The Impact Of Heat Dissipation On Rising Shelf Temperatures - Nortel Passport 15000 Hardware Description

The impact of heat dissipation on rising shelf temperatures

As soon as a cooling unit of an in-service Passport 15000 or 20000 is
unpowered, the air temperature inside the shelf immediately rises and the
temperature sensor readings by the cooling unit are suspended. The fabrics
continue to measure the internal temperature of the shelf. If the rise continues,
one or more FPs can eventually fail. When a fabric reaches 72 degrees Celsius
(161.6 degrees Fahrenheit), it automatically drops all traffic. When both
fabrics reach that temperature, traffic through the Passport stops until the
temperature for one or both drops below the threshold. A built-in hysteresis
prevents the fabrics from continuously toggling on and off at the temperature
threshold.
The air temperature inside the shelf depends on the ambient room
temperature and the heat dissipation of the shelf. As the ambient room
temperature or the heat dissipation increases, the air temperature inside the
shelf increases. The rate of rising temperature depends on the shelf
configuration, that is, the type and number of in-service cards, and the amount
of traffic they are handling.
Since the Passport 15000 or 20000 has a rating of up to 150 watts per card
slot, the air temperature rise within the shelf may be as high as 10 degrees
Celsius (50 degrees Fahrenheit) per card cage with the cooling unit in service.
When the cooling unit is unpowered, the temperature rise will be as high as
40 degrees Celsius (104 degrees Fahrenheit) per card cage. Since normal
operating conditions are below 40 degrees Celsius (104 degrees Fahrenheit),
the elevated temperature will result in service degradation. To determine
whether your shelf configuration will affect service when the cooling unit is
unpowered (for example, for replacing the entire unit), do the following.
Determine whether the total heat dissipation of your shelf configuration will
affect service when removing an entire cooling unit.
1 Calculate the power consumption of the selection of cards on your shelf.
(This may already have been done to determine the size of power cable
to your shelf.)
2 Calculate the power consumption of each card in the bottom cage and the
one in the cage directly above it.
3 Compare the power consumptions to the table "Maximum shelf heat
dissipation relative to ambient room temperature" (page 132).
Passport 15000, 20000 Hardware Description
Chapter 3 Shelf assembly 131
5.2S2