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AHU Specification

An AHU installation at a Data Centre

Air handling equipment shall be manufactured in accordance with the following specification, designed for horizontal or vertical air flow.

Units shall be matching in both internal width and height to ensure smooth efficient air movement through each section of plant with minimum turbulence and pressure loss.

Access shall be provided to each section of plant for inspection and maintenance purposes.

Units shall be constructed to eliminate the transmission of mechanical vibration.

For ease of handling, larger units shall be transported to site in sections for assembly by others.  All jointing gaskets, sealing materials and hardware shall be provided to allow assembly to be completed.

Suitable permanent lifting points shall be incorporated into the unit base frame or framework.

The units shall be complete with fixed identification, airflow and warning labels.

As a minimum the AHU shall be constructed to meet the leakage requirements of DW143 class B (BS1886 leakage class L2).

Unit frame

The unit framework shall be constructed using 50mm penta box section, manufactured from 18 swg (1.2mm) Z2 hot dip galvanised steel.

The frame shall be assembled using pre formed corner sections and seam welded internally.  Intermediate post work shall be fitted where necessary to provide a structure of strength and rigidity.  The frame shall be capable of supporting the components and fittings forming the air handling unit and withstanding the pressure within the air system under operating conditions. The frame shall be vapour sealed.

All post work around and downstream of cooling coils and other drain tray sections shall be fully insulated throughout their entire length. The insulation material shall have the same acoustic and thermal properties as that identified for cladding panels elsewhere in the specification.

The structural strength of the assembly shall in no way rely on the cladding panels. All strength shall be provided by the permanent framework.

The framework shall have a natural galvanised finish

All air inlet and outlets shall be suitable for flanged duct connection.

Enclosure and access Panels

All enclosure panels and access doors shall be nominal 45mm deep and double skinned. The outer skin shall be manufactured from 20 swg (0.9mm) B.S.C. colour coat plastisol (plastic coated steel). The standard colour shall be Goosewing Grey (BS 10A05). The inner panel skin shall be manufactured from 22 swg (0.7mm) Z2 hot dip galvanised steel. The cavity shall be packed with slab rockwool insulation, with a density of 45kg/m³ (thermal conductivity of 0.035 W/mK), compressed between the inner and outer skins, to form a panel with excellent thermal and acoustic properties. On units large enough for internal access the floor panels shall have reinforced insulation to facilitate maintenance access.

Internal floor panels are to be welded in place. All other panels shall be flush mounted into the unit frame and be fully removable.

Access doors shall be provided to areas of regular maintenance. Door furniture shall be either hinged or lift off operation.

All panels shall be located on closed cell neoprene acoustic gaskets, about their perimeter.

Casing attenuation

Casing sound reduction shall not be less than:

63 125 250 500 1000 2000 4000 8000 dB(LIN) dB(A)
Sound reduction (dB) 22 21 39 50 50 48.5 51.5 47 32 47.5

Unit base skid

All air handling units are fitted with a steel base, fabricated from galvanized steel, designed to support the unit at the relevant structural points.

Weather protection

When units are to be installed externally, they shall be provided with a trussed pitched roof fitted over all elements of the framework.

The roof shall be manufactured from 0.7mm Z2 hot dip galvanised steel with a finish to match the AHU frame work.

The roof shall be flashed and sealed where jointing is necessary to prevent water ingress.

All unducted fresh air intakes and exhaust air discharges shall be fitted with either weather hoods or louvres complete with a bird/vermin screen.

Standard features

1. Unit constructed to meet the leakage requirements of BS1886 leakage class L2 (DW143 class B).
2. Frame to be vapour sealed.
3. Fan motors wired to local isolators.
4. Fan assemblies mounted on vibration isolators.
5. Fan assemblies earth bonded.
6. Fan discharges fitted with internal flexible duct connectors.
7. Post work insulated around and downstream of cooling coils.
8. Coils installed on slide rails.
9. Drain trays manufactured to eliminate ponding and extended beyond the component casing to allow inspection and cleaning.
10. Panel and bag filters fitted with inclined manometers, HEPA filters with vertical manometers.
11. Bag filters installed in frames with pockets in vertical orientation.
12. Man access sections fitted with reinforced floor panels.
13. Air inlet and outlets suitable for flanged duct connection.
14. All units fitted with flush base skids.
15. All sections fitted with permanent lifting facility.
16. Access doors adjustable to allow for seal deterioration.
17. All non-access enclosure panels removable.
18. All unit sections and components fitted with identification and warning labels.
19. Finish: Framework; self-finish galvanised  
                  Panels; plastisol coated

Optional Extras (not an exhaustive list)

1. Unit constructed to meet the leakage requirements of BS1886 leakage class L1 (DW143 Class C) or to exceed BS1886 leakage class L1 (DW143 Class D).
2. Fan motors wired to local isolators complete with auxiliary contacts.
3. Drive guards shall be fitted to all fan assemblies.
4. View glasses shall be fitted to all fan sections.
5. View glasses shall be fitted to all access sections.
6. View glasses shall be fitted to all humidifier sections.
7. Unit access areas fitted with bulkhead lights, pre wired to external switches.
8. Fan sections fitted with bulkhead lights, pre wired to external switches.
9. Humidifier sections fitted with bulkhead lights, pre wired to external switches.
10. Test points shall be fitted between all components.
11. All access doors shall be key lockable.
12. The unit shall be fitted with guttering, down comers and shoe discharges.
13. Barkell Limited shall attend site to complete assembly, following final positioning by others.
14. The units shall be leakage tested at works.
15. The units shall be witness leakage tested at works.
16. The units shall be leakage tested on site.
17. Non-standard colours available.
18. Floating hinges for low leakage applications.
19. Integral trunking within the AHU frame work.
20. Integral enclosures can be provided for controls or power distribution equipment.
21. A comprehensive controls package can be supplied for each AHU.


Contact an AHU sales engineers for more information