Page 39 - Sustainable On-Site CHP Systems Design, Construction, and Operations

18 CHP B a s i c s

A promising alternative to using fossil fuels to power CHP plants is the use of
biofuels (liquid and gas). Today, biogas from wastewater treatment plants and landfills
(landfill gas) is routinely used to fuel CHP systems, and some systems are beginning to
be powered from liquid biofuels including biodiesel made from waste oils or vegetable
oils or plant oils. With respect to ethanol, however, some controversy exists as corn is
used in the making of ethanol and the increased demand for ethanol contributed to the
surge in food prices (corn is a staple of many manufactured food products as well as
feed for livestock). Scientists are working on ways to produce biofuel from switch grass
and other cellulose waste products or from algae or from fast growing plants that can
grow in poor soil with little water or fertilizer instead of from food stock. As noted, one
benefit of biofuels is that CO is resequestered during the growing cycle removing carbon
2
from the atmosphere to help reduce global warming.
Today, we are facing the challenges of climate change, global warming, and how to
reduce greenhouse gas emissions. ASHRAE’s policy statement on global warming in
effect acknowledges that greenhouse gases are linked to global warming and that
greenhouse gas emissions must now be taken seriously by its members and by the
world community. Architects and engineers responsible for engineered building facili-
ties lasting 30 to 40 years minimum on average or longer can minimize such global
warming impacts well into the future by advocating sustainability through cost-effective
CHP today. Energy experts know that there is no “silver bullet” (to use a horror mythology
metaphor), but there is “silver buckshot,” meaning that there are a lot of little things
that, added together, will make a significant difference. Energy experts and govern-
ment officials strategic plan for both the short and long term is to increase the use of
CHP because of its inherent high source fuel utilization efficiency. Further, ASHRAE
building sustainability goals are likely to be significantly advanced through efficient
and value-based on-site sustainable CHP systems differentiated using life-cycle cost
analysis and eco-footprint methods. Improvements continue to reduce CHP plant emis-
sions, and new generation equipment and emission controls are achieving orders of
magnitude reductions in emissions when compared to earlier years.
The centralized plants of large energy users, for example, hospitals, universities, or
research campuses are ideal candidates for CHP installations. However, evaluating
costs and benefits can make ROI projections difficult, especially with new facilities that
lack historical operating data. Fortunately, in such cases, CHP engineers can readily
find and employ thoroughly tested CHP optimization software as a valuable resource
for evaluating alternative approaches during the projects feasibility study phase.
Ultimately, the feasibility of any CHP approach will depend on the magnitude, dura-
tion, and coincidence of electrical and thermal loads and on the selection of the prime
movers and the waste heat recovery systems.

References
1. Pierce, M., 1995, “A History of Cogeneration before PURPA,” ASHRAE Journal, May
1995, vol. 37, pp. 53–60.
2. Katipamula, S. and Brambley, M. R., 2006, Advanced CHP Control Algorithms: Scope
Specification. PNNL-15796, Pacific Northwest National Laboratory, Richland, WA.
3. Meckler, M., 2001, “BCHP Design for Dual Phase Medical Complex,” Applied Thermal
Engineering, November, Edinburgh, UK: Permagon Press, pp. 535–543.