Fans and Air Handling Units Will Rea and Paul Pilutti February 16th, 2011 HTS Lunch and Learns Available Online • Visit www.htseng.com • Engineering Tools • Resource Center Contents Fans • Fan Curves • Fan Laws • Fan Types • Examples AHUs • Haakon vs. McQuay • Indoor vs. Outdoor • Unique Designs • Fans in AHUs FANS Motivation We use fans to move air • All occupied building require some fresh air • Use air to control temperature and humidity • Remove smells • Exhaust harmful particles Fan Curves Do Not Select Line System Resistance Curve BHP Line RPM Curve • Drawn for a one pressure, changes with altitude, temperature Fan Types Right fan for each application! Centrifugal • Forward Curved • Backwards Incline (Airfoil) • Radial • Tubular Axial • Prop • Tubeaxial • Vaneaxial • Plenum Static Pressure Fan Types Tubular Centrif Airfoil Plenum Forward Curve Prop Fan CFM Fan Types – Centrifugal – Forward Curve Pressure: 0.5” – 5” Airflow: 1000 CFM – 300,000 CFM + Same Slope issue Overloading Fan Types – Centrifugal – AirFoil Pressure: 0.5” – 14”+ Airflow: 1000 CFM – 300,000 CFM + Variety of Blades, BI(flat), STAF, DTAF Non-overloading Fan Types – Centrifugal – Tubular Pressure: 0.5” – 10” Airflow: 1000 CFM – 100,000 CFM + Tube SW, mixed flow, Fan Types – Inline – Propeller Pressure: 0” – 1” Airflow: 100 CFM – 100,000 CFM + Exhaust from space to space, No duct work Fan Types – Inline – Plenum Pressure: 1” – 12”+ Airflow: 1000 CFM – 250,000 CFM + Pressurization fan Fan Types – Inline – Axial Fan Pressure: 0” – 6”+ Airflow: 200 CFM – 90,000 CFM + Pressurization fan Fan Wall - Application • 20+ direct drive plenum fans in an array • How are they isolated? • How do you service them? • What is the efficiency • Inlet damper on each fan? • They do improve the second octave band sound Fan Testing • AMCA method • Test from Blocked off SP -Wide open CFM Direct vs. Belt Drive Direct Drive • No drive losses • Recommend 1000 CFM and lower • Single fan speed • More difficult to service • Exception: High CFM, Medium Static, Belts can affect space Belt Drive • 1000 CFM and over • Can be sheaved (gear change) for any fan speed • Motor service/replacement easier Fan Laws • All Constant Geometry Systems Changing RPM Law • RPM change Constant CFM/RPM Law • Changing Air Density Constant SP Law • Changing Air Density Constant Mass Flow • Changing Air Density Example 1 - Changing RPM Law Problem • AHU already installed on site • Client says they want more cooling • Do not want to pay more money • How much more possible Current • FC Fan • 10000 CFM • 1.56” TSP • 6.4 BHP • 641 RPM • 10 HP Motor Installed Example 1 - Changing RPM Law Example 1 - Changing RPM Law Original • 10000 CFM • 1.56” TSP • 641 RPM • 6.4 BHP with 10 HP Motor Predicted Maximum • 11601 CFM • 2.10” TSP • 744 RPM • 10 BHP with 10 HP Motor (example only – don’t do this) • Fan works, do coils, filters, dampers? Example 1 - Changing RPM Law Example 2 - Constant CFM/RPM Problem • Fan rated for sea level • Building in Calgary – 3438’ • Tubular Centrifigual Fan • Determine new conditions at 1322 RPM Current • 10000 CFM • 0 ft altitude – 29.92” Hg • 1.56” TSP • 4.1 BHP Example 2 - Constant CFM/RPM Example 2 - Constant CFM/RPM Sea Level • 29.92” Hg • 10000 CFM • 1.56” TSP • 4.1 BHP Calgary • 26.18” Hg • 10000 CFM • 1.37” TSP • 3.6 BHP • Any density/temperature change requires new fan curve Example 2 - Constant CFM/RPM Example 3 - Constant Mass Flow Problem • Temperature done at Sea Level • Building in Denver – 5280’ • Plenum Fan • Maintain constant mass flow for cooling Current • 0 ft altitude – 29.92” Hg • 10000 CFM • 3.00” TSP • 6.96” BHP • 