Author Archives: Dr Ahmed Alammar

Modelling of solar-driven cooling system

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.

Comparison of solar collectors

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.