Geowell™ Technology > Well field controller
Well Field Controller
The principal job of the well field controller is to interface the geothermal source/sink to the building HVAC system in a seamless way. Without the well field controller, all of the geothermal pumps must operate any time there is a load. This necessitates the use of variable frequency drives (VFD) for each well pump to control the speed according to the load. However, when pumps operate below 40% of the design speed, the VFD is an inefficient and expensive solution.
ARB/Geowell design layout preferably employs addressable rows of wells that are activated or de-activated to meet the building part-load. The well field controller uses PLC with a proprietary algorithm to control the operation of well rows consistent with the current building load.
By operating specific wells, while allowing others to seek thermal equilibrium, one can extend the operation of the geothermal well field. Testing experience has shown that wells, that are approaching their max (min) design temperature, take typically 7 hours to recover. The Figure below demonstrates that the well thermal response, based on measured thermal relaxation, is predictable.
The controller keeps track of the amount of time that each well row has operated, and looks for ways to de-activate these wells, while re-activating other rows. In this way, the controller maximizes the availability of the SCW geothermal well field.
The functions of the controller include:
- activation of the specific well field (rows) to meet the current building load
- de-activation of specific well field rows (rows) to allow thermal relaxation
- (de)activation of the geothermal system based on max/min well temperature set points, and simultaneous signaling (BACnet) the building management system (BMS) for HVAC backup and updating status
- optional "bleed" trigger
- status signal for pump maintenance
- emergency signal with backup records.