Patent ID: 8865016

Claim:
A process for operating a near-surface geothermal installation, comprising the step of bringing about the transfer of thermal energy with a triazole-free composition which, as well as water, comprises a) 9.2 to 49.5% by weight of at least one C 2 - to C 3 -alkylene glycol, of a C 2 - to C 3 -polyalkylene glycol or glycerol, b) 0.1 to 4% by weight of at least one corrosion inhibitor, in which the corrosion inhibitor is an alkali metal, alkaline earth metal or amine salt of a compound of the formula where R 1 is branched C 6 -C 13 -alkyl, or C 5 - or C 6 -cycloalkyl or polycycloalkyl having 6 to 13 carbon atoms, which may be substituted by one or two C 1 -C 4 -alkyl groups, R 2 is hydrogen or C 1 -C 6 -alkyl and R 3 is C 1 -C 11 -alkylene in a straight or branched chain, with the provisos that c) the composition has good biodegradability (is “readily degradable”) according to test method OECD 301 A, d) the composition has an anaerobic biodegradability of at least 75% according to test method OECD 311, e) the corrosion inhibitor or all corrosion inhibitors used have good biodegradability (are “readily degradable”) according to OECD 301 A (for water-soluble corrosion inhibitors) or OECD 301 B (for sparingly water-soluble corrosion inhibitors).