Ground-Loop Designs

A design turns ground properties into something you can price and drill: a borefield laid out in rows and columns, sized to hold the building's load inside your temperature limits. It is a web-native alternative to GLHEPRO, and the sizing runs on the GHEDesigner engine.

You do not need engineered loads to start

If the mechanical contractor has not delivered loads yet, you can still size a field. The Loads step has an Estimate loads for me panel that builds a full year from the building type, its square footage, and the site climate.

The result is labeled Loads source: ESTIMATED on the review screen, with the reminder "Planning estimate - replace with engineered loads for final design." That is exactly the right use: bid the job now, refine when the real numbers arrive.

Starting a design

Click New design on the Ground-loop designs tab. A dialog opens, Start a ground-loop design, offering two routes:

• Pick a site you have already assessed. Each row shows the coordinates, the date, the conductivity, and the confidence badge. The address, coordinates, and ground properties carry straight into the wizard, so nothing has to be retyped or converted. The dialog notes that picking a site does not use a report - it does not spend an assessment against your fair-use allowance.
• Start a blank design. You enter the ground properties yourself.

A completed assessment also has its own Start ground-loop design button, which is the natural path if you have just finished looking at results.

Step-by-Step: Size a borefield

The wizard shows a stepper across the top: 1 Site & ground / 2 Field / 3 Loads / 4 Construction / 5 Review.

Step 1 - Site & ground

Site address autofills ground properties when you pick an address, and there is a Use current location button if you are standing on the site.

Three properties are required, and are filled for you when you started from an assessment:

Hand-entered properties get a MANUAL badge so you can see at a glance which numbers you supplied. Design name is optional: a design saved without one is listed under its site address instead, or as "Untitled design" if it has neither. Name it after the job and you will find it again.

Note the conductivity units. The assessment headline is in Btu/hr·ft·°F, but it prints the W/m·K value directly beneath it - read that one and type it. There is no arithmetic to do, and starting from a saved assessment skips the retyping entirely.

Step 2 - Field

Two modes sit at the top: Saved site borefield, which picks up a layout you drew with the site planner's borefield tool, and Quick rectangle, which is the default.

In Quick rectangle you lay the field out with Rows, Columns, and Spacing in feet (default 20). There is no "number of boreholes" field - the count is rows times columns.

Spacing is a floor, not an exact value. The engine optimizes spacing between the value you set and twice it, to fit the available land while meeting your temperature limits. Set it to the closest you are willing to drill, not to what you hope to end up with.

Step 3 - Loads

Two fields on this step are required and easy to miss: Peak heating and Peak cooling, both in MBH. At least one of them must be greater than zero or the wizard will not let you past this step. If you need the conversion, the form gives it to you: 1 ton = 12 MBH.

They are easy to miss because Estimate loads for me and Typical test profile fill them in silently. If you type the twelve months by hand, or import a CSV, you have to enter the peaks yourself - the CSV template carries only month, heating, and cooling.

There is a second gate behind that one: every month needs a value in both columns. Clear the peak error and the step will still hold you with "Fill in all 12 heating and cooling months (0 is fine)." A zero is a perfectly good answer for a month with no load.

The rest of the step is monthly energy in kBtu, heating and cooling, twelve rows. There are four ways to fill it:

1. Estimate loads for me - pick a Building type (Office, School, Warehouse, Retail, or Residential / multifamily), enter the Conditioned area in square feet, and the tool generates a full profile from that and the site climate. Every value stays editable.
2. Typical test profile - a sample profile, useful for seeing how the wizard behaves.
3. Import CSV - with a Template CSV provided to match the format.
4. Type the twelve months in by hand.

Annual heating and cooling totals are not something you enter. Those are computed from the twelve months and shown on the Review step. The peaks are the opposite: you enter them, and Review echoes them back.

Step 4 - Construction

How the borehole is built, and the limits the engine must respect.

Min EFT and Max EFT are your inputs, not an output to check afterwards. Set them to your heat pump's real operating window and the engine sizes the field to stay inside it across the whole design horizon. Design years is that horizon - the default of 20 is what "will this still work in twenty years" means here.

Max depth is a ceiling, not a target. It is the deepest you are willing or able to drill, and the engine solves underneath it.

Step 5 - Review & run

A summary of everything: name, location, ground properties, the field as "Rectangle 8×8 @ 20 ft", the computed annual heating and cooling in kBtu, the peaks you entered in MBH, the borehole spec, your EFT limits, and depth and years. Loads source says whether the loads were entered or estimated, and on an estimated set it names the building type, area, and climate it used.

Check it, then click Run sizing. There is no separate save step.

Sizing can take a few minutes on a large field, and you do not have to sit there: the design keeps running if you leave the page, and the result appears when it is ready.

Reading the result

Saved designs are listed with the design name as the heading, the status, the borehole count and depth ("1 boreholes · 79 ft each"), the date, and whether the design came From assessment. Designs are company-wide, so your crew sees them.

Open one and the detail page leads with the numbers you will quote: boreholes, depth per borehole, and total drilling, with a borehole layout figure below them. Export PDF and All designs sit in the page header, top right. If the engine raised any warnings while solving the field, an Engine notes section appears as well; on a clean run there is nothing to show and it stays hidden.

The entering fluid temperature envelope is the chart to read. It projects how the loop fluid drifts across the design years as the ground around the field warms or cools. Because you set Min and Max EFT as inputs, a successful sizing already respects them - the envelope shows you how much margin you ended up with, and where in the design life it gets tightest.

Balance drives all of it. Where annual heating and cooling are close, the ground recovers each year and the field is stable. Where one dominates heavily, the ground trends that way and the engine compensates with more boreholes, more depth, or wider spacing.

If the sizing will not converge

A design that fails shows up in the list with a Failed status and the note "Sizing failed - open to review and re-run." Open it and use Edit & re-run: you go back into the wizard with your inputs intact, change what you need, and run it again.

What to change is whichever constraint you actually have room on: raise Max depth, widen Spacing, add rows or columns, or if your equipment genuinely allows it, widen the EFT window. The failure means the field could not meet your limits as constrained, so something in those limits has to give.

If a result looks too good, check the confidence badge on the assessment behind it. A low-confidence estimate with a wide conductivity band can produce an optimistic design. See Reading Your Results.

Related Topics

• Running an Assessment - produce the ground properties
• Reading Your Results - how much to trust them
• Thermal-Conductivity Tests - anchor them to a real measurement