Page 406 - Sustainable On-Site CHP Systems Design, Construction, and Operations

Governmental Facility—Mission Critical 379

have three load-shed levels (though up to 32 levels are widely available in some control
packages). One rule of thumb suggests loads can be shed in decrements no greater than
30 percent of normal load.
Meeting all the criteria for federal–state matching funds in multifunction buildings
will involve some extremely testing financial acrobatics. Where this is not easily accom-
plished, internal accounting segregation of the costs of various types of infrastructure
may achieve many of the purposes served by physical segregation of load classes.

Reliability Worth
An assessment of CHP hosting critical operations power starts with consideration of
the nature and duration of the outage. In reliability studies, generally; there are two
common baselines:

• Momentary: 5 to 10 seconds, maximum
• Extended: 10 seconds, minimum
The effects of momentary outages can be mitigated with equipment such as fly-
wheels or batteries. The effects of extended outages can be mitigated by getting the
emergency management facilities high on the regional restoration order rankings of the
local utility (if it is not already). A CHP-COPS feasibility study should include consid-
eration of these approaches.

The EPA Economic Study
A case study—keeping reliability considerations constant—comes from research pre-
12
pared by the U.S. Environmental Protection Agency. In this study, the value of reliable
service was determined for a 1500-kW CHP system running in island mode for a repre-
sentative commercial customer of the PG&E. When power delivery is disrupted, cus-
tomers generally experience losses that are much greater than the cost of the electricity
not delivered. While the cost of service determines the electric rates, the value of that
service is different for each customer.
Estimates of typical annual values for the number of momentary outages and total
time of extended outages can be found from utility bills and/or facility records. (Many
organizations have a job ticket that tracks power loss recovery costs.) The direct cost
impact of momentary outages on either a dollar-per-incident or dollars-per-minute
basis is calculated. If the momentary outage results in an extended disruption at the
facility, the direct cost impacts of extended outages on a dollar-per-minute or dollars-
per-hour basis is calculated.
The cost value represents an annual direct operation cost that could be avoided
with a properly configured CHP system. This is treated as operating savings in a CHP
feasibility analysis. Dividing this total cost value by the number of unserved kilowat-
thours (average power demand in kilowatt times total annual outage time in hours)
produces a value of service estimate similar to those included in Table 23-2.
Table 23-2 shows that even momentary outages result in extended disruptions to
the normal routine of business. Thirty-minutes is used as an assumed recovery time; as
would be the case where HVAC equipment needs to be manually reset after an outage,
or personal computer workstations that need to undergo a hard reboot. The cost of an
outage for the representative PG&E commercial customer is estimated at $45,000 per