Direct and Indirect Geothermal Pumping

The controls of both the open and the closed direct systems are very simple, because they consist of only a differential thermostat and a pump. The differential thermostat starts and stops a constant-speed pump whenever the detected temperature difference is favorable. In more sophisticated systems, it adjusts the speed of variable-speed pumps (or selects a small or a larger constant-speed pump for operation). What AT is favorable is a function of not only the availability of free cooling or free heating, but also of the cost of pump operation, which increases the AT thermostat set point. 

When the measured AT is favorable, but is insufficient to condition the building on its own, the geothermal energy resource needs to be supplemented to meet the total energy need. This can be done by using conventional means, such as supplementing it by starting a furnace in the winter (or air conditioner in the summer). 

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