Geothermal Systems: Pay Attention to Control Sequence
By Winston Huff - December 2010 - HVAC
Managers have tools available, such as alternative power and temperature systems, to reduce the cost of power. For example, a geothermal system circulates water through underground wells to operate a heat-pump system for thermal comfort. On hot days when the geothermal system cannot meet a facility's cooling needs, the controls system usually is set up to operate until the cooling capacity is exhausted. The system then uses grid power to cool the facility. As a result, the system runs off the geothermal system in the morning and switches to grid power in the afternoon during the period of peak power demand, when electricity costs are high.
The problem with this control sequence is the facility is buying power from the utility at the most expensive time and when it is least reliable. Managers instead should operate the facility off grid power in the morning, when utility costs are the lowest, and save the cooling capacity of the geothermal system for the peak-load time of the afternoon. In the end, the facility buys cheap power in the morning and does not use the more costly power during the peak afternoon time.