1511 RPM Example 3 - Constant Mass Flow Example 3 - Constant Mass Flow Sea Level • 29.92” Hg • 10000 CFM • 3.00” TSP • 6.96 BHP • 1511 RPM Denver • 24.71” Hg • 12106 CFM • 3.63” TSP • 10.20 BHP • 1829 RPM Example 3 - Constant Mass Flow Example 4 - Air Balancing Report Problem • Air balancer reports different than design • DWDI AF Fan • Set for 1961 RPM design • Require design CFM Design Balancing Report • 10000 CFM 9350CFM • 2.5” TSP 2.3” TSP • 7.7 BHP 7.8 BHP • 1961 RPM 1961 RPM Example 4 - Air Balancing Report Example 4 - Air Balancing Report Balancing Report • 1962 RPM • 9350 CFM • 3.00” TSP • 7.8 BHP New RPM Setpoint • 2098 RPM • 10000 CFM • 3.43” TSP • 9.54 BHP Example 4 - Air Balancing Report Air Handling Units Motivation Factory built unit • Combine fan, heat, cool, humidity, heat recovery into one unit • Were built in the field, now factory built • High quality, limitless options AHUs • Treat ventilation air • Commonly come with SPP • Economizer section • Heat recovery • Coils • Humidifiers • Burners • Integral condensing units, steam generators Haakon vs. McQuay • Haakon – single product, fully custom • Haakon – Higher pressure rating • McQuay – three products, Semi-custom and packaged • McQuay can be shorter • McQuay is cheaper below 20000 CFM • Difference in base rail Haakon Structure • Structural steel base, not formed • 2”/4” fibreglass insulation • Almost unrestricted configuration • Almost infinite material/component options • Pool, Low Temp Dehumidification, chiller, condensers... Indoor vs. Outdoor • Add extra fold in roof • Hoods if required • Snow might come in, OA section drain pans Haakon – Unique Designs • Heat Recovery, Low Temp Dehumidification, SPP Haakon – Unique Designs • Heat Recovery, Gas Furnace, Integral Refrigeration, SPP Haakon – Unique Designs • Angled discharge, structural cut out Haakon – Unique Designs • Heat Recovery, Integral Humidification, SPP, Pipe chase inside Haakon – Unique Designs • Inline Fans, Dampers, UV, Lights, Can work on while unit is operating McQuay Rooftop Product • Semi-custom, wide variety of options • Heatwheels, Packaged DX, Gas heat • Fixed aspect ratio, 5 box sizes • Most compact in mid-large size units Vision/Skyline • Near Custom • Lots of components, variable aspect ratio, open sizes • Can ship in sections • 2” Injected Foam insulation • Skyline has additional seams/paint for outdoor use Fans in AHUs • Why do you use FC, AF, Plenum, Centrif, • Normal AHU (3-5”, >10000CFM) DWDI – AF most efficient • Below – use FC • Any blow through, use an evase • Plenum if outlet conditions are poor • Worse on curve, better in reality • Better acoustics for plenum • Or AF with evase and silencers ASHRAE 90.1/189.1 Efficiency Laws for Fans • Mandate a maximum BHP/CFM, or maximum nameplate HP • Exceptions for 1HP or less EF, and pressurized spaces • Similar to chiller, higher design BHP allowed for VAV • Gives credit for components (filters, RF, Heat Recovery) • 189.1 (High Performance Buildings) - 10% stricter Air Flow Monitoring Station • Factory built into AHU or ductwork • Provides digital readout and/or BAS signal • Important in VAV/demand ventilation • Some styles penetrate into airstream – affect performance • Haakon uses small openings on inlet bell • Does not intrude into the airstream Openings on inlet VAV Systems • Fan may be selected differently • Using a VFD the RPM of the fan is slowed • CFM and TSP reduced along system curve • System typical changes to introduce additional static Next Time – March 16th Humidification • Isothermal vs. Adiabatic • Dispersion Types • Steam Generators • Economizer vs. Design Day