scope:

Guideline series VDI 4640 deals with the thermal utilisation of the underground down to a depth of approximately 400 m. It discusses the following applications:

Ground source heat pump systems

(see VDI 4640 Part 2)

• heat pump systems for heating
• heat pump systems for heating and cooling

Note: In cooling operation, the cooling can be achieved via the heat pump and/or directly from the underground by circumventing the heat pump.

• chillers for cooling Ground heat exchangers or the groundwater directly (see VDI 4640 Part 4) are used as heat transfer media:
• Ground heat collectors, borehole heat exchangers and other special ground heat exchanger designs are in use as ground heat exchangers.
• The groundwater can derive from wells, but also from mineshafts or from tunnel drainage.

Underground thermal energy storage

(see VDI 4640 Part 3)

storage systems for heating Solar energy, waste heat and environmental heat are examples for heat sources used.

storage systems for cooling (heat sink: "environmental cold")

storage systems for heating and cooling

− in conjunction with heat pumps

− without heat pumps, using "environmental cold/heat"

Ground heat exchangers or direct use of the groundwater as a heat transfer fluid (aquifer storage) are used.

Direct uses (see VDI 4640 Part 4)

A heat pump or a chiller is not used in:

• cooling with groundwater
• heating with groundwater
• air heating/cooling in the underground