Mammoth 800 to 5500 CFM: Dedicated Outdoor Air System with Enthalpy Wheels (VHC) User Manual

Page 6

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MAMM-VHC-IOM-1A (JANUARY 2013)

Roofcurbs supplied by others must be designed with the

same dimensions and cross member arrangement as per

Mammoth roofcurb drawings and must be designed to

evenly withstand perimeter and cross section static loads.

Inspect the equipment exterior and interior for damage

and for shipped loose parts. Ensure there is no damage to

internal components such as fans, motors, dampers, en-

thalpy wheel, insulation and structures. File a claim with the

shipping company if the unit is damaged. Check the pack-

ing slip against all items received. If any items are missing,

sign the carrier’s bill of lading with the notation “Shipment

Received Less Item #___.”

Spreader bars are required to prevent damage to the roof

flange. Rollers may be used to move the unit across the

roof. Lifting holes are provided in the base rails as shown in

Appendix C

. Refer to submittal documents for overall unit

dimensions and

Appendix D

for unit weights.

On vertical discharge units, secure all ducts to the roofcurb

and building structure. Do not secure ductwork to the unit.

For unit and duct opening sizes see submittal drawings.

Insulate and weatherproof all external ductwork, joints and

roof openings with counter-flashing and mastic in accor-

dance with applicable codes. Ductwork running through

roof decks must comply with local fire codes. Ducts pass-

ing through unconditioned spaces must be insulated and

covered with a vapor barrier. Flexible connectors should

be installed close to the unit in the duct leading to occupied

spaces to minimize noise transmission.

Duct Design Considerations

The discharge ductwork immediately downstream from the

fan is critical for successful applications. Poorly designed

ductwork can degrade fan performance and contributes to

excessive pressure drop and noise.
When designing ductwork in the field, it is important to

use a straight discharge duct of the correct dimensions to

obtain maximum fan performance. The straight section of

ductwork helps the airflow to develop a uniform velocity

profile as it exits the fan and allows the velocity pressure to

recover into static pressure. See Figure 1

For 100% recovery of velocity pressure into static pres-

sure, the straight portion of the discharge duct must be at

least 2.5 times the discharge diameter to the length of the

straight portion of ductwork.
As an example of how to size the straight portion of duct,

assume the fan has a 13.5”x 9.5” discharge outlet = 0.89

Roofcurbs Supplied by Others

Rigging and Placing the Unit

Field Fabricated Ductwork

IMPORTANT

Mammoth is not liable for any damages, costs or other is-

sues arising from roofcurbs supplied by others.

IMPORTANT

This information is referenced from AMCA Fans and Sys-

tems Publication 201.

IMPORTANT

The hoods for these units are not installed from the fac-

tory and must be installed on site. They should be in-

stalled after the unit is installed. Hoods are shipped on top

of the unit. When rigging the unit, make sure the hoods

are secured and are not damaged by the spreader bars.

See

Appendix B

for hood installation.

CAUTION

All panels must be in place when rigging.

Centrifugal fan

Cutoff

Discharge duct

100% effective duct length

2½ diameters at 2,500 FPM

Figure 1: Duct design

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