Study Of The Heat Transfer, Hydraulics And Noise Characteristics Of Small Diameter Tube Fan Coil Unit

Fan Coil Unit(FCU) is a mature product in the central air-conditioning market. Customers are very cost conscious in this increasingly competitive industry. The hydronic coil can contribute 24-45% of the FCU product cost and is an area of focus for cost reductions and value engineering. Most manufacturers currently use 9.52 mm diameter copper tubes in their FCU designs and technology advancements have presented a potential smaller 7mm diameter copper tube to be replace the 9.52 mm tube with significant cost savings.This article focuses on the heat transfer and hydraulic study for small diameter tube fan coil unit. Theoretical calculations, analysis, and conclusions from the feasibility study of using 7mm diameter copper tube in lieu of 9.52 mm in FCU applications are found below:The heat transfer area of 7mm diameter FCU is similar as 9.52 mm. The total heat capacity, sensible heat capacity, water pressure drop(WPD), air pressure drop(APD) are all suitable for small FCU applications. Additional performance improvements are realized as the air pressure drop is reduced 28%, which reduces motor energy consumption. Theoretical calculations and analysis show the 7mm diameter copper tube is feasible.Prototype FCU were built to verify the theoretical calculations and analysis. The test results indicate the total heat capacity of 7mm diameter copper tube application can reach 98.8%~105.8% of original product’s 9.52 mm diameter application, and sensible heat capacity can reach 97.7%~ 103.2%. The air pressure drop tests were equal to theoretical calculations which reduce motor energy consumption. The WPD is slightly increases, but maximum WPD is not greater than 60 kPa which meets the standard industry applications. Both theoretical calculation and experiment conclude that the 7mm diameter copper tube design is feasible.For the low frequency noise issue in the Fan Coil Unit, the author studied the problem by modal analysis and normal analysis under the experiment, and drew a conclusion that strengthening the fan deck can favorably reduce the low frequency sound output for the Fan Coil Unit.According to the research results, smaller diameter tube Fan Coil Units are feasible by meeting required heat capacity and hydraulics requirements. Product costs are significantly reduced by the 22-35% reduction in copper tube and aluminum fin material consumption. Low frequency sound is reduced by strengthening the fan deck and improved the FCU’s quality. Overall, the 7mm diameter copper tube design promoted a completive product in a cost sensitive industry.