Figure 1. Process of Evaporative Cooling (Shuaibu et al., 2019)
Water consumption of a solar powered evaporative air cooler constructed using locally available materials such as galvanized iron, thin wooden strips, carradiator fan and submersible water pump of low power types has been experimentally investigated while cooling a room space of approximately a volume of 43.5 m3. Test results on the cooler configurations indicated the water consumption ranging from 6400-14400 cm3, the period it takes to refill the water tank ranging from 10-22.5 hours, temperature drop ranging from 4.6-7.2 °C while the cooling effectiveness calculated has been between 35.4%-97.3%. In this work, humidity and temperature control unit has been integrated to control water supply thereby regulating the humidity level of the room space while cooling. This system consumes 0.05 kWh of energy for 6 hours of operation as against 6.75 kWh energy consumption of a 1.5 HP AC. This technology is efficient in improving the indoor air quality and it is suitable for cooling application in villages, and other remote areas where there is no grid extension.
Evaporative cooling system operates in a way in which hot dry air is passed through wetted pad, get cooled by water and then be channeled into a building space as shown in Figure 1.
Figure 1. Process of Evaporative Cooling (Shuaibu et al., 2019)
The high level of fossil fuels consumption instead of the environmentally friendly renewable energy sources leads to the significant increase in harmful/greenhouse gas emissions which leads to climate change. Insight of this, massive and excess use of energy has raised people's concern on the limited energy resources, deterioration of the global climate as well as the disappearance of ozone layer (Heidarinejad et al., 2010).
Heating ventilation and air conditioning (HVAC) system takes nearly half the total energy supply to the buildings due to the fact that the mechanical compressor based air conditioning system are energy intensive during the working process (Dodoo et al., 2011). Therefore, there is an urgent need to improve the energy efficiency of the HVAC system as well as promoting new technology to replace conventional systems thereby decreasing the amount of electrical energy use and the release of CO2 into the atmosphere during the operation.
Another issue is the instability of power in Nigeria over decades and Nigeria is endowed with abundant solar radiation but yet the national energy supply is almost entirely dependent on conventional energy sources which are fast depleting (Kim et al., 2011). In view of these problems, it is important to invent an alternative cooling system which utilizes this abundant solar energy and which does not cause any bad effects on ecosystem while reducing our indoor temperature to comfort zone and one of the promising technology is an evaporative cooling system which will be powered strictly by solar energy.
After a successful design and construction of this system (Shuaibu et al., 2019), experimental water consumption analysis of different configuration of the constructed system has been conducted at Sokoto Energy Research Centre (SERC) in Usmanu Danfodiyo University, Sokoto (UDUS), Sokoto State, Nigeria using three identical offices of 4.75 m (length) x 3.16 m (width) x 2.90 m (height), so as to obtain the test results and analyze. Different parameters that are crucial in the performance evaluation of number of types of configurations of the constructed system were taken into account.
The effect of different configurations on water evaporation and average system cooling efficiency as well as the corresponding average relative humidity were investigated.
At the same time test results of inlet relative humidity, temperature and the corresponding outlet conditions were recorded. Based on these, the following parameters were recorded using 'HTC-1 digital meter' and 'PsyCalc.' software.
The following were computed using appropriate theoretical expressions for individual system configurations.
This test has been conducted with air cooler mounted outside a room and by the window with only air duct (louver) inside a room to be cooled. The outside and inside dry bulb temperatures, the corresponding relative humidity values and room wet bulb temperatures were recorded and plotted as shown in Figures 2a and 2b.
Figure 2. Variations with Time for Outdoor System Without Ventilation (a) Temperature (b) Relative Humidity
In this test, the constructed system has been operated indoor without ventilation to observe its performance and thus, the outside and inside dry bulb temperatures, the corresponding relative humidity values and the room wet bulb temperatures were recorded and plotted as shown in Figures 3a and 3b.
Figure 3.Variations with Time for an Indoor System Without Ventilation (a) Temperature (b) Relative Humidity
Here, the constructed air cooler has been operated indoor with only door opened so as to observe its performance and thus, the outside and room dry bulb temperatures, the corresponding relative humidity figures as well as indoor wet bulb temperatures were recorded and plotted as shown in Figures 4a and 4b.
Figure 4. Variations with Time for an Indoor System with Door Ventilation (a) Temperature (b) Relative Humidity
In this case, the constructed evaporative air cooling system has been mounted outside a room and by the window with only air duct (louver) inside a room and with only door opened. The outside and the corresponding room cooling parameters were plotted as shown in Figure 5a and 5b.
Figure 5. Variations with Time for an Outdoor System with Door Ventilation (a) Temperature (b) Relative Humidity
Significant temperature drop for outdoor system without ventilation, indoor system without ventilation, indoor system with door ventilation and outdoor system with door ventilation respectively, were observed and plotted in Figure 6.
