Properties of different ethyl alcohol based secondary fluids used for GSHP in Europe and USA

Abstract

The extensive use of ground source heat pumps (GSHP) for heating and cooling purposes has made Sweden the European leader in geothermal energy utilization, in terms of the installed capacity, as well as extracted thermal energy. The commercially available ethyl alcohol based fluids in Sweden are distributed as 88 - 95 wt-% ethyl alcohol concentrate, including up to 12 wt-% of denaturing agents in form of propyl alcohol (8 to 10 wt-%) and n-butyl alcohol (2 wt-%). In Switzerland the commercial ethyl alcohol products contain 2 vol-% methyl ethyl ketone and 0.5 vol-% methyl isobutyl ketone, whereas in Finland commercial products contain up to 1.8 vol-% methyl ethyl ketone and 2.7 vol-% methyl isobutyl ketone. In North America the most common denaturing agents for ethyl alcohol based secondary fluid are methyl alcohol (methanol) (3.76 - 10 wt-%) and pine needle oil (up to 0.5 vol-%). The chemical character of these denaturing agents can in different ways affect the thermophysical properties. Thus, the aim of this paper was to investigate the thermophysical properties of different commercially available alcohol blends in Europe and United States. The results showed that the commercial product commonly used in Sweden (EA18 + PA1.6 + BA0.4) has the best thermophysical properties among different ethyl alcohol based products found in Europe when taking into consideration all thermophysical properties. Pure MA20 poses better thermophysical properties than EA18+MA2 and the lowest viscosity among all investigated alcohol blends. MA20 has as well good properties but special care needs to be taken due to high toxicity of methyl alcohol. Moreover, EA18+MA2 does not have good thermophysical properties compared to other ethyl alcohol blends and products containing small amounts of propyl and butyl alcohol or ketones are more recommended instead.