Aquifer Thermal Energy Storage
In 1974 the International Energy Agency was formed, a forum of 28 advanced economies. Their key areas are: Energy Security, Environmental Protection, Economic Growth, Engagement Worldwide.
Within the Environmental Protection area the ECES Implementing Agreement was established in 1978. The full name of the ECES is: Implementing Agreement for a Program of Research and Development on Energy Conservation through Energy Storage.
The most frequently used storage technology is the Aquifer Thermal Energy Storage technology. The term Aquifer Thermal Energy Storage (ATES) reference to the temporary storage of heat or cold in underground layers. These layers can be sand, sandstone, clay, chalk which all consist ground water. In combination with a heat pump and a heat exchanger, buildings but also whole neighborhoods can be heated or cooled.
The technology
At a depth of 250 to 600 feet two storage wells are created, a warm site and a cold site near each other. A heat pump and an plate heat exchanger are installed and connected to the wells.
In the winter
In the winter warm water with a temperature between 60F and 70F is pumped to the surface with a heat pump from the warm well. Energy from this water is transferred to the local water circuit, and the 40F to 50F left over cold water is re-injected back into the ground into the cold well. The warm water in the local water circuit can now be used inside buildings for heating or straight as warm tap water.
In the summer
In the summer cold water is pumped up from the cold well. Via a plate heat exchanger, heat from the house is transferred to the cold water. In this way energy from the house is extracted and the house is cooled. The warm water is re-injected into the warm well and stored for uses again in the winter.
Savings
The initial investment in the system is earned back over a period of 5 years. After that period a saving of about 75% on the electricity bill is not unheard of for people who use their air-conditioning system in the summer. The availability of ATES is dependent of a suitable geologic formation underneath the area of the building.
Example
With hundreds of systems installed, here is one example. The data of a complex existing besides a cruise ship terminal, out of office buildings, a hotel, an art center and apartments.
Key data Aquifer Thermal Energy Storage System (project fully operational):
| Heating capacity ATES | 4 060 kW |
| Heat delivered by storage | 2 760 MWh |
| Cooling capacity ATES | 4 060 KW |
| Cold delivered by cold storage | 2 290 MWh |
| Maximum flow rate groundwater winter | 17 600 ft3/h |
| Maximum flow rate groundwater summer | 17 600 ft3/h |
| Pumped quantity winter | 14 000 000 ft3 |
| Pumped quantity summer | 11 600.000 ft3 |
| Number of warm wells | 2 |
| Number of cold wells | 2 |
| Aquifer depth | 300 – 600 ft below sea level |