Pump curve
This panel holds the library of circulating pumps available to the hydraulic network. Each pump is described by its head-flow characteristic and its efficiencies; the network solver then finds where each pump's curve meets the resistance of the circuit it sits in. The five default pumps, described below, let you solve a network before your own pump is chosen; replace a slot with the manufacturer's curve of your pump as soon as it is known.
Defining a pump - The library holds five pump slots, listed in the Pump box at the top of the panel. Pick one there to edit its curve and efficiencies; everything below the box applies to the pump shown in it. Slots cannot be added or deleted; an unused slot keeps its default name and curve.
The five slots start out as five real pumps, from the smallest to the largest, each read off the maximum curve of its Grundfos data sheet:
| Slot | Pump | Shutoff head | Last point read | Power input | |---|---|---|---|---| | Pump 1 | UPS 15-58 FC, speed 3 (wet rotor, 60 Hz) | 5.9 m | 0.7 m at 3.6 m³/h | 87 W | | Pump 2 | UP 26-116 F (geothermal flow-center pump, 60 Hz) | 11.3 m | 1.6 m at 7.7 m³/h | 385 W | | Pump 3 | MAGNA3 32-100 F, MAX curve (60 Hz) | 10.2 m | 1.5 m at 10.2 m³/h | 180 W | | Pump 4 | MAGNA3 40-180 F, MAX curve (60 Hz) | 17.9 m | 2.9 m at 24.8 m³/h | 614 W | | Pump 5 | TPE3 40-240-S, 100 % then power limit (dry rotor, 50 Hz) | 24.8 m | 6.8 m at 35.9 m³/h | 1.7 kW |
The overall efficiency (pump × motor) of each slot is the one its data sheet gives in the middle of the maximum curve, from about 21 % for the two single-speed wet-rotor circulators to about 67 % for the dry-rotor pump. The curves are digitised from the published graphs, to the tenth of a metre and of a cubic metre per hour: close enough to size a loop, not a substitute for the manufacturer's selection software. The slots keep their names, Pump 1 to Pump 5, because the nodes of a drawing refer to a pump by its name.
Each slot carries its rank in front of its name — 1 - Pump 1, 2 - Pump 2 and so on — in the box and in the list it drops down. The number is fixed and identifies the slot's column in the table below and its entry in the chart legend, even after the pump is renamed. It is not part of the name.
Rename a pump by typing over the name in that same box and pressing Enter (or clicking elsewhere); the leading number stays where it is and cannot be typed over. The name is what the hydraulic inspector offers in its Pump curve combo box, so name them after the model or the position they occupy rather than leaving Pump 1, Pump 2. Renaming follows through to the network: every pump node that referenced the old name is re-pointed to the new one. Two pumps cannot share a name, and a blank name is refused — in both cases the former name comes back.
H-Q points - Enter the manufacturer's curve as up to eight flow-head pairs, flow in m³/h and head in metres. All eight rows are on screen at once whenever the panel has the height for them. Points may be entered in any order; they are sorted and duplicates averaged. A published curve usually stops well before the head reaches zero. The panel completes it, extrapolating back to a shutoff head at Q = 0 if the first point is not there and extending the tail down to the runout flow where H = 0, beyond which the pump can supply no head at all. Both completed segments are drawn dashed, distinct from the points you supplied. Without this completion, the solver could place the operating point on a non-physical extension of a truncated curve.
Motor η (motor efficiency) - The electrical-to-mechanical efficiency of the motor. About 95 % is a reasonable estimate for a motor above 50 hp, and 80 to 90 % for a smaller or repeatedly rewound one (U.S. DOE and Hydraulic Institute, 2006); the small circulators of a ground loop are often lower still. The distinction between the two efficiencies, and the way an operating point is read off the intersection of a pump curve with a system curve, are covered in U.S. DOE and Hydraulic Institute (2006) and, for geothermal loops specifically, in Lamarche (2023), Ch. 7.
Pump η (hydraulic efficiency) - The mechanical-to-fluid efficiency of the pump itself, at the operating point. This is a different quantity from the motor's, and the two multiply.
Pelectrical = Pfluid / (ηpump · ηmotor)
Typical values are 25 to 45 % for a small wet-rotor circulator and 60 to 80 % for a well-sized centrifugal pump. Setting ηpump=100% neglects pump losses and therefore gives an optimistic estimate of the required shaft or electrical power.
Summary & charts: the five characteristics, side by side
The chart - All five pumps are drawn together, each in its own colour, to show which curves pass above the required head at the required flow. The pump currently selected in the Pump box is drawn thicker and carries the markers of the points you entered; the dashed tail of each curve is the completion down to H = 0 described above.
The legend is interactive. Click a pump's name to hide its curve, click again to bring it back; a hidden pump stays in the legend, greyed out. The axes cover all five curves and do not change when one is hidden.
Metrics
Pump characteristics is a table of the whole library, not of the pump on display: one row per characteristic, one column per pump, in the order of the chart legend. Each column is headed by the pump's number — the same number the Pump box shows in front of its name — and its full name is in the tooltip of every cell. The column of the pump currently selected is in bold.
The rows are read from the curve itself and from the two efficiency fields above:
- Shutoff head — the head at Q = 0, the top of the characteristic;
- Runout flow — the flow at H = 0, its right-hand end;
- Peak fluid power — the largest value of ρ·g·Q·H anywhere on the completed curve, that is, the most hydraulic work this pump can deliver at any point of its range;
- Flow at peak power — where on the curve that maximum falls;
- Pump efficiency and Motor efficiency — the two values entered for that pump;
- Peak electrical power — the peak fluid power divided by the product of the two efficiencies, an order of magnitude for the motor the pump will need.
The operating points of the solve are not repeated here. They are in the console, page Pumping & operating point: one line per pump node found in the drawing, identified by its node number, with its control mode, its flow and head, its hydraulic power, the combined efficiency ηp·ηm, the electrical power Phyd/(ηp·ηm) and Cap., the share of the assigned curve's capacity the point uses — the larger of the two fractions a curve bounds, flow against runout and head against shutoff. A curve is used only in CS mode: a pump in ΔP-c or Q-c is its setpoint, so its Cap. is a dash and no curve warning is issued for it. Which network each pump serves is on page Critical path & networks.
Points drawn on the chart. Only the operating points of pumps in CS mode are plotted, in the colour of their pump and larger than the entered points, each with crosshairs down to both axes (thicker for the pump on display). A pump in constant-head or constant-flow mode does not operate on its curve, so its point is not drawn; it still appears in the console, where the Ctrl. column gives its mode.
GLN in practice: pump selection
Read the operating point, not only the curve. A pump whose curve passes above the required head at the design flow will work, but its position on its own curve decides its running cost and its life. Aim for the best-efficiency point: a pump running far to the left of it, throttled by an over-restricted circuit, is noisy, inefficient and wears its bearings.
Avoid sizing against a head that includes a safety margin on every branch. The margins add up, and a pump chosen for a head that never occurs runs far to the right of its intended point, draws more power than predicted and may cavitate. Size against the computed critical path and apply a single margin.
For a ground-loop circuit, remember that the fluid is not water. Antifreeze raises the viscosity, which raises the friction and shifts the system curve up. The effect grows as the loop gets colder, when the pump works hardest. The hydraulic network evaluates each network's fluid at its own configured temperature; make sure that temperature reflects the coldest condition you expect, not an annual average.
A variable-speed pump can be solved in constant-head or constant-flow control, but there is no speed-scaled curve: the affinity laws are not applied. To analyse a variable-speed drive at reduced speed, enter the scaled curve as a separate pump slot.