Hydraulic network

This panel is where the piping that connects the various components of a ground-source heat pump system is drawn and solved. You lay out the network as a P&ID diagram (nodes for components, edges for pipes), assign the properties of each element, then compute the pressures, the flow distribution and the head the circulating pump must supply. The hydraulic balance computed here tells whether every borehole receives the flow assumed by the thermal design: a correctly sized field that is piped unevenly will not deliver the performance predicted by GHE Analysis.

Nodes, pipes and what the solver reads

Whatever you draw, the solver sees only two kinds of object, nodes and pipes, and every panel, table and result column of this module is organised around them.

A node is a point where a pressure is computed. Every component of the catalogue is a node, or a small cluster of them: a valve, an elbow, a tee, a pump, an expansion vessel. What a node contributes to the calculation is its elevation z, which sets its hydrostatic term, and its minor loss coefficient K, the local loss of the fitting. A few node types carry more: a pump adds head, a three-way valve splits a flow, and a node marked as the pressure reference fixes the level of the whole circuit. A pipe joins exactly two nodes and carries a flow between them. What a pipe contributes is its length, its internal diameter and its roughness, which together give the distributed friction loss. Its length is typed, never measured off the drawing.

A network can be solved when its nodes and pipes are complete and consistent, and the result is reliable when their values match the real installation. The two tables at the bottom of the window list the nodes and the pipes, with their inputs on the left and their computed values on the right.

The solution is a steady, isothermal snapshot: the pressure at every node and the flow in every pipe, for one operating condition. Its limits are listed under Known modelling limits, in Solving, below.

The Network and components panel

The box on the left of the panel holds, from top to bottom, the properties of the selected network, the palette of components and a row of buttons.

The network and its properties - A drawing may hold several independent networks, connected components that share no pipe. Each has its own entry in the selector, its own static pressurization and its own fluid temperature.

• Static pressure (kPa): the pressurization applied to that network's fixed reference node. It shifts every pressure by a constant; it does not change the flows.
• Temperature (°C): the temperature at which that network's fluid properties are evaluated. Two networks at different temperatures are each solved with their own density and viscosity.
• Reference z (m): an elevation offset for the selected network only. It enters no calculation; it is a convenience so that a node's own Elevation can be typed relative to a local datum — the plant-room floor, say — instead of everything being counted from one absolute zero.

The fluid itself, water or a given antifreeze at a given concentration, comes from the shared Heat carrier fluid panel and applies to the whole project.

The list of networks is built from the drawing: a loop appears in the selector as soon as no pipe joins it to the rest, and two networks merge as soon as a pipe connects them. Networks are therefore not added, removed or renamed by hand.

The component palette - The palette groups the components in seven families, each in its own colour, from Active components at the top to Treatment items at the bottom. An item can be clicked and then placed, or dragged straight onto the canvas; its tooltip gives the full name when the label does not fit. The full list, family by family, is the Component catalogue of the Catalogues section.

Setting a component before you place it - Picking a component in the palette shows in the Properties panel the values it will carry once placed: its K, its elevation, its kind and, for a borehole, its length and leg diameter. The identity strip then reads to place instead of a node number. Values edited there apply to every component of that type placed afterwards: set a borehole to 180 m once and every following borehole is 180 m, until you change it. These presets belong to the project, and New resets them to the defaults.

Kind - Components that differ only by their symbol or their default K share one palette entry, and the Kind field of the inspector selects the variant: the two-way valve (gate, ball, butterfly, balancing, purge, safety), the three-way valve (mixing, diverting), the heat pump (water-water, water-air), the heat exchanger (plate, coaxial, shell-and-tube) and the temperature and pressure instruments (gauge, sensor). On all of them except the heat pump, Kind changes the symbol and seeds the default K, but leaves a K you have typed yourself untouched.

On the heat pump, Kind changes the drawing. A water-air unit exchanges with air on its building side and has a single water circuit: choosing Water-air removes the load circuit and its two ports, together with any pipe still attached to them, and the status bar says how many pipes were removed. Choosing Water-water again re-creates the circuit, with the default K. The source side is not affected: its two ports keep their position, their K and their piping, so a field already connected stays connected.

