Alternative alcohol blends as secondary fluids for ground source heat pumps.

The most common secondary fluid used for the borehole heat exchangers in Sweden is an aqueous solution of ethyl alcohol (EA) due to its relatively good thermophysical properties and low toxicity. Commercially available ethyl alcohol based fluids in Sweden contain up to 10 wt-% denaturing agents in form of propyl alcohol (PA) and n-butyl alcohol (BA). The aim of this paper was to investigate the performance of the existing ethyl alcohol blend containing two denaturing agents and alternative alcohol blends in terms of the pressure drop and heat transfer in the BHE and comparison with ethyl alcohol based secondary fluid. Experimental results showed that the presence of these denaturing agents improves thermophysical properties such as specific heat capacity, thermal conductivity and dynamic viscosity when added in small concentration. EA18 + PA1.6 +BA0.4 and EA18.4 + PA1.6 present the best characteristics in terms of the heat transfer and pressure drop. Both blends are giving higher heat transfer coefficient by 9.4 % (EA18 + PA1.6 + BA0.4) and 8.11 % (EA18.4 + PA1.6) than pure EA20. Both blends are giving as well lower pressure drop than EA20 by up to 2.7 % (EA18 + PA1.6 + BA0.4) and 3 % (EA18.4 + PA1.6). EA18 + PA1.6 + BA0.4 gives 1.4 % higher heat transfer coefficient and EA18.4 + PA1.6 gives lower pressure drop by up to 0.4 % when these two blends are compared.