Absorption refrigeration systems (ARSs) dominated the refrigeration industry for much of the 19th century. Increased access to electricity in the later part of that century triggered gradual replacement of the ARSs with the vapor-compression systems (VCSs). The higher performance per unit cost, lower volume per unit cooling capacity, and favorable operational and maintenance characteristics of the VCSs fueled their vast market penetration particularly in the residential air conditioning sector. Despite their great advantages, VCSs consume significant electrical energy and use refrigerants that are not environment friendly. Significant increase in the demand for air conditioning in developing countries, rise in fuel costs, and environmental impacts of power production cycles have raised concerns about the long-term sustainability of the living standard this technology has offered to the world population. Thus, development of alternative more efficient technologies with less environmental impact is of great interest.
ARSs could play a larger role in the future cooling market if compact, inexpensive, high performance, and robust systems are developed. Such systems are particularly attractive in combined heating, cooling and power (CCHP) systems where in the ARS is powered by waste heat. Recent advancements in solar-thermal collectors have also enhanced the prospect of solar-cooling using ARSs. Hybrid systems powered by solar energy and natural gas could conceivably provide year-round cooling, space heating, and hot water to a building. Implementation of such a system could enhance fuel efficiency and utilization of renewable energy and reduce the electrical grid load during the peak demand for air conditioning.
Among the different heat-powered cooling cycles LiBr-water deliver the highest performance using low quality heat (100 to 200 °C). A double-effect LiBr-water system can deliver a primary COP of 1.2-1.3, which can match or exceed the primary COP of a typical VCS. Primary COP factors in a multiplier for the primary energy consumption (a multiplier of 3.18 is used in US corresponding to an average power production efficiency of 31.4%). Despite their great performance, LiBr-water systems are not economical at small scales. A typical absorption refrigeration system (ARS) consists of large heat exchangers (HXs) that constitute most of the system size and cost. In this work, nanoengineered membranes are implemented to greatly enhance the transport processes involved within the system and reduce the HXs size and cost. The membrane-based HXs are integrated together into new configurations with significantly higher surface area per volume compare to the existing technology. The new system configuration along with the advance material and manufacturing technologies that the new generation ARS benefits from promise an inexpensive, reliable, and low maintenance ARS.
In a conversation with TechConnect News, Dr. Saeed Moghaddam stated that their novel approach to the design of heat exchangers is promising a reduction in size and, therefore, material usage of 1 to 2 orders of magnitude. Dr. Moghaddam and his team in Nanostructured Energy System Laboratories (NESLabs) at the University of Florida have conducted extensive experimental studies over the past two years and have shown that their concept works. Dr. Moghaddam further stated that at this point realization of the technology in the market place depends on cost-effective manufacturing of the HXs. They are currently building systems with 1-2 Ton refrigeration capacity and expect a prototype within 1.5 years.
Visit http://http://www2.mae.ufl.edu/saeedmog/ to to learn more about Dr. Moghaddam’s research.
Written by: Susan Stewart 12 December 2012, Nano Science and Technology Institute News