Placing a single borehole - Each of the three boreholes of the palette places a whole borehole in one gesture: two legs, a U-bend at the foot and a connection point at the head of each leg. The borehole is dropped at its head and extends below it. In the isometric view, the single-U and double-U boreholes also come with their piped head (elbows, and for the double-U the tees joining the two circuits), ending on two connections labelled Supply and Return. By default the legs are 225 m long with a 32.7 mm bore, the U-bend sitting at −225 m; the coaxial borehole is 150 m long. After placement the U-bend is left selected, so its Borehole length field in Properties is ready to edit: one entry sets both legs and moves the U-bend to z(head) − length. Selecting every U-bend of a field sets all the depths at once. Leg diameters are edited on the Pipe page.

The button row under the panel - The row under the panel holds five command buttons, with the help button set apart at the right end; each has a tooltip.

Icon	Button	What it does
	Undo (Ctrl+Z)	Steps back through the drawing history, inspector edits and table entries alike. A batch edit over a selection undoes as one step.
	Redo (Ctrl+Y)	Steps forward again.
	Save as archetype	Saves the current selection as a reusable sub-network in the archetype library, so a plant room or a borehole head drawn once can be dropped into any later project.
	Insert an archetype	Opens the archetype gallery and inserts the chosen one, with a preview that follows the cursor until you click.
	Capture the view	Writes a PNG of what the canvas is showing — or, when the flow animation is running, a 30 s animated GIF, and the icon then shows a movie camera. See Capturing the view, under Showing the network.
	Help	Opens this page in the console, in place of the results. Any console page button brings the results back.

Show table is not in this row but in the main toolbar, at its right end. It shows and hides the Nodes and Pipes tables at the bottom of the window. The tables are hidden when the module opens, leaving the full height to the drawing; while they are hidden, Properties moves to the bottom of the Network panel and the Histogram panel appears under the console.

The canvas

The canvas and its grid - Nodes carry the standard P&ID symbols; pipes show their diameter and length. The canvas is a schematic and carries no distances: a pipe's length is typed in its Properties panel (see Pipe length, below), and the grid only gives a freshly drawn pipe a starting length of one metre per square. The Grid button of the floating toolbar hides the grid and turns the snapping off with it. Pinch a trackpad to zoom, scroll with two fingers to pan, or hold the right mouse button to pan; F frames the whole drawing. The full list of gestures and keyboard shortcuts is in the Shortcuts chapter, near the front of this manual.

View selector - The first list above the canvas switches the canvas to the plan or isometric convention. In isometric view, nodes snap to a 30° lattice and pipes are drawn along its three directions: 30° up to the right, 30° down to the right, and vertical. A header run and a borehole drop can then be drawn together, the drop being vertical. The isometric view is a drafting mode, not a 3D view: the elevation remains the z typed on each node, which is what the solver reads. Switching views moves nothing already drawn and changes no length; it only changes where the next node snaps and which directions a pipe can take.

Presentation selector - The second list above the canvas sets what the colours of the drawing represent. It holds Design and two groups of modes, Inputs and Results, whose headings cannot be selected.

Design, alone at the top, shows the drawing in its own colours, without results. The network is still solved as you draw: hovering a pipe or a node opens its callout on an orange background, with its inputs and the results of the latest solve.

Inputs — Elevation z, Diameter Ø, Length L — colour the drawing with values you typed and need no solve. They reveal a mistyped elevation or an undersized header before the network is computed.

Results — Flow Q, Velocity, Pressure, Head H, Friction Δh — show the solution. The hover callout of a pipe lists the same quantities in the same order.

Two diagnostic modes close the group. Reynolds Re shows the flow regime in three fixed colours: blue for laminar flow (Re < 2300), green for the transition band, red for turbulent flow (Re > 4000). Nodes have no Reynolds number and stay grey; the exact value of a pipe is in its hover callout. Head loss shows where the head is lost, element by element, in metres: a pipe shows its friction alone, fD·L/D·v²/2g, and a node the loss of its own fitting, merged reducers included. This differs from Friction Δh, where a pipe shows R·Q², which includes the share of the fittings at its two ends; showing the fittings on the nodes as well would count them twice. The hover callouts give the Head loss value in every mode, marked "(friction)" on a pipe, next to its Δh, and "(fitting)" on a node.

