18 May 2017
The most common secondary fluid used for the borehole heat exchangers in Sweden is aqueous solution of ethyl alcohol (EA). Commercially available ethyl alcohol based fluids in Sweden and other European countries contain various denaturing agents. Ethyl alcohol based secondary fluids in Sweden are distributed as ethyl alcohol concentrate, including up to 12 wt-% denaturing agents in form of propyl alcohol (PA) and n-butyl alcohol (BA). In other European countries, like Switzerland and Finland, the commercial products containing a mixture of methyl ethyl ketone and methyl isobutyl ketone (up to 4.5 vol-%) are used for GSHP application. The chemical character of these denaturing agents can in different ways affect the thermophysical properties. Therefore, the aim of this paper was to investigate the performance of commercially available alcohol blends in Europe in terms of pressure drop and heat transfer in the BHE. The results show that the most commonly used product in Sweden (EA18+PA1.6+BA0.4) presents the best characteristics in terms of higher heat transfer (up to 10 %) and lower pressure drop (up to 2.7 %) among different commercial products found in Europe. Another commercial product used in Switzerland showed second best performance in terms of higher heat transfer (up to 5 %) and lower pressure drop (up to 2 %). Moreover, other products containing higher concentrations of denaturing agents presented the worst performance in terms of lower heat transfer (up to 8 %) and higher pressure drop (up to 1 %) compared to EA20.