AHU Design - AIRAH.pdf

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)