Page 415 - Sustainable On-Site CHP Systems Design, Construction, and Operations

388 Ca s e S t u d y 6

designs for greater operating economies along with a third CHP alternative employing a
direct CGT exhaust gas-fired two-stage absorption chiller, and then compare the eco-foot-
print and life-cycle cost for each of the three CHP options with the previously referenced
EPGS supplying comparable annual electric power requirements.
Finally, using the eco-footprint of the EPGS as a baseline, the most promising CHP
alternative of the above three will also be explored as a potential “cap and trade”
candidate to further reduce its first cost and therefore enhance its sustainability from
both an energy and greenhouse gas emissions standpoint.

Introduction
What does one mean by the term “sustainability,” and is it different from building sus-
tainability or combined heat and power (CHP) sustainability? Ray Anderson, chairman
of Interface Inc. was quoted as stating “sustainability implies allowing a generation to
meet its needs without depriving future generations of a way to meet theirs.” The board
of directors of the American Society of Heating, Refrigerating, and Air-Conditioning
Engineers (ASHRAE) approved the position document “Building Sustainability” on
June 23, 2002, which stated, “ASHRAE supports building sustainability as a means to
provide a safe, healthy, comfortable indoor environment while simultaneously limiting
the impact on the Earth’s natural resources.”
A subtle additional component for CHP sustainability is implied in Mr. Ander-
son’s use of the words “allowing a generation to meet its needs.” The latter recognizes
the mechanical, electrical, plumbing (MEP) consultant’s real-world need to justify (or
sustain) value-added CHP benefits for its clients. What better way to attract funding
for CHP than to utilize LCC methods to select among traditional versus more attrac-
tive CHP alternatives to secure client commitment and thereby advance overall green
project sustainability?
Other factors in addition to LCC analysis include waste heat versus prime energy
utilization, building operator skill sets, reliability, local utilities real-time costs, related
environmental concerns, for example, greenhouse gas emissions, eco-footprint, and
green marketing benefits to refocus initial client goals when setting long-term budgetary,
building design, and operational parameters. This is particularly true when considering
whether to employ on-site cooling CHP systems that rely in part or exclusively on avail-
able local gas and electric utilities to serve their new or renovated, large-scale, tenant-
occupied or leased building facilities. And when doing so, one must realistically ask:
how foreseeable are future energy costs likely to be, present world conditions being what
they are?
Among the many chiller technologies available in the market today, single- and two-
stage lithium bromide (LiBr)–water absorption chillers have proven to be the most cost-
efficient topping-cycle options or hot water for converting available high-temperature
waste heat, for example, 350 to 400°F (177 to 204°C), into chilled water cooling. On the
bottoming-cycle end of available cascading lower-temperature waste heat (e.g., 200 to
250°F or 93 to 121°C), ammonia-water absorption chillers to produce ice for thermal
energy storage (TES) and desiccant regeneration for dehumidification equipment (e.g.,
outdoor air pre-conditioners) are employed.
Although the previously referenced indirect fired two-stage and single-stage LiBr-
water absorption chillers utilize steam or hot water for activation, they can also employ
waste heat directly to generate chilled water. In fact, efforts to supply turbine exhaust