Page 192 - Sustainable On-Site CHP Systems Design, Construction, and Operations

The Engineering Pr ocess 165

Schematic Design and Design Development
During the preliminary or schematic design phase of the engineering design effort,
major equipment selections are finalized although subsequent modifications may be
needed. Since the number, size, and type of CHP equipment is typically set at this stage
of design, any change in the basic assumptions regarding the basis of design is costly
and delays the project completion. At this stage, CHP systems are generally represented
schematically. A schematic flow and temperature diagram is generally developed for
each operating system; though, sometimes more than one system can be combined
within a single drawing. A schematic diagram should identify all major equipment
including valves, interconnecting pipe, flows, temperatures, and instrumentation. A
table should be provided that shows the heat balance. Typical systems for a CHP plant
to show in the diagrams include

• Fuel (e.g., natural gas, fuel oil, biodiesel)
• Combustion air
• Engine exhaust
• Emission controls
• Steam, condensate, and feedwater (if using a HRSG—heat recovery steam
generator)
• Jacket water (if using an engine generator)
• Hot water
• Chilled water
• Condenser or cooling water
• Fire suppression
• Lube oil

The schematic design includes preparation of basic floor plans, elevations, and
sections necessary to understand the scope of work, and the preparation of outline
specifications. At this phase, they are sometimes called block diagrams because they
show the basic equipment in location and to scale but not all the connections or details.
The budget construction cost estimate should be updated.
Design development furthers the design effort established, submitted, and approved
in the schematic design stage. Load and energy use calculation are typically required
for review at this stage to help ensure that the owner’s project requirements are being
met and that the assumptions made during earlier stages are still valid.

Specifications
Some owners and general contractors rarely read the specifications, which can be a
costly mistake. Every word, every sentence, every paragraph, every section in the spec-
ification is important, albeit some more than others. No portion or section of the speci-
fication that does not apply should be in the documents. Specifications include general
conditions for the project, basic materials and methods of construction and specific
pieces of equipment.