Open-loop Systems
Open Loop System
This type of ground connection method is used less frequently, but may be employed cost-effectively if ground water is plentiful. Open loop systems are the simplest to install and have been used successfully for decades in areas where local codes permit. In this type of system, ground water from an aquifer is piped directly from a well to the building where it transfers its heat to a GSHP.
After the water leaves the building, it is expelled back into the same aquifer via a second well, called a discharge well, located a suitable distance from the first. Local environmental officials should be consulted whenever an open loop system is being considered.
Because open-loop systems utilize water on a “once through” basis, they are often referred to as “pump and dump” systems. The performance of the GSHP system may degrade over time if water quality issues are present (high mineral or dissolved solids content, etc) or if the water supply diminishes for any reason.
Standing Column Well System
Standing column wells have become an established technology in some regions, especially the northeastern United States. Standing column wells are typically six inches in diameter and may be as much as 1500 feet deep.
Temperate water from the bottom of the well is withdrawn, circulated through the heat pump’s water-refrigerant heat exchanger and returned to the top of the water column in the same well. Usually, the well also serves to provide potable water.
However, ground water must be plentiful for a standing well system to operate effectively. If the standing well is installed where the water table is too deep, pumping may become cost prohibitive. Under normal circumstances, the water diverted for building (potable) use is replaced by constant-temperature ground water which makes the system act like a true open loop system.
If the well-water temperature climbs too high or drops too low, water can be "bled" from the system to allow ground water to restore the well water temperature to the normal operating range. Permitting conditions for discharging the bleed water vary from locality to locality.
Contact our engineering department to discuss possible options for your GSHP system and for geothermal design services.