AHU Design - AIRAH.pdf

1. Presented by GJ Walker Air Handling Systems

2. AHU Design
 Combination of design principles;
 Structural
- Cabinet sizing
- Base frame design
 Insulation requirement
 Air movement
 Filtration
 Heat exchange performance
 Heat recovery design and method
 Acoustic considerations
 Spatial limits, building design or accessibility.
 Commercial considerations and limits!

3. 15 Year Changes
 Cabinet construction Folded galvanized sheet,
pin insulated to Cool room panel ‘butt joint’
panels to pentapost modular construction.
 DWDI forward curved fans, to DWDI backward
curved fans, to backward curved AC plug
fans, to EC plug fans.
 Speed control; multispeed motors – VSD – EC.
 5/8” coil tube to ½” coil tube. Commercial
reasons.
 Reduction in use of electric heat.
 Demise of hot/cold Deck Multizone units to
individually zoned MZ units.

4.  Lower coil face velocities (<2.0 m/s) to
achieve lower coil air pressure drops.
 Prevalence of heat recovery.
 Efficiency of equipment.
 ‘Decimal point’ engineering.
 Larger AHU’s factory built over site build.
 Technical submissions
 Bespoke manufacturer software providing
greater detail on technical submissions.
 Scaled AutoCAD files, Revit, BIM.

5. Forward Curved Centrifugal –
Direct Drive - CSR
• Cheap but very inefficient, 315W motor input
power more than double rated motor output!
• 3 speed hard wired but limited range b/w
speeds.
• Maximum ~ 1,000 l/s @ 450Pa
• Banned in Europe ERP2015
• DC brushless and EC type fans taking their
place.

6. ERP2015

7. DWDI Forward Curved Centrifugal
• Up to 250 to1000 diameter
• Lower revving fan, often quieter.
• Overloading type characteristics
• Smaller area of overall fan curve for
application
• ‘written out’ of specification due to
maximum outlet velocity and need to
operate of the right of the curve.
• Impellor not as robust as backward curved
• Certified laboratory values not per normal
install.
• Correctly tensioned belt system leads to
approx 4% overall efficiency loss.

8. DWDI Backward Curved centrifugal
• 250 to 1400 diameter
• High revving can be unattractive at smaller
air volumes (>2500rpm at <500l/s)
• Non-overloading through limits of range.
• Operable to high statics
• Correctly tensioned belt system leads to
approx 4% overall efficiency loss.
• Laminar blade and aerofoil for higher
efficiency.

9. Backward Curved Plug Fan – AC
• Ease of installation
• Direct couple fewer maintainable parts and
greater efficiency.
• Standard parts re TEFC motor.
• Must be VSD driven.
• Motor speed v fan speed – lack of flexibility.
• Flexibility in duct take off.

10. Backward Curved plug fan – EC
• 110 to 900 diameter, max motor 7.4kW
• All in one; Fan & VSD
• Many fan profiles, constantly developing.
• Compact
• 1 x supplier in control of whole assembly.
balancing is therefore to a much higher
tolerance.
• Outside of critical applications can be hard
mounted.
• EC motor – locked into one replacement
supplier.

11. Three Phase AC Motor Limits

12. Motor Power v Motor Speed

13. Psychometrics basics

14. Coil Options

15. Coil Performance & Design

16. Structural
 Cabinet style
 Galvanized sheet steel and insulated
 Pre-insulated panel type
 Pent-a-post type aluminium frame
 Insulation types
 Single skin - Fibreglass/tontine/polyolefin.
 Double skin - Polyurethane/polystyrene/PIR/phenolic
structures (X-Flam)
 Internal panel
 Foil skin/ double skin
 Stainless steel
 Perforated metal/sound steel
 External Panel –All skins are not equal!
 Colourbond standard, colourbond permaguard, Aluminium.

17. Base Frame Design
Lifting point design Certified Lifting Lugs

18. Vibration Isolation
 Open spring mount
 25/50/100 deflection
 Seismic rated
 Laterally restrained
 RIS rubber in shear

19. Run Around Coil System
• Low efficient heat recovery.
• AHU easily accommodate additional coil in
cabinet with minimal additional plant
room space.
• Return and outside air can be remote
• no cross contamination of exhaust and
return
• Dampers required to avoid constant
elevated pressure drop.
• Can be used for ‘free’ reheat.

20. Heat Recovery - Rotary wheels
• Highly efficient form of heat
recovery up to 75%
• More moving parts than plate or
run around – maintenance high.
• ‘slim’ across airway = less plant
room space
• Return and outside air must run
adjacent to each other.
• cross contamination of exhaust
and return – purge sector.
• Dampers required to avoid
constant elevated pressure drop.
• Limited pressure differential b/w
exhaust and supply.

21. Evaporative Cooling
(direct and indirect)
• Improved development of technology, microprocessor systems
controlling evaporative cooling.
• Lower pressure drop to conventional pad type system
• Untreated water can be used.
• Direct and indirect systems.

22. Plate Heat Exchanger
• Highly efficient form of heat recovery up
to 75%
• less moving parts than plate or run around
– maintenance low.
• ‘wide’ across airway = more plant room
space
• Return and outside air must run adjacent
to each other.
• no cross contamination of exhaust and
return
• Dampers required to avoid constant
elevated pressure drop.
• Can be used for ‘free’ reheat.

23. Heat Pipe
• Free precool and reheat
• Increases latent capacity without
additional energy consumption,
enables cooling coil to meet the
dewpoint faster and with greater
efficiency
• No moving parts to break down or wear
out.
• Often allows downsizing of entire
HVAC systems (per all heat recovery).
• Helps prevent IAQ problems associated
with high humidity.
• Strangely our most prevalent market
for this product is WA

24. AHU Rental Equipment
500 kW AHU

25. Manufacturing
 Rare for products to be ‘off the shelf’ outside of
smaller FCU’s.
 Commercial decisions more protracted , AHU’s often
critical path items in overall build programs.
 Lead times 4 – 6 weeks local build with stock items.
 Ex-stock
 Motors
 Panel
 Fans (generally)
 Heat exchange coils – sometimes.
 Low cost economy supply 10 weeks
 Heat exchange coils
 Local 4 weeks – expensive
 Import – 8 weeks (50% of local price)