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 well-designed borehole field targets the lowest possible maximum g-function value: a lower plateau means that the same ground load produces a smaller temperature penalty at the borehole wall, directly widening the EFT margin from the temperature limits and improving heat pump efficiency over the full design life. Use this chart together with the GHE Designer to compare layout alternatives and identify the configuration that minimises the long-term g-function.

Energy cost - Shows the hourly operating cost - geothermal heat pump, auxiliary heating, auxiliary cooling, and system total - as time series, together with a stacked monthly bar chart decomposed by tariff rule. This chart is populated only when the Energy Cost module contains at least one active tariff rule; it remains empty otherwise. The monthly stacked bars reveal seasonal cost patterns and the relative weight of each tariff rule over the year.

Sankey diagram - The Sankey diagram condenses a full year of simulation into one picture of where the energy comes from, what converts it, and where it ends up. Every other chart answers when; this one answers how much, and through what. The width of each band is proportional to the annual energy it carries, so the diagram can be read at a glance: a band twice as thick carries twice the kilowatt-hours.

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.

The hot water draws its own band of electricity. The heat pumps make the water, so that electricity reaches the same node as the compressor work — but as a second band, stacked under the first and named for what it does. The two are not bought at the same efficiency: in cooling the water is condenser heat that would otherwise have gone to the ground, and at the default setting of ∞ it costs nothing at all, so the band simply is not there. Give the cooling DHW COP a finite value and the band appears, sized at one unit of electricity for every COP units of water. In heating it is always present, since hot water is made with real compressor work. The band from the cooling heat pump to the hot water node is labelled Condenser → DHW rather than heat recovery, because recovery is the whole story only when that COP is ∞.

The three demand nodes state their own coverage. Each of them — cooling, heating and domestic hot water — is captioned with the energy actually served and the percentage of that demand it represents, so what is covered and what is not can be read without adding the bars up. The two space figures are the same numbers as Space coverage on page 3 of the console, built from the same terms; the hot water node merges the two modes, since the diagram has a single water node where the console has a cooling and a heating column. A demand node whose coverage is zero is still drawn, captioned 0 % covered, with its uncovered bar below it: an unserved demand is the most important thing on the page, and it is not the same as a piece of equipment the project does not have.

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 — a bar hanging below the cooling, heating or DHW demand node whenever the equipment could not meet it, labelled with the missing energy and the fraction of that demand it represents. Each bar names its own perimeter, and the three do not slice the shortfall the same way as the console does: Uncovered space cooling and Uncovered space heating leave the hot water out, while Uncovered DHW counts the hot water alone and merges both modes, the diagram having a single water node. The console's Uncovered line, by contrast, is per mode and includes that mode's hot water. The three bars still add up to the console's two columns — it is the same shortfall, grouped differently — and each bar's percentage is the complement of a coverage figure on page 3: Space coverage for the two space bars, DHW coverage for the water one, read across both modes. Domestic hot water is the one to watch: its coverage is limited by the condenser heat available in cooling and by the spare capacity in heating, so a system that looks adequate on the EFT chart can still leave a visible DHW deficit here.
• 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, because it rejects the building load plus its own electricity to the ambient air rather than to the ground. Each circulation pump has one, because its electricity becomes friction heat in the fluid and the simulation does not carry that heat back into the ground load. 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.

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 built from the same terms as the corresponding console figures, so the two panels cannot disagree.

The diagram adapts to the space it is given, and it always gives up text before geometry. On a short panel the captions under the hatched bars go first, then the footer line; on a narrow one the labels beside the bars go, and below a certain width only the column headings remain. The bars and bands themselves are never dropped, and hovering reports every value exactly whatever the captions have had to give up.

Hovering any band displays a tooltip with its exact annual energy, which is the reliable way to read a thin band. 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 says so instead of drawing an empty skeleton, since the equipment side of the balance simply does not exist.

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 chart types including the energy cost bars.

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.