Conference Paper

Proceedings of ASim Conference 2012: 1st Asia conference of IBPSA-China, Japan, Korea

Study on effect of change in differential pressure set point on chilled water temperature difference

Hiroyuki Honda, Tatsuo Nagai, Kuniaki Mihara and Katsuhiro Miura

Abstract: As an energy-saving techniques such as variable water volume system assumes that the chilled water delta T is constant. However, at low loads, the delta T is much lower than the design. The reduction factor for the delta T may be considered to be variable. Thus, when the differential pressure set point is large, the delta T is reduced. The effect of the differential pressure setting on the delta T is still unclear. The purpose of this study was to clarify the effect of the differential pressure set point on delta T. A heat medium-temperature-difference experiment was performed to confirm that changing the differential pressure set point reduced the delta T. In the experiment, low, medium, and high cooling loads were considered, and the differential pressure set point was set to 100, 200, and 300 kPa to consider the reduction in the delta T due to differences in load on the secondary side of the excessive differential pressure. Next, we reproduced the experiment in a simulation using the inlet water temperature of the AHU for each experimental case; using the temperature difference between the heat medium and the chilled water inlet, we attempted to reproduce the experiment. The results showed that for a low load, the chilled water delta T decreased when the differential pressure set point was increased for a medium temperature difference. To reduce the delta T at low loads by increasing the differential pressure, the two-way valve is the minimum opening to cause hunting. The coil in the simulation also confirmed that hunting of the water flow rate was the cause of the reduced delta T of the air-handling unit. In conclusion, the delta T can be reduced by using a two-way valve as the minimum opening for a low cooling load with a large differential pressure for the flow rate to cause hunting.
Pages: 283 - 290
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