinder
In order to ensure that the heat pump operates reliably and efficiently, it is essential
that the flow rates specified in the technical data for the heating circuit can be
guaranteed. The following table lists the required minimum cross-sections for the
pipework on the heating circuit side. On systems with a separating cylinder or low
loss header, these cross-sections must, as a minimum, be observed up to the
separating cylinder (e.g. incl. the BSP/BSH) or the low loss header.
Approximate pipework
calculation for heating water
flow rates and Cu pipes without
bends (observe residual head of
pump).
Air heat pump
Nominal water flow rate
Minimum cross-section,
heating circuit pipework
Pressure loss
per metre
Flow velocity
BWL-1S(B)-07
19.7 l/min
Pipe Ø 35x1.5 /
28x1.5
0.75 mbar/m /
2.4 mbar/m
0.41 m/s /
0.67 m/s
BWL-1S(B)-10 400V
28.8 l/min
Pipe Ø 35x1.5
1.5 mbar/m
0.60 m/s
BWL-1S(B)-14 400V
34.1 l/min
Pipe Ø 35x1.5
2.0 mbar/m
0.71 m/s
BWL-1S(B)-10 230 V
31,8 l/min
Pipe Ø 35x1.5
1,7 mbar/m
0,66 m/s
BWL-1S(B)-14 230 V
40,4 l/min
Pipe Ø 35x1.5
2,6 mbar/m
0,84 m/s
- The DHW cylinder must be equipped with an internal indirect coil suitable for the
heating output of the heat pump.
- The internal indirect coil should have a surface area of at least 0.25m² per kW of
heating output.
- The pipework must be sufficiently large (> DN 25).
DHW cylinders