Pressure, Head H and Elevation z are node quantities: they differ at the two ends of a pipe, which is painted with a gradient. Flow, velocity, friction, diameter and length belong to the pipe as a whole, which is painted in one colour.

The colour bar is described under The colour scale, in Reading the results.

Drawing - Pick a component in the palette, then click the canvas to place it. Dropping a component onto a pipe inserts it into that pipe, which is split in two at the drop point; the two halves keep the diameter, roughness and name of the original, and share its length in proportion. The pipe about to be split is highlighted during the drag. This works for a component dragged from the palette as well as for a node already on the drawing, and the Weld nodes on drop button of the floating toolbar turns it off. The free end of a pipe can also be dropped onto a port of a heat pump, an exchanger or another composite device, which welds it there: the dropped node disappears and its pipes connect to the port. The weld is refused, with a message in the status bar, for a node carrying a component (a pump welded onto a port would break the device) and for a manifold take-off, whose cluster is regenerated.

Double-clicking a pipe splits it in two and puts a plain junction at the cut, ready to be given a type in Properties: this is the quickest way to insert a fitting in a line already drawn. To connect two nodes, hover one and drag from the ring that appears around it; dragging from the middle of the node moves it instead. For several runs in a row, use the Pipe tool (T): it stays armed and chains from one node to the next until you click its button again, press T or Esc, or right-click. Pressing T with a node selected, or with the cursor on a lit ring, starts the pipe from that node, leaving only the far end to click; otherwise the first click picks the start.

The circuit highlight Selecting anything on the drawing lights the whole network it belongs to and dims the rest. The highlight follows the pipes outward from the selected node, pipe, device or manifold. A heat pump or an exchanger belongs to two networks, one on each side, and selecting it lights both.

The floating toolbar - The floating toolbar over the canvas holds the two selectors described above and, below them, six toggles, listed here from top to bottom. Each has a tooltip and stays pressed while it is on.

Icon	Button	What it does
	Pipe tool (T)	Arms the pipe tool: click a node, then the far end of the run, and the tool stays armed and chains from one node to the next.Leave it by clicking the button again, by pressing T or Esc, or with a right-click. See Drawing, above.
	Grid	Shows and hides the grid, and the snapping with it.
	Colour by family	Tints each component with the colour of its palette family. Design mode only, since the result modes use colour for values.
	Weld nodes on drop	Dropping a node onto another joins the two, and dropping a component onto a pipe inserts it into that pipe. Turning it off lets you place a component beside a line without connecting it. A drop is refused when both nodes already carry a component type.
	Draw to scale (Ø)	Draws every pipe, and the arms of the fittings that continue it, with a stroke proportional to its diameter. See Drawing pipes to scale with their diameter, under Showing the network.
	Animate the flow	Animates the computed flow, and cycles through two ways of showing it: dashes, then beads , then off. Reads the solved flow, so it does nothing in Design mode. See Animating the flow, under Showing the network.

Node and pipe properties

The fields of the inspector for a selected node, then for a selected pipe. What each component does with them is given in the Component catalogue of the Catalogues section.

Node type and category - The type sets the symbol and the default minor loss coefficient. Changing the type resets K to that type's default, so set the type first and adjust K afterwards.

K, the minor loss coefficient - The fitting loss, as ΔP = K·ρv²/2. Selecting a type seeds K with that type's usual value; a manufacturer's figure for the actual component is always preferable. A node's K is divided equally among its connected pipes, each applying its share at its own velocity.

The default K of each fitting, and how it compares with published American and European values, are discussed under Minor loss coefficients, in the Catalogues section.

Elevation z - The height of the node above the datum, in metres. Elevation matters: the solver drives the flow with the piezometric head, pressure plus ρg·z, so a borehole leg carries a large hydrostatic term on top of its friction.

