**Winter 2009**

U.S. National Work Group (USNWG) for the Development of Commercial
Hydrogen Measurement Standards

*By Juana Williams*

The U.S. National Work Group (USNWG) for the Development of Commercial
Hydrogen Measurement Standards met on August 26 and 27, 2008, at Air
Products and Chemicals Inc., Allentown, Pennsylvania. Both the Device
Subcommittee and Fuel Specifications Subcommittee met to further the
development of legal metrology requirements for hydrogen refueling
applications. An overview of key topics discussed by each Subcommittee
is included in the articles below. The USNWG Subcommittee's meeting
summaries will be available on the NIST WMD web sit at
http://ts.nist.gov/WeightsAndMeasures/index.cfm under "W&M Resources"
click on the link to "Developing Commercial Hydrogen Measurement
Standards." This article provides an overview of the USNWG discussions,
upcoming meeting schedule, and related national activities.

***USNWG Devices Subcommittee (DS) August 2008 Meeting***

The DS revisited several specification paragraphs that apply to
equipment design and discussed other paragraphs in the proposed Hydrogen
Gas Measuring Devices code that apply to the performance test of
hydrogen dispensers.

*Design Specifications* - The DS agreed that the design requirement
which permits making adjustments to the ratio between the indicated and
actual delivered quantity of product is intended to apply to elements
and features in the system that affect only the indications (e.g. change
the flow calibration factor). The DS is also considering further
modification to the proposal to include definitions for "device" and
"assembly" to further clarify where adjustments are permissible. The DS
discussed the inherent design of nozzles that might allow a small amount
of air to be trapped during pressurization and result in contamination
of the fuel entering the sample bottle. The DS would like some guidance
on how to ensure that no connection can occur between a nozzle and
vehicle tank when there is a difference in the pressure ratings for
these two components.

*Performance Tests* - The DS recognized that it is possible during the
fill process for hydrogen to heat the test tank which introduces
uncertainty into the test procedure. This effect along with high
pressures during fill may affect the geometry of a tank and affect the
test results during the volumetric test methods. The DS agreed to
postpone its discussions of the minimum test draft and tank sizes
necessary to simulate various fills (e.g., 1/3, 2/3, and 3/3 fill) so
that it can harmonize wherever possible with SAE guidelines on fill
protocol to be published in December 2008. The DS agreed that the flow
rates and pressures achieved during the test should represent those that
occur during normal delivery and include the scenario of topping off the
tank to demonstrate any variables that have an effect on the system's
performance. It is anticipated the SAE report will address fill
protocols that avoid over heating and over filling the vehicle tank. If
controls on the flow rate are necessary to meet the fill protocol, then
the DS will need to address the question of whether or not this feature
will interfere with the test of the performance of the dispenser at the
manufacturer's declared minimum measured quantity. As the DS began its
review of accuracy requirements, equipment manufacturers were not in
agreement on the ability of their equipment to achieve the proposed 1.5
% Acceptance Tolerance and 2 % Maintenance Tolerance. The proposed
tolerances agree with the maximum permissible errors specified in
corresponding OIML Recommendation 139 "Compressed gaseous fuel measuring
systems for vehicles." A majority of manufacturers indicate obtaining
accuracies of 3 % to 10 % for equipment in use. The DS will continue its
discussion of tolerances and user requirements, test procedures, and
collection of test data at the upcoming December 2008 meeting.

***USNWG Fuel Specifications Subcommittee (FSS) August 2008 Meeting***

The August meeting marked Robert "Bob" Boyd's (Linde North America,
Inc.) first meeting as Chair of the Subcommittee.

The FSS reviewed draft code proposals for method of sale (MOS) and fuel
quality requirements for commercial hydrogen refueling applications.

