Catalogues

This section gathers the three catalogues used to seed a drawing: components, fitting losses and pipes.

None of it is needed to build or solve a network, and most of it is shown on screen as you work: the palette is the component catalogue and the Pipe type list is the pipe catalogue. It is collected here for use away from the software, for instance to choose diameters, check a coefficient against a manufacturer's sheet or justify a figure to a client or a reviewer.

Component catalogue

Each entry shows the symbol drawn on the canvas, in the colour of its family, its name in the palette, the tables and the console, and its hydraulic role. The default K values are discussed under Minor loss coefficients, below.

Active
	Pump	A two-port machine: it must sit in series on a single line, with exactly one suction pipe and one discharge pipe; wired to three pipes or more, it is reported as an error in the console. Pump curve picks which curve from the Pump curve panel it follows; left unset, it falls back to the middle of that library. Discharge toward names the neighbour it pushes into, which reorients the two pipes so the symbol triangle and the computed direction always agree. Control is CS, constant speed, following the H-Q curve; ΔP-c, constant head; or Q-c, constant flow — the same three acronyms label the mode here and on the pumping page of the console.
	2-way valve	The general-purpose throttling/isolation element. Fully open, K starts at 0.3 for the gate / isolation kind, 0.05 for a full-port ball valve and 1.0 for a butterfly valve, and at 5 for the balancing kind. That 5 is only a seed: on a balancing valve K is the design variable, the one you adjust to distribute the flows, and a partly closed valve runs far higher — a manufacturer's Kv at the setting you intend is the figure to enter. Purge and safety valves are normally-closed branches rather than in-line resistances.
	3-way valve	Mixing or diverting. Assign the common port, then set the split with the slider: each branch's loss becomes K/a² with a the open fraction, so the flow split results from the solve, not directly from the slider position. It is solved as a true 3-way valve only with a common port assigned and exactly three pipes attached; failing either, it is solved as a plain fitting carrying its K — its position then has no effect at all — and the console names it and badges it on the drawing.
	Check valve	K ≈ 2.5 while it passes. Flow the other way is blocked: the solver closes the valve and says so. Its passing direction is the Flow toward row of the Properties panel.

Fittings
	Junction (coupling)	A plain connection point, K = 0.
	30° elbow	K ≈ 0.2 (fabricated).
	45° elbow	K ≈ 0.35 (moulded).
	60° elbow	K ≈ 0.6 (fabricated, two or more miters).
	90° elbow	K ≈ 0.9 — the fitting where published sources disagree most; a swept bend can run as low as 0.4, a sharp socket-fusion elbow as high as 1.2.
	U-bend	K ≈ 1.8 (two 90° elbows); the foot of a single borehole leg, placed automatically by the borehole archetypes of the Hydraulic network panel.
	Tee	K ≈ 1.5, the branch value; flow continuing through the run costs about a third of that.
	Cross	Four-way fitting; can also carry a merged reducer on any one arm.
	Reducer	K ≈ 0.3. Placed on its own between two pipe sizes, it is a component like any other. It can instead be merged onto one arm of a tee or a cross — the usual case when the reduction sits straight on a fitting with no pipe between them: pick the arm in that fitting's Reducer on field, or drop a reducer from the palette onto the fitting and it is merged instead of replacing it. The arm then carries the reducer's K on top of the fitting's own, and only on that arm; what is described is two pieces, the fitting at its own port size and a reducer to the branch pipe — the assembly usually stocked when a branch is several nominal sizes below the run. The arm is named by the neighbour it leads to: if that pipe is deleted or redrawn, the reducer loss is no longer applied, and the console names the fitting and badges it on the drawing.
	Manifold	The header of a ground heat exchanger — not a single component but one node per take-off, linked in series by short header segments, so every take-off appears in the Nodes and Pipes tables. Branches sets the take-off count. K per take-off is the minor loss of each take-off, applied to every one of them, not only the first. Take-off spacing, the real centre-to-centre distance between take-offs (0.10 to 0.30 m on a typical manifold, defaulting to 0.15 m), is a physical input decoupled from the drawing: the header segments carry it as friction, while the canvas keeps a readable two-square spacing. Header Ø sets the internal diameter of every header segment at once, from the pipe catalogue; those segments are hidden on the drawing, so this is where they are sized. Size the header at least like the largest pipe it feeds or collects: it carries the full flow. Take-offs added later inherit it, and Mixed means the segments were edited to different sizes in the Pipes table. Rotation turns the whole manifold in 5° steps. Axis node at the other end moves the header's single axis connection from one end to the other, which is how the take-offs end up on the other side without redrawing.

