Residential scale solar driven cooling systems versus conventional air-conditioning in hot arid areas: a comparative study
In this study, performance, energy efficiency, cost competitiveness, and global warming assessments of residential scale solar thermal and off-grid Photovoltaic driven DC air-conditioning systems versus conventional AC driven air-conditioning system in hot, arid areas is carried out. The first system is an integrated solar thermal driven residential air-conditioning. This system consists of evacuated tube solar collector arrays of area 36 m2 with high reflective parabolic surface used at the back, a silica gel-water adsorption chiller of 8 kW nominal cooling capacity, and hot and cold-water storage tanks of 1.8 and 1.2 m3 in volume, respectively. While the second system is an off-grid PV electrically driven DC compressor air-conditioning system. This system is a split air-conditioning unit with a cooling capacity of (26000 BTU) 7.62 kW that requires an input power of 1.8 kW with R410a (1550) refrigerant. Those solar-driven systems are compared with a grid connected AC driven vapor compression Air-Conditioning having 8 kW nominal cooling capacity. Experimental results show that the indoor thermal comfort conditions are achieved in the hottest days of the year for space with a floor area of 80 m2 with 14 residences for both systems. Comparison between the systems is based on the lifespan of 20 years, cooling capacity 8 kW and 18 hours' daily operation in the cooling session. The results clearly indicate that: Compared with conventional vapor AC driven air-conditioning system, the solar thermal driven cooling system has an energy consumption of 10.94%, with the Total Equivalent Warming Impact (TEWI) of 9.96% while the cost per kW cooling is higher by 295.96%, respectively. While, the off-grid PV driven DC air conditioning system has an energy consumption of 0%, with TEWI of 0.65% and cost per kW cooling is lower by 54.88%, respectively. Therefore, the off-grid PV electrically driven DC compressor air-conditioning system can be recommended for use in the residential sector based on its low cost per kW cooling, no grid energy consumption, and very low environmental impact on global warming. However, this system further cost reduction can be cut from the energy storage, battery subsystem, in case this system is on-grid connected.