When it comes to installing geothermal systems vertical closed loop has many advantages over open loop systems.
Open loop systems
Require water from one or multiple aquifers be pumped to each unit and then directed back to a return well(s). Depth could be as shalow as 50 feet and are generally average approx 200ft. These systems are very effective and are in use through out the country on many succesful installations.
Closed Loop Systems
Require a series of 5" borings drilled into the grod generally 200 to 400 feet deep. High density poylethelyne piping is then installed into the boring. A high efficiency bentonite groute is then pumped into the boring to maintian the shape of the boring and promote even heat exchange. The HDPE piping is run from the geoexchange or source loop system into the building or home. The HDPE piping is charged with a glycol (antifreeze) soluiton The geo exchange loops move the fluid utilizing a pressurized or non pressurized pumping system.
What is a Hybrid System
In our region the heating load is generally greater than the cooling load. For this reason we must design the geo exchange loop for the worst case which would be the heating BTUs required for the installaiton. The peak heating BTU's only are required on a design day heating day which is generally less than 2% o fthe heating season.
If the geo exchange loop can be designed to handle the heating and cooling requirements and made smaller by not sizing to handle the peak load we can reduce the amount of borings required. This can be accomplished by installing or utilizing an existing boiler to inject the heating BTUs into the geo exchange loop during these design day conditions which again are less than 2% of a normal heating season. The cost savings in most cases would adjust the price of a closed loop installaiton to be equal or less than an open loop design.
By installing a Hybrid closed loop system the only real poisitive to installing an open loop over a closed loop design would be eliminated. There would be no need to have a system installed that the operation and design output of the geo exchange system be left to chance.