Charts

The Charts panel displays interactive time-series plots of all simulation outputs over the full design horizon. Select the variable to display from the first drop-down list at the top-left of the chart. The last entry of that list, the Sankey diagram, is the exception: it summarises the whole simulation as a single annual energy balance rather than as a curve against time.

Series visibility via the legend - Each series entry in the chart legend can be clicked to toggle that series on or off. When several curves overlap - for example the hourly and daily EFT profiles - hiding the denser series clarifies the view without discarding any data. The legend entry re-enables the series with a second click.

Entering fluid temperature (EFT) - Plots the hourly EFT, the daily average EFT, and the monthly average EFT on the same time axis, together with horizontal lines marking the cooling and heating temperature limits (T_Lim,C, T_Lim,H) and, where applicable, the freezing threshold of the heat carrier fluid. This is the primary diagnostic chart: a EFT profile that consistently approaches T_Lim signals an undersized borehole field or insufficient flow rate. A pronounced sustained drift in the EFT profile over successive years reveals a thermally imbalanced field that may require a corrective strategy — beginning with measures on the building side, such as improving the building envelope (insulation upgrades, high-performance glazing, reduction of thermal bridges), adjusting solar gains (shading devices, solar heat-gain coefficient of glazing, overhangs), or reducing internal heat gains through more efficient equipment and controls — before adding mechanical supplements such as a solar supplement or a cooling tower.

ΔT displays the temperature difference between the entering and leaving fluid for each simulation hour, separated by heating and cooling mode. A ΔT that departs significantly from the design value indicates an off-design flow condition or an unusual building load pattern.

Thermal loads (Q) - Overlays the building demand (Q_b), the heat pump output (Q_HP), and the auxiliary equipment contribution (Q_Aux). The ground loads series (Q_g) shows the hourly heat exchanged with the ground: positive values represent heat rejection to the ground (cooling mode) and negative values represent heat extraction (heating mode). When DHW loads are defined, the domestic hot water demand and the fraction actually covered appear as separate series. Heating loads are plotted as positive values; cooling loads as negative. This chart makes it easy to identify hours when the heat pump operates at full load, when auxiliary equipment engages, and when building demand is partially unmet.

Coefficient of performance (COP) - Plots the instantaneous COP and the mean COP corrected for part-load cycling, together with the number of active heat pumps and the number of installed heat pumps. The spread between the instantaneous and corrected COP curves quantifies the cycling degradation penalty governed by C_d. Low part-load ratios combined with a high C_d can significantly reduce the effective system COP relative to the manufacturer rating.

Effective borehole thermal resistance (R_b^*) - Plots R_b^* to reflect the variation of convective resistance with EFT. A spike in R_b^* at low flow rates corresponds to the laminar-to-turbulent transition. Use this chart to confirm that the design flow rate is keeping the circuit in the turbulent regime during peak periods.

g-function - Displays the thermal response function of the borehole field on a logarithmic time axis. The g-function is the core transfer function that converts ground loads into temperature changes at the borehole wall. Its shape encodes the geometry of the borehole field: a steeper rise at long times indicates stronger thermal interaction between boreholes, typical of dense rectangular fields. A lower long-term value means a smaller temperature change at the borehole wall for the same ground load (see g-function on the Ground heat exchanger page); use this chart with the GHE Designer to compare layouts.

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Sankey diagram - The Sankey diagram shows the annual energy balance of the system: where the energy comes from, what converts it and where it ends up. The width of each band is proportional to the annual energy it carries.

The flow runs from left to right through five columns — cooling demand, cooling equipment, the ground, heating equipment, and heating and DHW demand — with the ground storage as the pivot in the middle. On the cooling side, the heat pump, the geocooling exchanger and the auxiliary equipment each take their share of the building's cooling demand; the heat pump and the geocooling exchanger reject it to the ground, while the auxiliary cooling rejects it to the ambient air. On the heating side, the ground gives that heat back to the heat pump, which serves the heating demand and part of the domestic hot water demand; the auxiliary heating is fed by electricity alone. The circulation pumps appear on both sides. A separate electricity bar feeds the heat pumps, the auxiliary equipment and the pumps, so the electrical input of the system is visible in the same units as the thermal flows it drives.

Hot water has its own electricity band, stacked under the compressor band of the heat pump. In cooling, at the default DHW COP of ∞, the hot water costs no electricity and the band is absent; with a finite COP it carries one unit of electricity per COP units of water. In heating the band is always present. The band from the cooling heat pump to the hot water node is labelled Condenser → DHW.

