The 800 solar collectors in the Drake Landing Solar Community act as the primary energy source, sending collected energy into the short term thermal storage (STTS) tanks, via a glycol/water heat exchanger. The collection of solar energy occurs whenever the sunlight is strong enough to produce useful heat. On a typical summer day the collection system is capable of producing 1.5 megawatts of thermal power. From the STTS, the thermal energy will be sent through the district loop, to be utilized by homes as needed. If there is more solar heat available than is currently needed by the homes (which is always the case during summer, when little or no heat is required), energy will be transferred from the STTS tanks to seasonal storage in the borehole field.
Alternatively, if the homes require more energy than is currently being collected, the temperature of the STTS will fall, triggering a call to transfer heat from the borehole thermal energy storage (BTES) field into the STTS, for delivery to the homes. Only if the BTES field cannot deliver the required energy to the STTS will the backup natural gas boiler located in the subdivision's Energy Building operate, delivering heat directly into the district loop, for immediate transfer to the homes. Use of the backup boiler is most likely late in the heating season, when the BTES has been discharged.
Inside each home a standard thermostat controls an automatic valve. When heat is required, the valve is opened, and the heated water flows through the water/air heat exchanger in the air handler unit (replacing furnace). The blower distributes the warmed air throughout the home, similar to conventional forced air delivery. The warm water in the district loop is flowing at all times during the heating season, to ensure that heat is instantly available whenever needed.