Final Report: Solar-Thermal Adsorption Refrigerator (STAR)EPA Grant Number: SU835998
Title: Solar-Thermal Adsorption Refrigerator (STAR)
Investigators: Choi, Jun-Ki
Institution: University of Dayton
EPA Project Officer: Page, Angela
Project Period: September 1, 2015 through August 31, 2016
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2015) RFA Text | Recipients Lists
Research Category: P3 Awards , Pollution Prevention/Sustainable Development , Sustainability , P3 Challenge Area - Energy
Refrigeration and air conditioning have a substantial impact on people, prosperity and the planet. For a century, refrigeration has improved people’s lives and enhanced prosperity by enabling perishable food and medicines to be safely shipped and stored without spoiling. However, this has come at a significant cost to the planet. Older refrigerants made from chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) attacked the ozone layer in the stratosphere, which led to increased amounts of ultraviolet (UV) radiation reaching the Earth’s surface and that threatened human health, increasing rates of skin cancer and eye disease, and threatening the marine plankton that are the foundation of the marine life food chain. While CFCs and HCFCs are being phased out, and while their replacements, hydrofluorocarbons (HFCs) such as R-134, do not attack the ozone layer, they have high global warming potentials (GWPs): HFCs can cause as much as 12,240 times more warming as an equivalent mass of carbon dioxide. In addition, modern refrigeration technologies are large consumers of electricity: refrigeration uses approximately 9% of the world’s electricity production, and this electricity consumption accounts for nearly 1 billion tons of CO2-equivalent greenhouse gas emissions.
The benefits of refrigeration are widely enjoyed in industrialized countries. However, despite its broad success, modern refrigeration has not reached places like the Bihar state in India, where the electric grid is unreliable and the residents cannot afford local photovoltaic systems. While demand for refrigeration is low, there are a few critical applications, such as refrigerating vaccines, where the need for refrigeration is urgent and immediate. In 2005, only 33% of the children in Bihar India were fully vaccinated. Vaccine supply is a key issue in the region. In a 2015 survey of 124 Primary Health Centres (PHCs) in Bihar, only 15% had a 1-week supply of vaccines and 60% had no vaccines on site. Lack of refrigeration was a major contributor: of the 124 PHCs, 42 facilities had no electricity and another 31 had no reliable electricity, and in two facilities with electricity, the ice lined refrigerator used to store vaccines was not working. We are partnering with SAAP (Solar Alternatives and Associated Programs), in Patna, a city in Bihar, to develop an alternative refrigeration technology that does not require electricity, and uses environmentally benign materials, like ethanol and activated carbon that can be produced locally in Bihar. This alternative technology, Solar Thermal Adsorptive Refrigeration (STAR), uses solar energy and the tendency of ethanol to adsorb onto the surface of activated carbon to drive a refrigeration process. A key philosophy in the development of this project, both in the United States and in India, has been a focus on “appropriate technology” design principles, using locally available materials and expertise to implement sustainable, culturally acceptable solutions to engineering problems.
The primary goal of this project was to build a prototype that would demonstrate the potential for adsorptive refrigeration, using ethanol and activated carbon as the adsorption pair, to produce cooling at temperatures between 2⁰C and 8⁰C. This prototype also was used to complete a preliminary lifecycle analysis to determine the environmental impact of this radical new technology.
The project group has built a small bench-scale prototype that consists of a vacuum chamber, a freezer compartment, and an adsorption bed of activated carbon, connected by tubing and valves that allow the vacuum chamber and adsorption bed to be isolated from one another. The prototype operates in two modes. In the cooling mode, liquid ethanol in the vacuum chamber evaporates, and the ethanol vapors flow to the adsorption bed, where they adsorb onto the surface of the activated carbon. The heat to generate the ethanol vapors is drawn from the freezer compartment through the walls of the vacuum tube, leading to evaporative cooling. The cooling mode can continue until the activated carbon is saturated with ethanol. In the regeneration mode, valves connecting the adsorption bed and the vacuum chamber are closed and the adsorption bed is heated, causing the ethanol to desorb and the partial pressure of ethanol vapor in the adsorption bed to increase. When the valve connecting the adsorption bed and vacuum chamber is opened, the ethanol vapors flow, cooling as they move through the line, and condense in the vacuum chamber, setting the stage for a second cooling stage. This prototype has been repeatedly used to obtain temperatures between 2⁰C and 8⁰C on the external wall of the vacuum tube, and full cycle of cooling and regeneration has been run.