Fixed-pressure node No closed network may carry more than one. It is the pressurization point (the expansion vessel, the open reservoir or the fill connection), and only those three component types may carry it. Its value is the Static pressure of the network, set in the Network panel.

Two fixed nodes in the same closed loop over-determine it and force a non-physical flow between them; the console warns and badges both nodes. For that reason only the first pressure reference placed on a network is armed. A second expansion vessel is placed without a fixed pressure, a console note says which node carries the reference, and it remains a vessel in every other respect. The reference is a checkbox and can be moved by hand.

The pressure itself belongs to the network, not to the node: the field under the checkbox and the Static pressure row of the Network panel edit the same number, and every reference node of that network reads it. Two nodes of one network therefore cannot hold two different pressures.

A fill / make-up connection may carry the reference, but it does not by default. It holds the loop at its set pressure only while it is open; in normal operation it is closed, and what holds the pressure is the expansion vessel.

Pipe type - The Type list is the pipe catalogue: standard thermoplastic (PE) pressure pipe, in a Metric family whose nominal size is the outside diameter in millimetres (DN) and an Imperial family whose nominal size is the IPS size in inches. Within each family the entries are grouped by SDR, the ratio of outside diameter to wall thickness, because that is what decides the bore. Every entry spells out its bore, so the two families compare without a conversion.

Picking an entry fills the internal diameter below and seeds the roughness at 0.0015 mm, the design value for PE. Both fields remain editable afterwards. The list holds thermoplastic pipe only, SDR being a thermoplastic designation.

The first entry, Custom, sets nothing. The list shows it whenever the diameter matches no catalogue size, for instance after you type a diameter of your own.

Where the catalogue sizes come from, why the roughness is 0.0015 mm and what a wrong roughness costs are under The pipe catalogue and its roughness, in the Catalogues section.

Pipe length - This field is the only way to set a pipe's length. The drawing carries no distances, so moving a node never changes a length; this is what allows a horizontal header and a 150 m borehole leg to be drawn on the same schematic.

A freshly drawn pipe carries a seed length: its drawn distance, at one metre per grid square. The seed lets a network be solved before every length has been typed, but it is not a measurement: a 150 m borehole leg is drawn a few centimetres long. A network solved on seed lengths converges and colours normally while being wrong, so every seed must be replaced by the real length, like any other input of the model.

The Length column of the Pipes table marks every pipe still carrying its seed with a small orange bar; sort on that column to list them. Typing a length clears the mark. Retyping the same value does not, since an unchanged value is ignored: to keep a seed as it is, type another value, then the one you want.

Splitting a pipe shares its length between the two halves in proportion, and both halves keep the state of the pipe they came from: a length you had entered stays entered, a seed stays a seed. A pipe cannot be shorter than the elevation it spans; a warning appears under the field and on page 4 of the console.

Solving

The network is solved in the background after every change; there is no button to press. A solve needs:

• A closed path for the fluid. An open branch between two dead ends carries no flow, which is the correct result.
• A roughness smaller than the bore. Above ε/D = 0.05 the network is still solved, but the friction factor is extrapolated and the console says so; a roughness equal to or larger than the bore blocks the pipe.

A network that cannot be solved is left out and the others are computed anyway, so an orphan node or a half-drawn branch does not stop the computation. Networks left out carry no results: they keep their design colours and are excluded from the colour scale. Page 4 of the console names each of them with the reason, and the components concerned are badged on the drawing. The table below lists the messages and what to do about them.

A network that converges with no flow anywhere is usually correct: without a closed loop nothing circulates, and the pressure still rises by ρgH through a pump. Conversely, a solve on seed lengths looks entirely normal; check the orange bars of the Length column before trusting any number.

Continuous recomputation - The network is recomputed after every change: moving a node, editing a cell in the tables, changing a property, and also changing the heat carrier fluid or a pump curve. The canvas colours, the result columns and the four console pages are updated each time, including in Design mode, which only hides the colours. The solver finds the nodal pressures by Newton-Raphson, driven by the piezometric head so that two nodes at different heights feel ρg·Δz between them, with pumps folded out of the system and solved on their own curve. Friction follows Darcy-Weisbach throughout, with the friction factor taken from the Swamee-Jain form of the Colebrook-White law above Re = 4000, from 64/Re below Re = 2300, and interpolated between the two across the transition band.

