Proposed Test Methodology and Performance Rating Standard for Residential Fuel Cell Systems
Mark W. Davis, Michael W. Ellis and Brian P. Dougherty

The National Institute of Standards and Technology has proposed a new performance rating system for residential fuel cells which can help prospective fuel cell buyers to evaluate fuel cell systems based on a standardized set of metrics. The standard would test fuel cells and then provide buyers with figures on annual net electricity used or generated, fuel consumption, water use, thermal energy output and other details that could be used to consider the value of different fuel cell systems. NIST expects to present their testing and performance-rating procedures to standard development organizations during the summer.

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"Proposed Test Methodology and Performance Rating Standard for Residential Fuel Cell Systems" (471Kb PDF)

Executive Summary
A test method and rating standard is proposed for residential fuel cell systems (RFCSs). The proposed approach extends previously developed test procedures for fuel cells by establishing specific test methods and calculation procedures that are applicable to residential fuel cell systems. These methods and procedures provide the end user with metrics that can be used to evaluate the merit of a RFCS in a particular application.

In the proposed standard, RFCSs are classified into four types: Type I - Grid independent, electrical load following; Type II - Grid interconnected, constant power; Type III - Grid interconnected, thermal load following; and Type IV - Grid interconnected, water heating. Test procedures are described that yield simplified models for the performance of each system based on appropriate load characteristics and ambient conditions.

For Type I systems, the steady fuel use, thermal energy output, and water use are expressed as functions of the electrical part-load ratio and the ambient temperature. In addition, the thermal energy output, electrical output, fuel use, and water use (for RFCS humidification) associated with a hot water simulated use test are evaluated as functions of electrical part-load ratio and ambient temperature. Transient electrical load factors are measured and applied to the thermal energy output and the fuel consumption to incorporate the system's performance under transient electrical loads.

For Type II systems, electrical power remains constant and the steady fuel use, thermal energy output, and water use are expressed as functions of ambient temperature. In addition, the thermal energy output, electrical output, fuel use, and water use (for RFCS humidification) associated with a hot water simulated use test are evaluated at rated power and specific values of ambient temperature.

For Type III systems, the system output follows the thermal load and the steady fuel use, electrical output, and water use are expressed as functions of thermal part-load ratio and ambient temperature. In addition, the electrical output, fuel use, and water use (for RFCS humidification) associated with a hot water simulated use test are evaluated at specific values of ambient temperature.

For Type IV systems, the system operates to meet the hot water requirement and the thermal energy output, electrical output, fuel use, and water use (for RFCS humidification) associated with a hot water simulated use test are evaluated at specific values of ambient temperature.

For each system type, steady and simulated use models are combined to predict the performance of the system in response to typical residential electrical and thermal loads for various representative climates. For units that draw ventilation air from the indoors, the performance is corrected to account for the energy required to condition outdoor air to replace the ventilation air. The annual performance is expressed in terms of the impact on the end user's net electricity use or generation), fuel use, and water use.