A life cycle assessment (LCA) of this prototype has been performed. Among many impact assessment measures, the Phase-I study adopted “Tool for the Reduction and Assessment of Chemical and other Environmental Impact” (TRACI), which was developed by the U.S. Environmental Protection Agency (EPA)’s National Risk Management Research Laboratory. It allows for quantification of the potential environmental effects such as global warming, ozone depletion, acidification, smog formation, human health criteria-related effects, eco-toxicity, and fossil fuel depletion effects. Results showed that significant reduction of the life cycle environmental impacts can be achieved from STAR compared to a conventional refrigerator. Successful replacement of a conventional fridge with STAR can annually reduce: 292 ~ 1,170 kg CO2-eq of global warming potential (GWP); 104 ~ 418 H+ moles-eq. of acidification; 1.15 ~ 4.61 kg benzene- eq. of carcinogenics; 6,850 ~ 27,400 kg toluene-eq. of non-carcinogenics; 1.2 ~ 4.78 kg N-eq. of eutrophication; 0.556 ~ 2.22 kg PM2.5-eq. of respiratory effects; 0.0078 ~ 0.031 g of CFC-11 eq. of ozone depletion; 0.564~2.26 g NOx-eq. of smog. Low and high numbers indicate the amount of reductions when compared with average electricity consumption of a modern energy efficient fridge (i.e., 350 kWh/yr) and an old 1990s era fridge (i.e., 1,400 kWh/yr) respectively. Considering typical lifetime of a conventional fridge of 13 to 19 years, the reduction of aforementioned environmental impacts of the STAR can be scaled significantly.
Although our current prototype cannot provide the same refrigeration capacity, functionality, and aesthetic quality as conventional refrigerators at this moment, our models show that one successful replacement of a conventional fridge with STAR technology can achieve up to 22 tons of lifetime CO2 emission reduction. This is equivalent to the annual CO2 emission from three typical U.S. households. Considering a $100 billion worldwide market for refrigeration equipment and over 80 million domestic refrigerators produced per year, even a small percentage adoption of the proposed STAR can significantly reduce environmental impacts worldwide. Our current LCA results didn’t include the CFC and HCFC contents in the old conventional fridges since those refrigerants have been prohibited. Despite that fact, LCA results showed that STAR technology still reduced ozone depletion effects because it doesn’t consume electricity, which contributes to the ozone depleting components in the life cycle when the electricity is generated from fossil fuels. If CFC and HCFC contents in the old fridge are considered in the LCA study, much higher reduction of the ozone depletion is surely expected.
Refrigeration is an essential part of modern life, improving human health by preserving food and essential medicines, such as vaccines. Unfortunately, not everyone shares the benefits of refrigeration. People in very poor rural areas of developing countries, such as the Bihar province of India, have so little access to reliable sources of electricity, either through a grid or from solar powered PV cells, that even essential services like refrigeration for storing vaccines is not reliably available or affordable.
This project has successfully built a prototype that demonstrates adsorptive refrigeration with ethanol and activated carbon as the adsorption pair. The STAR prototype has been repeatedly used to obtain temperatures between 2⁰C and 8⁰C on the external wall of the vacuum tube, and full cycle of cooling and regeneration has been run. Results from the LCA showed that a significant reduction of various life cycle environmental impacts can be achieved from STAR technology compared to conventional refrigerators.