Tab Journal Spring 2013 - (Page 10)

System Effect: CASE STUDY Kevin Underwood, TBE Engineered Air Balance Co., Inc. A common term used to describe some inlet and outlet conditions that affect the performance of fans is “system effect.” The term refers to the results obtained after the fan was tested in a laboratory compared with how the fan was installed. A case study was performed on an exhaust fan that was not performing as submitted on recent project. The following was the original submittal data for the subject fan: Flat Blade Centrifugal Blower n Model 245 CPS n Design SP = 1.00” w.c. n Design Motor HP = 5.0 n n Counterclockwise Up-Blast n Design CFM = 8195 n Design Fan RPM = 1080 After the exhaust was proportioned within the system, the fan was operating at 80% of the design CFM, and the motor was operating at nameplate amps. STEP 1: Evaluate the air balance measurements and compare them with the fan curve data. The air balance measurements are correct. The missing component is the effect of the back draft damper on the discharge of the fan. This data has to be added back into the air balance measurements. Initial Conditions New Conditions CFM= 6590 8195 SP= 1.76 2.72 RPM= 1285 1598 HP= 4.66 8.96 AMPS= 6.1 11.73 Motor FLA= 6.55 Motor HP= Damper 5 1286 RPM 4.66 BHP 1.76 SP 6590 CFM 10 TAB Journal Spring 2013

Table of Contents for the Digital Edition of Tab Journal Spring 2013

Minimum CFM and Terminal Box Sizing: What a TAB agent should know
Controlling Variable Air Flow Rates
System Effect: Case Study
The Importance of Duct Leakage Testing in Hospitals
Direct Drive Fans & Fan Banding: A New Direction for Air Handling Systems
Effective Fire System Testing from Door to Door
Not All VFDs are Created Equal
Tech Talk

Tab Journal Spring 2013