Thermal
	Heat pump	Two forms, chosen by Kind. Water-water is what the palette places: two independent internal circuits, source and load, under one four-port body. Water-air has a single water circuit — its building side is air, drawn as two duct antennae and a finned coil — and therefore two ports instead of four.Either way it is a composite component: each port is drawn as an ordinary junction, but it belongs to the body — it moves with it and cannot be selected or retyped on its own. Selecting the device highlights it whole, every circuit included; the two circuits of a water-water unit never touch each other.Changing Kind converts the device, it does not merely rename it — see Kind on the Hydraulic network page.
	Auxiliary heat/cool	A boiler, chiller or other auxiliary unit added alongside the heat pump(s).
	Heat exchanger	Isolates two fluid loops — typically an antifreeze ground loop from a water building loop — as a composite component of its own, with two internal circuits and four ports. Plate, coaxial or shell-and-tube by Kind.
	Radiator	A terminal emitter on the building side, drawn as the convention draws it: a panel divided by its elements. Hydraulically it is an in-line component with two ports carrying a K, like any fitting. Like the rest of the module it computes no heat transfer: it is drawn so that the circuit feeding it can be sized. Its K starts at 5, the radiator valve rather than the panel dominating the loss, which is an order of magnitude and not a specification: an emitter is given by its pressure drop at nominal flow, so read it off the data sheet and convert it to K.
	Fan-coil unit	The other terminal emitter, where the air is blown across the coil; its symbol is a finned coil crossed by an arrow. Two ports and a K, like the radiator, with the same caution: the K starts at 30, because a finned coil typically loses 10 to 30 kPa at its nominal flow, but the data sheet gives the actual figure. Neither emitter carries a fan power or an air flow; nothing in this module reads them.

Ground heat exchanger
	Single-U borehole	One circuit down and back — the standard configuration. Places the whole archetype (two legs, a U-bend at the foot) in one gesture. See Placing a single borehole on the Hydraulic network page.
	Double-U borehole	Two circuits in parallel down the same hole. Each carries half the total flow, so the borehole's pressure drop falls to roughly a quarter of the single-U value, not a half — the loss goes as the square of the flow. The Reynolds number of each leg halves with the flow, which is the number to check: a double-U is where a leg falls out of turbulence first.
	Coaxial borehole	A centre tube inside an annulus, drawn as two named legs. Measured field pressure drops depart from the textbook value — see Vautrin et al. (2024).

Instrumentation
	Flow meter	Confirms the design flow was actually achieved; standard placement is at the field connection.
	Temperature	Gauge (local dial) or transmitter (feeds a control system) by Kind, told apart on the drawing by the ISA sub-letter I/T.
	Pressure	Same gauge/transmitter convention as Temperature.
	Energy meter	Reads a thermal or electrical energy quantity at that point, for commissioning or monitoring.

Storage & safety
	Expansion vessel	Absorbs the fluid's thermal expansion; normally carries the network's pressure reference (only the first one placed is armed). See Fixed-pressure node on the Hydraulic network page.
	Reservoir	An open, vented reservoir; may also carry the pressure reference.
	Buffer tank	Hydraulically decouples a variable-flow side from a constant-flow side. One water circuit, so two ports on the same side — its Connections on the right checkbox, on the device page, moves the vessel to the other side of them.
	Fill / make-up valve	Where the loop is charged and topped up; carries the pressure reference only while open, not by default.

Treatment
	Y-strainer	Catches fusion beads, drilling debris and backfill before they reach the plant.
	Air separator	Removes dissolved air that a purge alone leaves behind — the air that surfaces after the first heating season.
	Dirt separator	Removes suspended solids circulating on a return line.

Minor loss coefficients

The loss through a fitting is written ΔP = K·ρv²/2, the loss-coefficient form used in the standard handbooks (Idelchik, 1994; Crane, 2013; ASHRAE, 2021). GLN gives every component a default K so that a network can be solved as soon as it is drawn. These defaults are generic values of the order found in the handbooks, not figures taken from one of their tables. For elbows and the U-bend they fall within, or very close to, the range of the thermoplastic data compared below. The tee takes the PPI value for flow into the branch, and the butterfly valve the PPI value for a fully open valve. The reducer and the check valve are on the low side of the published figures, and the ball and gate valves are not tabulated by either source. Crane and ASHRAE tabulate coefficients that vary with the pipe size and cover mostly steel, copper and PVC fittings: for a standard 90° elbow in threaded steel, ASHRAE gives 1.5 at 1 in and 1.0 at 2 in.

These values are only defaults. They exist to get a first solution, not to describe a particular installation. It is the user's responsibility to enter K values consistent with the components that will actually be installed on site, preferably from the manufacturer's data sheets, and to revise them whenever the equipment is selected or changed.

Published values for thermoplastic fittings. The table below compares the GLN defaults with two published sources, one American (PPI, for PE) and one European (GF, for PP and PVDF).

Sources: PPI values from Plastics Pipe Institute, Handbook of PE Pipe, Ch. 6, Table 2-2, which gives equivalent lengths, converted here to K at f = 0.025, and whose values PPI itself attributes to Crane TP-410 (in its 1957 edition, 410-C); GF K_r from Georg Fischer Piping Systems, Technical Handbook, p. 21, which covers PP and PVDF fittings and gives a single value for a tee; the PPI butterfly-valve figure applies above 8 in. Neither source lists a U-bend: its row is twice the 90° elbow, which is also how the GLN default was set. A dash means the source does not cover that fitting.

