This paper concern PV – vapour compression cooling system for agro-products storing in Rwanda. The full article is available in the link below.
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This is one of the projects with our collaborators at the University of Port Harcourt and ColdHubs in Nigeria that aims securing the cold chain in Sub-Saharan Africa. The project is led by Dr Muhammad Imran. In this project we integrate solar absorption and vapour compression systems in order to overcome the thermodynamic limitaitons due to the ambient conditions. For more information about the project, please visit at Aston’s website.
One of the project important stages is obtaining the environmental data to provide the available daily solar energy (e.g. daily sunshine hours and solar irradiation). The data is essential to model the proposed solar cooling system. In Kigali / Rwanda, the average daily solar radiation is around 5 KWh/m2/day, and the minimum and maximum daily sunshine hours are about 4 and 9 hours, respectively.
We utilise TRNSYS (Transient System Simulation) software to integrate different components of the solar thermal driven adsorption cooling system. Evacuated tube solar collector with a total aperture area of 52 m2 is chosen to provide the heat required to drive the adsorption chiller with a cooling capacity of 4.5 KW. A cold store of 38 m3 is modelled using TRNSYS3D integrated with SketchUp software to provide the actual time dependent cooling load to the system. The weather data for Kigali is directly chosen from TRNSYS database to use with all relevant components. The main challenge is that there are certain days throughout the year where solar energy is insufficient to drive the chiller.
A Rough Comparison between PV (photovoltaic solar panel) integrated with vapour compression and ETC (evacuated tube solar collector) integrated with thermal driven solar cooling systems has been conducted to estimate the cooling capacity that can be produced using an area of 100 m2 of each PV and ETC. It is found that for the same panels’ area, the ETC collector produces a slightly higher cooling capacity than the PV collector for thermal driven and vapour compression cooling systems, respectively under Kigali/Rwanda environmental conditions.
We estimated and compared the cost of a conventional vapour compression chiller / PV system and thermal driven adsorption chiller / ETC. A cooling capacity of 4.5 KW is considered for the cost estimation to meet the Cooling demand of an existing cold room under climate conditions of Rwanda for 24 /7 operation. The cost estimation included the initial cost for each system as well as to running and maintenance costs for a time-period of 25 years (this excluded pumps and control cost because they are existing in all systems). It is found that the adsorption / ETC chiller exhibits the lowest cost. Maintenance is a key cost factor vapour compression / PV system.
There are a lot of resources for heat that can be harvested to directly power your heat driven cooling system without any intermediate heat-to-power subsytem to power a conventional vapour compression cooling unit. This means that your sustainable cooling package is much simpler, cheaper and easier to maintain. Simple sustainable cooling will lead to sustainable economic growth and secured cold chain.
Yes, you can take thermal driven cooling (adsorption or absorption) further than you thought to support your farming business and comunity “Cooling is not a luxry”!
Although agriculture is central to most of sub-Saharan African countries, the food system remains insecure due to the significant losses of products such as milk, meat, and vegetables. The lack of food cold chains is due to energy poverty and unreliable power supply. The available mechanically driven vapour-compression cooling technologies are energy-intensive, utilise environmentally harmful gases (i.e. CFC and HCFC) and require capital investment unaffordable by smallholder farmers. These barriers hamper the development of agro-post-processing industries such as dairy, fruit ripening or preservation for export to key markets.
Africa is the sunniest continent on the earth, low-tech solar-driven cold store offers the required cooling with nearly free running cost. Nevertheless, barriers to the adoption of new technologies include capital and implementation costs and lack of familiarity with technology. Aston University jointly with the University of Rwanda will explore both the technological and commercial viability of implementing new solutions to solar-powered cooling chains.
The proposed solution centres on developing a standalone cold store using sorption-cooling technology, driven primarily by solar heat, and with minimal need for energy storages. We will design and optimise a solar system to provide continuous operation and develop a 1D numerical demonstration model. Alongside, we will collect data on the commercial viability of the investment, investigating the potential additional income generation through longer storage and the ability of accessing urban markets with higher price levels
In Alignment with GCRF goals, CL-Africa targets:
- Equitable Access to Sustainable Development.
- Secure and resilient food system.
- Sustainable health and wellbeing.
- Affordable, reliable, sustainable energy.
- Sustainable Economies and Society.
- Sustainable livelihoods supported by strong foundations for inclusive economic growth and innovation.
- Resilience and action on short-term environmental shocks and long-term environmental change.
- Sustainable cities and communities.
- Sustainable production and consumption of materials and other resources.
In alignment with UN Goals:
- CL-Africa leads to a sustainable food cold chain to save million tons of wasted food under the current situation of inadequate food cold chain in SSA, which directly contributes to Goal 2 (zero hunger).
- Having resilient food cold chains will increase the market opportunities for smallholder farmers and improving their livelihood. They will be able to get their perishable product to urban markets, which directly contributes to Goal 8 (decent work and economic growth).
- The proposed technology is predominantly driven by solar heat as a clean renewable source, which is a stepping stone towards Goal 7 (affordable and clean energy).