Known modelling limits - Valves are modelled by a loss coefficient only. There is no C_v model and no equivalent-length model, so a manufacturer's C_v must be converted to K by hand. A check valve carries its K in the direction it passes and closes against it. The direction it passes is the Flow toward row of its Properties page, which is also the way its two pipes are drawn. When a check valve closes, the console names it: either the valve is doing its job, or a branch was drawn the wrong way round. A check valve whose direction cannot be read from the drawing (it needs exactly two pipes, one of them drawn away from it) is left open with its K in both directions, and the console reports it too.

Dividing a node's K equally among its pipes under-states the loss at a change of section. Each pipe applies its share at its own velocity: right for a fitting whose pipes are the same size, too low otherwise, since half of the coefficient then acts on the slow side and contributes almost nothing. On a reducer joining 100 mm to 32 mm the loss comes out about half of what the same K referred to the small bore would give. Where a reduction matters, enter a K already scaled for it.

The solve is isothermal. Temperature enters only through the fluid properties of each network. There is no heat transfer along the pipes and no coupling with the ground model.

Reading the results

The colour scale - The colour bar beside the drawing is graduated over the range that was actually used to colour it, with five values from the minimum at the bottom to the maximum at the top. It uses as many decimals as needed for the five values to differ, so a narrow range still gets a readable scale. A single value appears only when the field is uniform, for instance with no flow anywhere, and the drawing is then painted in one colour.

A recomputation updates the colours and the bar but never changes the display mode you chose.

The Nodes and Pipes tables - The two tables at the bottom of the window are an input grid as well as a report: columns on a white background are inputs, those on a tinted background are computed. Both open on their essential columns, the ones used to size a network; right-click any column header to switch to All columns and back. The lists below give every column, marked input, computed or check.

Units follow the current unit system, and each header shows its unit.

Nodes table, column by column - One row per node of the drawing, ports of composite devices included.

Pipes table, column by column - One row per pipe, and only real pipes: the internal edges of a composite device are excluded.

The three checks, Velocity, Friction/m and ΔP minor, are advisory: each compares a value with a window suited to an ordinary ground loop, which a design may leave for good reasons. The verdict is shown in the cell itself: blue background below the window, green inside, red above, with a symbol at the right-hand edge, ↓, ✓ or ↑. Selecting or hovering the row repaints the background, but the symbol remains. Sorting on one of these columns also sorts the verdicts.

Editing. A first click selects the row and shows the component on the drawing; a click on a row already selected, or a double-click, opens the editor.

Editing several rows at once. Select a set of rows, then edit one of them: the value applies to every selected row of that table. Setting one diameter on forty borehole legs is one entry, and one Ctrl+Z undoes the whole batch. If the row you edit is not part of the selection, only that row changes.

Selection is shared with the drawing in both directions: objects selected on the canvas are selected in the tables, and the reverse. Selected rows take the pale orange of the multiple-selection frame on the drawing.

ΔP is not the friction loss - These two columns answer different questions and coincide only on a horizontal pipe. ΔP is what a gauge reads between the two ends. Friction is the energy the flow actually dissipates, which is what the pump has to supply. The solver balances

(P inlet − P outlet) + ρg·(z_in − z_out) = friction + minor losses

so on a sloping pipe the two differ by the whole hydrostatic term. On a 150 m borehole leg that term dominates by more than an order of magnitude, and the sizing check therefore reads the Friction columns rather than ΔP. Across a pump, the added head can even make the outlet pressure exceed the inlet's.

Borehole conditions - When the result tables are hidden, a Histogram panel appears under the console, its title giving the number of boreholes found. It shows how flow Q, velocity v, Reynolds Re, friction Δh, pressure drop ΔP and friction gradient Δh/L are spread over the boreholes, with the same symbols as the presentation selector. Boreholes are recognised by their U-bend, so a field drawn by hand is counted like one generated by the Network Builder. Each borehole contributes one value per quantity, taken over both of its legs: flow, velocity and Reynolds are averaged, friction and pressure drop are summed over the whole borehole, and the gradient is that sum per metre of pipe, both legs counted — so a 150 m borehole is divided by 300 m, which is the basis the 100 to 400 Pa/m criterion is written on.