The three demand nodes show their coverage. Each of them, cooling, heating and domestic hot water, is captioned with the demand and the percentage of it that is served. The two space figures are the same as Space coverage on page 3 of the console; the hot water node merges the two modes. A demand node with zero coverage is still drawn, captioned 0 % covered.

The equipment captions are the console's figures. A heat pump node is captioned with the energy it delivers and its seasonal COP, exactly as the console shows them: the Heat pump line of page 1 and Heat pump sCOP on page 3, space heating or cooling only, the hot water having its own band. Because the bar also carries the electricity the heat pump draws, it is taller than the number beside it. The cooling auxiliary is likewise captioned with the cooling it serves, not with the heat it rejects.

Three families of hatched bars carry most of the diagnostic value. Hatching always marks energy that is not part of a closed loop inside the diagram:

• Uncovered demand — the hatched lower part of a demand bar. The bar stands for the whole demand, and what the incoming bands do not fill is what the equipment could not serve. The caption gives the percentage served; hovering the node gives the uncovered energy. Space cooling and space heating exclude the hot water, while the DHW node counts the hot water alone, both modes merged; the console's Uncovered line is per mode and includes that mode's hot water. Watch the DHW node: a system that looks adequate on the EFT chart can still leave a visible DHW deficit.
• Ground surplus or deficit — the annual imbalance between what is injected into the ground and what is extracted from it, attached to the ground node itself so that node conserves energy. A red bar is a surplus, heat injected year after year that is never recovered; a blue bar is a deficit, make-up heat drawn from the far field. This is the same imbalance that the EFT chart shows as a slow drift over successive years, but quantified in kilowatt-hours per year, which makes it directly comparable between two design alternatives.
• Energy leaving the balance — a short stub to the right of a piece of equipment whose output the diagram does not follow any further. The auxiliary cooling has one, captioned to ambient, because it rejects the building load plus its own electricity to the ambient air rather than to the ground. Each circulation pump has one, captioned not in ground load, because its electricity becomes friction heat in the fluid and the simulation does not carry that heat back into the ground load. In a real loop that heat is not lost: it reduces the extraction in heating and adds to the injection in cooling. Hovering a stub gives the annual amount. Together with the ground imbalance, these stubs are what allow every node in the diagram to balance exactly: what enters a node is what leaves it.

The diagram checks its own balance. Every equipment node must give out what it receives. If one does not, by more than 0.1 % of its throughput, the footer names it and the energy unaccounted for, in place of the hatching legend. Such a message means the diagram and the console no longer agree, and should be reported.

A footer line under the diagram states its own balance: the electricity that went in, the thermal energy delivered to the space and water heating, and their ratio — the seasonal coefficient of performance of the whole system. All three are computed like the corresponding console figures.

The diagram always fills the panel, whatever the size of the project, and a column with nothing to show is left out: a heating-only project has no Cooling equip. column. On a small panel, the diagram hides text before bands: first the captions under the hatched bars, then the footer line, then the labels of the equipment where they no longer fit, the smallest energies giving way first. The labels of the three demand nodes are never hidden. Hovering still reports every value.

Hovering any band displays a tooltip with its exact annual energy, which is the reliable way to read a thin band. Hovering a node lists what enters and what leaves it, which explains why a heat pump bar is taller than its caption, and gives the uncovered energy of a demand node. The Restore view button of the main toolbar redraws the diagram to fit the panel.

The diagram is built from the building thermal loads, so it is not available when ground loads are imposed directly on the borehole field: in that mode the panel displays a message instead.

Summary & charts: navigating the chart panel

Zoom options - Hold the left mouse button and drag to draw a rubber-band selection rectangle; the chart instantly zooms into the selected area. Scrolling the mouse wheel zooms along the time axis around the cursor position. Zooming is available on all time-series charts.

Restore-view button - The Restore view button in the main toolbar resets the zoom for all charts simultaneously, returning to the full simulation span and the auto-scaled Y axis. Use it after zooming in to quickly recover the overall picture of the simulation.

Value callout - The callout button in the main toolbar activates a floating tooltip. Once active, hovering over any point in the chart displays the exact time and value in a label that follows the cursor. Clicking a point pins the callout in place so the value can be read or copied; clicking elsewhere dismisses it. The callout is particularly useful for reading peak EFT values or identifying the exact hour of maximum ground load.