A technical and economic investigation of the use of deep cold seawater for air conditioning in coastal communities in Ghana

Air conditioning has become a very important feature of buildings in Ghana today for maintaining comfortable indoor conditions for occupants. On the other hand, besides its high capital cost, air conditioners are expensive to operate because of their high power demand especially in the warm and humid tropical climate of Ghana. Investigation carried out in the country has shown that they contribute over 60% of the power consumed by air conditioned buildings. This has made it necessary as a nation to look for ways to reduce the power demand of air conditioners and already energy labels on air conditioners has been introduce to help the consumer to choose efficient models. Another direction in the search to reduce power consumed by air conditioners and other appliances in buildings is in the use of renewable energy. Already advances have been made in the introduction of solar water heaters and solar lighting in the country but use of renewable energy in conventional air conditioning systems is still far from reaching large commercial application. One area of renewal energy air conditioning technology that has remained untapped in the country is the use of the naturally-occurring cold seawater from deep down the ocean for air conditioning application ashore. This technology is referred to as seawater air conditioning (SWAC). At a depth of 1km and below, the seawater temperature is 5oC which is suitable for air conditioning application. There are several places in the world today where this technology has been successfully applied to air condition coastal communities or for air conditioning of coastal communities. By replacing the use of conventional electrically-driven chillers in air conditioning systems, this technology has a very high potential for reducing the high energy demand used today for air conditioning in communities close to the shore. This thesis carried out investigation into the technical and economic viability of applying SWAC technology for coastal communities in Ghana. The investigation was conducted on four locations along the coastline, namely, Keta, Accra, Cape Coast and Takoradi for cooling loads ranging from 1,000 TR (tons cooling) to 13,000 TR. The first stage of the investigation was technical, which was aimed to determine whether or not the cold seawater pumped from the ocean deep met the technical requirement for air conditioning application when it arrived ashore. Cape Coast and Takoradi sites could not meet this requirement for the range of load under investigation. Accra met the technical requirement for loads starting from 5,500 TR whilst Keta met the requirement from 5,000 TR. The second stage of the thesis is the economic investigation for the two sites that passed the technical investigation, namely, Accra and Keta. Using the method of Cost of Ownership calculation, SWAC technology at Keta site turned out to be more economical than the conventional chiller system at loads from 8,500 TR. At Accra site, SWAC technology was more expensive than the conventional chiller system but showed a good potential to catch up at higher cooling loads above the 13,000 TR limit investigated in this thesis. The conclusion of this work is that the potential for SWAC application in Ghana looks very promising and further research is recommended, especially for higher cooling loads beyond the 13,000 TR limit used in this work. It is also recommended for the future research to investigate the use of the SWAC technology in hybrid combination with conventional absorption cooling system powered by solar heating.

Source: KNUST