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| 1. Have you taken all reasonable steps to reduce both
electric and heat energy consumption at your facility? Obviously, if you
can make improvements in the way you use energy in your facility, these
will translate into lower operating costs and perhaps reduce the size
of the cogeneration system needed and your investment. 2. Is the average electric load at your facility
greater than 150 kW/mo, 78,000 kWh/mo and heat load greater than 4,100
therms? While CHP systems incorporating smaller generators are available,
facilities with larger energy needs can generate proportionately larger
savings and a shorter pay-back period. To make sure your CHP system
is running at full capacity most of the time, only plan on generating
a portion of your total electric and thermal needs. You'll still need
a utility connection to supply some portion of your load and an on-site
boiler to handle peaks in your thermal demand. 3. Is the average thermal load at your facility equivalent
to 1 million Btu/hr or more? This could take the form of low-pressure
steam, hot water, an absorption chiller load - or a combination of all
three. Facilities with a greater thermal load than an electrical one,
may find that a bank of microturbines or a single large gas turbine
offer a better ratio of heat output to fuel input than reciprocating
engine-driven generators. On the other hand, excess electrical power
is a salable commodity that can often be fed back into the grid for
additional savings. Heat production is necessarily restricted to on-site
or district heating use. Excess heat is usually released as waste heat,
lowering overall efficiency. 4. Is the duration of your simultaneous need for heat
and electric power greater than 4, 000 hours per year? While some applications
are feasible when simultaneous electric and thermal demand is around
2,000 hours per year, economics favor systems that operate about half
the year. Thermal processing loads tend to be rather constant, whereas
space heating or space cooling loads tend to be alternately seasonal.
Facilities with substantial space heating needs in the winter and space
cooling needs in the summer are generally good candidates for CHP systems. 5. Are local electric rates high in relation to the
local cost and availability of natural gas? Known as the "spark-spread,"
the greater the differential between the price of electricity and the
price of natural gas (on an equivalent Btu basis), the greater the likelihood
that a CHP system will provide substantial savings. Also, if you envision
installing an on-site generator capable of producing more electric power
than can be consumed on premises, it helps to be serviced by a utility
that buys excess power fed back into the grid. 6. Is your physical site suitable for the installation
of a CHP system? You'll need sufficient space to house the generators,
heat-exchangers, switchgear and control systems. Small systems can be
located outdoors in special drop-over or ISO-type containers, however,
larger systems may need their own room or free standing building. There
should also be a supply of natural gas to the facility; or, in the case
of diesel engine driven systems, sufficient fuel storage capacity on-site.
Environmental factors should also be considered such as state and local
air quality standards, and noise ordinances relating to engine exhaust
and cooling fans. 7. Is electric service reliability a major economic
concern? Many businesses today need electric service with reliability
nearing 99.9999% - the so-called Six Sigma goal. In many areas of the
country, utilities are incapable of delivering that kind of reliability
on a regular basis. In contrast, on-site CHP systems, when designed
with sufficient redundancy, standby generators and Uninterruptible Power
Supply (UPS) systems, offer significantly better reliability than local
utilities. They are less vulnerable to storm damage, transformer or
transmission line failures, and with proper maintenance, will offer
decades of reliable operation. If your answers to the above questions are affirmative,
then your facility is a likely candidate for a CHP system. The next
step in determining the viability of a CHP system for your facility
is to do a simple cost analysis and calculate the number of years for
such a system to pay for itself. A cost analysis is best done with the help of a representative
from a system manufacturer or a consulting engineer familiar with CHP
systems, such as IPSI. However, the factors that go into the calculation
are: 1) average retail electricity costs per kWh; 2) cost of natural
gas (or diesel) per million Btu; 3) number of anticipated hours of operation
per year, and; 4) installed cost of the CHP system per kW of capacity
(electrical and thermal). Typical installed costs for single unit projects
is $1,000/kW, multiple unit projects is $850/kW, mulitiple unit projects
with absorption cooling is $1,3900/kw and for mulitple unit distributed
generation (no thermal) projects is $650/kW.Based on various formulas,
these numbers combine to yield an annual cost savings and pay-back period. SOME CHP SYSTEMS COMPARISONS Whether the prime mover in your CHP system is a diesel
engine, a reciprocating natural gas engine, a gas turbine, or a fuel
cell, each technology has characteristics that may make one or another
better suited to your particular application. In general, systems based
on reciprocating engines offer the greatest electrical output per Btu
of input energy and the highest overall efficiency. Both the reliability
and availability of CHP systems are in the range of 90 - 95%. Here are
some characteristics of typical CHP systems. Diesel generator CHP system - Diesel engines represent
the prime mover with the lowest installed cost, very high reliability,
minimal maintenance and excellent electric load-following characteristics.
