ASHRAE Journal - September 2014 - 92

COLUMN IAQ APPLICATIONS

CO and Portable Generators
BY STEVEN J. EMMERICH, MEMBER ASHRAE; ANDREW K. PERSILY, PH.D., FELLOW ASHRAE; LIANGZHU (LEON) WANG, PH.D., MEMBER ASHRAE

Concerns exist about the hazard of acute residential carbon monoxide (CO) exposures
from portable gasoline-powered generators, which can result in death or serious
adverse health effects. As of April 23, 2013 and as shown in Figure 1, the U.S. Consumer
Product Safety Commission (CPSC) databases contain records of at least 800 deaths
(involving 597 incidents) from CO poisoning caused by consumer use of a generator
in the period of 1999 through 2012.1 Typically, these deaths occur when consumers use
a generator in an enclosed or partially enclosed space or, less often, outdoors near a
partially open door, window or vent. While avoiding the operation of such generators
in or near a home would reduce indoor CO exposures significantly, it may not be realistic to expect such usage to be eliminated completely.
Another means of reducing these exposures is to
decrease the amount of CO emitted from these devices.
The magnitude of such reductions needed to reduce
exposures to a specific level depends on the complex
relationship between CO emissions from these generators and occupant exposure. To better understand the
CO emissions from portable generators, the potential for
reducing these emissions and the impacts on occupant
exposure, a multi-year research effort was conducted
involving both experimental and simulation studies.2,3

Measurements of CO Emissions From Portable Generators
To better understand CO emission rates from both
stock (currently available) and reduced-emission prototype portable generators, experiments were conducted
in a single zone shed and in a three-bedroom test house
with an attached garage. This column summarizes the
measurements conducted in the shed; the tests with the
generator operating in the attached garage are described
in Emmerich et al. (2013). As discussed in that report,
previous measurements of CO emissions from generators have been conducted in ambient air or in chambers
with very high air change rates. By conducting these
tests in an enclosed space with more realistic ventilation
conditions, the O2 levels will decrease as the generator
operates, providing more relevant measurement results.
The shed experiments were conducted in a 43 m3
single-walled, uninsulated timber structure for the
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purpose of measuring the CO emission rates and O2 consumption rates of the generators tested. Photo 1 shows a
generator installed in the shed along with the load bank
used to place an electric load on the generator. The shed
had two operable windows at both sidewalls and an
exhaust fan, which were used to vary the air change rate
during the tests from about 0.5 h-1 to 10 h-1. Tests were
conducted with three different generators that were
configured in multiple ways. Two unmodified "stock"
(i.e., in their as-purchased condition) generators were
tested. The first generator had a full-load power rating
of 5.5 kW with a 10 hp, carbureted, single cylinder gasoline engine and no CO emission control technology.
The second generator was powered by a carbureted 11 hp
single-cylinder gasoline and had a full-load power rating of 5.0 kW. This generator was tested in both its stock,
unmodified condition and modified as a low-CO emission prototype. The modifications included an engine
management system (EMS) with sensors and actuators
for electronic fuel injection (replacing the carburetor)
and a muffler with a small catalytic converter. The third
generator was similar to the second, but with an output
rating of 7 kW and a different EMS.
Steven J. Emmerich is a mechanical engineer, and Andrew K. Persily, Ph.D., is the
group leader of the Indoor Air Quality and Ventilation Group at the National Institute of
Standards and Technology (NIST), Gaithersburg, Md. Liangzhu (Leon) Wang, Ph.D., is
assistant professor in the Department of Building, Civil and Environmental Engineering
at Concordia University in Montreal.

ASHRAE Journal - September 2014

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