Feasibility Study and Design of a Seawater Air-Conditioning System for a University Building in Fiji

Abstract

The demand for space cooling in Fiji is increasing rapidly due to a high infrastructure development rate in the country. Seawater air conditioning is a solution to the problem of space cooling using renewable energy. In this work, a feasibility study and design of a SWAC system for a university building is carried out. The feasibility study included the cooling load calculations, the availability of seawater and the location of the building. The cooling load was estimated using CAMEL software which came to be about 509 kW. Local bathymetry charts were studied to determine the depth of ocean to be 1000 m closest to the shore at which water temperatures about 6°C can be obtained. The distance from shore at which the cold water was available was approximately 12 km. A 1:15 scaled down model of the building was constructed to find the ideal chilled water supply rate and temperature. Optimal design parameters were found to be a chilled water temperature of 7°C and a cold-water flow rate of 100L/min. A temperature of 23°C was achieved inside the building after about 15 mins. The design phase of the system included the entire buildings supply and return duct system divided among 5 AHUs. The length of the seawater suction pipeline was estimated using the depth and the distance to be around 12 km. The diameter of the seawater suction pipe was optimized using cost of pipe installation and pumping power to be 0.4m, corresponding to a pumping power of 5 kW. A heat exchanger with a capacity of 500 kW, like the total cooling load of the project was selected to transfer heat between the seawater loop and the chilled water loop. The chilled water pumping power was calculated after the design of the full chilled water supply pipeline to be 4 kW. The total cost for the implementation of the SWAC system for the Marine Sciences building was estimated to be $1.04M and the payback period was estimated to be 13.8 years compared to a conventional split-type system.