Experimental energy performance of open cooling towers used under low and variable approach conditions for indirect evaporative cooling in buildings

Abstract

The success of chilled ceilings and displacement ventilation systems as a means of sensible cooling in buildings has prompted a review of evaporative cooling technology as an effective means of generating the required cooling water. When such cooling water is generated at low approach conditions (2–5 K), at the higher temperatures required in these systems (14–18°C), very high levels of availability result. In many north western European locations the levels of availability are such that the prospect of supplanting rather than simply supplementing the refrigeration system, for sensible cooling purposes, arises. The viability of the technique, however, largely depends on achieving low approach conditions, at acceptable levels of energy performance. Hence the need to investigate the energy performance of the process. This paper presents the results of recent experimental research into: i) the achievement of low approach conditions in an evaporative cooling test rig; and ii) the energy performance of this test rig when generating cooling water, indirectly, at the temperatures required for chilled ceilings. Energy performance is presented for a range of specifi c conditions and typical annual effi ciencies of cooling water generation are determined. Results are compared with typical energy effi ciencies of conventional, vapour compression based, refrigeration systems. A signifi cant potential for improved annual energy performance, is shown.