Cisco GoQAM Installation And Operation Manual page 37

Considerations When Using Side by Side Equipment Racks
Often, side-by-side equipment racks will not include an internal wall between them.
You should take extreme care when installing modulators in these types of systems.
There is approximately an 18°F (10°C) rise from inlet air temperature to exhaust air
temperature on a GoQAM. This rise in temperature could have a cumulative effect
on temperature from one rack to the adjacent one. You must take extreme care not to
exceed the 122°F (50°C) maximum inlet air temperature requirement in these
situations.
Considerations When Using Racks with a Wall on One Side
Rack installations that have the outer wall or side of the rack in place on the exhaust
side of the GoQAM should note that without sufficient airflow through the rack, the
heated exhaust air may re-circulate back to the input side of the GoQAM. Depending
on the situation, this re-circulation air could eventually exceed the specified 122°F
(50°C) maximum.
Measuring the Inlet Air Temperature
If you are concerned about inlet air temperature, you should measure the
temperature of the inlet air in the actual rack as you plan to use it. You should have
all cabling in place and all adjacent units installed and running.
Important! Opening the door on the back panel of the rack can have an adverse effect
on the managed airflow. If access to the door on the back panel is not controlled, you
should take the inlet air temperature with the back panel door open since, in most
instances, opening the door will re-direct the airflow in an adverse manner.
Stacking Considerations
You have two main options for stacking GoQAMs in a rack. The option you choose
depends on your system requirements. One option is to stack the GoQAMs in a rack
containing a top-mounted exhaust fan with vented panels on the front and back. The
second option is to place a top-vented rack over a floor plenum forced air vent. The
requirements for these two stacking options are described next in this section.
Option 1 – Using a Rack With a Top-Mounted Exhaust Fan
This stacking option uses a 40 RU configuration containing up to 32 GoQAMs. The
remaining 8 RUs are configured with 4 RUs at the bottom and 4 RUs at the top.
The 4 RU space at the bottom is covered with a vented panel on both the front and
the back. This panel allows air to freely enter the rack to cool the modulators.
4004834 Rev D
Stacking Guidelines
21