Viessmann VITOCAL 300-G Technical Manual page 38

Design information
Note
Up to 4 brine distributors can be connected to a flow or return pipe. If
more than 4 brine distributors are required, additional geothermal col-
lector circuits are also required. The brine distributors and geothermal
collector circuits must be designed and sized by a specialist contractor
(e.g. Viessmann geothermal department or an engineering consul-
tancy).
Example calculations for sizing the heat source
Selection of the heat pump
Building heat load (net heat load)
DHW heating supplement for
a 3-person household
Power-OFF periods
Total heat load of the building
System temperature (at min. outside temp. –14 °C)
Heat pump operating point
3
The heat pump with a heating output of 6.4 kW (incl. supplement for power-OFF periods, excl. DHW heating), refrigerating capacity
= 4.9 kW corresponds to the required output.
²
K
Sizing the geothermal collector
Average specific extraction rate ³
= 4.9 kW
²
K
F = ² /³ = 4900 W/25 W/m
E K E
The number X of required pipe circuits (PE pipe 32 × 3.0 (2.9)) @ 100 m length each results from:
X = F · 1.5/100 = 200 m
E
Selected: 3 pipe circuits @ 100 m length (Ø 32 mm × 3.0 (2.9) mm with 0.531 l/m)
Required amount of heat transfer medium (V
Take the content of the geothermal collector including all supply lines, plus the volume of fittings and the heat pump into consideration.
Provide manifolds corresponding to the number of pipe circuits.
The low refrigerating capacity and the connection length mean that a supply line of PE 32 × 3.0 (2.9) is adequate.
Supply line: 10 m (2 × 5 m) with PE 32 × 3.0 (2.9)
V = Number of pipe circuits × 100 m × Pipeline volume + Supply line length × Pipeline volume
R
= 3 × 100 m × 0.531 l/m + 10 m × 0.531 l/m = 159.3 l + 5.31 l = 165 l
Selected: 200 litre (incl. heat transfer medium in the fittings and the heat pump)
Geothermal collector pressure drop
Flow rate, heat pumps with 6.2 kW: 1200 l/h
Flow rate per pipe circuit = (900 l/h)/(3 circuits of 100 m) each = 300 l/h per pipe circuit
Δp = R value × pipe length
Δp = 32 Pa/m × 100 m = 3200 Pa
Pipe circuit
Δp = 315 Pa/m × 10 m = 3150 Pa
Supply line
Δp = 40000 Pa = 400 mbar (max. ext. pressure drop, primary side)
permissible
Δp = Δp + Δp
Pipe circuit Supply line
Result:
The intended geothermal collector can be used with a heat pump with 6.2 kW rated heating output, since Δp = Δp
exceed the value for Δp
VIESMANN
38
(cont.)
2
= 25 W/m
E
≈ 200 m
2 2
2 2
· 1.5 m/m /100 m = 3 pipe circuits
)
R
= 3200 Pa + 3150 Pa = 6350 Pa ≙ 63.5 mbar
.
permissible
4.8 kW
0.75 kW (see chapter "DHW heating supplement": 0.75 kW < 20 % of building heat
load)
3 × 2 h/d (only 4 h are taken into consideration, see chapter "Mono-mode opera-
tion")
5.76 kW
45/40 °C
B0/W35
R value (resistance value) for PE 32 × 3.0 (2.9) (see tables Pressure
drop for pipelines):
■ At 300 l/h ≈ 31.2 Pa/m
■ At 1600 l/h ≈ 314.7 Pa/m
+ Δp does not
pipe circuit supply line
VITOCAL 300-G