UFC 3 -520-01
June 10, 2002
13-1.5
For facilities having emergency generating systems in excess of 200 kW, or
where energy monitoring systems exist or are planne d for installation, evaluate the
installation of a demand controller. The economic viability should be based on the
ability to reduce demand charges by peak-shaving with the emergency generator(s)
typically provided for such facilities as hospitals and communications installations. The
utility company's permission will be required if the two electrical systems must
interconnect.
13-2
CLASSIFYING EMERGENCY POWER LOADS.
13-2.1
Once the need for backup power has been established, the next step is to
decide which type of backup power system will satisfy the load requirements. The total
load, uninterruptible power requirements, and demand duration all influence the
selected backup power method. For example, a relatively small computer load that only
has to be safely shut down following a power outage has a different need than a
communications system that must operate continuously until normal power is eventually
restored. In the first case, a UPS system with a small battery might be adequate. In the
second case, UPS power might be backed up with larger batteries as well as an engine
generator.
13-2.2
As part of the backup power equipment selection process, classify each load
as to the type of power that it should have. The following simple classifications are
recommended as the starting point:
13-2.2.1 Critical--loads in this category require continuous power and can not
experience even momentary power disruptions. Loads in this category usually include
computer and communications systems. These loads wi ll likely require the use of a
UPS system.
13-2.2.2 Essential-- loads in this category require backup power, but momentary
power loss is acceptable. Loads in this category usually include heating, ventilating,
and air conditioning loads to vital facilities or other load types that can be deenergized
for short periods without severe consequence. Engine generator backup is often
acceptable for these loads.
13-2.2.3 Nonessential--loads in this category can be deenergized for extended
periods without severe consequence. Although these loads might be classified as
nonessential, they might still be capable of being energized from engine generators,
depending on the facility design.
13-2.3
Determine which loads are continuous, non-continuous, or non-coincident.
Continuous loads are energized for periods greater than 3 hours, such as lighting and
HVAC equipment. Non-continuous loads do not meet the definition of continuous and
the proportion of on to off time varies with each load. Non-coincident loads are
dissimilar loads, fed from a common source that are not likely to be energized at the
same time.
13-3
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