Indirect-Direct Evaporative Cooling Report

The California Energy Commission (Energy Commission) and Davis Energy Group (DEG) are pleased to announce the publication of a final report on an improved indirect-direct evaporative cooling (IDEC) system. This research has developed an advanced two-stage evaporative cooling system that can replace vapor compression cooling on residential and small commercial buildings in dry climates. The report, written for the Public Interest Energy Research (PIER) Buildings program, summarizes four years of research, development and testing of this improved IDEC system.

PIER's research was motivated by the fact that compressor-based cooling has become a standard feature of residences in California, even in mild coastal climates. Air conditioning comprises 30% of all electric use in California on hot afternoons . This demand on the electric grid continues in 2004 as housing developments expand from older population centers along the California coast to hotter inland climate zones. The PIER report shows that the IDEC system can reduce peak cooling demand and energy use by 80-90% in hot California valley climates. PIER's research builds on prior IDEC development work begun in 1992 with support from the Energy Commission’s pre-PIER Energy Technologies Advancement Program. Though test results from that research were quite promising, this latest development of the unit exceeds both the energy performance and durability of the prior design; this new unit is on the path to commercialization by a national manufacturer.

This final project report describes work by contractor Davis Energy Group to:

• Improve IDEC design flexibility and quality by developing a unique indirect heat exchanger with improved performance,
• Reduce manufacturing costs and improve unit quality by developing an advanced rotationally-molded cabinet with integral top mount blower,
• Correct many of the current evaporative cooling technology maintenance concerns — corrosion in particular — by several measures including housing the unit in a cabinet of engineering polymer,
• Lower operating costs by increasing evaporative effectiveness, and
• Reduce power consumption by means of computer-optimized airflow and by the use of an advanced blower motor that benefits from the low-speed operation regime most common in IDEC operation.

The research has been successful in developing a highly energy-efficient indirect-direct evaporative cooler that in laboratory tests has outperformed all other known IDEC units. Measured cooling efficiencies in 104° F outdoor air range from a low of 40 Btu/w-hr (Energy Efficiency Ratio, or EER) at high speed to a high EER of 136 at 50% of full air delivery. These values far exceed the EERs of 10 to 12 for high-efficiency vapor compression air conditioning systems in 104° F outdoor air. The new IDEC unit can deliver the equivalent of 2.5 cooling tons while only consuming about 500 watts, thus facilitating the use of a relatively small photovoltaic array to remove a home’s cooling load from the electric grid.

Unique optional switching technology allows the unit to seamlessly blend photovoltaic DC power and grid AC power, without the use of an inverter, when photovoltaic power is available. Specific project accomplishments are included in the report's executive summary. The complete report, titled "Development of an Improved Two-Stage Evaporative Cooling System," plus related appendices and attachments, can be downloaded from the Commission's PIER Buildings final reports webpage (www.energy.ca.gov/pier/buildings/reports.html).

DEG and the Speakman Company of Wilmington, DE are currently negotiating a license agreement for manufacturing and marketing of this advanced IDEC unit. Speakman will be marketing the cooling unit under the product name OASys through their CRS (for Clean, Renewable and Sustainable) business unit (www.speakmancrs.com). Additional product testing will be completed soon at the U.S. National Renewable Energy Laboratory in Colorado. A pre-production OASys unit will be demonstrated at the American Council for an Energy-Efficient Economy’s “Technology Showcase” to be held at their Summer Study in late August of 2004. Other pre-production units are undergoing field-testing in seven Sacramento homes and at other sites in the Southwestern U.S. Production units are expected to be available by the end of 2004.

Contacts:

Philip Spartz
California Energy Commission
pspartz@energy.state.ca.us
(916) 654-4592

Jerry Best
Davis Energy Group
info@davisenergy.com
(530) 753-1100

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