Page 108 - Sustainable On-Site CHP Systems Design, Construction, and Operations

86 CHP B a s i c s

site. With advances in analysis and experience, the uncertainty of whether the assem-
bled CHP system meets both customer expectations and regulatory requirements are
reduced, but on-site engineering and fabrication are still required to ensure proper
interfaces and interactions between the parts and the site. These activities may be eco-
nomically acceptable for a larger CHP system, but the lower revenue of a smaller CHP
system often requires minimal on-site labor to be economical. Hence, packaged systems
exist for CHP systems whose electrical output power is in the order of 1 MW or less.
In the subsequent discussions, each of the primary characteristics of a packaged
CHP system is described, with emphasis on how the characteristic benefits the CHP system.

Preengineered
Every CHP system is preengineered to some degree. As with every CHP system design,
primary CHP system components are selected that are compatible with the utility infra-
structure, provide outputs to meet customer requirements, and that satisfy safe and
environmentally acceptable practices. Preengineering is particularly critical to enhance
the value proposition of packaged systems through optimized design, added function-
ality, and minimal use of on-site labor. The preengineering benefits are

• Compatible components that are optimally integrated
• Maximum/additional functionality
• Robust system control
Preengineering ensures that the prime mover and TAT device are optimally matched
to achieve the highest level of fuel utilization, defined as the quotient of useful electrical
and thermal output energy to fuel input energy (see Chap. 17). The TAT device capacity
must be consistent with the quantity and quality of waste heat available. Additionally,
proper matching ensures that the properties of the waste heat leaving the prime mover
can be efficiently used as input to the TAT device. For example, if the TAT device
imposes excessive pressure loss at the waste heat flow rate, then the prime mover will
experience excessive backpressure and its output may be unacceptably degraded. Or, if
the waste heat temperature exceeds a TAT device allowable limit, a wasteful heat loss
could be required to reduce temperature. In either case, the system output and fuel
utilization are reduced. Preengineering can avoid these issues through the proper selec-
tion of components, including the selection of multiple or multimode TAT devices. For
example, a heat exchanger to heat air or water may alleviate the above excessive inlet
temperate issue while producing another useful energy stream.
Preengineering can add functionality to the CHP system. For example, the selected
TAT device might be capable of providing alternative thermal energy streams such as
heating or air-conditioning, thereby expanding the utility of the CHP system. The system
can also be designed to have dual mode capability. In this case, the CHP system can
operate either parallel to the utility electrical grid (“grid connected”) or independent of
the grid (“grid independent” or “island-mode”). Preengineering ensures the existence
of the proper technology to meet required start-up or transition timing. The CHP
system can be preengineered to operate on multiple fuels if the appropriate pumping,
valves (including fluid compatible internal materials), metering, and emission control
devices are properly integrated. As described below, added functionality can provide a
distinguishing performance benefit for a packaged CHP system.