A field test was conducted recently in the hydronic cooling system of a medium-size building. This test was the second phase of a study of the possible use of drag-reducing additives in hydronic systems for pumping power reduction. In the first phase of the field test we measured how much pumping power savings was achievable in this system, regardless of heat transfer reduction in the heat exchangers. We measured about 30% of pumping power savings. The recent second phase of the field test work had a different goal, namely to ascertain whether it is possible to control or eliminate the heat transfer reduction in the heat exchangers. This is an important issue because a loss in heat transfer capacity would lead to reduced chiller efficiency and therefore reduced net energy savings. We did indeed show in the second test that the use of an improved non-ionic surfactant did in fact allow us to control fully the heat transfer in the heat exchangers (both evaporator and cooling coils) by means of intentional temporary degradation of the drag-reducing properties of the solution. Even with full elimination of heat transfer reduction, we still achieved an overall 12% (limited by the small size and the configuration of the system) in pumping power savings, with no measurable effect on the heat transfer capacity of the evaporator or on the compressor power, even at full load. Furthermore, it was possible to eliminate the heat transfer reduction by degradation induced by components already existing in the system (pump and control valves). These issues and other aspects of the test strategy, implementation, and measurements are described.

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