*MOS* - The FSS modified proposed requirements for marking and labeling
equipment and signage in specific units of measurement for pressure. The
FSS now recommends use of the "megapascal" or the abbreviation for that
term "MPa" as the SI unit (metric) of measurement for labeling pressures
on refueling equipment and corresponding price signage rather than using
the term "bar." The numerical value for the pressure rating will follow
the letter "H" which identifies the fuel as hydrogen (e.g., H35 or H70).
The FSS agreed that the use of MPa is consistent with recent
recommendations from the CSA America and SAE for labeling components
with pressure ratings. This modification also agrees with the FSS's
decision to follow guidelines in NIST Special Publication (SP) 330 *The
International System of Units (SI)* and SP 811 *Guide for the Use of the
International System of Units (SI)* for use of the SI measurement
system. The FSS also has under review 16 CFR Part 309 "Labeling
Requirements for Alternative Fuels and Alternative Fueled Vehicles,"
which includes the FTC requirements for posting the hydrogen fuel rating
on dispensers. In this instance a disclosure of the amount of the
principal component of a fuel is expressed as a minimum percentage on a
label in a fashion similar to what is now required in octane posting for
gasoline pumps.

*Fuel Quality* - The FSS also discussed separate fuel quality standards
for hydrogen fuel cell and internal combustion engine vehicles and a
starting point for a fuel quality laboratory manual. The FSS
acknowledges there will be differences in the type and level of
contaminants and particulates as a result of hydrogen production from
different feedstock. However, the FSS agreed to focus on the current
proposed standard rather than begin discussions on separate fuel quality
standards based on production sources or ICE and fuel cell vehicle
configurations.

The current fuel quality proposal is the culmination of work by SAE,
ISO, and later work by California. Like California's Division of
Measurement Standards (DMS), the FSS agreed to move forward with the
currently proposed table that specifies the maximum levels for
contaminants and particulates in hydrogen fuel. The DMS and FSS will
work with this table as an interim standard until an accredited
standards developing organization recognizes this or another fuel
quality standard.

California law required the Division of Measurement Standards (DMS) to
have hydrogen fuel quality standards in place on or before January 1,
2008. California's interim standard for hydrogen fuel quality took
effect on September 11, 2008. To read about this regulation go to
<http://www.cdfa.ca.gov/dms/hydrogenfuel/hydrogenfuel.html> and click on
"Hydrogen Fuel."

*Quality Laboratory Procedures* - DMS continues its work on test
procedures using the fuel sampling apparatus it obtained in March 2008.
The FSS also agreed that it will consider and not attempt to reinvent
laboratory procedures under development by the ASTM. The FSS will work
to align the Method of Sale requirements with those in related hydrogen
standards and continue its work to address Field Sampling Procedures and
a Laboratory Manual for hydrogen dispensing applications.

***Next Work Group Meeting***

As this article goes to publication both Subcommittees of the U.S.
National Work Group (USNWG) for the Development of Commercial Hydrogen
Measurement Standards will have met (December 2 to 4, 2008, at
MicroMotion, Inc. in Boulder, Colorado).

The hydrogen and weights and measures communities provided only a
limited response to the USNWG's request for test procedures and types of
equipment that are currently in use to verify the performance of
hydrogen refueling equipment. The USNWG must now move forward to
establish preliminary minimum specifications for standards, suitable
laboratory and field test procedures, and guidelines on the
uncertainties associated with gravimetric, volumetric, and master meter
test methods with existing input from stakeholders. Test procedures and
performance data will be discussed at the December 2008 USNWG meeting.

***Hydrogen Proposals Submitted to the National Conference on Weights
and Measures Specifications and Tolerances and Laws and Regulations
Committees***

The USNWG submitted proposals to the 2009 agendas of the National
Conference on Weights and Measures Specifications and Tolerances and
Laws and Regulations Committees to include items on both Committees'
Developing Items Agendas. These new proposals for draft codes are being
developed by stakeholders in the legal metrology community and are
intended to address the design, performance, and user requirements and
test procedures for NIST Handbook 44 and new definitions and method of
sale and fuel quality requirements for NIST Handbook 130 for gaseous
hydrogen applications. These proposals are being disseminated to
encourage input from the weights and measures community on draft
criteria and to promote participation of all stakeholders in their
further development.