Where European practice tabulates these coefficients. In Europe the same quantity is written ζ (zeta) and is tabulated, fitting by fitting and by material, in the informative Annex A of DIN 1988-300, the DIN standard — also a DVGW code of practice — for sizing drinking-water pipework. ζ and K are the same number in the same equation, so a value taken from it can be entered in the K field unchanged. Two cautions before doing so: that standard covers drinking water installations, so its fittings are those of building services rather than a fused ground loop; and it presents its ζ as reference values, to be checked against the manufacturer's data once the actual product is known.

Reading the columns. The sources do not express quite the same quantity.

The PPI column is converted. PPI tabulates equivalent lengths in pipe diameters, not loss coefficients. They are converted here with a friction factor f = 0.025, representative of PE at the Reynolds numbers of a ground loop; at f = 0.02 the values would be a fifth lower.

The 90° elbow is where the sources differ most, because of the bend radius: PPI's 1.0 assumes a moulded elbow of R/D ≈ 1.5, and GF distinguishes a swept elbow (0.4) from a sharp one (1.2). A socket-fusion elbow behaves like the sharp figure; a long sweep, or pipe simply bent to a radius, like the low one. The GLN default of 0.9 sits between them.

A tee is two coefficients, and GLN carries one. Flow through the run and flow into the branch differ by a factor of three (PPI: 0.5 against 1.5). The solver applies a single K per node, split across its pipes, and the default is the branch value, the one that matters at a manifold take-off or a reverse-return tee. On a tee that carries its flow mostly through the run, 0.5 is closer; in either case, check the result against a manufacturer's figure.

K depends on the flow regime. Handbook coefficients are usually given for fully turbulent flow. As the Reynolds number falls, which is what happens with a cold glycol mixture, the loss through a fitting becomes larger than a constant K predicts. Lamarche (2023), Ch. 7, mentions two methods that model this dependence, the two-parameter method of Hooper and the three-parameter method of Darby, and uses a simpler equivalent-length correction instead (his Eq. 7.21). In his worked example with propylene glycol at 5 °C, this correction raises the fitting losses by about 21 % for a 20 % solution and by 62 % for a 40 % one, by volume. GLN applies no such correction: it uses the K entered, whatever the temperature. How much this matters depends on the share of the fitting losses in the total, and that share varies widely. In Example 3 of the Examples and verification window, a complete ground-source system, fitting losses are a small part of the loss in the borehole field, about a third in each fan-coil loop, and about half in the building loop, where the heat pumps and the plate heat exchanger sit. Where the share is large, enter a K already corrected for the operating temperature.

The pipe catalogue and its roughness

The catalogue is described where it is used, under Pipe type on the Hydraulic network page; what follows is where its numbers come from. The metric family takes its outside diameters and SDR series from ISO 4427 (EN 12201) and the imperial family from ASTM D3035 and F714. Every bore in the table is computed as ID = OD·(SDR − 2)/SDR, so the same SDR reads the same way in both families: a dn 32 pipe is 24.9 mm inside in SDR 9 and 26.2 mm in SDR 11. That identity takes the wall as exactly OD/SDR, which is the convention of the geothermal design references; the bores of Lamarche (2023) agree with it within 0.1 mm. Manufacturers' tables give a slightly smaller bore. ISO 4427 tabulates a minimum wall, rounded up to the next 0.1 mm and followed by a tolerance (3.6 mm in SDR 9 and 3.0 mm in SDR 11 at dn 32), and for flow calculations the Plastics Pipe Institute (2022), Ch. 6, deducts twice the average wall, taken as the minimum plus 6 %, which gives 24.5 and 25.8 mm at dn 32. At a fixed flow, that bore raises the friction by about 7 % in SDR 11 and 9 % in SDR 9. Where that margin matters, enter the manufacturer's inside diameter.

The seeded roughness of 0.0015 mm is the design value the Plastics Pipe Institute (2008) recommends for PE and the other thermoplastics — its Table 2-1 groups PE with the other thermoplastics, brass, glass and lead under a single smooth pipe entry at 0.000005 ft, and notes that any pipe at or below that figure behaves as one — drawn tubing included.

The same value seeds every pipe you draw, and it is the only roughness this module assumes: a ground loop is thermoplastic pipe, from the borehole legs to the headers. Two independent sources support treating PE as smooth — Lamarche (2023), whose Ch. 7 examples also serve as verification cases for this module, solves PE loops as hydraulically smooth (ε = 0), while noting that a roughness of about 0.02 mm is sometimes suggested and would have a slight influence; and Javed and Spitler (2022) measured the pressure loss of four types of heat exchanger in a 200 m borehole and found the standard procedures adequate for smooth single- and double-U tubes.