However, unless the installation includes diesel catalytic exhaust systems
and particulate traps, local air quality standards may limit the system's
use to less than 300 hours per year. Diesel CHP systems are suitable
for applications in the range of 300 kW to 10 MW electrical output and
1.5 MBtu to 45.2 MBtu thermal output. These systems require on-site
fuel storage. Lean-burn gas engine generator CHP systems - Recent
advances in natural gas engine combustion technology have created a
reciprocating engine generator system with excellent performance and
very low emissions. Lean-burn engine generators feature emissions of
less than 0.85 grams of NOx per brake horsepower-hour. Without exhaust
aftertreatment, these generators are suitable for high-hour use in most
geographic areas of the US. With catalytic exhaust aftertreatment, these
systems are suitable for even the most environmentally sensitive areas
of the country - such as California's south coast. These systems also
feature fast availability and installed costs that are about one-half
that of CHP systems based on gas turbines. Practical systems range in
size from 300 kW to 10 MW or more electrical, and 1.5 MBtu to 45.2 MBtu
thermal output. Gas turbine generator CHP systems - Systems based on
microturbines or larger gas turbines have the advantage of greater thermal
output per Btu of input. Although costing considerably more per kW of
capacity, and having somewhat lower overall efficiency than reciprocating
engine-based CHP systems, turbine-based systems have slightly higher
availability and lower maintenance. Gas turbines have been favored for
very large CHP systems where high-quality heat or high-pressure steam
is a required output for industrial processing. Microturbines have been
favored for their compact size, low noise, clean operation and where
fuel may be of low or variable quality. The size of gas turbine systems
ranges from 30 kW to hundreds of megawatts. Emissions are similar to
that of a lean-burn gas engine generator CHP system. Fuel cell CHP systems - Fuel cells convert a fuel (usually
natural gas) directly into electricity and heat without going through
a typical combustion process. The main byproduct is water. While fuel
cells are very clean and reliable, they are the most expensive to purchase
of all available CHP technologies. Most installations to date have been
small or demonstration projects. THE ENVIRONMENTAL FACTOR Greater use of natural-gas based CHP systems would have
the effect of reducing the demand for electricity from the nation's
power grid. Since the lion's share of this power is produced by older
coal-fired power plants, a reduction in electric demand would reduce
carbon dioxide, nitrogen oxides, particulates and other noxious emissions
by a similar amount. In this way, CHP is a technology that reduces pollution
by preventing pollution. In addition, because CHP systems allow commercial
and industrial users to operate at higher energy efficiencies, costs
are reduced and natural resources are conserved. APPLICATIONS THAT ARE CANDIDATES FOR CHP Advancing technology has made CHP systems suitable for
a much wider range of applications than in the past. Some of the typical
applications include: • Hospitals • Greenhouses • Hotels • Industrial/chemical plants • Manufacturing • Commercial facilities • Government facilities • Colleges and universities • Food processing • Health clubs • Swimming pools • Nursing homes •
District heating • Landfills and sewage treatment plants •
Coal mining and oil fields CONCLUSION CHP systems that produce both electricity and heat from the same fuel offer energy savings of up to 35% for a wide range of facilities that can make use of both forms of energy. The potential for large savings in energy expenditures is the main reason to consider CHP. Whether you choose a system based on a reciprocating engine-driven generator or a gas turbine-driven generator depends on the size of the application and the proportion and quality of energy you need as heat. For more information, contact your consulting engineering firm, IPSI or your local power generation representative.
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