Page 194 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

172 Cha pte r F o u r

In addition, other chemicals used for fire suppression may impact the ozone in the
stratosphere. Of particular concern are halons, which are organic compounds that contain
bromine atoms in addition to chlorine and fluorine. A bromine atom can have an even
greater impact than a chlorine atom has on the concentration of ozone in the stratosphere.
To compare the impact of the various refrigerants and fire suppression chemicals on
the ozone in the stratosphere, a scale has been developed called the ozone depletion
potential (ODP). One of the refrigerants typically referred to as CFC-11 has been given
the ranking of 1 on the ODP scale, and the other chemicals are compared to CFC-11 on
a mass basis. Most compounds are ranked with a value less than 1, except for those with
bromine atoms, which may be higher.
There is concern that some of the alternatives to CFCs and other chemicals used for
refrigeration and fire suppression may have an impact on another global atmospheric
phenomenon, specifically global warming. Global climate change is of major interest, as
changes in the global climate may cause weather and ocean level variations that can
adversely impact humans and the environment. Carbon dioxide (CO ) is a common
2
compound in the troposphere that most living creatures expire. Scientists have shown
that its concentration in the troposphere has been increasing in the last few centuries,
and there is concern that the additional CO and other chemicals in the atmosphere that
2
may come from anthropogenic processes may have a blanketing effect, causing average
temperatures to rise. There is much debate over the importance of CO and these other
2
gases in overall climate change.
Carbon dioxide has been given a global warming potential (GWP) of 1. Several
refrigerants and fire suppression chemicals have also been given a GWP ranking based on
the GWP of CO on a mass basis. Many different sources list many different values for ODPs
2
and GWPs as their values are estimated from very complex models and scenarios. The
GWPs and ODPs of many refrigerants are given in the LEED-NC 2.2 and 2009 Reference
Guides. These and several other compounds are listed in Table 4.4.1 and are based on Tables
1-5 and 1-6 of The Scientific Assessment of Ozone Depletion, 2002, a report of the World
Meteorological Association’s Global Ozone Research and Monitoring Project; those that are
not updated in this 2002 report are from The Scientific Assessment of Ozone Depletion, 1998.
The ODPs and GWPs are based on the mass of the noted refrigerant or fire suppression
chemical with respect to the mass of the associated base chemical, CFC-11 and CO ,
2
respectively. In the case of the GWP, note that there are significantly larger quantities of
CO emitted on a mass basis into the atmosphere than there are of most other refrigerants.
2
In addition, there is much scientific debate on the relative impact that water vapor has
on the global climate. Regardless, the other refrigerants and fire suppression chemicals
have been ranked with a GWP as compared to that of CO , so that designers and
2
regulators can make informed decisions as to the use of these chemicals from both an
ODP and a GWP perspective. More information on these compounds and other ozone-
depleting compounds can be found on the U.S. Environmental Protection Agency Ozone
Depletion website: http://www.epa.gov/ozone/strathome.html.
The ODPs and GWPs are both sets of comparative environmental scales of certain
chemicals. If chemicals are going to be chosen based on both of these environmental
concerns, then there also needs to be a comparative environmental ranking between the
scales. The USGBC has developed a formula for use in LEED certification that gives a
comparative ranking of 1 to 100,000 between the relative importance of the mass of CO
2
to the mass of CFC-11 for global warming and ozone depletion potential, respectively.
The relative multiplier 100,000 lb /lb will be used in the overall certification
CO2 CFC11
equation presented later in this section [Eq. (4.4.5)].