Page 160 - Sustainable On-Site CHP Systems Design, Construction, and Operations

Fundamental Concepts 133

Subsequent Analysis
After collecting the data, the engineer will proceed with the following tasks.
Step 1—Identification of Barriers
The intent of this first step is to identify any major uncontrollable obstacle that will
prevent the project from being implemented. Typical examples of barriers are existing
long-term corporate power purchase contracts that will not allow installation of on-site
power generation; local utility and regulatory policies that add CHP constraints and
costs; dense and vertical building environment like New York City; special require-
ments for the stack to exhaust the products of combustion; space for prime mover and
auxiliary equipment; noise levels constraints; etc. All these factors have to be consid-
ered at this stage; even if one of these obstacles is present, the developer must find a
way around any barrier before the project can proceed. The cost of overcoming these
obstacles should be included in the implementation budget.

Step 2—Conceptual Engineering
This stage refers to sizing and identifying prime mover technology along with ther-
mally operated equipment such as absorption chillers for waste heat utilization.
Conceptual engineering will be based on the site load requirements (peak and usage
profile) for

1. Electrical energy
2. Thermal energy
3. Cooling requirements
This information can be obtained from utility bills, submetering (electrical, steam/hot
water, chilled water) or in some cases, from trend data. Another approach for obtaining
the building load profiles is by calibrated simulation. This is the use of hour-by-hour
building energy simulation (such as DOE 2.1 E and eQuest) to “tune” or calibrate
various physical inputs to the program so that the observed (or actual) energy use (from
utility bills or other sources) matches closely with that predicted by the building energy
simulation. The accuracy of the calibrated simulation depends heavily on the data
available from the site personnel. The results of the calibrated simulation are set of
8760 hourly values for electrical demand, thermal energy for space heating, domestic
hot water, and cooling energy. This information along with proper tools can be used for
optimal sizing of the prime mover and thermally operated chiller with analytical tools
such as ORNL CHP Capacity Optimizer. In cases where the energy simulation program
equipped with models for CHP equipment, the analyst can apply the building simula-
tion program to fine tune the results obtained from preliminary results obtained from
the ORNL CHP Capacity Optimizer.
In cases where the site has already implemented (or plans to implement) energy
conservation measures (ECM), it is important to take into account these measures in the
optimal sizing of the prime mover(s) and, if applicable, to absorption chiller. In addition
to equipment sizing, the engineer or the CHP project developer will investigate the
proper prime mover technology (reciprocating engines, gas turbine, microturbine, etc.).
Although a tool such as the ORNL CHP Capacity Optimizer has the capability to size
the prime mover optimally, it is suggested that several alternatives (sizes, prime mover
technology, absorption chillers) be also investigated.