Lawrence Berkeley
National Laboratory
Environmental Energy Technologies
Indoor Environment Department
Energy Performance of Buildings Group

Project Purpose and Objectives
The purpose of this project is to determine the energy savings, peak-power reduction, and pollutant emission reduction potential for the decentralized power generation provided by the world’s first truly commercially-available fuel cell (PC 25 designed and built by ONSI®) with the waste heat integrated into the building’s thermal conditioning system (heating and cooling).

We will determine the electrical peak-power and power consumption, as well as, the cooling power demand, of office buildings for different Californian climates. Based on the electrical and cooling power demand, and the phase lag between these, we will determine the suitability of fuel cells as decentralized power generators for the most common non-residential building type.

Background
Cooling of non-residential buildings contributes significantly to electrical power consumption and peak-power demand. Although, office buildings do not have the highest power density of non-residential buildings, but, because of the huge amount of floor area, they are the biggest electricity consumers in the U.S. non-residential building sector. As the cooling and electrical power demand of office buildings in California are usually in phase, co-generation plants can provide both, the electrical power and the heat necessary to operate heat-energized chillers.

Base-load power plants have an efficiency of approximately 40%. This efficiency can be increased if the heat produced in the power plant is also used (for example, in a combined heat and power station). Among the existing large power plants, this is only achieved by district heating systems. However, district heating systems are only profitable for areas with high population density.

Decentralized power plants can provide electricity with little or no transmission losses. Co-generation plants additionally provide heat for nearby buildings or industrial processes. Many co-generation plants provide electricity by using internal combustion engines, which emit combustion by-products (e.g., NOX and CO) and work efficiently only if their size is relatively large.

As fuel cells do not work based on internal combustion, the exhaust for natural gas-driven units (indirect fuel cells) consists of CO2 plus very small amounts of combustion by-products (less than 2% of California standards for combustion engines; the South Coast Air Quality Management District (SCAQMD) granted blanket exemption for permitting requirements). Because moving parts are limited to pumps and cooling fans in fuel cells, the operation is very quiet, allowing fuel cell installation in the vicinity of buildings.

Fuel cells provide the opportunity to install local power plants with high availability and good efficiency. The only unit that is currently commercially available is the PC 25 200 kWel phosphoric acid indirect fuel cell designed and manufactured by ONSI®. Because of their modular character, their high availability, fuel cells are extremely suited to work as local co-generation plants.

As fuel cells do not work with internal combustion, exhaust for natural gas driven units contains CO2 and only very small amounts of combustion by-products (less than 2% of California standards for combustian engines; SCAQMD granted blanket exemption for permitting requirements). Moving parts in fuel cells are limited to pumps and cooling fans. Therefore, fuel cells operation is very quite, which allows installation close to buildings.

Besides the 40% electrical efficiency of the natural gas-driven PC 25 fuel cells, approximately 44% of the fuel is converted into heat that can be used for heating (space heating and DHW) and/or cooling (absorption or adsorption chiller, desiccant cooling) purposes. Thermal recovery at the current sites covers a broad spectrum. It ranges from a simple pump supplying an add-on hydronic space heating loop to a multiple-use processor-controlled heat exchange system for domestic hot water plus a heat pump source loop. Almost half of the sites utilize fuel cell’s thermal energy for domestic hot water and in two instances for laundry use. Space heating is the next dominant use. Other applications include water heating for industrial processes, swimming pools, HVAC tempering, and the like. Many sites use the waste heat for only half the year; however, even for those sites where waste heat is being used all year round, data for the waste heat usage are not available.

For a 200 kWel indirect fuel cell combined with a single-stage absorption chiller (COP 0.7), this waste heat translates into cooling power of more than 47 tons, providing an equivalent of additional electrical peak power of about 33 kWel. The latest generation of phosphoric acid fuel cells (PC25C) provides waste heat at temperatures up to 250oF, which allows the use of two-stage absorption chillers with COP of about 1.2.

Besides high availability, which qualifies fuel cells as emergency power generators, it is the waste heat integration which makes fuel cells so energy efficient. The high availability of fuel cells eliminates the need for emergency power generators, while their immediate proximity to the user minimizes the risk of transmission line failure. Waste heat integration reduces peak-power demand and increases energy efficiency. The character of the chemical reaction within the cell limits the emission of the combustion by-products found in other power plants (except for nuclear plants).

We have followed the development of the phosphoric acid fuel cell and its applications, particularly the waste heat integration potential for non-residential buildings, for some time. We have also studied the possibility of waste heat integration in the case of cooling systems using other heating sources.

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Last update of this page: March 11, 2004

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