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CHP Basics &
Benefits
CHP Basics |
CHP Benefits |
Technology Status |
Markets for CHP
Energy is the most significant driving
force of our economy. All buildings need electric power
for lighting and operating equipment and appliances.
One of the major consumers of energy in buildings is
the equipment for space conditioning. Most commercial
and institutional buildings for businesses, education,
and healthcare require space conditioning for cooling,
heating, and/or humidity control.
Two-thirds
of all the fuel used to make electricity in the U.S.
generally is wasted by venting unused thermal energy,
from power generation equipment, into the air or discharging
into water streams. While there have been impressive
energy efficiency gains in other sectors of the economy
since the oil price shocks of the 1970's, the average
efficiency of power generation within the U.S. has remained
around 33% since 1960. The average overall efficiency
of generating electricity and heat by conventional systems
is around 51 percent.
Integrated cooling, heating and power
systems can increase total system efficiency to as high
as 85%. This increase is accomplished by using thermal
energy from power generation equipment that otherwise
would be wasted for cooling, heating and humidity control
systems. These systems are located at or near the building
using power and space conditioning, and can save about
40% of the input energy required by conventional systems.
In other words, conventional systems require 65% more
energy than the integrated systems, as shown in the
above diagram.
Commercial buildings, college campuses,
hospital complexes, and government facilities are good
candidates for benefiting from integrated systems for
CHP for buildings.
The above description refers to what
is commonly known as a "topping cycle" CHP system. In
a topping cycle, the fuel is burned in a device that
generates electrical or mechanical energy and thermal
energy is recovered from the exhaust of this device.
In a "bottoming cycle" fuel is first burned in a boiler
or other device to generate usable thermal energy and
a portion of this thermal energy is extracted to generate
electrical or mechanical energy.
Most practitioners refer to systems
using a topping cycle when they discuss CHP, but this
point often is not clarified. Bottoming cycle systems
are equally valuable, particularly when they are fueled
by landfill gas, waste wood, or some other fuel that
otherwise would be wasted.
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Building owners may see several benefits
from deploying CHP systems including:
Building owners can reduce their
energy costs by deploying CHP systems because compared
to conventional systems these systems provide the following
advantages:
- Increased energy efficiency
- Reduced demand charge
- Reduced peak electric energy costs
As discussed above, CHP systems can
offer much higher total system energy efficiency than
conventional stand-alone equipment items for similar
degree of power reliability, comfort cooling, heating
and indoor air quality. Because of the higher energy
efficiency of the CHP system, it consumes nearly 40%
less fuel than conventional systems. The reduced fuel
consumption can significantly reduce energy costs.
Note that fuel cost will be even
lower if a waste fuel such as landfill gas, digester
gas, or waste wood is used to fuel the system. Even
though the need for equipment to process these fuels
into suitable form will increase system cost, using
low-cost, waste fuels can yield a project rate of return
that is far superior to systems that use natural gas
or distillate oil for fuel in many cases.
The cost of electricity to buildings
is generally based on power demand (measured in kW)
and electric energy usage (measured in kWh). The power
demand charge is generally a monthly charge ($/kW) based
on the peak/maximum power used during a month for a
specified period, generally 15 minutes to 30 minutes.
Power demand charge rates can vary with time-of-year.
CHP systems reduce power demand in two ways: 1) by generating
some of the power at site, and 2) by using thermal energy
from power generation equipment, instead of electricity,
for operating cooling, heating and/or humidity control
equipment.
The charge for electric energy usage
generally varies with the time-of-year and the time-of-day.
This charge is the highest during peak periods, generally
from 9AM until 3PM , and the least during off-peak period,
generally from midnight until 7AM . Therefore, primary
reduction in electric energy cost savings for using
CHP systems comes from avoiding purchase of electric
energy during peak periods.
Even though the initial cost of CHP
systems for buildings is higher than purchasing all
electric power needs and using conventional chillers
and boilers for cooling, humidity control and heating
needs, the life-cycle cost of the CHP systems is often
lower because of the energy cost savings over its useful
life of more than 20 years.
As discussed above, on an overall
basis, CHP systems can reduce energy costs for buildings.
If the incremental installed cost of CHP systems over
conventional systems is treated as an investment, and
the annual savings in its energy costs are treated as
the return on that investment, the return can be very
attractive.
Economic losses due to power outages
in the U.S. have cost American businesses billions of
dollars. The following table shows the economic impact
of power outages on some industries.
| Industry |
Avg.
Cost of Power Outage $/hr |
|
Brokerage Operations |
$6,480,000 |
|
Credit Card Operations |
$2,580,000 |
|
Airline Reservations
|
$90,000 |
|
Telephone Ticket Sales |
$72,000 |
|
Cellular Communications |
$41,000 |
Since CHP systems generate power on-site
or near-site, these systems improve power reliability
by either reducing or eliminating a building's dependence
on the electric power grid, and by providing an additional
power option to the building. Also, because CHP systems
are located at or near buildings, power outages experienced
because of losing a distribution line are improbable.
The higher the number of buildings
that use CHP systems, the lower the demand on the electric
grid will be. In areas where the grid is at or near
capacity, the reduced demand provided by CHP will result
in increased grid reliability.
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Descriptions of the various technologies
that form integrated CHP systems is available through
the following links:
- Distributed Power
Generation
Distributed power generation is used for producing
electric power on-site or at a location close to where
electric power is needed. Waste heat from these power
generators is recovered for operating thermally-activated
machines. Additional information on generators that
can be used in CHP systems is available at:
- Heat Recovery
Heat recovery technologies allow recovery of thermal
energy from the exhaust gases and cooling systems
of distributed power generation equipment.
- Thermally-Activated
Machines
Thermally-activated machines can use recovered heat
to provide heating, cooling, or humidity control in
buildings. Additional information is available at
the DOE
Distributed Energy Program.
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While CHP systems can be used in virtually
any application, they tend to be most attractive in
selected commercial, institutional, and industrial applications.
CHP systems can help reduce the cost
of heating, cooling, or providing power to a wide variety
of commercial and institutional facilities. Additional
CHP benefits can include increased power supply reliability,
better occupant comfort, improved indoor air quality,
and reduced boiler emissions. Promising applications
include:
CHP systems can help manufacturers
reduce production cost by recycling energy that currently
is being wasted. Additional benefits CHP systems may
include eliminating or reducing waste product disposal
cost (via combustion as fuel), increasing power supply
reliability, obtaining “free” space conditioning
from wasted heat, improving power quality, and improving
public image as an environmentally responsible firm.
Industries that frequently benefit from CHP include:
- Petroleum refining
- Chemical process plants
- Food processing
- Glass industry
- Steel industry
- Metal Casting
- Forest products
- Paper manufacturing
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