The soil as a source of energy

Concept
The ground below our feet can be used as a medium for sustainable energy storage and supply. During the warmer summer months, the excess heat within buildings can be channelled into the permeable subsoil layers (‘aquifers’) where it is stored and then retrieved for use in the colder winter months. Conversely, the winter cold can be stored and used for interior climate control (air conditioning) during the summer. The soil thus becomes an energy storage medium. This system of heat-and-cold storage is a Dutch development.

An underground heat-and-cold storage system offers a very interesting option for sustainable new-build and redevelopment projects. Buildings are heated by means of a ‘heat pump’ which draws energy from the groundwater and raises the temperature of circulating water to the required level, usually around 22 degrees Celsius, by means of heat exchangers. The heated water is then pumped into the building in question (which may be either residential or non-residential). During the summer, the system can be reversed, whereby cold water is used to ensure a moderate interior climate. The technology is particularly suitable for use in well-insulated and compact buildings.

The heat pump itself can be powered by either electricity or gas. It must be of appropriate capacity to provide the required basic output: it must not be too big or too small. Various sustainable energy sources can be used: heat from the subsoil, the warm return air output of a ventilation system, outside air, surface water, etc.

There are currently two types of storage system: the open system (which draws heat energy from aquifers) and the closed system (which incorporates underground heat exchangers). For technical – and often legal – reasons, it is necessary to ensure an energy balance between the heat and the cold that is stored and subsequently used.

Unique Selling Points
• This is a tried-and-tested technology which has been used in many projects over the course of many years. Europe’s largest energy storage project is at Eindhoven University of Technology.
• The major advantage of energy storage is that it provides both sustainable heating and sustainable cooling. This enables significant reductions in energy consumption to be achieved, thus greatly reducing the payback period, which is typically between one and seven years, depending on a number of variables.
• The system is readily assimilated into its surroundings. Being underground, it does not detract from the aesthetic quality of a building or area, and it does not produce noise or smells.
• The system can be installed in both new-build projects and renovations.

Climate impact
Interior heating accounts for almost 80% of energy consumption in both residential and non-residential buildings. In the Netherlands, energy consumption by (non sustainable) air-conditioning systems continues to rise year on year. A heat and cold storage system can achieve a reduction in fossil fuel usage of between 40-70%, and therefore also greatly reduces CO2 emissions. In the case of a direct cooling system which draws on the groundwater, the energy saving can be as high as 90%.

Market parties and research institutes
Arcadis, De Bam-Ruiter, Deerns, DHV, DWA, Ecofys, Eneco, ETP, Forteck, Haijtema, Geocomfort, Grontmij, GTI, Halmos Adviseurs, IF Technology*, Ingenieursbureau Linssen, Nuon, Schreuder Group, Tauw, Techniplan, TNO Built Environment, Valstar Simones, A. de Jong Group (NB This list is not comprehensive)

Best-practice reference projects in the Netherlands
• Office buildings: Rijkswaterstaat (Utrecht), TU Eindhoven, T-Mobile (The Hague), ING Bank (Amsterdam), Nike (Hilversum), Shell (Amsterdam), Kender Thijssen (Veenendaal), Rijksmuseum (Amsterdam)
• Schools: Eindhoven Campus, Hogeschool Leeuwarden
• New-build residential developments: Bavel, Overhoeks (Amsterdam), Paleiskwartier (Den Bosch), Broekpolderweg (Beverwijk)
• Hospitals and hotels: UMC Utrecht, Huis ter Duin (Noordwijk), Kurhaus (Scheveningen)
• Business premises: Larenstein (De Bilt), Maaldrift II (Wassenaar), many glasshouses, Wavin (Hardenberg), IKEA (Duiven and other locations)

Potential obstacles to international business
• Experiences of foreign parties in projects to date (confidence, etc.).
• Approval for use of groundwater as storage medium.
• Combination of technical, legal and economic factors which must come together. Geology, and in particular the presence of suitable aquifers, largely determines the possibility of underground energy storage. This said, there would appear to be good possibilities in large parts of Europe, Asia and elsewhere.