Saaf side access housings (sah) – AAF International SAH User Manual

Page 20

SAAF Side Access Housings (SAH)

with SAAF Cassette Gas-phase Chemical Filters

Installation, Operation, and Maintenance Instructions

A typical pressure drop profile for an SAH might be as shown

in Table 3 below:

9.1.1 continued

Table 3: Nominal Pressure Drop (∆P) @ 250 fpm Nominal Airflow Velocity
Pressure Component

Initial ∆P (in. w.g.)

Final ∆P (in. w.g.),

Recommended or Actual

External pressure

1.0

loss from inlet and

outlet ducts
2” PerfectPleat

0.11

1.0

HD Cassette with

0.73

SAAF Oxidant
HD Cassette with

0.73

SAAF Oxidant
After-filter

M-Pak Filter

0.23

1.5

TOTALS

2.80

4.96

9.1.2 Issues to be Considered When Selecting the Fan: There

are a number of issues to be considered when determining the fan

design and selection criteria:

1. If the fan is selected for the maximum pressure drop shown

(4.96 in. w.g.) then it will have been selected for an operating

point that will rarely occur. This may be inefficient in terms of

energy usage (motor HP), physical fan size, and product cost.
2. If the fan is selected for the maximum pressure drop shown

(4.96 in. w.g.) then it will deliver far more than the required

airflow at the lower start-up pressure drop (2.80 in. w.g). Unless

the airflow is controlled by using balancing dampers or a variable

speed drive this may result in discomfort from high discharge

velocities, high noise levels, high energy use, and inefficient filter

performance.
3. Conversely, if the fan is selected for the minimum pressure

drop shown (2.80 in. w.g.) then it will deliver far less than the

required airflow at the higher final pressure drop (4.96 in. w.g).

This may result in inadequate air supply. Alternatively the filters

can be replaced before they reach their final recommended

pressure drop which results in higher filter replacement costs.

Other factors to be considered are:

4. The space available inside the cabinet. This may limit the fan

style or size that can be accommodated within the cabinet. This

may require the use of an external stand-alone fan.
5. The costs associated with providing non-standard fans or fan

or motor control systems.
6. The type of fan to be selected. For instance will a non-overloading

fan wheel be required.
7. Power available in terms of voltage, phase, and frequency.
8. Special parameters such as special electrical, environmental,

explosion, or temperature requirements,

As is evident from this discussion there are a number of factors to

be considered when selecting the appropriate fan.

9.1.3 AAF’s Policy Regarding the Provision of Internally

Mounted Fans: Items 1 & 2 are standard offerings, item 3 is

an option:

1. When the size of the cabinet allows, AAF will supply a fan

capable of generating the design airflow at the average pressure

drop through the system. In the case of the table above the

average pressure drop is 0.5 x (2.8 + 4.96) = 3.88 in. w.g. An

external pressure drop of 0.1 in. w.g. will be assumed. A

backward inclined non-overloading fan wheel will be supplied

unless otherwise advised.
2. When the size of the cabinet limits the fan selection (normally

on smaller SAH sizes such as size 102 through 204) AAF will

advise the maximum performance that can be supplied by a fan

that will fit into the space available. An external pressure drop of

0.1 in. w.g. will be assumed. A backward inclined non-overloading

fan wheel will be supplied unless otherwise advised.
3. When the customer specifies a fan performance that is different

from that based on the design airflow at the average pressure

drop through the system and the size of the cabinet is not an

obstacle AAF will select a fan to meet the specified requirements.

See AAF’s submittal drawing for the order in question for the details

of the fan supplied and its performance.

AAF has a policy of continuous product research and

improvement and reserves the right to change

design and specifications without notice.

ISO Certified Firm

The USGBC Member logo and LEED

are trademarks owned by

the U.S. Green Building Council and are used by permission.

GPF-3-106 MAR '11 QG 2M

AAF International Building

9920 Corporate Campus Drive

Louisville, Kentucky 40223-4051

Customer Service 888.223.2003

Fax 888.223.6500
www.aafintl.com