An open-loop system is used less frequently, but may be cost-effective 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. This type of system uses ground water from an aquifer and is piped directly from the well to the building, where it transfers its heat to a heat pump. After it leaves the building, the water is disposed of by one of three methods.
- Surface drainage – to a low area such as a pond, river, lake or stream, etc. In the summer, this water can be used to irrigate lawns, crops and the like.
- Sub surface – to a dedicated drain-field sized to the required volume of water of the heat pump.
- Re-injection or discharge well – water is pumped back into the same aquifer through a separate discharge well. In many areas this is not allowed.
In properly operating systems, the water leaving the heat pump is of the same quality as it enters. Local codes require that it not be used as “potable” water.
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