Figure 6. Average Temperature Drop Based of Different System Configurations
The cooling efficiency or effectiveness ( ) of the evaporative air cooler of each configurations were computed as the ratio of the mean degree of cooling (Tdb-out - Tdb-in) to the wet bulb depression (Tdb-out – Twb) using the Equation,
where,
Tdb-out and Tdb-in, are the outside and inside dry-bulb temperatures respectively and Twb is the air wet-bulb temperature.
This heading describes the water consumption analysis of the system for individual configurations after six hours of operation. Figure 7 shows the water consumption profile on how frequent the water tank is to be refilled.
Figure 7. Volume of Water Consumed Out of Full 3 Tank (24000 Cm ) Within Six Hours of Operation (Peak Sunshine Period) for Different Configurations
Note: Designed Depth of tank, H=15 cm; Length of tank, L=40 cm; Width of tank, B=40 cm; Hours of operation (Peak sunshine period), Sp =6 hours and Depth of water consumed after 6 hours =h, which varies based of configurations.
Thus, volume of tank has been calculated using the equation, V=L*B*H (cm3) while volume of water consumed in 6 hours for each configurations has been calculated using the equation, Vc =L*B*h (cm3).
Thus, the time it takes to exhaust full tank of water bases of configurations has been calculated using the Equation.
Having discussed the procedures of indoor and outdoor configuration of the system, the following were the results obtained.
This heading discussed experimental work on the solar powered evaporative cooling system using thin wooden strips as an evaporative pad for four different types of system configurations. The system configurations were described in introduction according to the way the cooler has been operated to supply cool air into the room space. These configurations were termed as the outdoor system without ventilation, indoor system without ventilation, indoor system with door ventilation and outdoor system with door ventilation configurations. Individual system configurations has been tested on different day and over a period of six hours to study the variation in dry-bulb temperatures between surrounding (outside) and the room (inside) as well as their corresponding relative humidity values under constant air flow of 62.84 m/s (fan speed) and water flow rate of 66.67 cm3/s (pump capacity) using direct current (DC) fan of 3.96 W and submersible pump of 5.0 W respectively. The data recorded has been then analyzed and main performance features of indoor configuration were compared with outdoor configuration. For each of the configurations results shown in Figures 2a, 3a, 4a and 5a. there has been significant with temperature drop on average of 4.6 °C, 7.2 °C, 7.1 °C and 5.5 °C for the outdoor system without ventilation, indoor system without ventilation, indoor system with door ventilation and outdoor system with door ventilation respectively were observed. The corresponding average relative humidity of 30.4%, 54.9%, 30.9% and 28.0% were respectively observed as shown in Figures 2b, 3b, 4b, and 5b for the various configurations. One of the features observed in this research is the fact that the water consumption is much less in indoor system without ventilation due to low level of vapor escape and is higher in outdoor system with door ventilation due to high vapor escape from the room as shown in Figure 6. Also in Figure 6, it has been revealed that higher the water consumption, the lower the time it takes to replenish the tank with water.
From the operational and maintenance perspective the indoor system configurations have more advantage because water feeding is much easier and the water consumption is less.
Research and development have shown that the technology can be applied for cooling of office and domestic buildings in the hot and dry parts of the world.
This research work has been based on the effects of configurations on the water consumption of the constructed evaporative air cooling system.
In light of the above, experimental investigations were carried out on four configurations which were classified as the “outdoor system without ventilation”, “indoor system without ventilation”, “indoor system with door ventilation” and “outdoor system with door ventilation” configurations. They were all subjected to direct evaporative cooling tests under different environmental conditions. On each test configuration, the effects of inlet dry bulb temperature, relative humidity and air flow rates were studied. Also, the corresponding output results of the systems were observed and recorded. Each of the four configurations has been setup to cool a room space of 4.75 m x 3.16 m floor area and a height of 2.90 m, that is approximately a volume of 43.5 m3.
Test results on the cooler configurations indicated the water consumption ranging from 6400-14400 cm3, the period it takes to refill the water tank ranging from 10-22.5 hours, temperature drop ranging from 4.6-7.2 °C. The overall results proved the prospects of using thin wooden strips and other locally available materials for evaporative cooling application with very little energy and water consumption.
This system is a low energy consumption (9 W) type which comprises of many features such as 24,000 cm3 of water tank capacity which can serve water for almost 24 hours before refilling, high capacity of suction fan, water recirculation pump and usage of solar energy at lower cost. The system is ecofriendly and natural, electricity savers.
All praise belongs to Allah (S.W.T) the Lord of the worlds for giving us the opportunity to undertake this study. We wish to express our profound gratitude to the management of i-manager journal, the entire staff of Sokoto Energy Research Centre and Department of Chemistry and Energy Studies, Usmanu Danfodiyo University Sokoto- Nigeria, family, friends and well-wishers.