Page 109 - Sustainable On-Site CHP Systems Design, Construction, and Operations

Packaged CHP Systems 87

A critical aspect of preengineering is establishing the control system to help ensure
that the system operates predictably, reliably, and safely. The control system ensures
that the prime mover and TAT device operate as a system, recognizing that demands on
one unit affect the other unit, but the two devices likely have significantly different
response times. The consequences of a failure by one device, or the utility infrastructure,
may require protective steps by the other device, and neither unit is ever permitted to
operate outside its safe design space. These capabilities must be achieved for all steady-
state and transient conditions, including the transitions associated with dual mode or
multiple fuel capabilities.

Preassembled
The packaged CHP system is preassembled into a single module, or a few number of
modules, prior to shipping to a host site. In general, any module is designed to require
minimal on-site labor by including all components or auxiliary equipment, enclosures,
and precisely defined mechanical, electrical, and communication/control interfaces
both between individual modules and between the modules and the site. This includes
providing a support structure that efficiently integrates with building structures, clear
points for safe hoisting, and clear and separated fuel and electrical connectors. The size
and weight of each module must conform to shipping standards, and consider con-
straints to on-site options to locate it (e.g., standard elevator access and standard door-
way opening).
An important consideration of the module design is to ensure that component and
equipment layout does not compromise system performance. Inlet airflow, waste heat
gas, and exhaust flow paths cannot be long or tortuous. Proper thermal insulation must
be used to minimize energy loss, and isolation/ventilation used to avoid excessive
heating of components with maximum temperature limits or significant thermal degra-
dation (e.g., valves and electronics).
The module design should allow for efficient manufacturing and maintenance.
Component and equipment layout must consider fuel, electrical, and communication
requirements and the standardized methods (e.g., conduit layout, pipe size, and assem-
bly) to provide these services; codes can dictate acceptable options. The layout should
allow for an orderly assembly process (i.e., a component assembly can be completed
without interference from another device), including allowing intermediate quality
checks. Simultaneously, the component and equipment layout must provide mainte-
nance accessibility, allowing the use of larger equipment (e.g., a fork lift) if required.
Routine maintenance items should be particularly accessible. Part of the maintenance
consideration is specifying a durable enclosure to provide environmental protection
from rain, snow, wind, dirt, etc. The enclosure must include sealed access openings,
ventilation, and all code-required exterior safety markings such as for hot surfaces and
electrical voltage, for example.
A preassembled module of a packaged CHP system should be carefully inspected
to ensure that it conforms to the assembly process guidelines prior to shipment.
This includes ensuring that proper techniques were used (e.g., welded versus
screwed pipe assembly, electrical and communication wiring separation, secure
component mounting) and proper enclosure labels are visible (e.g., fuel, electrical
voltage, and hot surfaces). Performance testing prior to shipment should be part of
its prequalification.