6.4 Full experiment Part 4: Enclosed cooling system

Figures 70 to 73 illustrate that the rock bed can provide cool air, 5°C lower than the ambient temperature, from 10:00 am till 18:00 pm. From 18:00 pm, the ambient temperature drops gradually till the next day, 7:00 am.

The rock remains warmer than the ambient air during the evening from 18:00 pm till 7:00 am due to the flywheel effect explained in paragraph 6.1.3. The core of the rock is warmer than the ambient air and cools down much slower than the ambient air due to the rock’s thermal

mass.

During the peak temperature of the ambient air at 13:00 pm, the air from the rock bed showed a temperature difference of 29% on day one, 29% on day two, and 28% on day three. The system cooled the ambient air on average 28,5% over the three days the system was tested.

6.3.4 CONCLUSION

Using the solar heating system for cooling during the summer has shown positive results to cool the ambient air during the daytime by using the cooled ambient air during the night. The system also improves the indoor air quality by ventilating fresh ambient air through the system for 24 hours per day.

6.4 FULL EXPERIM ENT - PART 4: ENCLOSE D COOLING SYSTEM 6.4.1 INTRODUCTION

Part 4 of the experiment will focus on an enclosed cooling system; this system will use the cool ambient air during the evening and circulate the internal air during the day.

Figures 74 and 75 illustrate the enclosed cooling system for the day and night-time. As illustrated in Figure 74, the system will be enclosed to recirculate the cool air through the system. In Figure 75, it is illustrated that the system will be opened during the night-time to cool the rocks of the rock bed with means of cool ambient air.

Figure 74: Enclosed cooling system diagram: Daytime

Figure 75: Enclosed cooling system diagram: Night-time

6.4.2 M ETHODOLOG Y

The rock bed heat collector is filled to full capacity with 0.25m³ of rock. The outlet solar air heater will be connected to the rock bed heat collector’s inlet with 2 x 50mmØ U-PVC pipes. Figure 74 illustrates the inlet of the solar air heater and the outlet of the rock bed. As illustrated in Figure 74, the inlet of the covered solar air heater and outlet of rock bed, 2 x 50mmØ U-PVC at each inlet and outlet, will be open during the evening from 18:00 pm for circulation of cool ambient air and closed at 6:00 am. The glazed panel of the solar air heater is covered with a 500mm x 1000mm x 20mm thick chipboard with 50mm thick polystyrene fixed to the timber board.

The circulation fan will be powered by a solar panel during the day, 8:00 am till 16:00 pm, and after 16:00 pm till 8:00 am, the circulation fan will be powered by a 5000mah power bank.

The experiment was conducted for a duration of 72 hours/ 3 days from 6:00 am on 21 October 2021 till 6:00 am on 24 October 2021 during the summer season.

Four data loggers are used during the experiment. The results from each will be compared to determine the system’s efficiency. One data logger is placed at the outlet of the solar air heater, one within the rock bed heat collector, one at the outlet of the rock bed heat collector. One logger is placed on top of the rock bed heat collector box to track the ambient temperatures during the day and night.

6.4.3 RESULTS

Figures 76 to 78 illustrate the results from the enclosed cooling system. Each figure illustrates the results for one day from 6:00 am to 6:00 am (24 hours). Figure 79 illustrates the combined results for the 3-day experiment.

Figure 76: Enclosed cooling experiment results – Day 1

Figure 77: Enclosed cooling experiment results – Day 2

40 35 30 25 20 15 Enclosed Cooling Day 2

10 5 0 06:00:00 08:30:00 11:00:00 13:30:00 16:00:00 18:30:00 21:00:00 23:30:00 02:00:00 04:30:00 Amient Temperature Ambient Temperature Rock bed Storage Rockbed Outlet

Figure 78: Enclosed cooling experiment results – Day 3

Figure 79: Combined Results: Enclosed cooling experiment – 3 Days

Enclosed Cooling Day 3

50 45 40 35 30 25 20 15 10 5 0 06:00:00 08:30:00 11:00:00 13:30:00 16:00:00 18:30:00 21:00:00 23:30:00 02:00:00 04:30:00 Amient Temperature Ambient Temperature Rock bed Storage Rockbed Outlet

Figures 76 to 79 illustrate that the rock bed can provide cooled air, which is 5°C lower than the ambient temperature, from 10:00 am till 16:00 pm. Between 16:00 pm and 18:00 pm, the difference between the ambient air temperature and the rock bed is less than 2°C. From 18:00 pm, the ambient temperature drops gradually till the next day, 7:00 am. The discharging air should be ventilated to the ambient air and not back into the space/ room during the evening.

The rock remains warmer than the ambient air during the evening from 18:00 pm till 7:00 am due to the flywheel effect explained in paragraph 6.1.3. The core of the rock is warmer than the ambient air and cools down much slower than the ambient air due to the rock’s thermal

mass.

During the peak temperature of the ambient air at 13:00 pm, the air from the rock bed showed a temperature difference of 20% on day one, 19% on day two, and 17% on day three. The system cooled the ambient air on average 18,6% over the three days the system was tested.

6.4.4 CONCLUSION

When comparing the ventilated cooling experiment`s results with the enclosed cooling system, the ventilated system indicated an improvement of 10% on average. Due to the constant flow of air through the system, any radiant heat penetrating through the thermal insulation can be extracted. The enclosed system was not as efficient as the ventilated system. This can be due to any heat transferring through the thermal insulation cannot being extracted during the daytime as the system is enclosed. Furthermore, the enclosed system did not provide fresh air during the day.