Specifications

10 007-4603-001
2: Site Preparation Concepts
Calculating Thermal Load
You can calculate the thermal load as follows:
1. Add the wattages of all the items in the room.
2. Calculate Btu/hour by multiplying the total wattage by 3.41.
3. Calculate the kcal/hour by multiplying the total wattage by 3.23.
4. Calculate the tons of air-conditioning load by dividing Btu/hr by 12,000.
1 kBtu/hr = 1000 Btu/hr
12,000 Btu/hr = 1 ton of air-conditioning load
The calculations above yield results that represent the maximum thermal output of the
equipment. These calculations and the heat-dissipation numbers that Table 5-1 lists are
based on maximum rated wattage.
The thermal figures quoted in this guide are likely to be worst-case figures.
Some sources quote a “typical” thermal output for a system, which may be significantly
less than the numbers listed in this guide. Selecting an air-conditioning capacity that
accommodates the “worst-case” thermal output, however, helps to minimize system
problems later.
When you calculate the air-conditioning capacity that is required, be sure to include the
heat load from computer equipment that is already installed at the site, noncomputer
equipment that is already installed at the site, and the computer equipment that is being
added. Also remember to include noncomputer equipment that is already installed or will
be installed, and other factors such as solar gain, outside ambient air temperatures, and
the number of people who work in the room.
Thermal Gradient
Table 6-1 includes a maximum thermal gradient for each system. The thermal gradient is
the rate at which the temperature changes, which is typically expressed in degrees per
hour. Temperature changes that are more rapid than the given rate can damage some of
the components in the system.
Unless otherwise indicated, the thermal gradients listed apply whether or not the system
is operating.