Showing the network

Two display options make a network easier to read: pipe strokes drawn to scale with the diameter , and an animation of the flow .

Drawing pipes to scale with their diameter - The Draw to scale button of the floating toolbar draws every pipe, and the arms of the fittings that continue it, with a stroke proportional to its diameter. Changes of size can then be read on the drawing, and a mistyped diameter, such as a header in 32 mm with a branch in 75 mm, stands out without opening the table.

Fittings follow, arm by arm. Each arm of a tee, a cross or a manifold takes the size of the pipe attached to it, so a 100 × 100 × 30 tee is drawn with a heavy run and a light branch. A reducer's cone shows the two sizes it joins, and each take-off of a manifold the size of its own branch. A U-bend follows its two legs; its arc is only half a grid step wide, so a very large pipe is drawn wider than the bend and a step remains where they meet.

Animating the flow - The last button of the floating toolbar animates the computed flow, and it cycles through two ways of showing it: click once for marching dashes, again for beads , a third time to stop. The icon and the tooltip show which mode is running. Dashes travel along each pipe in the direction of flow, at a speed proportional to the fluid velocity; a pipe carrying less than 2 % of the fastest velocity in the network is drawn solid. Beads add the flow rate. Each bead is a packet of fluid: its area is the flow it carries, its speed is the fluid velocity, and at a branch it splits, one bead per outgoing pipe, in proportion to their flow rates. Where two branches meet again, beads that catch up with one another merge back into one. The same 2 % rule applies: a pipe at rest carries no beads at all.

Capturing the view - The camera button of the bottom row saves what the canvas shows, with the same framing, zoom and colour mode. It writes a PNG four times the size of the view on screen, about 4000 × 2800 px for a 1000 × 700 view: enough for a full page at 300 dpi. The factor is lowered if the image would exceed 40 Mpx. The colour scale is included; the floating toolbars are not.

Recording a film. When the flow animation is running, the button shows a movie camera and records 30 s of the view as an animated GIF at 15 frames per second, up to 1200 px wide, which plays in a browser, a document or a slide. The animation is advanced frame by frame, so the film shows 30 s of flow whatever the speed of the computer. A progress dialog reports the frames and can stop the recording; a film cut short says how many seconds it holds.

GLN in practice: flow balance, turbulence at peak load and part-load operation

A sound ground loop satisfies two conditions: every borehole receives very nearly the same flow, and that flow keeps the fluid turbulent at the peak of the heating demand. Both are assumptions made by the thermal design, and both can be verified in this panel before anything is buried. The first is read on the Histogram panel, where a balanced field stacks its bars on the zero line; the second on the Reynolds column of the Pipes table, on a borehole leg, at the peak condition. Reynolds is not one of the essential columns and must first be revealed by right-clicking a header and asking for All columns.

Design for the heating peak. At peak heating demand the most heat must cross the borehole wall, and the fluid is at its coldest and most viscous. A leg that turns laminar then degrades the heat exchange when the design relies on it most, so turbulence at peak load is the first condition to secure.

Part-load operation. Away from the peak, reducing the flow is generally worthwhile: pumping power falls steeply with flow, and a loop held at its design flow all year uses energy it does not need. Reducing the flow may take the boreholes into the laminar range. This is acceptable as long as the fluid leaving the field still meets the needs of the heat pump at the load it serves: at part load there is less heat to move, so the poorer exchange of a laminar leg matters less. That condition is thermal and is checked in GHE Analysis. In this module, the peak and the part-load condition are two separate solves: the first confirms turbulence at the heating peak, the second shows how far the regime moves when the flow is reduced.

German guidance is stricter and requires turbulence at minimum pump power, which leaves much less room to trade flow for pumping energy.

Network first, pump second. Settle the friction gradients and the flow balance first, read the head the critical path demands, and only then select the pump. How margins added branch by branch push a pump far from its best efficiency point is discussed under GLN in practice on the Pump curve page.