GSHP system
The GSHP System panel describes how the heat pumps are connected to the building and to the ground loop, and sets the circulation flow rates and pumping power that determine the parasitic (pumping) energy of the system. A schematic diagram on the panel updates as you change these choices.
System type - The system type sets how the heat pumps serve the building and how the ground loop is operated:
- Water-air (zone) — distributed water-to-air heat pumps, typically one or more per zone, sharing a common ground loop and delivering air locally.
- Water-water (zone) — distributed water-to-water heat pumps serving hydronic equipment within each zone.
- Water-water (loop) — a central water-to-water plant serving a building distribution loop.
- Geocooling variants — in cooling, the building is cooled directly by the ground loop with the compressor bypassed (so-called direct, passive or free cooling). During geocooling hours the heat pumps draw no compressor power, which can dramatically lower cooling energy; domestic hot water cannot be produced in those hours because it relies on the compressor.
Circulation flow rates - The source-side and load-side flow rates are entered for cooling and heating for the installed capacity. Specifying the flow at two operating points lets GHE Analysis represent how the circulators are staged or modulated across the load range rather than assuming a single fixed flow. Flow rate also feeds back into the borehole calculations through the Reynolds number and the convective resistance Rf.
Pumping power - The pumping power is the electrical power drawn by the circulators per unit of flow capacity. Together with the flow rates and the hourly loads, it sets the pumping energy that is added to the system's electricity consumption and folded into the seasonal COP.
Schematic diagram - The schematic redraws itself to reflect the selected system type and the presence of auxiliary or DHW equipment, giving a quick visual confirmation that the configuration matches your intent.
GHE in practice: pump sizing, hybrid systems and seasonal efficiency
Pumping is the parasitic load most often underestimated in GSHP system design. Oversized circulators, excessive antifreeze, or flow rates pushed well beyond what turbulence requires can quietly erode the seasonal efficiency a good ground field was meant to deliver. Aim for the lowest flow that keeps the loop turbulent at peak, control the flow rate where possible, and remember that geocooling — where the site permits it — is often the single largest efficiency opportunity in a cooling-dominant building, since it serves the cooling load with circulators alone.
Balanced ground loads first, hybrid equipment second. The most robust design strategy is to size the borehole field so that the annual ground loads are as balanced as possible between heating and cooling: a balanced field shows little long-term EFT drift and keeps the heat pumps efficient over the whole life of the system. When a balanced field cannot also cover the heating and/or cooling peaks within the temperature limits, the economical answer is often a hybrid system — the GSHP carries the bulk of the load while auxiliary equipment handles the extremes: a fluid cooler (dry cooler or evaporative cooling tower) to shed excess heat where cooling dominates, or an auxiliary heater to cover the heating peaks where heating dominates. As a rough trigger, supplemental rejection becomes attractive when one mode exceeds roughly 60 % of the total annual ground energy exchange, since the field would otherwise drift warmer (or cooler) year after year.
A particularly effective variant is to size the GSHP and borehole field to cover 100 % of one mode and to meet the other mode with the GSHP plus an auxiliary system. Capping the field at the smaller of the two seasonal demands removes the long-term thermal drift and shifts capital cost from permanent drilling to above-ground equipment that is easier to maintain and replace.